Physical Chemistry MCQs with Explanatory Answers

 

MCQs Set 2 with Explanatory Answers 

1. The mass of one mole of electrons is:

(a) 1.008 mg
(b) 0.55 mg
(c) 0.184 mg
(d) 1.673 mg

Reason

mass of 1 electron = 9.1×10⁻³¹ kg = 9.1 × 10⁻²⁵ mg
1 mole of electron = 6.02 × 10²³ electrons

 

Mass of 1 mole of electrons = mass of 1 electron × number of one mole of electron
                                            = (9.1 × 10⁻²⁵) × (6.02×10²³) 

                                            = 0.54782mg ≈ 0.55mg

The mass of one mole of electrons = 0.55 mg

 

2. The number of moles of CO₂ which contain 8.0 g of oxygen:

(a)0.25
(b)0.50
(c)1.0
(d)1.50

Reason

Mass of 1 mole or Molar mass of CO₂ = 12 x 16 x 2 = 44 g/mol

Mass of oxygen in 32 g of CO₂ = 16 x 2 = 32 g

32 g of oxygen is contained in 1 mole of CO₂

1 g of oxygen is contained in 1/32 mole of CO₂

8 g of oxygen is contained in = 1/32 x 8 = 0.25 mole of CO₂

3. The largest number of molecules are present in:
(a)3.6 g of water
(b)4.8 g of C₂H₅OH
(c)2.8 g of CO
(d)5.4 g of N₂O₅

Reason

The largest number of molecules will be present in that sample which has greatest number of moles.

Hence 3.6 g water having greatest number of moles out of given options will contain largest number of molecules. 

4. Which of the following formula represents an acid anhydride?

(a)CaO

(b)H₂O

(c)H₂SO₄

(d)SO₃

Reason

Oxides are called anhydride. Anhydrides are of two types:

1. Basic anhydrides or basic oxides which are oxides of metals like Na2O, MgO, CaO etc.

2. Acid anhydrides or acidic oxides which are oxides of non-metals like SO₂, SO₃, CO₂, NO₂, Cl₂O etc.

Out of given option, CaO is basic anhydride, H₂O is a neutral oxide (other examples includes NO, N₂O, CO), H₂SO₄ is an oxyacid itself and SO₃ is an acid anhydride. SO₃ dissolves in water to form H₂SO₄ (an oxyacid) . 

5. If an element M forms an oxide with formula MO, which of the following is a correct formula?

(a)MCl

(b)MS

(c)MCl₂

(d)Both b and c

Reason

In MO, oxidation number of M is +2. In MS and MCl₂, oxidation number of M is also +2. 

6. The formula of KAl(SO₄)₂ represents a total of:

(a)6 atoms

(b)7 atoms

(c)12 atoms

(d)14 atoms

Explanation

KAl(SO₄)₂ = 1K + 2Al + 2S + (4 x 2)O= 12 atoms 

7. How many neutrons are contained in the nucleus of an element with Z=27 and A= 59:

(a) 27

(b) 32

(c) 59

(d) 86

Explanation

No of neutrons = A – Z = 59 – 27 = 32

8. How many gram of NaOH are needed to make 1000 g of a 5% solution?

(a) 5g 

(b) 500 g

(c) 40 g 

(d) 50 g 

Reason 

9. What is the ratio of the weight of water formed to the weight of Hydrogen used in the formation of water?

(a) 1:8

(b) 1:9

(c) 8:1 

(d) 9:1

Reason 

10. Which one of the following compounds does not have the empirical formula CH₂O?

(a)Glucose

(b)Methyl methanoate

(c)Ethanol

(d)Methanal

 

Explanation 

11. Equal masses of methane and hydrogen are mixed in an empty container. At 25°C. The fraction of total pressure exerted by hydrogen will be?

(a) 1: 2

(b) 2:1

(c) 8:9

(d) 9:16

Solution 

Let x g of both gases be mixed.

12. A small spacecraft of capacity 10 m³ is connected to another of capacity 30 m³. Before connection, the pressure inside the smaller craft is 50 kPa and that inside the larger is 100 kPa.

If all measurements are made at the same temperature, what is the pressure in the combined arrangement after connection?
(a) 150 kPa
(b) 75 kPa
(c) 87.5 kPa
(d) 100 kPa

Reason

 

13. The densities of two gases are in the ratio of 1: 16. The ratio of their rates of diffusion is

(a) 1: 16

(b) 1: 4

(c) 16: 1

(d) 4: 1

Reason 

14. The molecules of a gas A travel four times faster than the molecules of gas B at same temperature. The ratio of    molecular weights (M_A / M_B) is

(a) 4 

(b) ¼ ^th

(c) 16 

(d) 1/16

Reason 

15. A mixture of H₂ and O₂ in 2:1 volume is allowed to diffuse through a porous partition what is the composition of gas coming out initially

(a) 1:2

(b) 4:1

(c) 1:4

(d) 8:1

Reason 

16. Which one of the following properties has the same value for hydrogen (H₂) and for deuterium (D₂) when compared at the same pressure and temperature?

(a) Average molecular speed 

(b) Density

(c) Average molecular K.E

(d) Molecular mass

Reason (Answer; c)

According KMT, all gases have same average KE at same same kelvin temperature. 

17. The molecules of a gas A travel 8 times faster than the molecules of gas B at same temperature. The ratio of         molecular weights (M_A / M_B) is

(a)1/64

(b)1/32

(c) 32

(d) 64

Reason 

(a)

(b)

(c)

(d)