Chemistry · Physics

Gases and Gas Laws

298 Questions

The study of gases and gas laws involves understanding the relationships between pressure, volume, and temperature of gases. This topic is essential for chemistry and physics sections in many competitive exams. Practice these questions to master concepts like the ideal gas law, partial pressure, and molecular properties.

Ideal gas law calculationsGas volume and pressureStoichiometry of gasesDensity of gasesBoltzmann constant applicationsThermal speed of sound

Gases and Gas Laws Questions

Multiple choice

Which of the following is not true about a flame photometer?

  1. 25-lb gauge for oxygen supply and 10-lb gauge for fuel is generally used.

  2. The flow rate of fuel-oxygen mixture usually varies from 2 to 10 cu. ft/h.

  3. An atomizer should have a tip of suitable shape to avoid a strike back.

  4. In flame photometry atoms in vapour state give line spectra and not band spectra.

  5. The usual glass or gelatin absorption filters have wide spectral bandwidths, of 35-45 nm.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This answer is correct as the given statement is wrong because it is the burner and not the atomiser who should have a tip of suitable shape to produce symmetrical flame and homogeneous flow and distribution of gases, in order to avoid a strike back in the burner from accidental fluctuations in the feed system.

Multiple choice

1 litre mixture of CO and CO2 is taken. This is passed through a tube containing red hot charcoal. The volume now is 1.6 litres. The volumes are measured under the same condition. Find volume of CO2 in the mixture.

  1. 400 ml

  2. 600 ml

  3. 800 ml

  4. 1000 ml

  5. 1200 ml
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let there be x ml CO in the mixture. Hence, there will be (1000 – x) ml CO2 . The reaction of CO2 with red hot charcoal may be given as,CO2 (g) + C(s) → 2CO(g)from reaction we have, x = 400 ml Therefore volume of CO = 400 ml and hence the volume of CO2 = (1000 – 400 ) ml = 600 ml Hence, this is the correct option.

Multiple choice

The vapour density of a mixture containing NO2 and N2O4 is 38.3 at 27°C. Calculate the moles of NO2 in 100 g of the mixture.

  1. 0.954

  2. 0.437

  3. 0.123

  4. 0.222

  5. 0.808
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Molecular mass of the mixture = 2 * 38.3 = 76.6 Let, mass of NO2 in 100 g of mixture = a g. Moles of NO2 + Moles of N2O4 = Moles of mixture i.e., (a / 46) + ((100 – a ) / 92) = (100 / 76.6) a = 30.1 g. Moles of NO2 in the mixture =( 20.1 / 46) = 0.437 (approx.). Hence, this is a correct option.

Multiple choice

A gas occupies a volume of 250 mL at 700 mm mercury pressure and 25oC temperature. What is the additional pressure required to reduce the gas volume to its 4/5th value at the same temperature?

  1. 125 mm Hg

  2. 150 mm Hg

  3. 175 mm Hg

  4. 200 mm Hg

  5. 225 mm Hg
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

P1 = 700 mm Hg, V1 = 250 mL, V2 = 250 (4/5) = 200 mL, P2 =? According to the Boyle’s law: P1V1 = P2V2   P2 = 250 × 700 / 200 = 875 mm Hg Required additional pressure = 875 – 700 = 175 mm Hg

Multiple choice

A flask containing 12 g of a gas of molecular mass 120 g at a pressure of 100 atm was evacuated by means of a pump until the pressure was 0.01 atm. Which of the following is the best estimate of the number of molecules left in the flask?

  1. 2 × 1018

  2. 3 × 1018

  3. 4 × 1018

  4. 6 × 1018

  5. 6×1023
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 P1V = n1RT              (i) P2V = n2RT                                                    (ii) (n2/n1 ) = (P2/P1)  n2 = (P2×n1) / P1 = (12/120) × (0.01/100) = 10-5 Since 1 mole contains 6.023 × 1023 molecules, 10-5 mole contains molecules = 10-5 × 6.023 × 1023 = 6.023 × 1018 (Approx. 6 × 1018)

Multiple choice

There are two sealed containers of the same capacity. 44 g of hydrogen is put in one container and 44 g of carbon dioxide is put in the other. If the pressure of carbon dioxide in the second container is 1 atm, then the pressure of hydrogen in the first container is

  1. 1 atm

  2. 10 atm

  3. 12 atm

  4. 22 atm

  5. 32 atm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(P1V1/P2V2) = (n1RT1/n2RT2) = (n1T1/n2T2)  V1=V2; T1=T2  (P1/P2) = (n1Phydrogen/n2Pcarbon dioxide) = 44/2 × 44/44 = 44/2 = 22 atm

Multiple choice

A mixture of 4 g of H2 and 128 g of HI is prompted in a 2 litre flask. What will be its respective active mass?

  1. 0.5 mol L-1

  2. 0.05 mol L-1

  3. 0.005 mol L-1

  4. 0.0005 mol L-1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mass of hydrogen = 4 g, Mol. mass of hydrogen = 2; Volume of the flask = 2 litres. Active mass of hydrogen = 4/2 X 2 = 1 mol L-1; Mass of HI = 128 g, Mol. mass of HI = 128 g, Volume of the flask = 2 litre. Active mass of hydrogen iodide = 128/(128 X 2) = 0.5  mol L-1