Pilot Experiment
To decide on the best volume and concentration of hydrochloric acid and best mass of magnesium a number of calculations were done and a pilot experiment conducted.
The equation for the reaction is:
Magnesium(s) + Hydrochloric Acid(l) Magnesium Chloride(l) + Hydrogen(g)
Mg(s) + 2HCL(l) MgCl2(l) + H2(g)
We were advised to use 0.1g of magnesium ribbon (found to be 10.9 cm long). The Relative Molecular Mass (RMM) of magnesium is 24, therefore the moles of magnesium to be used was:
Moles= 0.1
24
Moles= 0.00416
In the reaction above, 1 mole of magnesium reacts with 2 moles of hydrochloric acid. The concentration of acid was 1mol/dm3. Therefore the volume of hydrochloric acid used was:
Volume = 0.00416 * 2
1
Volume = 0.0083dm3
Volume = 8.3cm3
It was decided to use an excess of hydrochloric acid to ensure all the magnesium reacted, therefore 10cm3 of acid was used in the pilot experiment. At room temperature 10cm3 of hydrochloric acid was added to 0.1g of magnesium and the gas was collected (see fig 1). The volume of gas produced was measured every 15 seconds. It was found that the reaction was too rapid to be effectively measured, therefore 10cm3 of water was added to halve the concentration of the acid.
Investigation Experiment
I am going to investigate how temperature affects the rate of reaction between magnesium and hydrochloric acid. The procedure for the experiment is as follows;
* Using a measuring cylinder, measure 10cm3 of water and pour it into the side arm tube.
* Measure 10cm3 of hydrochloric acid (1 mol/ dm3) and add it to the water.
* Place the side arm tube in a water bath at 20OC, set up the apparatus below.
* Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs 0.1g.
* Coil the ribbon around a pencil and then drop it into the side arm tube and quickly put a bung on the side arm tube (this must be done quickly to prevent gas escaping).
* Every 15 seconds measure the volume of gas produced until less than 1cm3 of gas is produced every 15 seconds.
* Repeat experiment two more times (for accuracy) and record all results in a table.
* Repeat the experiment for temperatures of 0.5M, 1.0M, 1.5M and 2.0M (1mole/dm)
It is important that only the temperature is changed since this is what is being investigated.
