Answer the following questions: Alkali and Alkaline Earth Metals (Chemistry)

Alkali and Alkaline Earth Metals (Chemistry)

Brief Questions

26. Why sodium hydroxide is much more water soluble than chloride?

● NaOH is a strong base. It dissolves in water to give a strong alkaline solution. (NaOH. H₂O and NaOH.2H₂O) with the liberation of large amount of heat due to intense hydration.

● It is a deliquescent solid. The alkali metal hydroxides are strong bases.

● 36g of NaCl dissolves in 100g of water. The solubility does not increase with increase in temperature.

Q. Explain what to meant by efflorescence; 

27. Write the chemical equations for the reactions involved in solvay process of preparation of sodium carbonate.

The equations involved in this process are,

2NH₃ + H₂O + CO₂ → (NH₄)₂ CO₃

(NH₄)₂ CO₃ + H₂O + CO₂ → 2 NH₄ HCO₃

2NH₄ HCO₃ + NaCl → NH₄Cl + NaHCO₃

2 NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

28. An alkali metal (x) forms a hydrated sulphate, X2SO4. 10H2O. Is the metal more likely to be sodium (or) potassium.

● The metal (x) is more likely to be sodium. The extent of hydration of alkali metals is inversely proportional to its size. The increasing order of size is Li⁺ < Na⁺ < K⁺

● Since the size of Na⁺ is less than K⁺, Na⁺ is hydrated more. The formula of the hydrated salt is Na₂SO₄.10H₂O 

29. Write 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) Lithium metal with nitrogen gas

6Li + N₂ → 2 Li₃ N

ii) Heating solid sodium bicarbonate

Na₂CO₃.10H₂O    ^___373K­→   Na₂CO₃.H₂O + 9H₂O

Na₂CO₃.H₂O ^{___above 373K__}→ Na₂CO₃ + H₂O

iii) Rubidum with oxygen gas

Rb + O₂ → RbO₂ (Rubidium Super Oxide)

2Rb + O₂ → Rb₂O₂ (Rubidium Peroxide)

iv) Solid potassium hydroxide with CO₂

KOH + CO₂ → KHCO₃

v) Heating Calcium Carbonate

CaCO₃ → CaO + CO₂

vi) Heating Calcium with Oxygen

2Ca + O₂ → 2CaO

30. Discuss briefly the similarities between beryllium and aluminium.

Similarities between beryllium and Aluminium.

1. Beryllium chloride forms a dimeric structure like aluminium 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, BeF₄ ²⁻, 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.

31. Give the systematic names for the following

(i) milk of magnesia (ii) lye (iii) lime (iv) Caustic potash (v) washing soda (vi) soda ash (v) trona

i) Milk of magnesia – Magnesium hydroxide

ii) Iye – Sodium hydroxide

iii) lime - Calcium hydroxide or Calcium oxide

iv) Caustic potash - Potassium hydroxide

v) Washing soda - Sodium Carbonate

vi) Soda ash - Anhydrous Sodium Carbonate

vii) Trona - Mixture of Sodium Carbonate and Sodium bicarbonate

32. Substantiate Lithium fluoride has the lowest solubility among group one metal fluorides.

1) LiF is a covalent compound whereas other fluorides are ionic compounds

2) Size of Li⁺ is very small

3) Li Has high polarising effect power.

33. Mention the uses of plaster of paris

1) The largest use of Plaster of Paris is in the building industry as well as plasters.

2) It is used for immobilising the affected part of organ where there is a bone fracture or sprain.

3) It is also employed in dentistry, in ornamental work and for making casts of statues and busts.

34. Beryllium halides are Covalent whereas magnesium halides are ionic why?

Small size of Be atom, high electronegativity and high polarising ability of halide ions attached to Beryllium.

35. Alkaline earth metal (A), belongs to 3rd period reacts with oxygen and nitrogen to form compound (B) and (C) respectively. It undergo metal displacement reaction with AgNO3 solution to form compound (D).

Alkaline earth metal (A), belongs to 3rd period is Mg

5Mg + O₂ + N_{2 ­­­­­}^____Δ→ 2MgO + Mg₃N₂

                                (B)           (C)

Mg + 2AgNO₃ → Mg(NO₃)₂ + 2Ag

Symbol : Name

A. Mg : Magnesium

B. MgO : Magnesium Oxide

C. Mg₃N₂ : Magnesium Nitride

D. Mg(NO₃)₂ : Magnesium Nitrate

36. 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) heating calcium in oxygen:

2Ca + O₂ → 2CaO

b) heating calcium carbonate:

CaCO₃ → CaO + CO₂

c) evaporating a solution of calcium hydrogen carbonate:

Ca(HCO₃)₂ → CaCO₃ + CO₂ + H₂O

d) heating calcium oxide with carbon:

CaO + 3C ^__2000°C_→ CaC₂ + CO

37. Explain the important common features of Group 2 elements.

1. Their general electronic configuration is written as [Noble gas] ns²

2. The atomic and ionic radii of alkaline earth metals are smaller than the corresponding members of the alkali metals. On moving down the group, the radii increases due to gradual increase in the number of shells and screening effect.

3. Common oxidation state +2.

4. Ionisation enthalpy is low.

5. Hydration Enthalpies are high.

The hydration enthalpies of alkaline earth metal ions also decrease with increase in ionic size down the group. Be > Mg > Ca > Sr > Ba.

6. Electronegativity decreases as we go down the group.

7. When the alkaline earth metal salts moistened with concentrated hydrochloric acid and heated on a platinum wire in a flame, they show characteristic coloured flame

Element - Colour

Calcium - Brick Red

Strontium - Crimson Red

Barium - Apple Green

38. Discus the similarities between beryllium and aluminium.

Simiarities between Beryllium and Aluminium.

Beryllium shows diagonal relationship with aluminium.

In this case the size of these ions is not as close. However their change per unit area and electro negativity valves are almost similar.

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 [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, BeF₄^2-, 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.

39. Why alkaline earth metals are harder than alkali metals.

Alkaline earth metals are smaller in size and the atoms are tightly packed than in alkali metals.

40. How is plaster of paris prepared?

It is obtained when gypsum,

(CaSO₄.2H₂O), is heated to 393K.

2CaSO₄. 2H₂O (s) → 2CaSO₄ H₂O + 3H₂O

41. Give the uses of gypsum.

● Gypsum is used in making drywalls plaster boards. Plaster boards are used as the finish for walls and ceilings, and for partitions.

● Gypsum is heated to about 300 F produce plaster of Paris, which is also known as gypsum plaster. It is mainly used as a sculpting material.

● Gypsum is used in making surgical and orthopedic casts, such as surgical splints and casting moulds.

● 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.

● Gypsum is used in toothpastes, shampoos, and hair products, mainly due to its binding and thickening properties.

● Gypsum is a component to Portland cement, where it acts as a hardening retarder to control the speed at which concrete sets.

42. Describe briefly the biological importance of Calcium and magnesium.

I. Magnesium and Calcium also plays a vital role in biological functions.

1. A typical adult human body contains about 25g of magnesium and 1200g of calcium.

2. Magnesium plays an important role in many biochemical reactions catalysed by enzymes.

3. It is the co-factor of all enzymes that utilize ATP in phosphate transfer and energy release.

4. It is 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. Deficienty of Magnesium results into convulsion and neuromuscular irritation.

II. Calcium is a major component of bones and teeth.

1. It is also present in blood and its concentration is maintained by hormones (calcitonin and parathyroid hormone).

2. Deficiency of calcium in blood causes it to take longer time to clot.

3. It is also important for muscle contraction.

4. The main pigment that is responsible for photosynthesis, chlorophyll, contains magnesium which plays an important role in photosynthesis.

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

Since MgO is more stable than MgF,

MgO has high melting point than MgF.

M pt of MgO = 2852°C and MgF = 1263°C