S Block Elements(12th Grade > Chemistry ) Questions and answers for exam Preparation

12th Grade > Chemistry

S BLOCK ELEMENTS MCQs

Total Questions : 30 | Page 3 of 3 pages

Question 21. Which of the following reactions is not associated with 'solvay's 'process of manufacture of sodium carbonate?

NH3 + H2 + CO2 ⟶ NH4HCO3
NaCl + NH4HCO3 ⟶ NaHCO3 + NH4Cl
2NaHCO3 Δ→ Na2CO3 + H2O + CO2
2NaOH + CO2 ⟶ Na2CO3 + H2O

Discuss Question

Answer: Option D. -> 2NaOH + CO2 ⟶ Na2CO3 + H2O
:
D
Raw materials are

N a C l, C a C O_{3}, N H_{3}

:
The other reactions are all parts of the Solvay or Ammonia-soda process:

N H_{3} + H_{2} + C O_{2} ⟶ N H_{4} H C O_{3}

N a C l + N H_{4} H C O_{3} ⟶ N a H C O_{3} + N H_{4} C l

2 N a H C O_{3} Δ ⟶ N a_{2} C O_{3} + H_{2} O + C O_{2}

Question 22. Which one on reaction with NaOH solution gives inflammable gas?

S
Zn
NH4Cl
I2

Discuss Question

Answer: Option B. -> Zn
:
B

Z n + 2 H_{2} O + 2 N a O H ⟶ N a_{2} Z n (O H)_{4} + H_{2}

As you can see - Zinc liberates hydrogen gas.

Question 23. Which of the following will not under go disproportionation reaction in the presence of dilute (or) Conc NaOH

Discuss Question

Answer: Option D. -> F2
:
D
Fluorine generally only ever exhibits two oxidation states 0 and -1.

Question 24. To an acidified dichromate solution, Na₂O₂ is added and shaken. What is observed?

Blue colour
Orange colour changing to green directly
Copious evolution of oxygen
Bluish-given precipitate

Discuss Question

Answer: Option A. -> Blue colour
:
A
This is a standard question from many different exams. In this reaction,

C r O_{5}

is Chromium (VI) oxide peroxide - a blue coloured compound - is produced.

Question 25. On heating in air, sodium burns violently with golden yellow flame forming

Monoxide and chloride
Monoxide and carbonate
Peroxide and hydroxide
Monoxide and peroxide

Discuss Question

Answer: Option B. -> Monoxide and carbonate
:
B
Sodium combines with oxygen to form Sodium monoxide, which reacts with water to yield hydroxide. It then combines with

C O_{2}

to give sodium carbonate

Question 26. Reaction of

Z n (O H)_{2}

with

N a O H

produces:

Na2(ZnO2)
ZnO
Na2O
None of these

Discuss Question

Answer: Option A. -> Na2(ZnO2)
:
A

Z n (O H)_{2}

is amphoteric and reacts with

N a O H

Z n (O H)_{2} + 2 N a O H ⟶ N a_{2} Z n (O H)_{4}

The hydrated form of

N a_{2} Z n O_{2}

N a_{2} Z n (O H)_{4}

Question 27. Property of the alkaline earth metals that increases with their atomic number is

Ionisation energy
Solubility of their hydroxides
Solubility of their sulphates
Electronegativity

Discuss Question

Answer: Option B. -> Solubility of their hydroxides
:
B
As we go down the group - the solubility, stability & basic nature of the hydroxides of alkaline earth metals increases.

Question 28. Estimation by 'Flame photometry' is not helpful in the case of

Magnesium
Barium
Strontium
Calcium

Discuss Question

Answer: Option A. -> Magnesium
:
A
Mg does not give colour in the flame test

Question 29. The pair of compounds which cannot exist together in solution is

NaHCO3 and NaOH
NaHCO3 and H2O
NaHCO3 and Na2CO3
Na2CO3 and NaOH

Discuss Question

Answer: Option A. -> NaHCO3 and NaOH
:
A

N a H C O_{3}

is an acidic salt which can react with

N a O H

to give

N a_{2} C O_{3}

. Hence they can't be found together.

Question 30. Among

K O_{2}, N a_{2} O

and

B a O_{2}

unpaired electron(s) is/are present in:

Na2O and BaO2
KO2 and BaO2
KO2 only
BaO2 only

Discuss Question

Answer: Option C. -> KO2 only
:
C
This essentially boils down to the differences in the magnetic nature of the normal oxide

O_{2}^{-}

, the peroxide

O_{2}^{2 -}

and the superoxide

O_{2}^{-}

ions. Among these - the oxide and the peroxide do not contain unpaired electrons whereas the superoxide is paramagnetic (it has an unpaired electron).