Gas Laws

Question 1

What is meant by a volatile liquid?

Answer 1

A liquid with a low boiling point.

Question 2

In an experiment to determine the relative molecular mass of a volatile liquid, describe how would you carry out the experiment describe how you measured the mass, volume and temperature.

Answer 2

Mass: Get the mass of flask and foil, add liquid and arrange as in diagram. Heat until liquid is vaporised. Cool and reweigh and get mass of the sample by subtraction.
Volume: Fill the flask and empty into graduated cylinder
Temperature: Use thermometer to read the temperature of the water.

Question 3

In an experiment to determine the relative molecular mass of a volatile liquid, how many the pressure be measured?

Answer 3

With a barometer

Question 4

State Avogadro’s law.

Answer 4

This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

Question 5

What is an ideal gas?

Answer 5

A gas that obeys all gas laws at all temperatures and pressures.

Question 6

State one reason why ammonia deviates from ideal gas behaviour.

Answer 6

As it is polar.

Question 7

What is an ideal gas?

Answer 7

A gas that obeys all gas laws at all temperatures and pressures.

Question 8

Give one reason why a real gas like carbon dioxide deviates from ideal behaviour.

Answer 8

As collisions are not perfectly elastic.

Question 9

State Avogadro’s law.

Answer 9

This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

Question 10

Give one reason why carbon dioxide is more easily liquefied than helium.

Answer 10

Due to the stronger intermolecular forces.

Question 11

State Avogadro’s law.

Answer 11

This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

Question 12

Give two assumptions of the kinetic theory of gases.

Answer 12

• The average kinetic energy of the particles is proportional to the absolute temperature i.e kelvin.
• The collisions are elastic. There is no overall lose of energy as a result of collisions.

Question 13

Give two reasons why real gases deviate from ideal gas behaviour.

Answer 13

• There are forces of attraction between molecules.

- Collisions are not perfectly elastic as some energy can be lost to surroundings.

Question 14

State Gay-Lussac’s Law of combining volumes.

Answer 14

This states that gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure.

Question 15

What is an ideal gas?

Answer 15

A gas that obeys all gas laws at all temperatures and pressures.

Question 16

In the experiment to find the relative molecular mass of a volatile liquid, give an example of a liquid suitable for this experiment.

Answer 16

Methane / methanol

Question 17

In the experiment to find the relative molecular mass of a volatile liquid, describe how to determine the mass and the volume.

Answer 17

Mass: Weigh the flask, heat until all the liquid is vaporised, cool, dry and reweigh. The mass is the difference.
Volume: Fill the flask with water and empty into measuring cylinder.

Question 18

In the experiment to find the relative molecular mass of a volatile liquid, explain why the pressure of the vapour is the same as atmospheric pressure.

Answer 18

As the pinhole means that vapour is exposed to the air.

Question 19

In the experiment to find the relative molecular mass of a volatile liquid, explain why this method is unsuitable for non-volatile liquids.

Answer 19

As they do not vaporise easily.

Question 20

What modern instrumental technique could be used as a more accurate method to measure the relative molecular masses of volatile and non-volatile liquids as well as of solid and gaseous substances.

Answer 20

Mass spectrometer.