Calcium + Hydrochloric -> Calcium + Carbon Investigation

The apparatus will be set up as shown in the diagram and will be kept this way for each individual experiment so that it is a fair test. Other factors we need to keep constant so it is a fair test are all the variables: temperature and surface area. Not concentration as this is the variable we are testing. Also the apparatus needs to be cleaned after each test. To make it safe to carry out the test glasses need to be worn at all times and any spillages cleaned up quickly and hands washed. It is important to carry out the safety aspect of the test because it would be dangerous to do it if we didn't.

We will measure out 10g of calcium carbonate on a top pan balance and then it will be put into a conical flask. Then 50ml of hydrochloric acid will be put into the conical flask along with the calcium carbonate. At the same time a bung will be fitted on top of the conical flask with a delivery tube in it and the stopwatch will be started. The gas produced will travel through the delivery tube and into the burette, displacing the water in it. When 50cm of water has been displaced the timer will be stopped and the results will be recorded.

The experiment will be repeated but with weaker concentrations of hydrochloric acid. The order of the experiments are as follows:

Order

Hydrochloric Acid (ml)

Water (ml)

st

50

0

2nd

40

0

3rd

30

20

4th

20

30

5th

0

40

There is no point doing the experiment with just water and no hydrochloric acid because calcium carbonate doesn't react with water.

Results

Hydrochloric Acid (ml)

Water (ml)

Time for reaction (s)

50

0

5

40

0

9

30

20

26

20

30

43

0

40

87

These results show that the higher the concentration, the quicker the reaction takes place. This is what I said in my prediction. The reason a reaction is quicker when there is a higher concentration is there are more particles that are able to collide with each other and react. This is called the kinetic theory and is shown more clearly in the diagram.

Graph

The graph shows the time it takes for the reaction to take place increases as the concentration of the hydrochloric acid decreases. The graph loosely shows that, if you exclude the last recording, as you half the concentration, you double the time it takes for the reaction to take place.

Evaluation

The apparatus used was only as accurate as the people using it. Obviously the water being displaced out of the burettes had to be judged by eye. The equipment used could be bettered by using digital equipment. When we measured out the 10g of calcium carbonate, we used a digital top pan balance. This could not be more accurate and so we made sure that 10g was measured out exactly each time.

On their own these results aren't very reliable. For example, something could have been wrong with the equipment that we didn't know about and could have hampered the results. The best way to get the most reliable results is to do the whole experiment several times and then take the average of the results. Doing this would also show any data that is incorrect.

Chris Eland 5S2