Nuffield Advanced Chemistry - I am currently doing an experiment where I have to find the relative atomic mass of lithium. I am reacting lithium with hydrochloric acid and collecting the volume of hydrogen that is produced over water. The main problem is that hydrogen is lost in between when the lithium is put into the acid and when the bung is put on the conical flask. How could I improve my experiment to ensure no hydrogen gas is lost?

Practical investigations

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I am currently doing an experiment where I have to find the relative atomic mass of lithium. I am reacting lithium with hydrochloric acid and collecting the volume of hydrogen that is produced over water. The main problem is that hydrogen is lost in between when the lithium is put into the acid and when the bung is put on the conical flask. How could I improve my experiment to ensure no hydrogen gas is lost?

Igloo writes ...

You could try one or other of the following:

place the lithium in a small tube or container which stands in, or floats on, the acid while you put in the bung - then shake to spill out the lithium so that it mixes with the acid;

run the acid into the bottom of a boiling tube carefully so that the top remains dry. Hold the tube as near to horizontal as possible and place the lithium at the top above the acid and below where the bung will be - then put in the bung and tilt the tube so that the lithium drops into the acid;

wrap the lump of lithium in a ball of absorbent paper, e.g. from a Kleenex tissue - by the time the water reaches the metal, the bung will be safely in the flask. You may want to make use of a rubber band too. The acid you are dealing with is likely to be so dilute that there will be no reaction with the paper or rubber.

Carry out a risk assessment before starting any practical work. Don’t forget to wear gloves during this operation and to obtain clearance from your teacher before proceeding to carry out the experiment.

Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website. For further guidance see our tutorial on Risk Assessment.

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updated: 28 January 2004

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