**Question 1. What will be the minimum pressure required to compress 500 dm ^{3} of air at 1 bar to 200 dm^{3} at 30°C?**

**Answer:**

P_{1} = 1 bar,P_{2} = ? V_{1}= 500 dm^{3} ,V_{2}=200 dm^{3}

As temperature remains constant at 30°C,

P_{1}V_{1}=P_{2}V_{2}

1 bar x 500 dm^{3} = P_{2} x 200 dm^{3} or P_{2}=500/200 bar=2.5 bar

**Question 2. A vessel of 120 mL capacity contains a certain amount of gas at 35°C and 1.2 bar pressure. The gas is transferred to another vessel of volume 180 mL at 35°C. What would be its pressure?****Answer: **

** **V_{1}= 120 mL, P_{1}=1.2 bar,

V_{2} = 180 mL, P_{2} = ?

As temperature remains constant, P_{1}V_{1} = P_{2}V_{2}

(1.2 bar) (120 mL) = P2 (180mL)

**Question 3. Using the equation of state PV = nRT, show that at a given temperature, density of a gas is proportional to the gas pressure P.****Answer:**

According to ideal gas equation

PV = nRT or PV=nRT/V

**Question 4. At 0°C, the density of a gaseous oxide at 2 bar is same as that of dinitrogen at 5 bar. What is the molecular mass of the oxide?****Answer:**

Using the expression, d =MP/RT , at the same temperature and for same density,

M_{1}P_{1} = M_{2}P_{2} (as R is constant)

(Gaseous oxide) (N_{2})

or

M_{1} x 2 = 28 x 5(Molecular mass of N_{2} = 28 u)

or M_{1} = 70u

**Question 5. Pressure of l g of an ideal gas A at 27°C is found to be 2 bar. When 2 g of another ideal gas B is introduced in the same flask at same temperature, the pressure becomes 3 bar. Find the relationship between their molecular masses.****Answer:**

Suppose molecular masses of A and B are M_{A} and M_{B} respectively. Then their number of moles will be

**Question 6. The drain cleaner, Drainex contains small bits of aluminium which react with caustic soda to produce dihydrogen. What volume of dihydrogen at 20 °C and one bar will be released when 0.15g of aluminium reacts?****Answer:**

The chemical equation for the reaction is

2 Al + 2 NaOH + H_{2}0 -> 2 NaAl0_{2} + 3H_{2} (3 x 22400 mL At N.T.P)

2 x 27 = 54 g.

54 g of Al at N.T.P release

H_{2} gas = 3 x 22400 0.15 g of Al at N.T.P release

**Question 7. What will be the pressure exerted by a mixture of 3.2g of methane and 4.4g of carbon dioxide contained in a 9 dm ^{3} flask at 27 °C?**

**Answer:**

**Question 8. What will be the pressure of the gas mixture when 0.5 L of H _{2} at 0.8 bar and 2.0 L of dioxygen at 0.7 bar are introduced in all vessel at 27 °C?**

**Answer:**

Calculation of partial pressure of H_{2} in 1L vessel P_{1}= 0.8 bar,

P_{2}= ? V_{1}= 0.5 L , V_{2} = 1.0 L

As temperature remains constant, P_{1}V_{1} = P_{2}V_{2}

(0.8 bar) (0.5 L)

= P_{2} (1.0 L) or P_{2}

= 0.40 bar,

i.e., PH_{2} = 0.40 bar

Calculation of partial pressure of 02 in 1 L vessel

P_{1}‘ V_{1} = P_{2}‘V_{2}‘

(0.7 bar) (2.0 L) = P_{2} (1L) or P_{2}‘ = 1.4 bar, i.e.,Po_{2}= 1.4 bar

Total pressure =P_{Hz} + P_{Q2} = 0.4 bar + 1.4 bar = 1.8 bar

**Question 9. Density of a gas is found to be 5.46 g/dm ^{3} at 27 °C and at 2 bar pressure. What will be its density at STP?**

**Answer:**

**Question 10. 34.05 mL of phosphorus vapour weighs 0.0625 g at 546°C and 1.0 bar pressure. What is the molar mass of phosphorus?****Answer:**

**Question 11. A student forgot to add the reaction mixture to the round bottomed flask at 27 °C but instead, he/she placed the flask on the flame. After a lapse of time, he realized his mistake, and using a pyrometer, he found the temperature of the flask was 477 °C. What fraction of air would have been expelled out?****Answer:**

**Question 12.Calculate the temperature of 4.0 moles of a gas occupying 5 dm ^{3} at 3.32 bar (R = 0.083 bar dm^{3} K^{-1} mol^{-1})**

**Answer:**

**Question 13. Calculate the total number of electrons present in 1.4 g of dinitrogen gas.****Answer:**

Molecular mass of N_{2 }= 28g

28 g of N_{2} has No. of molecules = 6.022 x 10^{23} 1.4 g of

N_{2} has No. of molecules = 6.022 x 10^{23} x 1.4 g/28 g

= 3.011 x 10^{22} molecules.

Atomic No. of Nitrogen (N) = 7

1 molecule of N_{2} has electrons = 7 x 2 = 14

3.011 x 10^{22} molecules of N_{2} have electrons

= 14 x 3.011 x 10^{22}

= 4.215 x 10^{23} electrons.

**Question 14. How much time would it take to distribute one Avogadro number of wheat grains if 10 ^{10} grains are distributed each second ?**

**Answer:**

**Question 15. Calculate the total pressure in a mixture of 8g of oxygen and 4g of hydrogen confined in a vessel of l dm ^{3} at 27°C. R = 0.083 bar dm^{3} K^{-1} mol^{-1}.**

**Answer:**

**Question 16. Pay load is defined as the difference between the mass of the displaced air and the mass of the balloon. Calculate the pay load when a balloon of radius 10 m, mass 100 kg is filled with helium at 1.66 bar at 27°C (Density of air = 1.2 kg m ^{-3} and R = 0.083 bar dm^{3} K^{-1} mol^{-1}).**

**Answer:**

**Question 17. Calculate the volume occupied by 8.8 g of CO _{2} at 31.1 °C and 1 bar pressure. R = 0.083 bar LK^{-1} mol^{-1}**

**Answer:**

**Question 18. 2.9 g of a gas at 95°C occupied the same volume as 0.184 g of hydrogen at 17°C at the same pressure. What is the molar mass of the gas ?****Answer:**

**Question 19. A mixture of dihydrogen and dioxygen at one bar pressure contains 20% by weight of dihydrogen. Calculate the partial pressure of dihydrogen.****Answer: **

As the mixture H_{2 }and O_{2} contains 20% by weight of dihydrogen, therefore, if H_{2} = 20g, then O_{2} = 80g

**Question 20. What would be the SI unit for the quantity PV ^{2}T^{2}/n?**

**Answer:**

**Question 21. In terms of Charles’ law explain why -273°C is the lowest possible temperature.****Answer: **

At -273°C, volume of the gas becomes equal to zero, i.e., the gas ceases to exist.

**Question 22. Critical temperature for CO _{2} and CH_{4} are 31.1°C and -81.9°C respectively. Which of these has stronger intermolecular forces and why?**

**Answer:**

Higher the critical temperature, more easily the gas can be liquefied, i.e., greater are the intermolecular forces of attraction. Hence, Co_{2} has stronger intermolecular forces than CH_{4}.

**Question 23. Explain the physical significance of vander Waals parameters.****Answer:**

‘a’ is a pleasure of the magnitude of the intermolecular forces of attraction, while b is a measure of the effective size of the gas molecules.