Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Chemistry Guide Pdf Chapter 5 Alkali and Alkaline Earth Metals Text Book Back Questions and Answers, Notes.

## Tamilnadu Samacheer Kalvi 11th Chemistry Solutions Chapter 5 Alkali and Alkaline Earth Metals

### 11th Chemistry Guide Alkali and Alkaline Earth Metals Text Book Back Questions and Answers

Textual Questions:

Question 1.
For alkali metals, which one of the following trends is incorrect?
(a) Hydration energy: Li > Na > K> Rb
(b) Ionisationenergy: Li> Na> K> Rb
(c) Density: Li < Na < K < Rb
(d) Atomic size: Li < Na < K < Rb
(c) Density: Li < Na < K < Rb

Question 2.
Which of the following statements is incorrect?
(a) Li+ has minimum degree of hydration among alkali metal cations
(b) The oxidation state of K in KO2 is +1
(c) Sodium is used to make Na / Pb alloy
(d) MgSO4 is readily soluble in water
(a) Li+ has minimum degree of hydration among alkali metal cations

Question 3.
Which of the following compounds will not evolve H2 gas on reaction with alkali metals ?
(a) ethanoic acid
(b) ethanol
(c) phenol
(d) none of these
(d) none of these

Question 4.
Which of the following has the highest tendency to give the reaction, M+(g) M+(aq)
(a) Na
(b) Li
(c) Rb
(d) K
(b) Li

Question 5.
sodium is stored in
(a) alcohol
(b) water
(c) kerosene
(d) none of these
(c) kerosene

Question 6.
RbO2 is
(a) superoxide and paramagnetic
(b) peroxide and diamagnetic
(c) superoxide and diamagnetic
(d) peroxide and paramagnetic
(a) superoxide and paramagnetic

Question 7.
Find the wrong statement
(a) sodium metal is used in organic qualitative analysis
(b) sodium carbonate is soluble in water and it is used in inorganic qualitative analysis
(c) potassium carbonate can be prepared by solvay process
(d) potassium bicarbonate is acidic salt
(c) potassium carbonate can be prepared by solvay process

Question 8.
Lithium shows diagonal relationship with
(a) sodium
(b) magnesium
(c) calcium
(d) aluminium
(b) magnesium

Question 9.
Incase of alkali metal halides, the ionic character increases in the order
(a) MF < MCl < MBr < MI
(b) MI < MBr < MCl < MF
(c) MI < MBr < MF < MCl
(d) none of these
(b) MI < MBr < MCl < MF

Question 10.
In which process, fused sodium hydroxide is electrolysed for extraction of sodium?
(a) Castner’s process
(b) Cyanide process
(c) Down process
(d) All of these
(a) Castner’s process

Question 11.
The product obtained as a result of a reaction of nitrogen with CaC2 is
(a) Ca(CN)3
(b) CaN2
(c) Ca(CN)2
(d) Ca3N2
(c) Ca(CN)2

Question 12.
Which of the following has highest hydration energy
(a) MgCl2
(b) CaCl2
(c) BaCl2
(d) SrCl2
(a) MgCl2

Question 13.
Match the flame colours of the alkali and alkaline earth metal salts in the bunsen burner

 (p) Sodium (1) Brick red (q) Calcium (2) Yellow (r) Barium (3) Violet (s) Strontium (4) Apple green (t) Cesium (5) Crimson red (u) Potassium (6) Blue

(a) p – 2, q – 1, r – 4, s – 5, t – 6, u – 3
(b) p – 1, q – 2, r – 4, s – 5, t – 6, u – 3
(c) p – 4, q – 1, r – 2, s – 3, t – 5, u – 6
(d) p – 6, q – 5, r – 4, s – 3, t – 1, u – 2
(a) p – 2, q – 1, r – 4, s – 5, t – 6, u – 3

Question 14.
Assertion:
Generally alkali and alkaline earth metals form superoxides
Reason:
There is a single bond between O and O in superoxides.
(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
(d) both assertion and reason are false

Question 15.
Assertion:
BeSO4 is soluble in water while BaSO4 is not
Reason:
Hydration energy decreases down the group from Be to Ba and lattice energy remains almost constant.
(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
(a) both assertion and reason are true and reason is the correct explanation of assertion

Question 16.
Which is the correct sequence of solubility of carbonates of alkaline earth metals ?
(a) BaCO3 > SrCO3 > CaCO3 > MgCO3
(b) MgCO3 > CaCO3 > SrCO3 > BaCO3
(c) CaCO3 > BaCO3 > SrCO3 > MgCO3
(d) BaCO3 > CaCO3 > SrCO3 > MgCO3
(b) MgCO3 > CaCO3 > SrCO3 > BaCO3

Question 17.
In context with beryllium, which one of the following statements is incorrect?
(a) It is rendered passive by nitric acid
(b) It forms Be2C
(c) Its salts are rarely hydrolyzed
(d) Its hydride is electron-deficient and polymeric
(c) Its salts are rarely hydrolyzed

Question 18.
The suspension of slaked lime in water is known as
(a) lime water
(b) quick lime
(c) milk of lime
(d) aqueous solution of slaked lime
(c) milk of lime

Question 19.
A colourless solid substance (A) on heating evolved CO2 and also gave a white residue, soluble in water. Residue also gave CO2 when treated with dilute HCl.
(a) Na2CO3
(b) NaHCO3
(c) CaCO3
(d) Ca(HCO3)2
(b) NaHCO3

Question 20.
The compound (X) on heating gives a colourless gas and a residue that is dissolved in water to obtain (5). Excess of CO2 is bubbled through aqueous solution of B, C is formed. Solid (C) on heating gives back X. (B) is
(a) CaCO3
(b) Ca(OH)2
(c) Na2CO3
(d) NaHCO3
(b) Ca(OH)2

Question 21.
Which of the following statement is false?
(a) Ca2+ ions are not important in maintaining the regular beating of the heart
(b) Mg2+ ions are important in the green parts of the plants
(c) Mg2+ ions form a complex with ATP
(d) Ca2+ ions are important in blood clotting
(a) Ca2+ ions are not important in maintaining the regular beating of the heart

Question 22.
The name ‘Blue John’ is given to which of the following compounds?
(a) CaH2
(b) CaF2
(c) Ca3(PO4)2
(d) CaO
(b) CaF2

Question 23.
Formula of Gypsum is
(a) CaSO4 .2H2O
(b) CaSO4 .$$\frac{1}{2}$$H2O
(c) 3CaSO4 .H2O
(d) 2CaSO4 .2H2O
(a) CaSO4 .2H2O

Question 24.
When CaC2 is heated in atmospheric nitrogen in an electric furnace the compound formed is
(a) Ca(CN)2
(b) CaNCN
(c) CaC2N2
(d) CaNC2
(b) CaNCN

Question 25.
Among the following the least thermally stable is
(a) K2CO3
(b) Na2CO3
(c) BaCO3
(d) Li2CO3
(d) Li2CO3

II. Write brief answer to the following questions:

Question 26.
Why sodium hydroxide is much more water-soluble than chloride?
NaOH + H2O ⇌ Na+ + OH
1. This reaction is an exothermic reaction. Sodium hydroxide is a strong base, completely dissociated in an aqueous medium. The heat evolved increases the stability. This phenomenon is strong enough to prove that sodium hydroxide crystals are readily dissolved in water.

2. NaCl is geologically stable. If kept dry, it will remain a free-flowing solid for years. Water can dissolve NaCl because the Na+ ions are attracted by OH in water and Cl ions are attracted by H+ in water. The solubility of NaCl does not increase the temperature. Based on this, NaOH is much more soluble due to its exothermic nature than sodium chloride.

Question 27.
Explain what to mean by efflorescence.

1. Efflorescence is a process of losing water of hydration from hydrate.
2. Sodium carbonate crystallises as decahydrate which is white in colour.
3. Upon heating, it loses the water of crystallization to form a monohydrate.
4. Monohydrate (Na2CO3.H2O) is formed as a result of efflorescence.
Na2CO3 .10H2O → Na2CO3.H2O + 9H2O

Question 28.
Write the chemical equations for the reactions involved in the Solvay process of preparation of sodium carbonate.
2NH3 + H2O + CO2 → (NH4)2CO3
(NH4)2CO3 + H2O + CO2 → 2NH4HCO3
2NH4HCO3 + NaCl → NH4Cl + NaHCO3
2NaHCO3 → Na2CO3 + CO2 + H2O

Question 29.
An alkali metal (x) forms a hydrated sulphate, X2SO4 .10H2O. Is the metal more likely to be sodium (or) potassium?
X forms X2SO2. 10H2O. The metal is more likely to be sodium. So X is Na2SO4. 10H2O. It is otherwise called as Glauber’s salt.

Question 30.
Write a balanced chemical equation for each of the following chemical reactions.
(i) Lithium metal with nitrogen gas
(ii) heating solid sodium bicarbonate
(iii) Rubidum with oxgen gas
(iv) solid potassium hydroxide with CO2
(v) heating calcium carbonate
(vi) heating calcium with oxygen
(i) 6Li(s) + N2(g) → 2Li3N(s)
(ii) 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)
(iii) Rb + O2 → RbO2
(iv) 2KOH + CO2 → K2CO3 + H2O
(v) CaCO3 → CaO + CO2
(vi) 2Ca + O2 → 2 CaO

Question 31.
Discuss briefly the similarities between beryllium and aluminium.
Diagonal relationship:
As observed in alkali metals, beryllium shows a diagonal relationship with aluminium. Similarities between beryllium and aluminium:

1. Beryllium and aluminium have the same electronegativity values.
2. Their changes per unit area are closed.
3. BeCl2 and AlCl3 form a dimeric structure. Both are soluble in organic solvents and are strong Lewis acids.
4. Be(OH)2 and Al(OH)3 dissolve in excess alkali to give beryllate ion [Be(OH)4]2- and aluminate ion [Al(OH)4], respectively.
5. Be and Al ions have a strong tendency to form complexes, e.g. BeF42- and AlF63-
6. Both Be(OFI)2 and Al(OH)3 are amphoteric in nature.
7. Carbide of Be – beryllium carbide (Be2C) and Al – aluminum carbide (Al4C3) give methane on hydrolysis.
8. Both beryllium and aluminium are rendered passive by nitric acid.

Question 32.
Give the systematic names for the following
(i) milk of magnesia
(ii) lye
(iii) lime
(iv) Caustic potash
(v) washing soda
(vi) soda ash
(vii) trona
(i) Magnesium hydroxide
(ii) caustic soda(Sodium Hydroxide)
(iii) calcium oxide
(iv) Potassium Hydroxide
(v) sodium carbonate
(vi) sodium carbonate
(vii) Sodium Sesquicarbonate

Question 33.
Substantiate lithium fluoride has the lowest solubility among group one metal fluorides.
Lithium fluoride has high lattice enthalpy due to the small size of Li+ and F . So, due to the high lattice enthalpy, LiF is less soluble in water.

Question 34.
Mention the uses of plaster of paris.
The largest use of Plaster of Paris is in the building industry as well as plasters. It is used for immobilizing the affected part of organ where there is a bone fracture or sprain. It is also employed in dentistry, in ornamental work and for making casts of statues and busts.

Question 35.
Beryllium halides are Covalent whereas magnesium halides are ionic why?
Beryllium ion (Be2+) is smaller in size and it is involved in equal sharing of electrons with halogens to form a covalent bond, whereas magnesium ion (Mg2+) is bigger and is involved in the transfer of electrons to form an ionic bond.

Question 36.
Alkaline earth metal (A), belongs to 3rd period reacts with oxygen and nitrogen to form compound (B) and (C) respectively. It undergoes a metal displacement reaction with AgNO3 solution to form a compound (D).
Alkaline earth metal, 3rd → Magnesium(Mg) ……….(A)
2 Mg + O2 → 2MgO …………(B)
3 Mg + N2 → Mg3N2 ……….(C)
Mg + 2 AgNO3 → 2 Ag + Mg(NO3)2 ………….(D)
A – Magnesium
B – Magnesium oxide
C – Magnesium nitride
D – Magnesium nitrate

Question 37.
Write the balanced chemical equation for the following processes
(a) heating calcium in oxygen
(b) heating calcium carbonate
(c) evaporating a solution of calcium hydrogen carbonate
(d) heating calcium oxide with carbon
(a) 2 Ca + O2 → 2CaO
(b) CaCO3 → CaO + CO2
(c) Ca(HCO3)2 → CO2 + H2O + CaCO3.
(d) CaO + 3 C → CaC2 + CO

Question 38.
Explain the important common features of Group 2 elements.

1. Group 2 elements except beryllium are commonly known as alkaline earth metals because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the Earth’s crust.
2.  Many alkaline earth metals are used in creating colours and used in fireworks.
3. Their general electronic configuration is ns2.
4. Atomic and ionic radii of alkaline earth metals are smaller than alkali metals, on moving down the group, the radii increases.
5. These elements exhibit a +2 oxidation state in their compounds.
6. Alkaline earth metals have higher ionization enthalpy values than alkali metals and they are less electropositive than alkali metals.
7. Hydration enthalpies of alkaline earth metals decrease as we go down the group.
8.  Electronegativity values of alkaline earth metals decrease down the group.
9. Alkaline earth metal salts moistened with concentrated hydrochloric acid gave a characteristic coloured flame when heated on a platinum wire in a flame.

Question 39.
Discuss the similarities between beryllium and aluminium.
Diagonal relationship:
As observed in alkali metals, beryllium shows a diagonal relationship with aluminium. Similarities between beryllium and aluminium:

• Beryllium and aluminium have same electronegativity values.
• Their changes per unit area are closed.
• BeCl2 and AlCl3 form a dimeric structure. Both are soluble in organic solvents and are strong Lewis acids.
• Be(OH)2 and Al(OH)3 dissolve in excess alkali to give beryllate ion [Be(OH)4]2- and aluminate ion [Al(OH)4], respectively.
• Be and Al ions have strong tendency to form complexes, e.g. BeF42- and AlF63-
• Both Be(OFI)2 and Al(OH)3 are amphoteric in nature.
• Carbide of Be – beryllium carbide (Be2C) and Al – aluminium carbide (Al4C3) give methane on hydrolysis.
• Both beryllium and aluminium are rendered passive by nitric acid.

Question 40.
Why alkaline earth metals are harder than alkali metals?
The strength of metallic bond in alkaline earth metals is higher than the alkali metals due to the presence of 2 electrons in its outermost shell as compared to alkali metal which has only 1 electron in the valence shell. Therefore alkaline earth metals are harder than alkali metals.

Question 41.
How is plaster of paris prepared?
It is a hemihydrate of calcium sulphate. It is obtained when gypsum,
CaSO4.2H2O is heated to 393 K.
2CaSO4.2H2O(s) → 2CaSO4.H2O + 3H2O
Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO4 is formed. This is known as ‘dead burnt plaster’.

Question 42.
Give the uses of gypsum.

• The Alabaster variety of gypsum was used by the sculptors.
• Gypsum is used in making dry walls or plasterboards.
• Gypsum is used in the production of Plaster of Paris, which is used as a sculpting material
• Gypsum is used in making surgical and orthopedic casts.
• It plays an important role in agriculture as a soil additive, conditioner and fertilizer
• Gypsum is used in toothpaste, shampoo and hair products.
• Calcium sulphate acts as a coagulator in making tofu.
•  It is also used in baking as a dough conditioner.
• Gypsum is a component of Portland cement, where it acts as a hardening retarder to control the speed at which concrete sets.
• Gypsum is used to give colour to cosmetics and drugs.
• Gypsum plays a very important role in winemaking.

Question 43.
Describe briefly the biological importance of Calcium and magnesium.
Magnesium:

1. A typical adult human body contains about 25 g of magnesium and 1200 g of calcium.
2. Magnesium plays an important role in many biochemical reactions catalyzed by enzymes.
3. It is the co-factor of all enzymes that utilize ATP in phosphate transfer and energy release.
4. It also essential for DNA synthesis and is responsible for the stability and proper functioning of DNA.
5. It is also used for balancing electrolytes in our body.
6. Deficiency of magnesium results in convulsion and neuromuscular irritation.
7. The main pigment that is responsible for photosynthesis, chlorophyll, contains magnesium which plays an important role in photosynthesis.

Calcium:

1. Calcium is a major component of bones and teeth.
2. It is also present in blood and its concentration is maintained by hormones (calcitonin and parathyroid hormone).
3. The deficiency of calcium in the blood causes it to take a longer time to clot. It is also important for muscle contraction.

Question 44.
Which would you expect to have a higher melting point, magnesium oxide or magnesium fluoride? Explain your reasoning.

• Magnesium oxide has very strong ionic bonds as compared to magnesium fluoride.
• Mg2+ and O2- have charges of +2 and -2, respectively.
• Oxygen ion is smaller than fluoride ion.
• The smaller the ionic radii, the smaller the bond length in MgO and the bond is stronger than MgF2.
• Due to more strong bond nature in MgO, it has a high melting point than MgF2.

### 11th Chemistry Guide Alkali and Alkaline Earth Metals Additional Questions and Answers

Question 1.
Which of the following is radioactive in group one elements?
(a) Lithium
(b) Caesium
(c) Rubidium
(d) Francium
(d) Francium

Question 2.
Arrange the following in increasing order of hydration enthalpy.
(a) Rb+ > Li+ > Na+ > K+ > Cs+
(b) Cs+ > Rb+ > K+ > Na+ > Li+
(c) Li+ > Na+ > K+ > Rb+ > Cs+
(d) K+ > Na+ > Li+ > Rb+ > Cs+
(c) Li+ > Na+ > K+ > Rb+ > Cs+

Question 3.
Among the following pairs. which occurs in large amounts in seawater?
(a) Li, Rb
(b) Cs, Fr
(c) Na, K
(d) Be, He
(c) Na, K

Question 4.
1 mol of a substance (X) was treated with an excess of water, 2 mol of readily combustible gas were produced along with the solution which when reacted with CO2 gas produced white turbidity. The substance (X) could be
(a) Ca
(b) CaH2
(c) Ca(OH)2
(d) Ca(NO3)2
(b) CaH2

Question 5.
Spodumene and lepidolite are the minerals of …………
(a) lithium
(b) sodium
(c) potassium
(d) rubidium
(a) lithium

Question 6.
Na2O2 has a light yellow colour. This is due to
(a) presence of unpaired electron in the molecule
(b) presence of a trace of NaO2
(c) presence of KO2 ass an impurity
(d) none of the above
(b) presence of a trace of NaO2

Question 7.
Rock salt is a major source of ………….
(a) lithium
(b) potassium
(c) francium
(d) sodium
(d) sodium

Question 8.
When sodium reacts with excess of oxygen, oxidation number of oxygen changes from
(a) 0 to – 1
(b) 0 to 2
(c) – 1 to – 2
(d) +1 to -1
(a) 0 to – 1

Question 9.
The general molecular formula of rock salt or table salt is ……….
(a) NaI
(b) NaCl
(c) KCI
(d) KBr
(b) NaCl

Question 10.
The composition of common baking powder is
(a) starch, sodium bicarbonate, citric acid
(b) Sodium bicarbonate, tartaric acid
(c) starch, sodium bicarbonate, citric acid
(d) Starch, sodium bicarbonate, calcium hydrogen phosphate.
(d) Starch, sodium bicarbonate, calcium hydrogen phosphate.

Question 11.
The second ionization enthalpy of alkali metals is
(a) zero
(b) low
(c) high
(d) very low
(c) high

Question 12.
Which salt can be used to identify coloured cation
(a) borax
(b) microcosmic salt
(c) both (a) and (b)
(d) none of these
(c) both (a) and (b)

Question 13.
Which one of the following is the smallest atom?
(a) Francium
(b) Rubidium
(c) Lithium
(d) Sodium
(c) Lithium

Question 14.
Which fumes in the air?
(a) BeCl2
(b) MgCl2
(c) CaCl2
(d) BaCl2
(a) BeCl2

Question 15.
Consider the following statements.
(i) Alkali metals exhibit high chemical reactivity due to their low ionization energy.
(ii) Lithium is a very soft metal and even it can be cut with a knife.
(iii) Francium is a radioactive element in group 1 elements
Which of the above statements is/are not correct?
(a) (i) only
(b) (ii) only
(c) (i) and (iii)
(d) (i), (ii) and (iii)
(b) (ii) only

Question 16.
Which causes nerve signals in animals?
(a) Electrical potential gradient due to transfer of K+ ions
(b) Electrical potential gradient due to transfer of Na+ ions in (Na+ – K+) pumps
(c) Electrical potential gradient set up due to transfer of Ca2+ ions
(d) No nerve signal exists in animals.
(a) Electrical potential gradient due to transfer of K+ ions

Question 17.
Which one of the following gives red colour in flame test?
(a) Lithium
(b) Sodium
(c) Potassium
(d) Francium
(a) Lithium

Question 18.
Which of the following reaction produces hydrogen?
(a) Mg + H2O
(b) H2S4O8 + H2O
(c) BaO2 + HCl
(d) Na2O2 + 2HCl
(a) Mg + H2O

Question 19.
A major constituent of Portland cement (except lime) is
(a) Silica
(b) Alumina
(c) Iron oxide
(d) Magnesia
(a) Silica

Question 20.
Which one of the following alkali metals is highly reactive with water?
(a) Li
(b) Cs
(c) Rb
(d) K
(d) K

Question 21.
The elements belong to group-1 are called as
(a) Alkali metals
(b) Alkaline earth metals
(c) halogens
(d) chalcogens
(a) Alkali metals

Question 22.
Which of the following is insoluble in water?
(a) LiF
(b) NaCl
(c) KBr
(d) Li
(d) Li

Question 23.
Match the correct pair Element:

 (A) lithium (i) Sylvite (B) Sodium (ii) Spodumene (C) Potassium (iii) Rock Salt

(a) A – ii, B – iii, C – i
(b) A – i, B – ii, C – iii
(c) A – ii, B – i, C – iii
(d) A – i, B – iii, C – ii
(a) A – ii, B – iii, C – i

Question 24.
Which is the function of the sodium-potassium pump?
(a) Maintenance of ion balance
(b) Used in nerve impulse conduction
(c) Transmitting nerve signals
(d) Regulates the blood level
(c) Transmitting nerve signals

Question 25.
Lithium reacts directly with carbon to form
(a) Li2C2
(b) Li2C
(c) LiC2
(d) LiC
(a) Li2C2

Question 26.
Lithium shows diagonal relationship with
(a) Beryllium
(b) Carbon
(c) Magnesium
(d) Calcium
(c) Magnesium

Question 27.
Among the alkaline earth metals, which is radioactive in nature?
(a) Beryllium
(b) Calcium
(d) Barium

Question 28.
Choose the correct pair:

 (A) Pb(Me)4 (i) fertilizer (B) KCl (ii) photoelectric cells (C) Pb-Al alloy (iii) anti-knock additives (D) Cs (iv) air craft parts

(a) A – iii, B – i, C – iv, D – ii
(b) A – ii, B – iii, C – iv, D – i
(c) A – iv, B – ii, C – iii, D – i
(d) A – ii, B – iv, C – i, D – iii
(a) A – iii, B – i, C – iv, D – ii

Question 29.
Sodium reacts with acetylene to give
(a) Sodium ethoxide
(b) Sodium acetylide
(c) Sodium hydroxide
(d) Sodamide
(b) Sodium acetylide

Question 30.
The eighth most abundant among the alkaline earth metals is ………….
(a) Cu
(b) Be
(c) Mg
(d) Ca
(c) Mg

Question 31.
Choose the correct statement/s is are correct about alkali metals.
1. The oxides and peroxides are colourless when pure but the superoxides are yellow or orange in colour.
2. The peroxides are diamagnetic while the superoxides are paramagnetic.
3. Sodium peroxide is widely used as an oxidizing agent.
4. The alkali metal hydroxides are weak bases.
(a) 1, 2 and 4
(b) 2, 3 and 4
(c) 1, 2 and 3
(d) 1, 3 and 4
(c) 1, 2 and 3

Question 32.
The correct electronic configuration of alkaline earth metal is …………
(a) [noble gases] ns1
(b) [noble gases] ns2 np6
(c) [noble gases] ns2
(d) ns2 (n-1)d1-10
(c) [noble gases] ns2

Question 33.
Alkali metals except ______ form solid bicarbom
(a) Sodium
(b) Potassium
(c) Cesium
(d) Lithium
(d) Lithium

Question 34.
In fire works red colour flash is produced by ………….
(a) Ba
(b) Ra
(c) Sr
(d) Rb
(c) Sr

Question 35.
The by-product formed in the Solvay process
(a) calcium chloride
(b) calcium hydroxide
(c) calcium carbonate
(d) ammonium chloride
(a) calcium chloride

Question 36.
Consider the following statements.
(i) Beryllium has small size and high polarizing power.
(ii) Beryllium does not have d-orbitais in its valence shell.
(iii) Beryllium has low electronegativity and very low ionization enthalpy as compared to other alkaline earth metals.
Which of the above statements is/are not correct?
(a) (i) only
(b) (ii) only
(c) (iii) only
(d) (i) and (ii)
(c) (iii) only

Question 37.
_______ is used water treatment to convert the hard water to soft water.
(a) Sodium chloride
(b) Sodium bicarbonate
(c) Sodium hydroxide
(d) Sodium carbonate
(d) Sodium carbonate

Question 38.
When beryllium carbide reacts with water, the product mainly formed is
(a) ethane
(b) methane
(c) acetylene
(d) ethene
(b) methane

Question 39.
Choose the correct pair:

 (A) Sodium chloride (i) Petroleum refining (B) Sodium Carbonate (ii) domestic use (C) Sodium bicarbonate (iii) laundering (D) Sodium Hydroxide (iv) fire extinguisher

(a) A – ii, B – iv, C – iii, D – i
(b) A – ii, B – iii, C – iv, D – i
(c) A – iv, B – ii, C – i, D – iii
(d) A – iv, B – i, C – ii, D – iii
(b) A – ii, B – iii, C – iv, D – i

Question 40.
Which metal is used as radiation windows for X-ray tubes?
(a) Magnesium
(b) Sodium
(c) Calcium
(d) Beryllium
(d) Beryllium

Question 41.
______ pump play an important role in transmitting nerve signals.
(a) sodium-Magnesium
(b) sodium-potassium
(c) sodium-calcium
(d) sodium-lithium
(b) sodium-potassium

Question 42.
Which one of the following is used as a desulphurizing agent for iron and steel?
(a) Cd
(b) Mg
(c) Zn
(d) Be
(b) Mg

Question 43.
The fifth most abundant element in the earth’s crust is
(a) magnesium
(b) beryllium
(c) calcium
(d) strontium
(c) calcium

Question 44.
Which can be used in controlling galvanic corrosion?
(a) Iron
(b) Magnesium
(c) Calcium
(d) Beryllium
(c) Calcium

Question 45.
Which of the alkaline earth metal has the highest hydration enthalpy?
(a) Be
(b) Mg
(c) Ca
(d) Sr
(a) Be

Question 46.
The anomalous properties of beryllium is mainly due to its
1. small size
2. low electronegativity
3. high ionization energy
4. low polarizing power.
(a) 1,2, 3 and 4
(b) 2 and 4
(c) 1 and 3
(d) 1 and 3
(d) 1 and 3

Question 47.
______ and ______ ions have strong tendency to form complexes.
(a) Be and Al
(b) Be and Mg
(c) Ca and Sr
(d) Be and B
(a) Be and Al

Question 48.
______ is used as radiation windows for X-ray tubes.
(a) Mg
(b) Be
(c) Na
(d) Ca
(b) Be

Question 49.
A compound of calcium used in makig surgical and orthopedic casts is
(a) Dolomite
(b) Gypsum
(c) Feldspar
(d) plaster of Paris
(b) Gypsum

Question 50.
Which one of the following is covalent in character?
(a) BeCl2
(b) MgCl2
(c) CaCl2
(d) BaCl2
(a) BeCl2

II. Very short question and answers (2 Marks):

Question 1.
Why alkali metals and alkaline earth metals are called s-block elements?
Alkali metals and alkaline earth metals (group 1 & 2) are those in which the last electron enters the outermost s-orbital. As the s-orbital can accommodate only two electrons, the two groups belong to the s-block elements.

Question 2.
What are alkali metals?
Alkali metals consist of the elements: lithium, sodium, potassium, rubidium, cesium, and francium. They are all metals, generally soft and highly reactive. They form oxides and hydroxides and these compounds are basic in nature.

Question 3.
Write the mineral source of lithium, sodium, and potassium.

 Element Mineral source 1. Lithium Spodumene 2. Sodium Rock Salt 3. Pottasium Sylvite

Question 4.
Which is the radioactive element in group 1 element? What is its half-life period?
Francium is a highly radioactive element in group. It has a half-life of only 21 minutes.

Question 5.
The second ionization enthalpies of alkali metals are very high. Give reason.
The second ionisation enthalpies of alkali metals are very high. The removal of an electron from the alkali metals gives monovalent cations having stable electronic configurations similar to the noble gas. Therefore, it becomes very difficult to remove the second electron from the stable Configurations, already attained.

Question 6.
Alkali metals never found in a free state in nature. Why?
The loosely held “s” electron in the outermost shell of these elements make them the most electropositive metals. They readily lose electrons to give monovalent M ions. Hence they are never found in a free state in nature.

Question 7.
What is the diagonal relationship?
Similarity between the first member of group 1 (Li) and the diagonally placed second element of group 2 (Mg) is called diagonal relationship. It is due to similar size (rLi+ = 0.766 Å and Mg2+ = 0.12 Å) and comparable electronegativity values (Li = 1.0; Mg = 1.2).

Question 8.
LiClO4 is more soluble than NaClO4 Why?
The small size of the Li+  ion means that it has a very high enthalpy of hydration and so lithium salts are much more soluble than the salts of other group I. E.g. LiClO4  is up to 12 times more soluble than NaClO4.

Question 9.
Lithium carbonate is considerably less stable and decomposes readily. Give reason.
Li2CO3 is considerably less stable and decomposes readily.
Li2CO3 → Li2O + CO2
This is presumably due to the large size difference between Li+ and CO23- which makes the crystal lattice unstable.

Question 10.
Why alkali metals have high chemical reactivity? How does this change along with the group?
Alkali metals exhibit high chemical reactivity because of their low ionization enthalpy and their larger size. The reactivity of alkali metals increases from Li to Cs. since the value of ionization energy decreases down the group (Li to Cs). All the alkali metals are highly reactive towards the more electronegative elements such as oxygen and halogens.

Question 11.
What is action of heating on sodium carbonate?
Upon heating, it looses the water of crystallisation to form a monohydrate. Above 313 K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.
Na2CO3 .10H2O → Na2CO3 .H2O + 9H2O
Na2CO3 .H2O → Na2CO3 + H2O

Question 12.
Explain the action of hydrogen with alkali metals.
All alkali metals react with hydrogen at about 673K (lithium at 1073K) to form their hydrides, which are ionic in nature. Reactivity of alkali metals with hydrogen increases from Li to Cs.
2M + H2 → 2 M+H (where M = Li, Na, K, Rb and Cs)

Question 13.
Why are potassium and caesium, rather than lithium used in photoelectric cells?
Potassium and Caesium have much lower ionization enthalpy than Lithium. As a result, these metals easily emit electrons on exposure to light. Due to this, K and Cs are used in photoelectric cells.

Question 14.
Explain the action of halogen with alkali metals.
Alkali metals combine readily with halogens to form ionic halides M+X. Reactivity of alkali metals with halogen increases down the group because of a corresponding increase in electropositive character.
2M + X2 → 2M+X (M = Li, Na, K, Rb and Cs) (X F, Cl, Br and I)

Question 15.
The order ofionic mobility of the ions in aqueous solution is Cs+ > Rb+ > K+ > Na+. Account it.
Smaller the size of cation, the higher will be the hydration and its effective size will increase and hence mobility in aqueous solution will decrease. Larger size ions have more ionic mobility due to less hydration. Thus the degree of hydration of M+ ions decreases from Li+ to Cs+.

Consequently the radii of the hydrated ion decrease from Li+ to Cs+. Hence, the ionic conductance of these hydrated ions increases from Li+ to Cs+.

Question 16.
What happens when potassium Is treated with water?
Potassium reacts even more violently. The liberated hydrogen catches fire instantly and burns with a lilac coloured flame because of potassium.
2K + 2H2O → 2KOH + H2↑ + heat

Question 17.
Write notes on flame test for alkali metals.
When the alkali metal salts moistened with concentrated hydrochloric acid are heated on a platinum wire in a flame, they show characteristic coloured flame.
Eg:- Lithium – Crimson red; Potassium – Lilac

Question 18.
Li2CO3 decomposes readily whereas other carbonates are not. Why?
The carbonates (M2CO3) of alkali metals are remarkably more stable up to 1270 K above which they first melt and then decompose to form their oxides, whereas Li2CO3 is less stable and
Li2CO3 + ∆ → Li2O + CO2
This is due to the large size difference between Li and CO32- which makes the crystal lattice unstable.

Question 19.
Write the uses of sodium bicarbonate.
The uses of sodium bicarbonate are

• Primarily used as an ingredient in baking.
• Sodium hydrogen carbonate is a mild antiseptic for skin infections.
• It is also used in fire extinguishers.

Question 20.
Why group 2 elements are called alkaline earth metals?
Group 2 elements except beryllium are known as alkaline earth metals. These are so-called because their oxides and hydroxides are alkaline in nature and these metal oxides are found in Earth’s crust.

Question 21.
Write notes on the physical state of alkaline earth metals.
Beryllium is rare and radium is the rarest of all comprising only 10% of igneous rocks. Magnesium and calcium are very common in the earth’s crust, with calcium the fifth-most-abundant element, and magnesium the eighth. Magnesium and calcium are found in many rocks and minerals: magnesium in carnallite, magnesite, dolomite and calcium in chalk, limestone, gypsum.

Strontium is found in the minerals celestite and strontianite. Barium is slightly less common, much of it in the mineral barite. Radium, being a decay product of uranium, is found in all uranium-bearing ores.

Question 22.
Why beryllium has a distinctive character?
The distinctive character of beryllium is mainly due to its small size, high electronegativity and high polarizing power when compared to other elements in the same block.

Question 23.
What are the uses of Strontium?

1. 90Sr is used in cancer therapy.
2. 86Sr/ 86Sr ratios are commonly used in marine investigations as well as in teeth, tracking animal migrations or in criminal forensics.
3. Dating of rocks.
4. As a radioactive tracer in determining the source of ancient archaeological materials such as timbers and coins.

Question 24.
Write the uses of Barium.

1. Used in metallurgy, its compounds are used in pyrotechnics, petroleum mining and radiology.
2. Deoxidiser in copper refining.
3. Its alloys with nickel readily emit electrons hence used in electron tubes and in spark plug electrodes.
4. As a scavenger to remove the last traces of oxygen and other gases in television and other electronic tabes,
5. An isotope of barium 133Ba, used as a source in the calibration of gamma-ray detectors in nuclear chemistry.

Question 25.
How would you prepare beryllium hydride from beryllium chloride?
Beryllium chloride is treated with LiALH4 to get beryllium hydride.
2BeCl2 + LiAlH4 → 2BeH2 + LiCl + AlCl2

Question 26.
Why does solubility of sulphates of alkaline earth metal decreases? Explain.
The sulphates of the alkaline earth metals are all white solids and stable to heat. BeSO4, and MgSO4 are readily soluble in water; the solubility decreases from CaSO4 to BaSO4. The greater hydration enthalpies of Be2+ and Mg2+ ions overcome the lattice enthalpy factor and therefore their sulphates are soluble in water.

Question 27.
Which is the most abundant metal found in the human body? Explain how it works Inside the human body?

• Calcium is the most abundant metal found in the human body for e.g. in teeth and bones.
• Calcium is present in teeth and bones in the form of calcium phosphate and calcium carbonate and these make bone and teeth hard.
• Water in the human body as in the blood and inside cells, contain dissolved calcium ions.
• The calcium ions are involved in muscle movement and sending electricity around the brain and along nerves.

III. Short question and answers (3 Marks):

Question 1.
Write notes characteristic flame colouration of alkali metal salts.
When the alkali metal salts moistened with concentrated hydrochloric acid are heated on a platinum wire in a flame, they show characteristic coloured flame as shown below.

 Element Colour Lithium Crimson red Sodium Yellow Potassium Lilac Rubidium Reddish violet Caesium Blue

The heat in the flame excites the valence electron to a higher energy level. When it drops back to its actual energy level, the excess energy is emitted as light, whose wavelength is in the visible region.

Question 2.
Explain the various periodic trends in the alkali metals down the group.
in alkali metals, as we move down the group

• reactivity increases
• screening effect increases
• tendency to form cation by losing outer electron increases
• melting point and boiling point decreases

Question 3.
Write the properties of oxides and peroxides of alkali metals.
The oxides and the peroxides are colourless when pure, but the superoxides are yellow or orange in colour. The peroxides are diamagnetic while the superoxides are paramagnetic. Sodium peroxide is widely used as an oxidising agent.

The hydroxides which are obtained by the reaction of the oxides with water are all white crystalline solids. The alkali metal hydroxides are strong bases. They dissolve in water with evolution of heat on account of intense hydration.

Question 4.
How alkali metals react with oxygen? Explain with the equation.
1. All the alkali metals on exposure to air burn vigorously, forming oxides on the surface of the metals.
2. Lithium forms the only monoxide, sodium forms the monoxide and peroxide and the other elements form monoxide, peroxide, and superoxides.
4Li + O2 → 2Li2O (Lithium monoxide)
2 Na + O3 → Na2O2 (Sodium peroxide)
K + O3 → KO2 (Potassium superoxide)

Question 5.
Write the uses of sodium hydroxide.

1. Sodium hydroxide is used as a laboratory reagent
2. It is also used in the purification of bauxite and petroleum refining
3. It is used in the textile industries for mercerizing cotton fabrics.
4. It is used in the manufacture of soap, paper, artificial silk, and a number of chemicals.

Question 6.
What are the mineral sources of alkali metals?

 Element Mineral source Beryllium Beryl, Be3Al2Si6O18 Magnesium Camallite, KCl. MgCl2.6H2O Dolomite, MgCO3.CaCO3 Calcium Fluorapatite Strontium Celestite, SrSO4 Barium Barytes, BaSO4

Question 7.
Explain how alkali metal oxide reacts with water?
Alkali metal oxides M2O, M2O2, and MO2 are easily hydrolyzed by water to form the hydroxides
according to the following reactions:
M2O + H2O → 2M+ + 2OH
M2O, + 2H2O → 2M+ + 2OH + H2O2
2MO2 + 2H2O → 2M+ + 2OH H2O2 + O2

Question 8.
Write the uses of magnesium.

1. Removal of sulphur from iron and steel
2. Refining of titanium in the ‘Kroll” process.
3. Used as photoengrave plates in printing industry.
4. Magnesium alloys are used in aeroplane and missile construction.
5. Mg ribbon is used in synthesis of Grignard reagent in organic synthesis.
6. It alloys with aluminium to improve its mechanical, fabrication and welding property.
7. As a desiccant.
8. As sacrificial anode in controlling galvanic corrosion.

Question 9.
Copper and chlorine compounds make blue firework Why?

• To produce colours, fireworks experts hum the metal and chlorine together in a vapour, where the two elements are gases instead of solid.
• The burning excites the electron pushing them into a higher than normal energy level. As the electrons returns to their normal level, they release their extra energy as a colourful burst of light.
• True blue fireworks arc the hardest to make since the compound copper chloride breaks down in a hot flame.

Question 10.
Give uses of magnesium.

1. Removal of sulphur from iron and steel
2. Refining of titanium in the “Kroll” process.
3. Used as photoengrave plates in printing industry.
4. Magnesium alloys are used in aeroplane and missile construction.
5. Mg ribbon is used in synthesis of Grignard reagent in organic synthesis.
6. It alloys with aluminium to improve its mechanical, fabrication and welding property.
7. As a desiccant.
8. As sacrificial anode in controlling galvanic corrosion.

Question 11.
Give the structure of BeCl2 in the solid phase and Vapor phase.
Beryllium chloride has a chain structure in the solid-state as shown below, (structure-a). In the vapour phase, BeCl2 tends to form a chloro-bridged dimer (structure-c) which dissociates into the linear monomer at high temperatures of the order of 1200 K. (structure-b).

Question 1.
Compare the properties of Lithium with other elements of the group.
The distinctive behaviour of Li+ ion is due to its exceptionally small size, high polarising power, high hydration energy and non-availability of d-orbitals.

 Lithium Other elements of the Group Hard, high melting, and boiling point Soft, Lower melting and boiling point Least reactive (For example it reacts with oxygen to form normal oxide, forms peroxides with great difficulty and its higher oxides are unstable) More reactive Reacts with nitrogen to give Li3N No reaction Reacts with bromine slowly React violently Reacts directly with carbon to form ionic carbides. For example 2Li + 2C →  Li2C2 Do not react with carbon directly, but can react with carbon compounds. Na + C2H2 → Na2C2 Compounds are sparingly soluble in water highly soluble in water. Lithium nitrate decomposes to give an oxide decompose to give nitrites

Question 2.
Describe the biological importance of sodium and potassium.
1. Monovalent sodium and potassium ions are found in large proportions in biological fluids.
2. These ions perform important biological functions such as maintenance of ion balance and nerve impulse conduction.
3. Sodium – Potassium play an important role in transmitting nerve signals.
4. Atypical 70 kg man has 90g of Na and 170 g of K.

5. Sodium ions are found on the outside of cells, being located in blood plasma and in the interstitial fluid which surrounds the cells. These ions participate in the transmission of nerve signals, in regulating the flow of water across cell membranes and in the transport of sugars and amino acids into cells.

6. Potassium ions are the most abundant cations within cell fluids, where they activate many enzymes, participate in the oxidation of glucose to produce ATP and with sodium, are responsible for the transmission of nerve signals.

Question 3.
Explain the reaction of alkali metals with (i) Oxygen (ii) hydrogen (iii) halogens.
(i) Reaction with Oxygen:
All the alkali metals on exposure to air or oxygen bum vigorously, forming oxides on their surface. Lithium forms only monoxide, sodium forms the monoxide and peroxide and the other elements form monoxide, peroxide, and superoxides. These oxides are basic in nature.
4Li + O2 → 2Li2O (simple oxide)
2Na + O2 → Na2O2 (peroxide)
M + O2 → MO2
(M = K, Rb, Cs; MO2 – superoxide)

(ii) Reaction with hydrogen:
All alkali metals react with hydrogen at about 673 K (lithium at 1073 K) to form the corresponding ionic hydrides. Reactivity of alkali metals with hydrogen decreases from Li to Cs.
2M + H2 → 2M+H
(M = Li, Na, K, Rb, Cs)
The ionic character of the hydrides increases from Li to Cs and their stability decreases. The hydrides behave as strong reducing agents and their reducing nature increases down the group.

(iii) Reaction with halogen:
Alkali metals combine readily with halogens to form ionic halides MX. Reactivity of alkali metals with halogens increases down the group because of a corresponding decrease in ionization enthalpy.
2 M + X2 → 2 MX
(M = Li, Na,K, Rb, Cs) (X = F, Cl, Br, I)
All metal halides are ionic crystals. However, Lithium iodide shows covalent character, as it is the smallest cation that exerts high, polarising power on the iodide anion. Additionally, the iodide ion being the largest can be polarised to a greater extent by Li+ ion.

Question 4.
List out the uses of magnesium.
Magnesium is used:

• in the removal of sulphur from iron and steel.
• in the refining of titanium in the “Kroll” process.
• as photoengrave plates in the printing industry.
• Magnesium alloys are used in airplane and missile construction.
• Mg ribbon is used in synthesis of Grignard reagent in organic synthesis.
• It alloys with aluminium to improve its mechanical, fabrication and welding property.
• as a desiccant.
• as sacrificial anode in controlling galvanic corrosion.
• Magnesium is the co-factor of all enzymes that utilize ATP in phosphate transfer and energy release.

Question 5.
How is washing soda prepared? Discuss its properties.
Sodium carbonate is one of the important inorganic compounds used in industries. It is prepared by Solvay process. In this process, ammonia is converted into ammonium carbonate which then converted to ammonium bicarbonate by passing excess carbon dioxide in a sodium chloride solution saturated with ammonia.

The ammonium bicarbonate thus formed reacts with the sodium chloride to give sodium bicarbonate and ammonium chloride. As sodium bicarbonate has poor solubility, it gets precipitated. The sodium bicarbonate is isolated and is heated to give sodium carbonate. The equations involved in this process are,
2NH3 + H2O + CO2 → (NH4)2 CO3
(NH4)2 CO3 + H2O + CO2 → 2NH4HCO3
2NH4HCO3 + NaCl → NH4Cl + NaHCO3
2NaHCO → Na2CO3 + CO2 + H2O

The ammonia used in this process can be recovered by treating the resultant ammonium chloride solution with calcium hydroxide. Calcium chloride is formed as a by-product.

Properties:
Sodium carbonate, commonly known as washing soda, crystallises as decahydrate which is white in colour. It is soluble in water and forms an alkaline solution. Upon heating, it looses the water of crystallisation to form monohydrate. Above 373 K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.
Na2CO3 .10H2O → Na2CO3.H2O + 9H2O
Na2CO3.H2O → Na2CO3 + H2O

Question 6.
Compare the properties of Beryllium with other elements of the group.

 Beryllium Other elements of the family 1. Forms covalent compounds Form ionic compounds 2. High melting and boiling point Low melting and boiling point 3. Does not react with water even at elevated temperature React with water 4. Does not combine directly with hydrogen Combine directly with hydrogen 5. Does not combine directly with halogens. Halides are covalent Combine directly with halogens. Halides are electrovalent. 6. Hydroxide and oxides of beryllium are amphoteric in nature Basic in nature. 7. It is not readily attacked by acids because of the presence of an oxide film Readily attacked by acids 8. Beryllium carbide evolves methane with water. evolve acetylene with water. 9. Salts of Be are extensively hydrolyzed Hydrolyzed

Question 7.
State as to why
(a) Alkali metals show only +1 oxidation state.
(b) Na and K impart colour to the flame but Mg does not.
(c) Lithium on being heated in air mainly forms the monoxide and not the peroxide.
(d) Li is the best reducing agent in aqueous solution.
(a) Alkali metals have low ionization enthalpies. They have a strong tendency to lose 1 electron to form unipositive ions. Thus they show an oxidation state of+1 and are strongly electropositive.

(b) Valence electrons of alkali metals like Na and K easily absorb energy from the flame and are excited to higher energy levels. When these electrons return to the ground state, the energy is emitted in the form of light. Magnesium atom has small size so electrons are ’ strongly bound to the nucleus. Thus they need large amount of energy for excitation of electrons to higher energy levels, which is not possible in Bunsen flame.

(c) Due to the small size of Li+ it has a strong positive field, which attracts the negative charge so strongly that it does not permit the oxide ion (O2-) to combine with another oxygen atom to form peroxide ion.

(d) Among alkali metals, lithium has the most negative electrode potential (Ee = -3.04 V), so it is the strongest reducing agent in the aqueous solution.

Question 8.
Explain the properties and uses of Gypsum.
Properties of Gypsum:

1. Gypsum is a soft mineral, which is moderately soluble in water. The solubility of this mineral in water is affected by temperature. Unlike other salts, gypsum becomes less soluble in water as the temperature increases. This is known as retrograde solubility, which is a distinguishing characteristic of gypsum.
2. Gypsum is usually white, colorless, or gray in color. But sometimes, it can also be found in the shades of pink, yellow, brown, and light green, mainly due to the presence of impurities.
3. Gypsum crystals are sometimes found to occur in a form that resembles the petals of a flower. This type of formation is referred to as ‘desert rose’, as they mostly occur in arid areas or desert terrains.
4. Gypsum is known to have low thermal conductivity, which is the reason why it is used in making drywalls or wallboards. Gypsum is also known as a natural insulator.
5. Alabaster is a variety of gypsum, that is highly valued as an ornamental stone. It has been used by the sculptors for centuries. Alabaster is granular and opaque.
6. Gypsum has hardness between 1.5 to 2 on Moh’s Hardness Scale. Its specific gravity is 2.3 to 2.4.

Uses of Gypsum:

1. The alabaster variety of gypsum was used in ancient Egypt and Mesopotamia by the sculptors. The ancient Egyptians knew how to turn gypsum into plaster of Paris about 5,000 years ago. Today, gypsum has found a wide range of uses and applications in human society, some of which are enlisted below.
2. Gypsum is used in making drywalls or plasterboards. Plasterboards are used as the finish for walls and ceilings, and for partitions.
3. Another important use of gypsum is the production of plaster of Paris. Gypsum is heated to about 300 degrees Fahrenheit to produce plaster of Paris, which is also known as gypsum plaster. It is mainly used as a sculpting material.
4. Gypsum is used in making surgical and orthopedic casts, such as surgical splints and casting moulds.
5. Gypsum plays an important role in agriculture as a soil additive, conditioner, and fertilizer, It helps loosen up compact or clay soil and provides calcium and sulphur, which are essential for the healthy growth of a plant. It can also be used for removing sodium from soils having excess salinity.

Question 9.
Mention the biological importance of sodium and potassium.

1. Monovalent sodium and potassium ions are found in large proportions in biological fluids. These ions perform important biological functions such as maintenance of ion balance | and nerve impulse conduction.
2. A typical 70 kg man contains about 90 g of sodium and 170 g of potassium compared with only 5 g of iron and 0.06 g of copper.
3. Sodium ions are found primarily on the outside of cells, is located in blood plasma and in the interstitial fluid which surrounds the cells. These ions participate in the transmission of nerve signals, in regulating the flow of water across cell membranes, and in the transport of sugars and amino acids into cells.
4. Sodium and potassium, although so similar chemically, differ quantitatively in their ability to penetrate cell membranes, in their transport mechanisms, and in their efficiency to activate enzymes.
5. Thus, potassium ions are the most abundant cations within cell fluids, where they activate many enzymes, participate in the oxidation of glucose to produce ATP and, with sodium, are responsible for the transmission of nerve signals.
6. Sodium-potassium pumps play an important role in transmitting nerve signals.