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 hydrolysed
(d) Its hydride is electron deficient and polymeric
(c) Its salts are rarely hydrolysed

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?

1. Sodium hydroxide is stronger base whereas sodium chloride is a salt.
2. Sodium hydroxide dissolve freely in water with evolution of much heat on account of intense hydration.
3. In other words when the Na+ and OH ions break up, the OH ions are much smaller than Cl ions and are able to form a hydrogen bond with water.
4. Thus sodium hydroxide dissolves easily in water.

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 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 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?
Sodium: Because hydration is favoured by high charge density cations and of the two mono positive ions, sodium is smaller and will have higher charge density.
Thus, Na2SO4.10H2O is more readily formed.

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.

1. Beryllium chloride forms a dimeric structure like aluminium chloride with chloride bridges. Beryllium chloride also forms a polymeric chain structure in addition to dimer. Both are soluble in organic solvents and are strong Lewis acids.
2. Beryllium hydroxide dissolves in excess of alkali and gives beryllate ion and [Be(OH)4]2- and hydrogen as aluminium hydroxide which gives aluminate ion, [Al(OH)4]2-.
3.  Beryllium and aluminium ions have strong tendency to form complexes, BeF42-, AlF63-.
4. Both beryllium and aluminium hydroxides are amphoteric in nature.
5. Carbides of beryllium (Be2C) like aluminium carbide (Al4C3) give methane on hydrolysis.
6. 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 the lowest solubility among alkali metal fluoride due to its small size of Li+ and F ions, lattice enthalpy is much higher than that of hydration enthalpy.

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 immobilising 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?
Halogens are non-metals and beryllium is also a non-metal. Since non-metals always form covalent bonds with each other due to almost similar ionization potential and electronegativity. And Beryllium is smaller in size and has high polarizing power therefore, beryllium halides are covalent.

Magnesium is a metal and metals mostly form ionic bonds with non-metals due to vast difference in their ionization potential and electronegativity, therefore magnesium halides are always ionic.

Question 36.
Alkaline earth metal (A), belongs to 3rd period reacts with oxygen and nitrogen to form compound (B) and (C) respectively. It undergoes metal displacement reaction with AgNO3 solution to form 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 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 is known as alkaline earth metals. It contains soft, silver metals that are less metallic in character than the Group 1 elements. Although many characteristics are common throughout the group, the heavier metals such as Ca, Sr, Ba, and Ra are almost as reactive as the Group 1 Alkali Metals.
2. General electronic configuration can be represented as [Noble gas] ns2 where ‘n’ represents the valence shell.
3. All the elements in Group 2 have two electrons in their valence shells, giving them an oxidation state of +2. This enables the metals to easily lose electrons, which increases their stability and allows them to form compounds via ionic bonds.
4. The atomic and ionic radii of alkaline earth metals are smaller than the corresponding members of the alkali metals.
5. On moving down the group, the radii increases due to gradual increase in the number of the shells and the screening effect.
6. Down the group the ionisation enthalpy decreases as atomic size increases. They are less electropositive than alkali metals.
7. Compounds of alkaline earth metals are more extensively hydrated than those of alkali metals, because the hydration enthalpies of alkaline earth metal ions are larger than those of alkali metal ions.

Question 39.
Discus the similarities between beryllium and aluminium.
Similarities between Beryllium and Aluminium

1. Beryllium chloride forms a dimeric structure like aluminium chloride with chloride bridges. Beryllium chloride also forms polymeric chain structure in addition to dimer. Both are soluble in organic solvents and are strong Lewis acids.
2. Beryllium hydroxide dissolves in excess of alkali and gives beryllate ion and [Be(OH)4]2-and hydrogen as aluminium hydroxide which gives aluminate ion, [Al(OH)4].
3. Beryllium and aluminium ions have strong tendency to form complexes, BeF42-, AlF63-.
4. Both beryllium and aluminium hydroxides are amphoteric in nature.
5. Carbides of beryllium (Be2C) like aluminium carbide (Al4C3) give methane on hydrolysis.
6. 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 presence of 2 electrons in its outermost shell as compared to alkali metal which have only 1 electron in valence shell. Therefore alkaline earth metals are harder than the 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.

1. Gypsum is used in making drywalls or plasterboards. Plasterboards are used as the finish for walls and ceilings, and for partitions.
2. Another important use of gypsum is the production of plaster of Paris. Gypsum is heated to about 300 degree Fahrenheit to produce plaster of Paris, which is also known as gypsum plaster. It is mainly used as a sculpting material.
3. Gypsum is used in making surgical and orthopaedic casts, such as surgical splints and casting moulds.
4. 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.
5. Gypsum is used in toothpaste, shampoos, and hair products, mainly due to its binding and thickening properties.
6. Gypsum is a component of Portland cement, where it acts as a hardening retarder to control the speed at which concrete sets.

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 into 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 in blood and its concentration is maintained by hormones (calcitonin and parathyroid hormone).
3. Deficiency of calcium in blood causes it to take 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.

1. Magnesium fluoride – 1263°C
2. Magnesium oxide – 2852°C
3. The strength of ionic bonds usually depends on two factors – ionic radius and charge. Mg2+ and O2- have charges of +2 and -2 respectively. This is larger than the charge of other ions like.
4. Magnesium ions and oxygen ions also have small ionic radius.
5. Oxygen ion is smaller than fluoride
6. The smaller the ionic radii, the smaller the bond length and the stronger the bond. Therefore the ionic bond between magnesium and oxygen is very strong.

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

Question 1.
The reducing property of alkali metals follows the order
(a) Na < K < Rb < Cs < Li
(b) K < Na < Rb < Cs < Li
(c) Li < Cs < Rb < K < Na
(d) Rb < Cs < K < Na < Li
(a) Na < K < Rb < Cs < Li

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.
Li does not resemble other alkali metals in which of the following property?
(a) Li2CO3 decomposes into oxides while other alkali carbonates re thermally stable
(b) LiCl is predominantly covalent
(c) Li3N stable
(d) All of the above
(d) All of the above

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 solution which when reacted with CO2 gas produced a white turbidity. The substance (X) could be
(a) Ca
(b) CaH2
(c) Ca(OH)2
(d) Ca(NO3)2
(b) CaH2

Question 5.
The alkali metal used in photoelectric cells is
(a) Na
(b) Cs
(c) Rb
(d) Fr
(b) Cs

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

Question 7.
Be2C + 4H2O → 2X + CH4
X + 2HCl + 2H2O → Y
X and Y formed in the above two reactions is
(a) BeCO3 and Be(OH)2 respectively
(b) Be(OH)2 and BeCl2 respectively
(c) Be(OH)2 and [Be(OH)4]Cl2 respectively
(d) [Be(OH)4]2- and BeCl2 respectively
(c) BQ(OH)2 and [Be(OH)4]Cl2 respectively

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.
Magnesium burns in air to give
(a) MgO
(b) MgCO3
(c) MgCO3
(d) MgO and Mg3N2
(d) MgO and Mg3N2

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 word ‘alkali’ used for alkali metals indicates
(a) ashes of plants
(b) metallic luster
(c) soft metals
(d) reactive metals
(a) ashes of plants

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.
Select the correct statement
LiOH > NaOH > KOH > RbOH
Li2CO3 > Na2CO3 > K2CO3 > Rb2CO3
(a) Solubility of alkali hydroxides is in order
(b) Solubility of alkali carbonates is in order
(c) both are correct
(d) None is correct
(b) Solubility of alkali carbonates is in order

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

Question 15.
Which of the following ions form a hydroxide highly soluble in water?
(a) Ni2+
(b) K2+
(c) Zn2+
(d) Al3+
(b) K2+

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.
The carbide of which of the following metals on hydrolysis gives allylene or propyne?
(a) Be
(b) Ca
(c) Al
(d) Mg
(d) Mg

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 of the following is known as a variety of gypsum ?
(a) CaCO3
(b) CaSO4
(c) plaster of paris
(d) gypsum
(d) gypsum

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

Question 22.
Which one of the following is a radioactive element of alkali metal?
(a) Cesium
(b) Francium
(c) Potassium
(d) Sodium
(b) Francium

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.
The colour of potassium salt in flame is
(a) Crimson red
(b) Lilac
(c) Blue
(d) Yellow
(b) Lilac

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.
Which of the following element forms monoxide and peroxide?
(a) Lithium
(b) Potassium
(c) Rubedium
(d) Sodium
(d) Sodium

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 products obtained on reaction of Na2O2 with water are
(a) NaOH and H2O
(b) NaOH and H2O2
(c) Na2O and H2O2
(d) NaOH, Na2O
(c) Na2O and H2O2

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.
Statement – 1:
LiF has low solubility in water.
Statement – 2:
LiF has low lattice enthalpy.
In the above statements
(a) 1 alone is correct.
(b) Both 1 and 2 are correct
(c) 2 alone is correct
(d) Both 1 and 2 are incorrect
(b) Both 1 and 2 are correct

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

Question 34.
The ammonia used in the Solvay proves- recovered by using
(a) calcium chloride
(b) Calcium hydroxide
(c) calcium carbonate
(d) calcium oxide
(b) Calcium hydroxide

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.
Sodium carbonate decahydrate on heating ab 373K gives
(a) Na2CO3 .3H2O
(b) N2CO3 .5H2O
(c) Na2CO3
(d) Na2CO3 .H2O
(c) Na2CO3

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.
The product obtained on saturating a solution o sodium carbonate with carbon dioxide i,-.
(a) sodium bicarbonate
(b) sodium hydroxide
(c) sodium chloride
(d) sodium peroxide.
(a) sodium bicarbonate

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.
The used in baking cakes, pastries etc., is
(a) sodium chloride
(b) sodium carbonate
(c) sodium bicarbonate
(d) sodium hydroxide
(c) sodium bicarbonate

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.
Fluoraptite is the ore of
(a) magnesium
(b) beryllium
(c) potassium
(d) calcium
(d) calcium

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.
Strontium nitrate give _______ colour in fire works.
(a) violet
(b) bright red
(c) green
(d) orange
(b) bright red

Question 45.
Which of the alkaline earth metal has 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.
______ is a major component of bones and teeth.
(a) Na
(b) Be
(c) Ca
(d) Mg
(c) Ca

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

Question 1.
What are s-block elements?
The elements belonging to the group 1 and 2 in the modem periodic table are called s-block elements. The elements belonging to these two groups are commonly known as alkali and alkaline earth metals respectively.

Question 2.
What are alkali metals?
Alkali metals consists of the elements: lithium, sodium, potassium, rubidium, caesium 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.
Why does the ionization enthalpy of alkali metals decreases in a group?
Alkali metals have the lowest ionisation enthalpy compared to other elements present in the respective period. As we go down the group, the ionisation enthalpy decreases due to the increase in atomic size. In addition, the number of inner shells also increases, which in turn increases the magnitude of screening effect and consequently, the ionisation enthalpy decreases down the group.

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.
Why is the lithium salts are more soluble than the salts of other metals of group-1.
Lithium salts are more soluble than the salts of other metals of group 1. eg., LiClO4 is up to 12 times more soluble than NaClO4. KClO4, RbClO4, and CsClO4 have solubilities only 10-3 times of that of LiClO4. The high solubility of Li salts is due to strong solvation of small size of Li+ ion.

Question 7.
What is diagonaol relatiobship?
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.
Why does the solubility of carbonates and bicarbonates decreases in a group?
All the carbonates and bicarbonates are soluble in water and their solubilities increase rapidly on descending the group. This is due to the reason that lattice energies decrease more rapidly than their hydration energies on moving down the group.

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

Question 10.
What is washing soda?
Sodium carbonate, commonly known as washing soda, crystallises as decahydrate which is white in colour.

Question 11.
What is action of heating on sodium carbonate?
Upon heating, it looses the water of crystallisation to form 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.
How does Lithium shows similar properties with magnesium in its chemical behavior?

1. Both react with nitrogen to form nitrides.
2. Both react with oxygen to give monoxides.
3. Both the element have tendency to form covalent compounds.
4. Both can form complex compounds.

Question 13.
Why are potassium and caesium, rather than lithium used in photoelectric cells?
Potassium and Caesium have much lower ionization enthalpy than that of 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.
Write the chemical formula of the following compounds.
(a) Chile salt petre; (b) marble; (c) Brine
(a) Chile salt petre – NaNO3
(b) marble – CaCO3
(c) Brine – NaCl

Question 15.
The order ofionic mobility of the ions in aqueous solution is Cs+ > Rb+ > K+ > Na+. Account it.
Smaller the size of cation, 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+.

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

Question 16.
(a) Lithium Iodide is more covalent than Lithium fluoride, (b) Lattice enthalpy of LiF is maximum among all the alkali metals halides. Explain.
(a) According to Fajan’s rule, Li+ ion can polarise I ion more than the F ion due to bigger size of the anion. Thus, LiI has more covalent character than LiF.

(b) Smaller the size (intemuclear distance), more is the value of Lattice enthalpy since intemuclear distance is expected to be least in the LiF.

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.
Give two uses of alkali metals.

• Lithium metal is used to make useful alloys. For example with lead it is used to make ‘white metal’ bearings for motor engines, with aluminium to make aircraft parts, and with magnesium to make armour plates. It is used in thermonuclear reactions.
• Lithium is also used to make electrochemical cells.

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.
What are alkaline earth metals?
Group 2 in the modem periodic table contains the elements beryllium, magnesium, calcium, strontium, barium and radium are called alkaline earth metals.

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.
Write the uses of Beryllium.

1. Because of its low atomic number and very low absorption for X-rays, it is used as radiation windows for X-ray tubes and X-ray detectors.
2. The sample holder in X-ray emission studies usually made of beryllium
3. Since beryllium is transparent to energetic particles it is used to build the ‘beam pipe’ in accelerators.
4. Because of its low density and diamagnetic nature, it is used in various detectors.

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 emits electrons hence used in electron tubes and in spark plug electrodes.
4. As a scavenger to remove 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 does beryllium hydride can be prepared?
All the elements except beryllium, combine with hydrogen on heating to fdrm their hydrides with general formula MH2. BeH2 can be prepared by the reaction of BeCl2 with LiAlH4.
2BeCl2 + LiAlH4 → 2BeH2 + LiCl + AlCl3

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.
Write notes on plaster of paris.
It is a hemihydrate of calcium sulphate. It is obtained when gypsum, CaSO4.2H2O, is heated to 393 K.
2CaSO4 2H2O{s) → 2CaSO4 .H2)O + 3H2O
Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO4 is formed. This is known as ‘dead burnt plaster’. It has a remarkable property of setting with water. On mixing with an adequate quantity of water it forms a plastic mass that gets into a hard solid in 5 to 15 minutes.
Uses:
The largest use of Plaster of Paris is in the building industry as well as plasters. It is used for immobilising 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.

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.
Discuss the reaction of alkali metals with liquid ammonia.
Alkali metals dissolve in liquid ammonia to give deep blue solutions that are conducting in nature. The conductivity is similar to that of pure metals. This happens because the alkali metal atom readily loses its valence electron in ammonia solution. Both the cation and the electron are ammoniated to give ammoniated cation and ammoniated electron.
M + (x + y)NH3 → [M(NH3)x]+ [e(NH3)y)]

The blue colour of the solution is due to the ammoniated electron which absorbs energy in the visible region of light and thus imparts blue colour to the solution. The solutions are paramagnetic and on standing slowly liberate hydrogen resulting in the formation of an amide.
M+ + e + NH3 → MNH2 + $$\frac{1}{2}$$H2
In concentrated solution, the blue colour changes to bronze colour and become diamagnetic.

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.
Write the uses of sodium carbonate.

1. Sodium carbonate known as washing soda is used heavily for laundering
2. It is an important laboratory reagent used in the qualitative analysis and in volumetric analysis.
3. It is also used in water treatment to convert the hard water to soft water
4. It is used in the manufacturing of glass, paper, paint etc…

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.
Comapare the ionization energy of alkali metals with alkaline earth metals.
Members of group 2 have higher ionization enthalpy values than group 1 because of their smaller size, with electrons being more attracted towards the nucleus of the atoms. Correspondingly they are less electropositive than alkali metals.

Although IE1 values of alkaline earth metals are higher than that of alkali metals, the IE2 values of alkaline earth metals are much smaller than those of alkali metals. This occurs because in alkali metals the second electron is to be removed from a cation, which has already acquired a noble gas configuration. In the case of alkaline earth metals, the second electron is to be removed from a monovalent cation, which still has one electron in the outermost shell. Thus, the second electron can be removed more easily in the case of group 2 elements than in group 1 elements.

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.
Write the uses of calcium.

1. As a reducing agent in the metallurgy of uranium, zirconium and thorium.
2. As a deoxidiser, desulphuriser or decarboniser for various ferrous and non-ferrous alloys.
3. In making cement and mortar to be used in construction.
4. As a getter in vacuum tubes.
5. In dehydrating oils
6. In fertilisers, concrete and plaster of paris.

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.
Discuss the diagonal relationship between Lithium and Magnesium.
Similarity between the first member of group 1 (Li) and the diagonally placed second clement of group 2 (Mg) is called diagonal relationship. It is due to similar size (rLi+ = 0.766 Å and Mg2+ = 0.72 Å) and comparable electronegativity values (Li = 1.0; Mg = 1.2). Similarities between Lithium and Magnesium are

1. Both lithium and magnesium are harder than other elements in the respective groups
2. Lithium and magnesium react slowly with water. Their oxides and hydroxides are much less soluble and their hydroxides decompose on heating.
3. Both form a nitride, Li3N and Mg3N2, by direct combination with nitrogen
4. They do not give any superoxides and form only oxides, Li2O and MgO
5. The carbonates of lithium and magnesium decompose upon heating to form their respective oxides and CO2.
6. Lithium and magnesium do not form bicarbonates.
7. Both LiCl and MgCl2 are soluble in ethanol and are deliquescent. They crystallise from aqueous solution as hydrates, LiCl.2H2O and MgCl28H2O

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 corresponding decrease in ionisation 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.
Write the uses of alkali metals.

1. Lithium metal is used to make useful alloys. For example with lead it is used to make ‘white metal’ bearings for motor engines, with aluminium to make aircraft parts, and with magnesium to make armour plates. It is used in thermonuclear reactions.
2. Lithium is also used to make electrochemical cells.
3. Lithium carbonate is used in medicines
4. Sodium is used to make Na/Pb alloy needed to make Pb(Et)4 and Pb(Me)4. These organolead compounds were earlier used as anti-knock additives to petrol, but nowadays lead-free petrol in use.
5. Liquid sodium metal is used as a coolant in fast breeder nuclear reactors. Potassium has a vital role in biological systems.
6. Potassium chloride is used as a fertilizer. Potassium hydroxide is used in the manufacture of soft soap. It is also used as an excellent absorbent of carbon dioxide.
7. Caesium is used in devising photoelectric cells.

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 hydrolysed Hydrolysed

Question 7.
Explain the diagonal relationship of Beryllium with Aluminium.
Beryllium (the first member of group 2) shows a diagonal relationship with aluminium. In this case, the size of these ions (rBe2+ = 0.45 Å and rAl3+ = 0.54 Å) is not as close. However, their charge per unit area is closer. (Be2+ = 2.36 and Al3+ = 2.50) They also have same electronegativity values (Be = 1.5; Al = 1.5).
Properties:

1. Beryllium chloride forms a dimeric structure like aluminium chloride with chloride bridges. Beryllium chloride also forms polymeric chain structure in addition to dimer. Both are soluble in organic solvents and are strong Lewis acids.
2. Beryllium hydroxide dissolves in excess of alkali and gives beryllate ion and [Be(OH)4]2- and hydrogen as aluminium hydroxide which gives aluminate ion. [Al( OH4)
3. Beryllium and aluminum ions have strong tendency to form complexes, BeF42-, AlF63-.
4. Both beryllium and aluminium hydroxides are amphoteric in nature.
5. Carbides of beryllium (Be2C) like aluminum carbide (Al4C3) give methane on hydrolysis
6. Both beryllium and aluminium are rendered passive by nitric acid.

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 plaster boards. Plaster boards 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 degree 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.