MEASURING RATES DURING A REACTION
Background
Magnesium reacts with hydrochloric acid and gives off hydrogen gas. A graph of volume of
hydrogen produced against time can be used to measure the rate at different points of the
reaction.
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Aim
You are going to react magnesium with hydrochloric acid in order to see how the rate changes
during the reaction.
Safety
 Hydrochloric acid is an irritant.
 Hydrogen and magnesium are flammable. There should be no naked flames
in the laboratory.
Method
3
1) Measure out 10 cm of hydrochloric acid
using a measuring cylinder and place into
a boiling tube in a rack.
2) Set up a syringe using a clamp and a
stand.
100 cm3 syringe
3) Cut a 4 cm length of magnesium ribbon.
Rub the surface down with emery /
sandpaper. Fold it loosely in half.
reaction in boiling
tube
hydrochloric acid
4) Add the magnesium ribbon to the
hydrochloric acid, attaching the delivery
tube straight away and starting the timer
magnesium
5) Record the volume of gas every 10
seconds for 2 minutes in the table.
Results
Time (s)
0
10
20
30
40
50
60
70
80
90
100
110
120
Volume (cm3)
140
1) Plot a graph of the gas volume against
time.
2) Draw tangent to the line at 0 and 30
seconds to find the gradient and so rate of
reaction at each point.
Remember how to find the gradient:
For example, at 30 seconds:
3
Change in y = 140 – 52 = 88 = 1.5 cm /s
Change in x
60 – 0
60
120
100
Volume (cm3)
Analysis
140 – 52
3
= 88 cm
+
80
60
60 – 0
= 60 s
40
20
0
0
20
40
60
80
100
Time (s)
© www.CHEMSHEETS.co.uk
20-February-2017
Chemsheets GCSE 1165
rate at 0 seconds
rate at 30 seconds
Describe how the rate changes during the reaction. Explain, using collision theory, why the rate changes
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Explain, using collision theory, why the reaction eventually stops.
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© www.CHEMSHEETS.co.uk
20-February-2017
Chemsheets GCSE 1165