S-block (Group 2)

Question 1

The first element …………. differs from the rest of the elements in the group and shows diagonal relationship with ………

Answer 1

Beryllium

Aluminum

Question 2

Ionization energy order

Answer 2

Be > Mg > Ca > Sr > Ra > Ba

Due to poor shielding of 4f electrons

Question 3

Hydration Energies G1 G2 comparison

Answer 3

Decreases down the group

HE: G1 < G2

Question 4

Melting point order

Answer 4

Be > Ca > Sr > Ba > Mg

Question 5

Boiling point order

Answer 5

Be > Ba > Ca > Sr > Mg

Question 6

Density order

Answer 6

Ba > Sr > Be > Mg > Cr

Question 7

Melting and boiling point comparision in G1 and G2

Answer 7

G1 < G2

Due to better metallic bonding in G2

Question 8

Alkali earth metal hardness

Answer 8

These are comparatively softer than d-block elements because in d-block in addition to ns electrons (n-1)d electrons also take part in metallic bonding

But these are harder than alkali metals

Question 9

Flame test

Answer 9

Calcium - brick red
Strontium - crimson
Barium - apple green

Due to high ionization energy of Be and Mg electrons do not get excited

Question 10

G1 G2 reactivity comparison

Answer 10

G1 > G2

Question 11

Reaction of Be and Mg towards oxygen and water

Answer 11

Be and Mg are inert to oxygen and water due to formation of oxide film on their surface

Question 12

Powdered form of Be burns brilliantly in air to give

Answer 12

BeO and Be3N2

Question 13

Magnesium burns in air

Answer 13

with dazzling brilliance to give MgO and Mg3N2

Question 14

Ca, Sr, and Ba are readily attacked by air to form

Answer 14

their oxides and nitrides

(no peroxides and super oxides are formed)

Question 15

Reaction with Water (rates)

Answer 15

Be neither reacts with hot water nor with steam of cold water

Mg decomposed hot water
Mg + 2H2O —> Mg(OH)2 + H2 [hot water]
Mg + H2O —> MgO + H2 [Cold water}

Ca, Sr, and Ba react with increasing vigor even with cold water to form hydroxide.

Question 16

Reaction With Halogens

Answer 16

@ high temperature

M + X2 —> MX2

Question 17

Reactivity towards hydrogen

Answer 17

All elements except Be react with hydrogen to form their hydrides (MH2)

BeH2 can however be prepared by the reaction of BeCl2 and LiAlH4.

2BeCl2 + LiAlH4 —> 2 BeH2 + LiCl + AlCl3

Question 18

BeH2 and MgH2 Structure

Answer 18

Polymeric

Question 19

Reactivity towards acid

Answer 19

M + 2HCl —> MCl2 + H2

Generally dil. HCl and dil. H2SO4 are taken.

Question 20

Reactivity nature
Standard oxidizing and reduction potential order

Answer 20

• EM/M2+
  BE 1.97
  Mg 2.36
  Ca 2.84
  Sr 2.89
  Ba 2.92

Thus Ba is the best reducing agent and Be is the worst reducing agent in group 2

Question 21

Why is Be the worst reducing agent?

Answer 21

The reaction
BE(s) —> Be2+(aq) + 2e-
takes place in two steps.

Step 1:
Sublimation of BE solid to Be gas. This process requires energy to proceed

Step 2:
Ionization. This process requires a lot of energy due to the small size .

Step 3:
Be2+ (g) –H2O–> Be2+ (aq)
In this process energy is released which is much less than the energy required

hence it is worst reducing agent

Question 22

Solution in liquid ammonia

Answer 22

Like alkali metals the alkaline earth metals dissolve in liquid ammonia to give deep blue black solution ammoniated ions.

M+ (x+y) NH3 —> [M(NH3)x 2+ + 2e(NH3)y]

From these solutions the ammoniates [M(NH3)6]2+ can be recovered by evaporation of ammonia from the solution.

M(NH3)6 —> M(NH3)2 + 4NH3 + H2

Question 23

Concentrated solution of metals in ammonia are …………. colored

Answer 23

Bronze colored due to the formation of metal ion clusters.

Question 24

Structure of alkaline earth metal oxides

Answer 24

Rock salt structures

Question 25

Alkaline earth metal oxides react with water to form

Answer 25

Metal hydroxides

except BeO

MO + H2O —> M(OH)2

Question 26

Thermal stability and basic character of hydroxides

Answer 26

increase from Mg(OH)2 to Ba(OH)2

The G2 hydroxides are however less basic and less stable than the G1 hydroxides

Question 27

Be is ….. in nature and reacts with

Answer 27

Be is amphoteric in nature and reacts with both acid and alkali.

Be(OH) + 2OH- —> [Be(OH)4]2- Beryllate ion

Be(OH)2 + 2HCl + 2H2O —> [Be(OH2)4]Cl

Question 28

Carbonates in water

Answer 28

Carbonates of G2 are insoluble in water.

They can be precipitated by addition of sodium or ammonium carbonate to the solution of soluble salts of these metals.

Solubility of carbonates in water decreases as atomic number increases.

Question 29

Thermal stability of Carbonates

Answer 29

increases from BeCO3 to BaCO3.

MCO3(s) —> MO+(s) + CO2

BeCO3 is very unstable and can kept in CO2 atmosphere

Question 30

Solubility of Sulphates

Answer 30

BeSO4 and MgSO4 are readily soluble in water and the solubility decreases from CaSO4 to BaSO4

Question 31

Solubility of nitrates

Answer 31

Nitrates of all elements are soluble in water.

2M(NO3)2 –heat–> 2MO + 2NO2 + O2

Question 32

Nature of halides

Answer 32

Except for Be halides all other alkaline earth metal halides are ionic in nature

BeX2 is covalent and soluble in organic solvents

BeCl2 is polymeric

Question 33

Heating hydrated halides

Answer 33

CaX2 + yH2O —> CaX2 + yH2O
SrX2 + zH2O —> SrX2 + zH2O
BaX2 + zH2O —> BaX2 + zH2O

In case of Be and Mg halides on heating hydrolysis occurs.

MgCl2.6H2O –heat–> Mg(OH)2 + 2HCl + 4H2O
Mg(OH)2 –heat–> MgO + H2O

Question 34

Preparation of anhydrous BeX2

Answer 34

BeO + C + Cl <—600-900K—> BeCl2 + CO

(NH4)2 BeF4 –heat–> 2NH3 + 2HF + BeF2

Question 35

Hydrolysis of Nitrides

Answer 35

Be3N2 + 6H2O —> 2NH3 + 3Be(OH)2

Mg3N2 + 6H2O —> 2NH3 + 3Mg(OH)2

Question 36

Hydrolysis of Carbides

Answer 36

BeC2 + 2H2O —> C2H2 + Be(OH)2 [Acetylides]

CaC2 + 2H2O —> C2H2 + Ca(OH)2 [Acetylides]

Mg2C3 + 4 H2O —> C3H4 + 2Mg(OH)2 [Sesquioxide]

Be2C + 4H2O —> CH4 + 2Be(OH)2 [Methanoids]