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Test: Mole Concept, Volumetric & Redox - 1


20 Questions MCQ Test Physical Chemistry | Test: Mole Concept, Volumetric & Redox - 1


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QUESTION: 1

4.4g of CO2 and 2.24 litre of H2 at STP (273.15 K and 1 atm pressure) are mixed in a container. The total of molecules present in the container will be

Solution:

Number of moles of CO2 =

∵ 22.4 L of H2 has 1 mole of H2

∴ The number of moles in 2.24L 
The total moles are 0.2.
⇒ Total molecules in 0.2 moles 

QUESTION: 2

4I– + Hg2+ → HgI42– ; 1 mole of each Hg2+ and I– will form:

Solution:

Balanced reaction is as follows :
Hg2+(aq) + 4I- ​ (aq) ⇋​   HgI42-​ (aq)​

∵ 4 mole of I- produces = 1 mole of HgI42-​​
∴ 1 mole I- produces = 1/4 moles of HgI42-​​

QUESTION: 3

How many grams of I2 are present in a solution which requires 40 ml of 0.11N Na2S2O3 to react with it via the reaction: 
S2O32– + I2 → S4O62– + 2I–?

Solution:

Meq. of I2 = Meq. of Na2S2O3 = 40 × 0.11
∴ (W × 2 × 1000)/254  = 40 × 0.11
W of I2 = 0.558g

QUESTION: 4

Two elements A (atomic mass = 75) and B (atomic mass = 16) combine to yield a compound. The % by weight of A in the compound was found to be 75.08. The formula of compound is:
Solution:

Molecular weight of A2B3 = 75 × 2 + 16 × 3 = 198
198g of A2B3 =150g of A
∴ 10g of A2B3 =   = 75.08g of A

So option B is correct. 

QUESTION: 5

What weight of HNO3 is needed to convert 5g of Iodine into Iodic acid according to the reaction:
I2 + HNO3→ HIO3 + NO2 +H2O
Solution:

The balanced reaction is:
I2 + 10HNO3 → 2HIO3 + 10NO2 + 4H2O

(127 * 2)g of iodine requires (63 * 10)g of HNO3
Thus, 5g of I2 requires
= [(63 * 10)/(127 * 2)] * 5 = 12.4g 

QUESTION: 6

In the reaction, VO + Fe2O3 → FeO + V2O5, the  equilvalent weight of  V2O5 is equal to its
Solution:

QUESTION: 7

When BrO3– ion reacts with Br– ion in acid solution Br2 is liberated. The eq. weight of KBrO3 in this reaction is:
Solution:

10e + 2Br5+ → Br02

QUESTION: 8

The hydrated salt, Na2SO4.nH2O, undergoes 55.9 % loss in weight on heating and become anhydrous. The value of n will be:
Solution:

Molecular Mass of Na2SO4 is = 2 x 23 + 32 + 4 x 16 = 142 gm.

In 100g of the compound, 44.1 g Na2SO4 contains 55.9 g of H2O.
(∵ 55.9 % is water)
⇒ 1g Na2SO4 contains = (55.9/44.1)g H2O
∴ 142 g Na2SO4 contains = (55.9/44.1) x 142 = 180 g H2O .

Hence, the number of water molecules = 180/18 = 10
(Since the Molecular mass of H2O is 18).

Thus, the value of n is 10 and the formula is Na2SO4.10H2O.

QUESTION: 9

When a metal is burnt, its weight is increased by 24%. The eq. weight of the metal will be:
Solution:

Equivalent weight of O^2-(oxide) ion is: Molar mass of oxygen/charge on oxygen
= 16/2 = 8 g eq-1

One equivalent of the metal reacts with one equivalent of oxygen to form metal oxide.

Let M be the equivalent weight of the metal.
Therefore, M grams of the metal will react with 8g of oxygen.
The corresponding metal oxide will have a mass of 8 grams more than the mass of metal M. This 8 gram is 24% of M. 
i.e. M x 24/100 = 8 gram
Thus, M = 100 x 8/24 = 33.33 g

QUESTION: 10

One mole of potassium chlorate is thermally decomposed and excess of aluminum is burnt in the gaseous product .How many moles of aluminum oxide are formed?
Solution:

2KClO3 → 2KCl + 3O2

4Al + 3O2 → 2Al2O3

The molar ratio for the first reaction is 2:3 for KClO3:O2

Thus, if 1 mole of  KClO3 is decomposed, 1.5 moles of O2 is produced.

The molar ratio for the second reaction is: 3:2 for O2:Al2O3. 

3 moles of oxygen produces 2 moles of aluminium oxide. 

Since, we have 1.5 moles of oxygen, number of moles of Al2O3  produced =

 

QUESTION: 11

How much Cl2 at STP is liberated when one mole of KMnO4 reacts with HCl ?
Solution:

Potassium permanganate reacts with hydrochloric acid according to the following equation:
2KMnO4 + 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2

⇒ 2 moles of KMnO4 produces 5 moles of Cl2
⇒ 1 mole of KMnO4 will produce 2.5 moles of Cl2

∴ Volume of 2.5 moles of Cl2 = 56 litres

QUESTION: 12

Minimum quantity of H2S needed to precipitate 63.5g of Cu2+ is nearly:
Solution:

Chemical Reaction: Cu2++ H2S → CuS + 2H+

In this reaction, to precipitate 1 mol of Cu2+ we require 1 mol of H2S.
Moles of Cu2+ = 63.5 g / 63.5 g mol-1 = 1 mol
Hence, to precipitate 1 mol of Cu2+ we require 1 mol of H2S
i.e. Mass of H2S = 1 mol x 34 g mol-1 = 34 g

QUESTION: 13

2g of CaCO3 was treated with 0.1M HCl (500 ml). The volume of CO2 evolved at STP after heating the solution is:
Solution:
QUESTION: 14

10g of CaCO3 on heating gives 5g of the residue (as CaO). The % yield of the reaction is approx:
Solution:
QUESTION: 15

‘x’ g of KClO3 on decomposition gives ‘y’ ml of O2 at STP. The % purity of KClO3 would be
Solution:

The balanced eqn. will be:
2KClO3 = 2KCl+3O2

The no. of moles of Oxygen = y/22.4
3 moles of Oxygen is produced from 2 moles of KClO3
⇒ 1 mole will be produced from 2/3 moles of KClO3
∴ y/22.4 will be producing from (2/3) × (y/22.4)
Hence, the mass of KClO3 used = (2/3) × (y/22.4)×M

% Purity = (2 × y × M)/(3 × 22.4 × x)

QUESTION: 16

33.6g of an impure sample of sodium bicarbonate when heated strongly gave 4.4g of CO2. The % purity of NaHCO3 would be:
Solution:

Balanced Equation:
2NaHCO3 = Na2CO3 + CO2 + H2O

Moles of CO2 = 4.4/44 =0.1
∵ 1 mole of CO2 is produce by 2 Moles of NaHCO3
⇒ Moles of NaHCO3 =0.1×2/1 =0.2
∴ Wt. of NaHCO3 = 0.2 × 84 = 16.8gm
% Purity of NaHCO3 = (16.8/33.6) × 100 = 50%.

QUESTION: 17

0.16g of dibasic acid required 25ml of N/10 NaOH for complete neutralization. Molecular wt. of acid is:
Solution:

Dibasic acid NaOH; 

N1V1 = N2V2

M = 2 × E = 2 × 64 = 128

.

 

      

QUESTION: 18

The molar coefficients of AsO33– and MnO4- in the reaction are:

AsO33– + MnO4Θ → AsO43– + MnO2
Solution:

QUESTION: 19

Which of the following is a disproportionation reaction?
Solution:

A disproportionation reaction is a reaction in which a single element undergoes reduction and oxidation

i.e in option d), Cu has changed its oxidation state from +1 to 0 (i.e reduction) and +1 to +2 (i.e oxidation)

QUESTION: 20

Hydrogen and oxygen combine to form H2O2 and H2O containing 5.93% and 11.2 % hydrogen respectively. The data illustrates:​
Solution:

For predicting the law of chemical combination, we have to have find out the ratio of masses in both cases:
Let the total mass in each case be 100 grams.

For H2O2
​​Mass of hydrogen = 5.93 gm
Mass of oxygen = 100-5.93 = 94.07 gm
The ratio of the mass of hydrogen to the mass of oxygen, H:O = 5.93 : 94.07 = 1 : 16

For H2O
​Mass of hydrogen = 11.2 gm
Mass of oxygen = 100-11.2 = 88.8 gm
The ratio of the mass of hydrogen to the mass of oxygen, H:O = 11.2 : 88.8 = 1 : 32

As the ratio of the mass of hydrogen remains the same in both cases and the ratio of masses of oxygen in both cases (16: 32 or 1: 2) is a whole number ratio.

Therefore, the above data illustrate the law of multiple proportions.

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