Investigate the effects of changing the conditions of a reaction on the rates of chemical reactions by measuring the production of a gas.
It is important in this practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time and volume. This includes the safe use of apparatus, and monitoring chemical changes.
This outlines one way to carry out the practical. It is also possible to collect the gas in an inverted measuring cylinder in place of the gas syringe. Eye protection must be worn.
To investigate the effect of changing the conditions on the rate of a reaction.
Magnesium reacts with dilute hydrochloric acid to produce hydrogen:
magnesium + hydrochloric acid → magnesium chloride + hydrogen
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
The volume of hydrogen gas produced can be measured using a gas syringe.
Record the results in a table.
Describe how you can tell that the reaction is complete.
No more gas is produced, and the line on the graph becomes horizontal.
Suggest why the rate is not measured by finding the mass of hydrogen given off as the reaction takes place.
Hydrogen has a very low density, so the mass of gas that is lost is too small to be measured accurately.
It is also possible to use this experiment to investigate the effect of temperature on the rate of the reaction. The experiment is carried out in the same way, but:
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
|Hot hydrochloric acid||Causes skin and eye irritation; burns to the skin||Wear gloves and eye protection; do not heat above 60°C|
|Fizzing in the reaction mixture||Spray or foam escaping, which may damage skin and eyes||Use a large conical flask so there is plenty of space inside; do not look over the top when adding the magnesium ribbon|