Chemistry 08 – S-Block elements

1) A compound X on heating gives a colourless gas. The residue is dissolved in water to obtain Y. Excess CO2 is bubbled through aqueous solution of Y when Z is formed. Z on gentle heating gives back X. The X is

(a) CaCO3               (b) Ca(HCO3)2                (c) Na2CO3              (d) NaHCO3

(a) CaCO

2) X and Y are two metals. When burnt in air, X forms only oxide while Y forms oxide and nitride. The metals X and Y may be

(a) Ca and Mg                (b) Na and Mg                 (c) Li and Na              (d) Na and K

(b) Na and Mg

3) Which of the following statement regarding alkali metals is not correct?

(a) Alkali metals tarnish in air                

(b) They are kept under kerosene                

(c) All alkali metals form oxides on burning in air              

(d) The reaction of alkali metals with water increases in violence on descending down the group

(c) Alkali metals form, oxides, peroxides superoxides and sesquioxides. Reactivity with water increases due to rapid decrease in ionisation energy on moving down the group.

4) Which of the following on heating at 125°C gives Plaster of Paris?

(a) Borax               (b) Gypsum               (c) Alum               (d) Calomel

(b) Gypsum

5) A metal (X) on heating in nitrogen gas gives (Y). (Y) on treatment with H2O gives a colourless gas, which when passed through CuSO4 solution gives a blue colour. Identify the compound (Y).

(a) Mg(NO3)2               (b) Mg3N2               (c) NH3               (d) MgO

 (b) 3Mg + N2 →  Mg3N2 ;

        (x)                     (y)


Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3

    (y)                                               ↓ CuSO4

                                                 Blue colour

6) The lattice energy order for lithium halides is

(a) LiF > LiCl > LiBr > LiI                     (b) LiCl > LiF > LiBr > LiI                

(c) LiBr > LiCl > LiF > LiI                     (d) LiI > LiBr > LiCl > LiF

(a) Smaller is the size of anion, lesser is its polarization, more is ionic nature, more is lattice energy.

7) 1 mol of substance (X) was treated with an excess of water. 2 mol of readily combustible gas were produced alongwith 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 + 2H2O → Ca(OH)2 + 2H2

Ca(OH)2 + CO2 → CaCO3 + H2O

8) Chile saltpetre is

(a) NaNO3               (b) Na2SO4               (c) KNO3                 (d) Na2SO3

(a) NaNO3

9) Based on lattice energy and other considerations which one of the following alkali metal chlorides is expected to have the highest melting point

(a) LiCl               (b) NaCl               (c) KCl                 (d) RbCl

(b) Although lattice energy of LiCl higher than NaCl but LiCl is covalent in nature and NaCl ionic thereafter, the melting point decreases as we move NaCl because the lattice energy decreases as a size of alkali metal atom increases (lattice energy ∝ melting point of alkali metal halide)

10) The reagent commonly used to determine hardness of water titrimetrically is

(a) Oxalic acid                (b) Disodium salt of EDTA                (c) Sodium citrate                  (d) Sodium thiosulphate

(b) It form calcium and magnesium complex with EDTA

11) The elements of group IA provide a colour to the flame of Bunson burner due to

(a) Low ionization potential                      (b) Low melting point                 

(c) Softness                                                (d) Presence of one electron in the outermost orbit

(a) Low ionization potential

12) The alkali metal that reacts with nitrogen directly to form nitride is

(a) Li               (b) Na               (c) K               (d) Rb

 (a) 6Li + N2 → 2Li3N Lithium nitride.

13) Which of the following chemicals, in addition to water, are used for the manufacture of Na2CO3 by Solvay process

(a) NaCl,CO and NH3                     (b) NaCl,CO2 and NH3               

(c) NaCl,NH4Cl and CO2                (d) NaHCO3,CO and NH3

(b) NaCl,CO2 and NH3

14) Electrolysis of molten sodium chloride leads to the formation of

(a) Na and H2               (b) Na and O2               (c) H2 and O2               (d) Na and Cl2

                      Electrolysis

(d) 2NaCl          →            2Na   +   Cl2

      Molten                                     Cathode        Anode 

15) Sodium thiosulphate is prepared by

(a) Reducing Na2SO4 solution with H2S                   (b) Boiling Na2SO3 solution with S in alkaline medium              

(c) Neutralising H2S2O3 solution with NaOH            (d) Boiling Na2SO3 solution with S in acidic medium

                             NaOH 

(b) Na2SO3 + S      →       Na2S2O3

                                       Sod. thiosulphate

16) Which of the following sulphates have the highest solubility in water

(a) MgSO4               (b) BaSO4               (c) CaSO4               (d) BeSO4

(d) BeSO4 is most soluble because hydration energy is more than lattice energy.

BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO

Hydration energy decreases hence, solubility decreases.

17) The composition formulae of gypsum is

(a) (CaSO4)2 . H2O               (b) 2CaSO4               (c) CaSO4 . 2H2O              (d) 2CaSO4 . H2O

(c) CaSO4 . 2H2O

18) Gypsum Ca2SO4 . 2H2O on heating to about 120º Cforms a compound which has the chemical composition represented by

(a) (CaSO4)               (b) 2CaSO4 . H2O         (c) CaSO4 . H2O              (d) 2CaSO4 . 3H2O

                                      120º C

(b) 2(CaSO4 . 2H2O)       →       2CaSO4 . H2O + 3H2O

                Gypsum             Dehydration        Plaster of paris

19) The thermal stability of alkaline earth metal carbonates MgCO3 ,CaCO3 , BaCO3 and SrCO3 decreases as

(a) CaCO3 > SrCO3 > MgCO3 > BaCO3                    (b) BaCO3 > SrCO3 > MgCO3 > CaCO3         

(c) BaCO3 > SrCO3 > CaCO3 > MgCO3                    (d) MgCO3 > CaCO3 > SrCO3 > BaCO3

(c) Thermal stability increasing from top to bottom.

20) Match List I with List II and select the correct answer using the codes given below the lists List I List II

(a) A-4 B-3 C-2 D-1                (b) A-3 B-2 C-1 D-4          (c) A-4 B-2 C-3 D-1               (d) A-4 B-1 C-2 D-3

Screenshot 20200825 113422 2

(a)

(a) Peroxide is H2O2 (4)

(b) Super oxide is KO2 (3)

(c) Dioxide is PbO2 (2)

(d) Suboxide is C3O2 (1)

21) What is the formula of Plaster of Paris is

(a) CaSO4 . 2H2O                 (b) CaSO4 . 3H2O           (c) CaSO4 . H2O                (d) CaSO4 . 1/2H2O

(d) CaSO4 . 1/2H2O

or (CaSO4)2 . H2O

22) Select the correct formula of Globar salt

(a) MgSO4 . 7H2O                 (b) CuSO4 . 5H2O           (c) FeSO4 . 7H2O                (d) Na2SO4 . 10H2O

(d) Na2SO4 . 10H2O

23) A mixture containing 2.0 mol each of H2 and O2 is ignited so that water is formed. The amount of water formed is

2H2 + O2 → 2H2O

The moles of H2 require one mole of O2 to give two moles of 36 g water.

Here H2 is the limiting reactant.

24) Valency electrons in alkali metals are

Alkali metals valence shell configuration = ns1

25) Ferric alum has the composition (NH4)2SO4 . Fe2(SO4)3 . xH2O

26) Fusion mixture is NanCOn+1+KnCOn+1 . what is n

Fusion mixture is Na2CO3+K2CO3

n is 2

27) The maximum covalency of Be is

Be = [He] 2S2 2P0

maximum covalency is 4

Screenshot 20200825 113042 2

28) Among BeCO3, CaCO3, SrCO3 How many no. of these compounds are thermally more stable than MgCO3

BeCO3 < MgCO3 < CaCO3 < SrCO3

depends upon ionic character.

thermally more stable compounds is 2

29) Number of molecules of water of crystallization in MgCl2 is

Mg has a high charge density and also has empty d orbitals. This allows it to accommodate 6 water molecules in its hydration sphere.

30) 6 m mols of pure gypsum is heated to convert it completely to plaster of paris. What is the number of m mols of steam evolved in the process

                         Δ

CaSO4 . 2H2O → CaSO4 . 1/2H2O + 3/2H2O

        

        (s)                         (s)                      (g)

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