Samacheer Kalvi 11th Chemistry Guide Chapter 4 Hydrogen

Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Chemistry Guide Pdf Chapter 4 Hydrogen Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Chemistry Solutions Chapter 4 Hydrogen

11th Chemistry Guide Hydrogen Text Book Back Questions and Answers

Textual Questions:

I. Choose the best answer:

Question 1.
Which of the following statements about hydrogen is incorrect?
(a) Hydrogen ion, H₃O⁺ exists freely in solution.
(b) Dihydrogen acts as a reducing agent.
(c) Hydrogen has three isotopes of which tritium is the most common.
(d) Hydrogen never acts as cation in ionic salts.
Answer:
(c) Hydrogen has three isotopes of which tritium is the most common.

Question 2.
Water gas is
(a) H₂O(g)
(b) CO + H₂O
(c) CO + H₂
(d) CO + N₂
Answer:
(c) CO + H₂

Question 3.
Which one of the following statements is incorrect with regard to ortho and para dihydrogen ?
(a) They are nuclear spin isomers
(b) Ortho isomer has zero nuclear spin whereas the para isomer has one nuclear spin
(c) The para isomer is favoured at low temperatures
(d) The thermal conductivity of the para isomer is 50% greater than that of the ortho isomer.
Answer:
(b) Ortho isomer has zero nuclear spin whereas the para isomer has one nuclear spin

Question 4.
Ionic hydrides are formed by
(a) halogens
(b) chalogens
(c) inert gases
(d) group one elements
Answer:
(d) group one elements

Question 5.
Tritium nucleus contains
(a) 1p + 0n
(b) 2p + 1n
(c) 1p + 2n
(d) none of these
Answer:
(c) 1p + 2n

Question 6.
Non-stoichiometric hydrides are formed by
(a) palladium, vanadium
(b) carbon, nickel
(c) manganese, lithium
(d) nitrogen, chlorine
Answer:
(b) carbon, nickel

Question 7.
Assertion:
Permanent hardness of water is removed by treatment with washing soda.
Reason:
Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false
(d) Both assertion and reason are false
Answer:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question 8.
If a body of a fish contains 1.2 g hydrogen in its total body mass, if all the hydrogen is replaced with deuterium then the increase in body weight of the fish will be
(a) 1.2 g
(b) 2.4 g
(c) 3.6 g
(d) \(\sqrt{4.8}\) g
Answer:
(a) 1.2 g

Question 9.
The hardness of water can be determined by volumetrically using the reagent
(a) sodium thiosulphate
(b) potassium permanganate
(c) hydrogen peroxide
(d) EDTA
Answer:
(d) EDTA

Question 10.
The cause of permanent hardness of water is due to
(a) Ca(HCO₃)²
(b) Mg(HCO₃)²
(c) CaCl₂
(d) MgCO₃
Answer:
(c) CaCl₂

Question 11.
Zeolite used to soften hardness of water is, hydrated
(a) Sodium aluminium silicate
(b) Calcium aluminium silicate
(c) Zinc aluminium borate
(d) Lithium aluminium hydride
Answer:
(a) Sodium aluminium silicate

Question 12.
A commercial sample of hydrogen peroxide marked as 100 volume H₂O₂, it means that
(a) 1 ml of H₂O₂ will give 100 ml O₂ at STP
(b) 1 L of H₂O₂ will give 100 ml O₂ at STP
(c) 1 L of H₂O₂ will give 22.4 L O₂
(d) 1 ml of H₂O2 will give 1 mole of O₂ at STP
Answer:
(a) 1 ml of H₂O₂ will give 100 ml O₂ at STP

Question 13.
When hydrogen peroxide is shaken with an acidified solution of potassium dichromate in presence of ether, the ethereal layer turns blue due to the formation of
(a) Cr₂O₃
(b) CrO₄^2-
(c) CrO(O₂)₂
(d) none of these
Answer:
(c) CrO(O₂)₂

Question 14.
For decolourisation of 1mole of acidified KMnO₄, the moles of H₂O₂ required is
(a) \(\frac{1}{2}\)

(b) \(\frac{3}{2}\)

(c) \(\frac{5}{2}\)

(d) \(\frac{7}{2}\)
Answer:
(c) \(\frac{5}{2}\)

Question 15.
Volume strength of 1.5 NH₂O₂ is
(a) 1.5
(b) 4.5
(c) 16.8
(d) 8.4
Answer:
(d) 8.4

Question 16.
The hybridisation of oxygen atom is H₂O and H₂O₂ are, respectively
(a) sp and sp³
(b) sp and sp
(c) sp and sp²
(d) sp³ and sp³
Answer:
(d) sp³ and sp³

Question 17.
The reaction H₃PO₂ + D₂O → H₂DPO₂ + HDO indicates that hypo-phosphorus acid is
(a) tribasic acid
(b) dibasic acid
(c) monobasic acid
(d) none of these
Answer:
(c) monobasic acid
Solution:
Hypophosphorous acid on reaction with D₂O, only one hydrogen is replaced by deuterium and hence it is monobasic.

Question 18.
In solid ice, the oxygen atom is surrounded by
(a) tetrahedrally by 4 hydrogen atoms
(b) octahedrally by 2 oxygen and 4 hydrogen atoms
(c) tetrahedrally by 2 hydrogen and 2 oxygen atoms
(d) octahedrally by 6 hydrogen atoms
Answer:
(a) tetrahedrally by 4 hydrogen atoms
Solution:

Question 19.
The type of H-bonding present in ortho nitrophenol and p-nitrophenol are respectively
(a) intermolecular H-bonding and intra molecular f H-bonding
(b) intramolecular H-bonding and intermolecular H-bonding
(c) intramolecular H – bonding and no H – bonding
(d) intramolecular H -bonding and intramolecular H-bonding
Answer:
(b) intramolecular H-bonding and intermolecular H-bonding
                         

Question 20.
Heavy water is used as
(a) the modulator in nuclear reactions
(b) coolant in nuclear reactions
(c) both (a) and (b)
(d) none of these
Answer:
(c) both (a) and (b)
Solution:
(c) Heavy water is used as a moderator as well as coolant in nuclear reactions.

Question 21.
Water is a
(a) basic oxide
(b) acidic oxide
(c) amphoteric oxide
(d) none of these
Answer:
(c) amphoteric oxide
Solution:
Water is an amphoteric oxide.

II. Write brief answer to the following questions:

Question 22.
Explain why hydrogen is not placed with the halogen in the periodic table.
Answer:

• Hydrogen resembles alkali metals as well as halogens.
• Hydrogen resembles more alkali metals than halogens.
• The electron affinity of hydrogen is much less than that of halogen atoms. Hence the tendency to form hydride ion is low compared to that of halogens.
• In most of its compounds hydrogen exists in a +1 oxidation state. Therefore it is reasonable to place the hydrogen in group 1 along with alkali metals as shown in the latest periodic table published by IUPAC.

Question 23.
A cube at 0°C is placed in some liquid water at 0°C, the ice cube sinks – Why?
Answer:
In ice, each atom is surrounded tetrahedrally by four water molecules through hydrogen bonds. That is, the presence of two hydrogen atoms and two lone pairs of electrons on oxygen atoms in each water molecule allows the formation of a three-dimensional structure.

This arrangement creates an open structure, which accounts for the lower density of ice compared with water at 0°C. While in liquid water, unlike ice where hydrogen bonding occurs over a long-range, the strong hydrogen bonding prevails only in a short-range and therefore the denser packing. Hence, the ice cube sinks in water.

Question 24.
Discuss the three types of Covalent hydrides.
Answer:

1. They are the compounds in which hydrogen is attached to another element by sharing electrons.
2. The most common examples of covalent hydrides are methane, ammonia, water, and hydrogen chloride.
3. Molecular hydrides of hydrogen are further classified into three categories,
   • Electron precise (CH₄, C₂ H₆, SiH₄, GeH₄ )
   • Electron-deficient (B₂ H₆ ) and
   • Electron-rich hydrides (NH₃ , H₂O)
4. Since most of the covalent hydrides consist of discrete, small molecules that have relatively weak intermolecular forces, they are generally gases or volatile liquids.

Question 25.
Predict which of the following hydrides is gas on a solid (a) HCl (b) NaH. Give your reason.
Answer:
Sodium hydride (NaH) is gas on a solid. NaH is prepared by direct reaction of hydrogen gas with liquid sodium and it has a NaCl crystal structure. It is a tendency of deprotonating in many organic reactions. NaH is used in fuel cells.

Question 26.
Write the expected formulas for the hydrides of 4th-period elements. What is the trend in the formulas? In what way the first two numbers of the series different from the others?
Answer:
The expected formulas for the hydrides of 4th-period elements MH₄ (electron precise). M₂H₆ (electron-deficient) and MH₃ (electron-rich).
The trend in the formula is

• Electron precise hydrides – CH₄ C₂H₆, SiH₄, GeH₄
• Electron deficient hydrides – B₂H₆
• Electron rich hydrides – NH₃, H₂O

The first two members of the series KH, CaH₂ are ionic hydrides whereas the other members of the series CH₄, C₂H₆, SiH₄, B₂H₆, NH₃ are covalent hydrides.

Question 27.
Write the chemical equation for the following reactions.
Answer:
(i) the reaction of hydrogen with tungsten (VI) oxide NO₃ on heating.
(ii) hydrogen gas and chlorine gas.
Answer:
(i) Hydrogen can be used to reduce metal oxide into metal. Hydrogen reduces tungsten(VI) oxide into tungsten.
WO₃ + 3H₂ → W + 3H₂O

(ii) Hydrogen reacts with chlorine at room temperature under light gives hydrogen chloride.
H_2(g) + Cl_2(g) → 2HCl_(g)

Question 28.
Complete the following chemical reactions and classify them into (a) hydrolysis (b) redox (c) hydration reactions.

1. KMnO₄ + H₂O₂ →
2. CrCl₃ + H₂O →
3. CaO + H₂O →

Answer:

1. 2KMnO₄ + 3H₂O₂ → 2MnO₂ + 2KOH + 3H₂O + 3O_2(g)
   This reaction is a redox reaction.
2. CrCl₃ + 6H₂O₂ → [Cr(H₂O)₆)] Cl₃
   This reaction is a hydration reaction.
3. CaO + H₂O → Ca(OH)₂
   This reaction is a hydrolysis reaction.

Question 29.
Hydrogen peroxide can function as an oxidizing agent as well as a reducing agent. Substantiate this statement with suitable examples.
Answer:
Hydrogen peroxide can act both as an oxidizing agent and a reducing agent. Oxidation is usually performed in an acidic medium while the reduction reactions are performed in a basic medium.

In acidic conditions:
H₂O₂ + 2H⁺ + 2e^– → 2H₂O (E° = +1.77 V)
For example
2FeSO₄ + H₂SO₄ + H₂O₂ → Fe₂(SO₄)₃ + 2H₂O

In basic conditions:
HO₂^– + OH^– → O₂ + H₂O + 2e^– (E° = + 0.08V)

For Example,
2 KMnO_4(aq) + 3H₂O_2(aq) → 2MnO₂ + 2KOH + 2H₂O + 3O₂(g)

Question 30.
Do you think that heavy water can be used for drinking purposes?
Answer:

• Heavy water (D₂O) contains a proton and a neutron. This makes deuterium about twice as heavy as protium, but it is not radioactive. So heavy water is not radioactive.
• If you drink heavy water, you don’t need to worry about radiation poisoning. But it is not completely safe to drink, because the biochemical reaction in our cells is affected by the difference in the mass of hydrogen atoms.
• If you drink an appreciable volume of heavy water, you might feel dizzy because of the density difference. It would change the density of the fluid in your inner ear. So it is unlikely to drink heavy water.

Question 31.
What is the water-gas shift reaction?
Answer:
The carbon monoxide of the water gas can be converted to carbon dioxide by mixing the gas mixture with more steam at 400°C and passed over a shift converter containing iron/copper catalyst. This reaction is called as water-gas shift reaction.
CO + H₂O → CO₂ + H₂
The CO₂ formed in the above process is absorbed in a solution of potassium carbonate.
CO₂ + K₂CO₃ + H₂O → 2KHCO₃

Question 32.
Justify the position of hydrogen in the periodic table?
Answer:
Hydrogen resembles alkali metals in the following aspects.

1. Electronic configuration 1s¹ as alkali metals have ns¹.
2. Hydrogen forms unipositive H+ ion like alkali metals Na⁺, K⁺.
3. Hydrogen form halides (HX), oxides (H₂O) peroxide (H₂O₂) like alkali metals (NaX. Na₂O, Na₂O₂).
4. Hydrogen also acts as a reducing agent like alkali metals. Hydrogen resembles halogens in the following aspects.
5. Hydrogen has a tendency to gain one electron to form hydride ion (H^–) as halogens to form halide ion. (X^–).
6. Comparing the properties of hydrogen with alkali metals and with halogens, we can conclude that hydrogen resembles more alkali metals. In most of the compounds, hydrogen exists in a +1 oxidation state.
7. Therefore, it is reasonable to place the hydrogen in group 1 along with alkali metals as shown in the latest periodic table published by IUPAC.

Question 33.
What are isotopes? Write the names of isotopes of hydrogen.
Answer:
Atoms of the same element having same atomic number and different mass number are called isotopes.
Hydrogen has three naturally occurring isotopes, viz., protium (₁H¹ or H), deuterium (₁H² or D) and tritium (₁H³ or T). Protium ₁H¹ is the predominant form (99.985 %) and it is the only isotope that does not contain a neutron. Deuterium, also known as heavy hydrogen, constitutes about 0.015 %. The third isotope, tritium is a radioactive isotope of hydrogen which occurs only in traces (~1 atom per 1018 hydrogen atoms). Due to the existence of these isotopes naturally occurring hydrogen exists as H₂, HD, D₂, HT, T₂, and DT.

Question 34.
Give the uses of heavy water.
Answer:

1. Heavy water is used as a moderator in nuclear reactors as it can lower the energies of fast-moving neutrons.
2. D₂O is commonly used as a tracer to study organic reaction mechanisms and the mechanism of metabolic reactions.
3. It is also used as a coolant in nuclear reactors as it absorbs the heat generated.

Question 35.
Explain the exchange reactions of deuterium.
Answer:
When compounds containing hydrogen are treated with D₂O, hydrogen undergoes an exchange for deuterium. This reaction is known as the exchange reaction of deuterium.
2NaOH + D₂O → 2NaOD + HOD

HCl + D₂O → DCl + HOD

NH₄Cl + 4D₂O → ND₄Cl + 4HOD

These exchange reactions are useful in determining the number of ionic hydrogens present in a given compound. For example, when D₂O is treated with hypo-phosphorus acid only one hydrogen atom is exchanged with deuterium. It indicates that it is a monobasic acid.
H₃PO₂ + D₂O → H₂DPO₂ + HDO
It is also used to prepare some deuterium compounds:

Al₄C₃ + 12D₂O → 4Al(OD)₃ + 3CD₄
CaC₂ + 2D₂O → Ca(OD)₂ + C₂D₂
Mg₃N₂ + 6D₂O → 3Mg(OD)₂ + 2ND₃
Ca₃P₂ + 6D₂O → 3Ca(OD)₂ + 2PD₃

Question 36.
How do you convert parahydrogen into ortho hydrogen?
Answer:
Para hydrogen can be converted into ortho hydrogen in the following ways:

• By treating with catalysts platinum or iron.
• Bypassing an electric discharge
• By heating > 800°C.
• By mixing with paramagnetic molecules such as O₂, NO, NO₂.
• By treating with nascent/atomic hydrogen.

Question 37.
Mention the uses of deuterium.
Answer:

1. Deuterium is used to prepare heavy water which is used as a moderator in nuclear reactors.
2. Deuterium exchange reactions are useful in determining the number of ionic hydrogens present in a given compound.
3. It is also used to prepare some deuterium compounds.

Question 38.
Explain the preparation of hydrogen using electrolysis.
Answer:
High purity of hydrogen (>99.9%) is obtained by the electrolysis of water containing traces of acid or alkali or electrolysis of an aqueous solution of sodium hydroxide or potassium hydroxide using a nickel anode and iron cathode. This process is not economical for large-scale production.
At anode : 2OH^– → H₂O + ½ O₂ + 2e^–
At cathode : 2H₂O + 2e^– → 2OH^– + H₂
Overall reaction : H₂O → H₂ + 14 O₂

Question 39.
A group-1 metal (A) which is present ¡n common salt reacts with (B) to give compound (C) in which hydrogen is present in -1 oxidation state. (B) on reaction with gas to give universal solvent (D). The compound (D) reacts with (A) to give (B), a strong base. Identify A, B, C, D, and E. Explain the reactions.
Answer:
The metal that belongs to Group-1 which is present in common salt is Sodium(A).
The metal reacts with (B) to give compound (C) in which hydrogen is present in a -1 oxidation state.
2Na + H₂ → 2NaH
Hence, the (B) is hydrogen, and (C) is sodium hydride. (B) on reaction with gas to give universal solvent (D).
H₂ + O₂ → 2NaOH
The universal solvent (D) is water. The compound (D) on reaction with (A) to give (E) which is a strong base.
H₂O + 2Na → 2NaOH
The Compound (E) is Sodium hydroxide.
A – Sodium (Na)
B – Hydrogen (H₂)
C – Sodium Hydride (NaH)
D – Water (H₂O)
E – Sodium hydroxide (NaOH)

Question 40.
An isotope of hydrogen (A) reacts with diatomic molecule of element which occupies group number 16 and period number 2 to give compound (B) is used as a moderatorin nuclear reaction. (A) adds on to a compound (C), which has the molecular formula C₃H₆ to give (D). Identify A, B, C and D.
Answer:
An isotope of hydrogen (A) reacts with diatomic molecule of element which occupies group number 16 and period number 2 to give compound (B) is used as a moderator in nuclear reaction.
2D₂ + O₂ → 2D₂O
The isotope of hydrogen is deuterium(A), diatomic element is oxygen and the compound (B) is heavy water.
(A) adds on to a compound (C), which has the molecular formula C₃H₆ to give (D).
CH₃ – CH = CH₂ + D₂ → CH₃ – CHD – CH₂D
(C)                                     (D)
The compound (C) is propene and (D) is 1, 2 deutropropane.
A – Deuterium (D₂)
B – Heavy water (D₂O)
C – Propene (CH₃ – CH = CH₂)
D – 1, 2 deutero propene (CH₃ – CHD – CH₂D)

Question 41.
NH₃ has an exceptionally high melting point and boiling point as compared to those of the hydrides of the remaining element of group 15- Explain.
Answer:
When a hydrogen atom is covalently bonded to a highly electronegative atom such as nitrogen, the bond is polarized. Due to this effect, the polarized hydrogen atom is able to form a weak electrostatic interaction with another electronegative atom present in the vicinity.

This interaction is called hydrogen bonding. Hence, NH₃ has an exceptionally high melting point and boiling point as compared to those of the hydrides of the remaining element of group 15 due to intermolecular hydrogen bonding.

Question 42.
Why interstitial hydrides have a lower density than the parent metal?
Answer:

• d block elements form metallic or interstitial hydrides, on heating with dihydrogen under pressure.
• Hydrogen atoms being small in size occupy some in the metallic lattice producing distortion without any change in its type.
• The densities of these hydrides are lower than those of metals from which they are formed since the crystal lattice expands due to the inclusion of dihydrogen.

Question 43.
How do you expect the metallic hydrides to be useful for hydrogen storage?
Answer:
Metallic hydrides are usually obtained by hydrogenation of metals and alloys in which hydrogen occupies the interstitial sites (voids). Most of the hydrides are non-stoichiometric with variable composition (TiH _{1.5 – 1.8} and PdH_{0.6 – 0.8}), some are relatively light, inexpensive, and thermally unstable which makes them useful for hydrogen storage applications.

Question 44.
Arrange NH₃, H₂O, and HF in the order of increasing magnitude of hydrogen bonding and explain the basis for your arrangement.
Answer:

• The increasing magnitude of hydrogen bonding among NH₃, H₂O, and HF is HF > H₂O > NH₃
• The extent of hydrogen bonding depends upon electronegativity and the number of hydrogen atoms available for bonding.
• Among N, F, and O the increasing order of their electronegativities are N < O, H₂O > NH₃.

Question 45.
Compare the structures of HO and HO.
Answer:
Both in gas-phase and liquid-phase, the molecule adopts a skew confirmation due to repulsive interaction of the OH bonds with lone-pairs of electrons on each oxygen atom. Indeed, it is the smallest molecule known to show hindered rotation about a single bond.

H₂O₂ has a non-polar structure. The molecular dimensions in the gas phase and solid phase differ as shown in the figure. Structurally, H₂O₂ is represented by the dihydroxyl formula in which the two OH-groups do not lie in the same plane.

One way of explaining the shape of hydrogen peroxide is that the hydrogen atoms would lie on the pages of a partly opened book, and the oxygen atoms along the spine. In the solid phase of the molecule, the dihedral angle reduces to 90.2° due to hydrogen bonding and the O-O-H angle expands from 94.8° to 101.9°. Water has a bent structure and the H-O-H bond angle is 104.5°.

11th Chemistry Guide Hydrogen Additional Questions and Answers

I. Choose the best Answer:

Question 1.
Which one of the following elements mostly present in the sun and the stars?
(a) Hydrogen
(b) Lithium
(c) Helium
(d) Beryllium
Answer:
(a) Hydrogen

Question 2.
Hydrogen has similarities with
(a) Alkali metals and halogens
(b) Alkaline earth metals and halogens
(c) Alkalimetals and noble gases
(d) Halogens and noble gases.
Answer:
(a) Alkali metals and halogens

Question 3.
At room temperature normal hydrogen consists of …………….
(a) 25% ortho form + 75% para form
(b) 50% ortho form + 50% para form
(c) 75% ortho form + 25% para form
(d) 60% ortho form + 40% para form
Answer:
(c) 75% ortho form + 25% para form

Question 4.
Ionization energy of hydrogen is (in kJ mol^-1)
(a) 377
(b) 520
(c) 1413
(d) 1314
Answer:
(d) 1314

Question 5.
Consider the following statements:
(i) In the ortho form of the hydrogen molecule, the nuclear spins are opposed to each other
(ii) The magnetic moment of para-hydrogen is twice that of ortho hydrogen
(iii) By passing an electric discharge, para-hydrogen can be converted into ortho hydrogen. Which of the above statement is/are not correct?
(a) (i) only
(b) (iii) only
(c) (i) and (ii)
(d) (ii) and (iii)
Answer:
(c) (i) and (ii)

Question 6.
The predominant isotope of hydrogen is
(a) deuterium
(b) protium
(c) tritium
(d) heavy hydrogen
Answer:
(b) protium

Question 7.
The magnetic moment of para-hydrogen is ……………
(a) one
(b) zero
(c) twice
(d) maximum
Answer:
(b) zero

Question 8.
The number of naturally occurring hydrogens due to the existence of isotopes is
(a) 6
(b) 5
(c) 4
(d) 3
Answer:
(a) 6

Question 9.
The half-life period of tritium is ……………..
(a) 123.3 year
(b) 12.33 years
(c) 1 year
(d) 1600 years
Answer:
(a) 12.33 years

Question 10.
The correct order of melting point of isotopes of hydrogen is
(a) H < D < T
(b) T < D < H
(c) H < T < D
(d) D < H < T
Answer:
(a) H < D < T

Question 11.
Which one of the following is used to study the movements of groundwater?
(a) Deuterium
(b) Protium
(c) Tritium
(d) HD
Answer:
(a) Deuterium

Question 12.
Which of the following statement is correct about ortho-para hydrogen?
(a) The magnetic moment of para-hydrogen is twice that of a proton.
(b) Ortho form is more stable than para form
(c) Ortho form can be catalytically converted into the para form using platinum.
(d) At room temperature, normal hydrogen consists of 75% para form.
Answer:
(b) Ortho form is more stable than para form

Question 13.
Which of the following is produced by the bombardment of neutrons with lithium?
(a) Deuterium
(b) Protium
(c) Tritium
(d) Beryllium
Answer:
(c) Tritium

Question 14.
During electrolysis of water containing traces of acid, hydrogen is liberated at
(a) cathode
(b) anode
(c) both anode and cathode
(d) none of the above
Answer:
(a) cathode

Question 15.
Which of the following mixture of gases is called water gas?
(a) CO_2(g)  + H_2(g)
(b) CO_2(g) + N_2(g)
(c) CO_(g) + H_2(g)
(d) N_2(g) + H_2(g)
Answer:
(c) CO_(g) + H_2(g)

Question 16.
The catalyst used in the water gas shift reaction is
(a) Copper
(b) Nickel
(c) Platinum
(d) Palladium
Answer:
(a) Copper

Question 17.
The products formed during the cracking long chain hydrocarbon C₆H₁₂ are
(a) CO₂ + H₂O
(b) CO + H₂
(c) C₆H₁₀ + H₂
(d) C₆H₆ + 3H₂
Answer:
(d) C₆H₆ + 3H₂

Question 18.
The percentage of heavy water in normal water is
(a) 1.6 × 10⁴
(b) 1.6 × 10^-4
(c) 1.6 × 10^-3
(d) 1.6 × 10²
Answer:
(b) 1.6 × 10^-4

Question 19.
Hydrogen combines with carbon monoxide in the presence of copper catalyst will synthesize
(a) Ethanol
(b) Methane
(c) Methanol
(d) Methanal
Answer:
(c) Methanol

Question 20.
Lithium Aluminium Hydride is
(a) [LiAlH₃]
(b) Li[Al₂H₄]
(c) Li[AlH₂]
(d) Li[AlH₄]
Answer:
(d) Li[AlH₄]

Question 21.
Deuterium oxide is called
(a) hard water
(b) soft water
(c) heavy water
(d) heavy hydrogen
Answer:
(c) heavy water

Question 22.
Ammonia is synthesized by ______ process.
(a) Haber’s
(b) Bergius
(c) Decon’s
(d) Solvay
Answer:
(b) Bergius

Question 23.
Which of the following process is important in the food industry?
(a) Dehydration
(b) Dehalogenation
(c) Hydrogenation
(d) Carboxylation
Answer:
(c) Hydrogenation

Question 24.
The high melting and boiling points of water is due to
(a) Covalent bonding
(b) Hydrogen bonding
(c) Ionic bonding
(d) co-ordinate bonding
Answer:
(b) Hydrogen bonding

Question 25.
Which of the following is used for cutting and welding?
(a) Atomic hydrogen and oxy-hydrogen torches
(b) Liquid hydrogen
(c) Calcium hydride
(d) Sodium boro hydride
Answer:
(a) Atomic hydrogen and oxy-hydrogen torches

Question 26.
Water is an ______ oxide.
(a) acidic
(b) basic
(c) amphoteric
(d) neutral
Answer:
(a) acidic

Question 27.
Which one of the following is a universal solvent?
(a) Alcohol
(b) Ether
(c) CCl₄
(d) Water
Answer:
(d) Water

Question 28.
In CuSO₄.5H₂O, the number of water molecules forms co-ordinate bonds is
(a) 4
(b) 5
(c) 3
(d) 1
Answer:
(a) 4

Question 29.
Water does not react with
(a) Sodium
(b) Magnesium
(c) Beryllium
(d) Calcium
Answer:
(c) Beryllium

Question 30.
The number of water molecules in a hydrated crystal of Chromium chloride salt is
(a) 5
(b) 6
(c) 4
(d) 3
Answer:
(b) 6

Question 31.
Which set of metals does not have any effect on water?
(a) Ag, Au, Pt
(b) Na, Mg, Al
(c) Fe, Ca, Zn
(d) Fe, Pb, Na
Answer:
(a) Ag, Au, Pt

Question 32.
Temporary hardness of water is removed by ______ method.
(a) Dewar
(b) Clark’s
(c) Leibeg
(d) Haber
Answer:
(b) Clark’s

Question 33.
Consider the following statements.
(i) Silver, Gold, Mercury, and Platinum do not have any effect on water.
(ii) Carbon, Sulphur, and Phosphorous do not react with water.
(iii) Beryllium reacts with waterlessness violently.
Which of the following statements is/are not correct?
(a) (i) only
(b) (ii) and (iii)
(c) (iii) only
(d) (ii) only
Answer:
(c) (iii) only

Question 34.
The ion exchange bed used for the softening of hard water is
(a) Borates
(b) Zeolites
(c) Fluorides
(d) Phosphates
Answer:
(b) Zeolites

Question 35.
Water is an/a oxide.
(a) neutral
(b) acidic
(c) basic
(d) amphoteric
Answer:
(d) amphoteric

Question 36.
________ reactions are useful in determining the number of ionic hydrogens present in a given compound.
(a) Oxygen exchange
(b) Metal exchange
(c) Deuterium exchange
(d) Deuterium decomposition
Answer:
(c) Deuterium exchange

Question 37.
Which one of the following is used as water softener?
(a) Zeolites
(b) lime
(c) washing soda
(d) bleaching powder
Answer:
(a) Zeolites

Question 38.
Autoxidation of 2-alkyl anthraquinol gives
(a) Hydrogen peroxide
(b) Heavy water
(c) Hydrogen
(d) Water
Answer:
(a) Hydrogen peroxide

Question 39.
Which of the following is used to remove toxic and heavy metals from water?
(a) zeolites
(b) magnesia
(c) Bleaching agent
(d) lime
Answer:
(a) zeolites

Question 40.
Hydrogen peroxide solutions are stored in ______ container
(a) glass
(b) alkali metal
(c) plastic
(d) wooden
Answer:
(c) plastic

Question 41.
Consider the following statements.
(i) H₂O₂ is a powerful oxidising agent.
(ii) H₂O₂ is stored in dark coloured bottles
(iii) H₂O₂ is used as a moderator in nuclear reactors.
Which of the above statements is/are not correct.
(a) (i) only
(b) (i) and (ii)
(c) (iii) only
(d) (i), (ii) and (iii)
Answer:
(c) (iii) only

Question 42.
Disproportionation of hydrogen peroxide gives
(a) oxygen and hydrogen
(b) hydrogen and water
(c) hydrogen and ozone
(d) oxygen and water
Answer:
(d) oxygen and water

Question 43.
Which one of the following is prepared in the industry by the auto-oxidation of 2-alkylanthraquional?
(a) Heavy water
(b) Deuterium
(c) Hydrogen peroxide
(d) Tritium
Answer:
(c) Hydrogen peroxide

Question 44.
White pigment is
(a) Pb²(OH)₂(C0₃)₃
(b) Pb₃(OH)₂(C0₃)₂
(c) Pb₃(OH)(CO₃)₂
(d) Pb₂(OH)(CO₃)₃
Answer:
(b) Pb₃(OH)₂(C0₃)₂

Question 45.
Which one of the following is an electron-deficient hydride?
(a) C₂H₆
(b) B₂H₆
(c) GeH₄
(d) CH₄
Answer:
(b) B₂H₆

Question 46.
Compounds in which hydrogen is attached to another element by sharing of electrons are called _________ hydrides.
(a) Interstitial
(b) Molecular
(c) Saline
(d) Metallic
Answer:
(b) Molecular

Question 47.
Which one of the following is not a covalent hydride?
(a) Ammonia
(b) Methane
(c) Lithium hydride
(d) water
Answer:
(e) Lithium hydride

Question 48.
Each water molecule is linked to ______ other molecules through hydrogen bonds.
(a) five
(b) four
(c) six
(d) two
Answer:
(b) four

Question 49.
Which one of the following is used for hydrogen storage applications?
(a) Saline hydrides
(b) Interstitial hydrides
(c) covalent hydrides
(d) molecular hydrides
Answer:
(b) Interstitial hydrides

Question 50.
Hypo-phosphorus is a ______ acid.
(a) dibasic
(b) tribasic
(c) monobasic
(d) tetrabasic
Answer:
(c) monobasic

II. Very Short Question and Answers (2 Marks):

Question 1.
What are the isotopes of hydrogen?
Answer:
Hydrogen has three naturally occurring isotopes, viz., protium (₁H¹ or H), deuterium (₁H² or D) and tritium (₁H³ or T).

Question 2.
What is the nuclear reaction that takes place in the sun and other stars?
Answer:
The sun and other stars are composed mainly of 85 – 95% hydrogen which generates their energy by nuclear fusion of hydrogen nuclei into helium.

Question 3.
How is tritium prepared?
Answer:
Tritium is artificially prepared by bombarding lithium with slow neutrons in a nuclear fission reactor. The nuclear transmutation reaction for this process is as follows.
\({ }_{3}^{6} L i\) + \({ }_{0}^{1} n\) → \({ }_{2}^{4} \mathrm{He}\) + \({ }_{1}^{3} T\)

Question 4.
What are ortho and para hydrogens?
Answer:
In the hydrogen atom, the nucleus has a spin. When molecular hydrogen is formed, the spins of two hydrogen nuclei can be in the same direction or in the opposite direction as shown in the figure. These two forms of hydrogen molecules are called ortho and para hydrogens respectively.

Question 5.
Write the different forms of naturally occurring hydrogen?
Answer:
Due to the existence of three isotopes of hydrogen, Protium (H), Deuterium (D) and Tritium(T), naturally occurring hydrogen exists as H₂, HD, D₂, HT, T₂, and DT.

Question 6.
Why hydrogen gas is used as fuel?
Answer:
Hydrogen burns in the air, virtually free from pollution, and produces a significant amount of energy. This reaction is used in fuel cells to generate electricity.
2H_2(g) + O_2(g) → 2H₂O_(l) + energy

Question 7.
How is pure hydrogen prepared?
Answer:
High purity hydrogen (> 99.9 %) is obtained by the electrolysis of water containing traces of acid or alkali or the electrolysis of an aqueous solution of sodium hydroxide or potassium hydroxide using a nickel anode and iron cathode. However, this process is not economical for large-scale production.
At anode:
2OH^– → H₂O + \(\frac{1}{2}\)O₂ + 2e^–

At cathode:
2H₂O + 2e^– → 2OH^– + H₂

Overall reaction:
H₂O → H₂ + \(\frac{1}{2}\)O₂

Question 8.

how ¡s methanol synthesized from hydrogen? Give the uses of methanol.
Answer:

• Huge quantities of hydrogen are used for the synthesis of methanol from carbon monoxide in presence of a copper catalyst.
  CO_(g) + 2H_2(g) → CH₃OH_(l)
•  Methanol is an industrial solvent and a starting material for the manufacture of formaldehyde used in making plastics.

How is hydrogen prepared by steam reforming reaction?
Answer:
Hydrogen is produced on large scale by steam-reforming of hydrocarbons. In this method, a hydrocarbon such as methane is mixed with steam and passed over a nickel catalyst in the range 800- 900°C and 35 atm pressure.
CH₄ + H₂O → CO + 3H₂

Question 9.
What is water gas? How is it prepared?
Answer:
The mixture of carbon monoxide and hydrogen is called water gas. When steam is passed over a red-hot coke to produce carbon monoxide and hydrogen. The mixture of gases produced in this way is known as water gas (CO + H₂).
C + H₂O → (CO + H₂)Water gas /Syngas

Question 10.
How is hydrogen used in metallurgy? Prove it with an example.
Answer:
In metallurgy, for the extraction of pure metals from their mineral sources, hydrogen is used to reduce many metal oxides to metals at high temperatures.
CuO_(s) +H_2(g) → Cu_(s) +H₍₂₎O_(g)

Question 11.
How is Deuterium prepared?
Answer:
Normal water contains 1.6 × 10^-4 percentage of heavy water. The dissociation of protium water (H₂O) is more than heavy water (D₂O). Therefore, when water is electrolysed, hydrogen is liberated much faster than D₂. The electrolysis is continued until the resulting solution becomes enriched in heavy water. Further electrolysis of the heavy water gives deuterium.

Question 12.
What happens when steam is passed over red hot iron?
Answer:
When steam is passed over a red hot iron, the iron oxide will be formed with the release of hydrogen.
3Fe_(s) + 4H₂O_(l) → Fe₃O + 4H_4(g)

Question 13.
Write the physical properties of hydrogen.
Answer:
Hydrogen is a colorless, odorless, tasteless, lightest, and highly flammable gas. It is a non-polar diatomic molecule. It can be liquefied under low temperature and high pressure. Hydrogen is a good reducing agent.

Question 14.
What is the temporary hardness of water? How is it removed?
Answer:
Temporary hardness of water is due to the presence of soluble bicarbonates of magnesium and calcium. By heating/boiling, these salts decomposed into insoluble carbonate and hydroxide, respectively. The resulting precipitates can be removed by filtration.
Ca (HCO₃)_2(aq) → CaCO_3(s) + H₂O_(l) + CO_2(l)
Mg(HCO₃)_2(aq) → Mg(OH)_2(s) + CO_2(g)

Question 15.
Write the physical properties of water.
Answer:
Water is a colourless and volatile liquid. The peculiar properties of water in the condensed phases are due to the presence of inter molecular hydrogen bonding between water molecules. Hydrogen bonding is responsible for the high melting and boiling points of water.

Question 16.
How would you prepare Hydrogen peroxide?
Answer:
Hydrogen peroxide can be prepared by adding a metal peroxide to dilute acid.
BaO_2(s)+ H₂SO_4(aq) → BaSO_4(s) + H₃O_2(aq)

Question 17.
What is hard water? Give its types.
Answer:
Hard water contains high amounts of mineral ions. The most common ions found in hard water are the soluble metal cations such as magnesium & calcium, though iron, aluminium, and manganese may also be found in certain areas. The presence of these metal salts in the form of bicarbonate, chloride, and sulphate in water makes water ‘hard’.

Question 18.
What is meant by the temporary hardness of water?
Answer:
Temporary hardness is primarily due to the presence of soluble bicarbonates of magnesium and calcium.

Question 19.
Why the bond angle in the solid phase of H₂O₂ is reduced when compared to the gas phase of H₂O₂?
Answer:
Both the gas phase and solid phase, H₂O₂ adopt a skew configuration due to the repulsive interaction of the OH bonds with lone pairs of electrons on each oxygen atom. Indeed, it is the smallest molecule known to show hindered rotation about a single bond. In the solid phase, the dihedral angle is sensitive and hydrogen bonding decreases from 111.50 in the gas phase to 90.2 in the solid phase.

Question 20.
What are zeolites? Give its use.
Answer:
Zeolites are hydrated sodium alumino-silicates with a general formula, NaO.Al₂O₃ .xSiO₂ .yH₂O (x = 2 to 10, y = 2 to 6). Zeolites have a porous structure in which the monovalent sodium ions are loosely held and can be exchanged with hardness-producing metal ions (M = Ca or Mg) in water.

Question 21.
Prove that Hydrogen peroxide is a vigorous oxidizing agent and the solution of H₂O₂ is slightly acidic.
Answer:
H₂ O_2(aq) + 2 H₂O_(l) ⇌ H₃ O⁺_(aq) + HO⁺_2(aq)

H₃O⁺ Hydronium ion formation proves that solution of H₂O₂ is acidic. Because it donates H⁺ to H₂O to form H₃O⁺ ion.
H₂O₂ oxidizes Ferrous sulphate to Ferric sulphate in an acidic medium.
2FeSO_4(aq) + H₂SO_4(aq) + H₄O_2(aq) ⇌ Fe₂(SO₄)_3(aq)( + 2H₂O_(l)

Question 22.
What is the effect of shielding on ionization energy?
Answer:
As we move down a group, the number of inner shell electron increases which in turn increases the repulsive force exerted by them on the valence electrons, i.e., the increased shielding effect caused by the inner electrons decreases the attractive force acting the valence electron by the nucleus. Therefore, the ionization energy decreases.

Question 23.
What are ternary hydrides? Give example?
Answer:
Ternary hydrides are compounds in which the molecule is constituted by hydrogen and two types of elements, e.g., LiBH₄ or LiAlH₄.

Question 24.
How is hydrogen peroxide prepared?
Answer:
It can be prepared by treating metal peroxide with dilute acid.
BaO₂ + H₂SO₄ → BaSO₄ + H₂O₂

Na₂O₂ + H₂SO₂ → Na₂SO₄ + H₂O₂

Question 25.
What are hydrides? How are they classified?
Answer:
Hydrogen forms binary compounds with many electropositive elements including metals and non¬metals are called hydrides. It also forms ternary hydrides with two metals. E.g., LiBH₄ and LiAlH₄. The hydrides are classified as ionic, covalent and metallic hydrides according to the nature of bonding.

Question 26.
Write a note about gas hydrates.
Answer:
Gas hydrates are a kind of inclusion compound, where gas molecules are trapped in the crystal lattice having voids of the right size, without being chemically bonded. An interesting hydrate is that of the hydronium ion (H₂O) in the gas phase, similar to methane hydrate. Each water molecule is bonded to three others in the dodecahedron.

Question 27.
What are intra and inter-molecular hydrogen bonding?
Answer:
Hydrogen bonds can occur within a molecule is called intramolecular hydrogen bonding whereas between two molecules of the same type or different type is called intermolecular hydrogen bonding.

III. Short Questions and Answers (3 Marks):

Question 1.
Write notes on water-gas shift reaction?
Answer:
The carbon monoxide of the water gas can be converted to carbon dioxide by mixing the gas mixture with more steam at 400°C and passed over a shift converter containing iron/copper catalyst. This reaction is called as water-gas shift reaction.
CO + H₂O → CO₂ + H₂

The CO₄ formed in the above process is absorbed in a solution of potassium carbonate.
CO₂ + K₂CO₃ + H₂O → 2KHCO₃

Question 2.
Can we use concentrated sulphuric acid and pure zinc in the preparation of dihydrogen?
Answer:
Cone. H₂SO₄ cannot be used because it acts as an oxidizing agent also and gets reduced to SO₂
Zn + 2H₂SO₄ (Conc.) → ZnSO₄ + 2H₂O + SO₂
Pure Zn is not used because it is non-porous and the reaction will be slow. The impurities in Zn help in the constitute the electrochemical couple and speed up the reaction.

Question 3.
Write notes on isotopes of hydrogen.
Answer:
Hydrogen has three naturally occurring isotopes, viz., protium (₁H¹ or H), deuterium (₁H² or D) and tritium (₁H³ or T). Protium (₁H¹) is the predominant form (99.985 %) and it is the only isotope that does not contain a neutron.
Deuterium, also known as heavy hydrogen, constitutes about 0.015%. The third isotope, tritium is a radioactive isotope of hydrogen which occurs only in traces (~1 atom per 1018 hydrogen atoms). Due to the existence of these isotopes naturally occurring hydrogen exists as H₂, HD, D₂, HT, T₂, and DT.

Question 4.
What are ortho and para hydrogen? How will you convert one form into another?
Answer:
In the hydrogen atom, the nucleus has a spin. When molecular hydrogen is formed, the spins of two hydrogen nuclei can be in the same direction or in the opposite direction as shown in the figure. These two forms of hydrogen molecules are called ortho and para hydrogens respectively.

At room temperature, normal hydrogen consists of about 75% ortho-form and 25% para-form. As the ortho-form is more stable than para-form, the conversion of one isomer into the other is a slow process. However, the equilibrium shifts in favour of para hydrogen when the temperature is lowered.

The para-form can be catalytically transformed into ortho-form using platinum or iron. Alternatively, it can also be converted by passing an electric discharge, heating above 800°C and mixing with paramagnetic molecules such as O₂, NO, NO₂ or with nascent/atomic hydrogen.

Question 5.
Discuss the methods of preparation of hydrogen.
Answer:
High purity hydrogen (> 99.9%) is obtained by the electrolysis of water containing traces of acid or alkali or the electrolysis of an aqueous solution of sodium hydroxide or potassium hydroxide using a nickel anode and iron cathode. However, this process is not economical for large-scale production.
At Anode:
2OH^– → H₂O + \(\frac{1}{2}\)O₂ + 2e^–

At Cathode:
2H₂O + 2e^– → 2OH^– + H₂

Overall Reaction:
H₂O → H₂ + \(\frac{1}{2}\)O₂
Hydrogen is conveniently prepared in the laboratory by the reaction of metals, such as zinc, iron, tin with dilute acid.
Zn + 2HCl → ZnCl₂ + H₂↑

Laboratory preparation of Hydrogen

Question 6.
Write the chemical reactions to show the amphoteric nature of water.
Answer:
Water is amphoteric in nature and it behaves both as an acid as well as the base. With acids stronger than themselves (e.g., H₂S) it behaves as a base, and with bases stronger than themselves (e.g., NH₃) it acts as an acid.

1. As a base : H₂O_(l) + H₂S_(aq) → H₃ O_(aq) + HS^–_(aq)
2. As an acid : H₂O_(l) + NH_3(aq) → OH^–_(aq) + NH⁺_4(aq)

Question 7.
Write the reaction of halogens with water.
Answer:
The halogens react with water to give an acidic solution. For example, chlorine forms hydrochloric acid and hypo chlorous acid. It is responsible for the antibacterial action of chlorine water, and for its use as bleach.
Cl₂ + H₂O → HCl + HOCl
Fluorine reacts differently to liberate oxygen from water.
2F₂ + 2H₂O → 4HF + O₂

Question 8.
Discuss the nature of hydrated salts with suitable examples.
Answer:
Many salts crystallized from aqueous solutions form hydrated crystals. The water in the hydrated salts may form a co-ordinate bond or just present in interstitial positions of crystals.
Examples: Cr(H₂O₆₎ Cl₃₎ – All six water molecules form a coordinate bond. BaCl_2.2H₂O – Both the water molecules are present in interstitial positions.
CuSO₄ .5H₂O – In this compound four water molecules form co-ordinate bonds while the fifth water molecule, present outside the coordination, can form an intermolecular hydrogen bond with another molecule. [Cu(H₂O)₄]SO₄. H₂O.

Question 9.
Distinguish between Hard water and Soft water.
Answer:
Hard water:

• The presence of magnesium and calcium in the form of bicarbonate, chloride, and sulfate in water makes hard water.
• The cleaning capacity of soap is reduced when used in hard water.
• When hard water is boiled deposits of insoluble carbonates of magnesium and calcium are obtained.

Soft water:

• The presence of soluble salts of calcium and magnesium in water makes it soft water.
• The cleaning capacity of soap is more when used in soft water.
• When soft water is boiled, there is no deposition of salts.

Question 10.
How is the temporary hardness of water removed by Clark’s method?
Answer:
In Clark’s method, the calculated amount of lime is added to hard water containing magnesium and calcium, and the resulting carbonates and hydroxides can be filtered off.
Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O
Mg(HCO₃) + 2Ca(OH)₂ → 2CaCO₃+ Mg(OH)₂ + 2H₂O

Question 11.
Describe ion exchange method of softening water (or) Explain Zeolite (or) Permutit process.
Answer:

1. Hardness can be removed by passing through an ion-exchange bed like zeolites or resin-containing column. Thus, the zeolites work as a water softeners.
2. Zeolites are hydrated sodium alumini-silicates with a general formula, NaO.Al₂O₃.xSiO₂.yH₂O (x = 2 – 10, y = 2 – 6). They have high ion exchange capacity.
3. The complex structure can represent Na₂ – Z with sodium as exchangeable cations. This method is called zeolite or permit process.
4. Zeolites have a porous structure in which the monovalent sodium ions are loosely held and can be exchanged with hardness producing divalent metal ions (Ca or Mg) in water.
   Na₂ – Z_(s) + M²⁺_(aq) → M-Z_(s) + 2Na⁺_(aq)
5. When exhausted, the materials can be regenerated by treating them with aqueous sodium chloride. Hard minerals caught in the zeolite are released and they get replenished with sodium ions.
   M-Z_(s) + 2NaCl_(aq) → Na_(s)-Z_(s) + MCl_2(aq)

Question 12.
Write the uses of heavy water.
Answer:

1. Heavy water is widely used as a moderator in nuclear reactors as it can lower the energies of fast neutrons
2. It is commonly used as a tracer to study organic reaction mechanisms and mechanism of metabolic reactions
3. It is also used as a coolant in nuclear reactors as it absorbs the heat generated.

Question 13.
What are metallic hydrides? Explain about it.
Answer:

• Metallic hydrides are obtained by hydrogenation of metals and alloys in which hydrogen occupies the interstitial sites (voids). Hence, they are called interstitial hydrides.
• The hydrides show properties similar to parent metals and hence they are also known as metallic hydrides.
• They arc mostly non-stoichiometric with variable composition (TiH_1.5-1.818 and PdH_0.6-0.8).
• Some are relatively light, inexpensive, and thermally unstable which makes them useful for hydrogen storage applications. Example, TiH₂, ZrH₂, ZnH₂.

IV. Long Question and Answers (5 Marks):

Question 1.
Justify the position of hydrogen in the periodic table.
Answer:
The hydrogen has the electronic configuration of 1s¹ which resembles with ns¹ general valence shell configuration of alkali metals and shows similarity with them as follows:
(i) It forms unipositive ion (H⁺) like alkali metals (Na⁺, K⁺, Cs⁺)
(ii) It forms halides (HX), oxides (H₂O), peroxides (H₂O₂) and sulphides (H₂S) like alkali metals (NaX, Na₂O, Na₂O₂, Na₂S)
(iii) It also acts as a reducing agent.

However, unlike alkali metals which have ionization energy ranging from 377 to 520 kJ mol^-1, the hydrogen has 1,314kJ mol^-1 which is much higher than alkali metals.

Like the formation of halides (X^–) from halogens, hydrogen also has a tendency to gain one electron to form hydride ion (H^–) whose electronic configuration is similar to the noble gas, helium. However, the electron affinity of hydrogen is much less than that of halogen atoms. Hence, the tendency of hydrogen to form hydride ion is low compared to that of halogens to form the halide ions as evident from the following reactions:

\(\frac{1}{2}\) H₂ + e^– → H^–                                 ∆H = + 36 kcalmol^-1
\(\frac{1}{2}\) Br₂ + e^– → Br^–                                 ∆H = -55 kcalmol^-1

Since, hydrogen has similarities with alkali metals as well as halogens; it is difficult to find the right position in the periodic table. However, in most of its compounds hydrogen exists in+1 oxidation state. Therefore, it is reasonable to place the hydrogen in group 1 along with alkali metals as shown in the latest periodic table published by IUPAC.

Question 2.
What do you understand by –

1. Electron-deficient
2. Electron-precise
3. Electron-rich compounds of hydrogen? Provide justification with suitable examples.

Answer:

1. Electron deficient hydrides:
   Compounds in which central atom has an incomplete octet, are called electron-deficient hydrides. For example, BeH₂ , BH₃  are electron deficient hydrides
2. Electron precise hydrides:
   Those compounds in which exact number of electrons are present in a central atom or the central atom contains complete octet are called precise hydrides e.g., CH₄ , SiH₄, GeH₄ etc. are precise hydrides.
3. Electron rich hydrides:
   Those compounds in which central atom has one or more lone pair of excess electrons are called electron-rich hydrides. e.g., NH₃, H₂O.

Question 3.
Explain the uses of hydrogen.
Answer:
1. Over 90 % hydrogen produced in the industry is used for synthetic applications. One such process is the Haber process which is used to synthesis ammonia on large scales. Ammonia is used for the manufacture of chemicals such as nitric acid, fertilizers and explosives.
N₂ + 3H₂  2NH
2. It can be used to manufacture the industrial solvent, methanol from carbon monoxide using copper as a catalyst.
CO + 2H₂  CH₃OH
3. Unsaturated fatty oils can be converted into saturated fats called Vanaspati (margarine) by the reduction reaction with \(\frac{P_{t}}{H_{2}}\)
4. In metallurgy, hydrogen can be used to reduce many metal oxides to metals at high temperatures.
CuO + H₂ → Cu + H₂O

WO₃ + 3H₂ → W + 3H₂O
5. Atomic hydrogen and oxy-hydrogen torches are used for cutting and welding.
6. Liquid hydrogen is used as a rocket fuel.
7. Hydrogen is also used in fuel cells for generating electrical energy. The reversible uptake of hydrogen in metals is also attractive for rechargeable metal hydride battery.

Question 4.
What is the permanent hardness of water? How is it removed?
Answer:
The permanent hardness of water is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in it. It can be removed by adding washing soda, which reacts with these metal {M = Ca or Mg) chlorides and sulphates in hard water to form insoluble carbonates.

MCl₂ + Na₂CO₃ → MCO₃+ 2NaCl
MSO₄ + Na₂CO₃ → MCO₃ + Na₂SO₄

In another way to soften the hard water is by using a process called ion-exchange. That is, hardness can be removed by passing through an ion-exchange bed like zeolites or a column containing ion-exchange resin. Zeolites are hydrated sodium alumino-silicates with a general formula, NaO . Al₂O₃. ^xSiO₂. ^yH₂O (x = 2 to 10, y = 2 to 6).

Zeolites have porous structure in which the monovalent sodium ions are loosely held and can be exchanged with hardness producing metal ions (M= Ca or Mg) in water. The complex structure can conveniently be represented as Na₂ – Z with sodium as exchangeable cations.
Na₂ – Z + M²⁺ → M – Z + 2Na⁺

When exhausted, the materials can be regenerated by treating with aqueous sodium chloride. The metal ions (Ca² and Mg²⁺) caught in the zeolite (or resin) are released and they get replenished with sodium ions.
M – Z + 2NaCl → Na₂ – Z + MCl₂

Question 5.
Discuss the reaction of hydrogen with (i) Oxygen (ii) Halogens (iii) Alkali metals.
Answer:
(i) Reaction of hydrogen with oxygen.
Hydrogen reacts with oxygen to give water. This is an explosive reaction and releases lot of energy. This is used in fuel cells to generate electricity.
2H₂ + O₂ → 2H₂O

(ii) Reaction of hydrogen with halogens.
Similarly, hydrogen also reacts with halogens to give corresponding halides. Reaction with fluorine takes place even in dark with explosive violence while with chlorine at room temperature under the light. It combines with bromine on heating and reaction with iodine is a photochemical reaction.
2H₂ + O₂ → 2H₂O
In the above reactions, the hydrogen has an oxidation state of +1.

(iii) Reaction of hydrogen with alkali metals:
It also has a tendency to react with reactive metals such as lithium, sodium, and calcium to give corresponding hydrides in which the oxidation state of hydrogen is -1.
2Li + H₂ → 2 LiH
2Na + H₂ → 2NaH

These hydrides are used as reducing agents in synthetic organic chemistry. It is used to prepare other important hydrides such as lithium aluminium hydride and sodium borohydride.
4 LiH + AlCl₃ → Li[AlH₄] + 3LiCl
4 NaH + B(OCH₃)₃ → Na[BH₄] + 3CH₃ONa

Question 6.
Explain the structure of hydrogen peroxide.
Answer:
Both in gas-phase and liquid-phase, the molecule adopts a skew confirmation due to repulsive interaction of the OH bonds with lone-pairs of electrons on each oxygen atom. Indeed, it is the smallest molecule known to show hindered rotation • about a single bond.

H₂O₂ has a non-polar structure. The molecular dimensions in the gas phase and solid phase differ as shown in figure 4.5. Structurally, H₂O₂ is represented by the dihydroxyl formula in which the two OH groups do not lie in the same plane.

One way of explaining the shape of hydrogen peroxide is that the hydrogen atoms would lie on the pages of a partly opened book, and the oxygen atoms along the spine. In the solid phase of molecule, the dihedral angle reduces to 90.2° due to hydrogen bonding and the O-O-H angle expands from 94.8° to 101.9°.

Question 7.
Explain the uses of hydrogen compounds.
Answer:

• The hydrogen compounds such as sodium borohydride (NaBH₄) and lithium aluminium hydride (LiAlH₄) are commonly used as reducing agents in organic chemistry.
• Hydrides such as sodium hydride (NaH) and potassium hydride (KH) are used as strong bases in organic synthesis.
• Calcium hydride is used as a desiccant to remove moisture from organic solvents.
• Hydride complexes are catalysts.
• Atomic hydrogen and oxy-hydrogen torches for cutting and welding.
• Hydrogen is used in fuel cells for generating electrical energy.
• Liquid hydrogen is used as a rocket fuel as well as in space research.
• Metallic hydrides are used in battery applications.

Question 8.
Write notes on intermolecular hydrogen bonding.
Answer:
Intermolecular hydrogen bonds occur between two separate molecules. They can occur between any number of like or unlike molecules as long as hydrogen donors and acceptors are present in positions which enable the hydrogen bonding interactions. For example, intermolecular hydrogen bonds can occur between ammonia molecule themselves or between water molecules themselves, or between ammonia and water.

Water molecules form strong hydrogen bonds with one another. For example, each water molecule is linked to four others through hydrogen bonds. The shorter distances (100 pm) correspond to covalent bonds (solid lines), and the longer distances (180 pm) correspond to hydrogen bonds (dotted lines).

In ice, each atom is surrounded tetrahedrally by four water molecules through hydrogen bonds. That is, the presence of two hydrogen atoms and two lone pairs of electrons on oxygen atoms in each water molecule allows the formation of a three-dimensional structure. This arrangement creates an open structure, which accounts for the lower density of ice compared with water at 0°C. While in liquid water, unlike ice where hydrogen bonding occurs over a long-range, the strong hydrogen bonding prevails only in a short-range and therefore the denser packing.

Question 9.
What is hydrogen bonding? Discuss its properties and applications.
Answer:
Hydrogen bonding is one of the most important natural phenomena occurring in chemical and biological sciences. These interactions play a major role in the structure of proteins and DNA. When a hydrogen atom (H) is covalently bonded to a highly electronegative atom such as fluorine (F) or oxygen (O) or nitrogen (N), the bond is polarized.

Due to this effect, the polarized hydrogen atom is able to form a weak electrostatic interaction with another electronegative atom present in the vicinity. This interaction is called a hydrogen bond (20 – 50 kJ mol^-1) and is denoted by dotted lines (………).

It is weaker than the covalent bond (> 100 kJ mol^-1) but stronger than the vander Waals interaction (< 20 kJ mol^-1). Hydrogen bond has a profound effect on various physical properties including vapour pressure (H₂O and H₂S), boiling point, miscibility of liquids (H₂O and C₂H₅OH), surface tension, densities, viscosity, heat of vaporization and fusion, etc. Hydrogen bonds can occur within a molecule (intramolecular hydrogen bonding) and between two molecules of the same type or different type (intermolecular hydrogen bonding).

A hydrogen bond occurs not only in simple molecules but also in complex biomolecules such as proteins, and they are crucial for biological processes. For example, hydrogen bonds play an important role in the structure of deoxyribonucleic acid (DNA), since they hold together the two helical nucleic acid chains (strands).