To determine the relative molecular mass of a Volatile Liquid

CALCULATIONS - gas equations

Give an example of a liquid suitable for use in this experiment

Propanone

Draw a large labelled diagram of an arrangement of apparatus you used to carry out this experiment

Conical flask approximately ¾ immersed in beaker of water //

tinfoil lid //

pinhole and rubber band

In your diagram, show

i) how the volatile liquid was vaporised

ii) how the temperature of the vapour was obtained

i) hotplate (bunsen burner, heat source) under beaker

ii) thermometer in water

With reference to your diagram, explain why the pressure of the vapour at the end of the heating stage of the experiment was known to be equal to the atmospheric pressure at your location

Some vapour escaped because of pinhole

With reference to your diagram, explain how the volume of the vapour was measured

Fill the conical flask with water and pour into a graduated cylinder

With reference to your diagram, describe how the mass of the vapour in the container at the end of the heating stage was found

Find initial mass of conical flask, tin foil lid and rubber band. At end of experiment, find mass of conical flask, tin foil lid, rubber band and vapour. Subtract initial mass from end mass

Calculation - 2019 Q3 part d)

Bromine (Br₂)(M_r = 160) has a significantly greater relative molecular mass than water (M_r = 18). Account for the volatility of bromine (boiling point 58.8^oc) compared to that of water (boiling point 100^oc)

Hydrogen bonds in water /

dipole-dipole forces in water /

van der Waals forces in bromine /

intermolecular forces in water are stronger /

intermolecular forces in bromine are weaker /

bromine is non-polar /

water is polar

Volatile

Easily vaporised

Why is this method unsuitable for liquids that are non-volatile?

They do not vaporise easily / boiling points too high / boiling points too near boiling point of water / have to vaporise below 100^oc

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?

Mass spectrometer

How may the pressure be measured?

Barometer