The Reaction Between Calcium Carbonate and Hydrochloric Acid

A higher temperature makes the atoms move faster by providing them with more energy. As they heat up they vibrate. When they got hotter they vibrate at higher speeds and further. This cause much more collisions. Yet again this means that there is a greater chance of successful collisions, which means a faster rate of reaction. When the atoms do collide into each other they hit each other with more force as they are moving faster. This makes it more likely that the collisions contain the minimum activation energy. Yet again this is another way of increasing the chance of creating more successful collisions, which means a faster rate of reaction.

Fig. 2.a

Increasing Temperature

As you can see from the above graph, figure 2.b, the time taken for the reaction to be completed decreases as temperature increases.

Predictions

> I think that the rate of reaction will be higher at higher concentrations. This is because:

More particles in the same space.

?More collisions

?More successful collisions and a faster reaction.

> I also think that the rate of reaction will be higher when the surface area is greater. This is because:

More surface for collisions to occur

?More collisions

?More successful collisions and a faster reaction.

Variables

The dependent variable is the time taken to displace 30cm3 of water measured in seconds.

The independent variable for my first experiment is concentration measured in mol/dm3.

The independent variable for my second experiment is surface area measured which shall be measured by the different sizes of the calcium carbonate particles.

I will use four different concentrations of acid 2, 1.5, 1 and 0.5 molar solutions.

In the second experiment I will use four different sizes of the particles of calcium carbonate large, small and mid-size chips as well as powder.

I have chosen to use four variables for each part of the experiment because I think that it will give me a large enough range to compare results and draw conclusions.

I will repeat every experiment three times and take an average of the three to try to make my results more accurate and to avoid anomalous results. For example if one of the three results are very different to the other two, the result is anomalous, I can point it out easily and do that replica again.

The control variables to ensure my experiment is a fair test are:

* Volume of acid measured in ml.

* Source of water.

* Dilution techniques and chemicals used.

* Amount of calcium carbonate.

* Surface Area of calcium carbonate (second experiment).

* Concentration of hydrochloric acid (first experiment).

* Stopwatch used.

* Thickness of Glassware.

(These will be kept the same)

I will use the following amounts of the control variables:

* Volume of acid will be 5ml.

* Source of water will be tap water from one single tap.

* Dilution techniques will be kept standard and chemicals used will be the same.

* Amount of calcium carbonate will be 3g for first experiment but 1g for second experiment.

* Surface Area of calcium carbonate (second experiment) will be small chips.

* Concentration of hydrochloric acid (first experiment) will be 2 molar.

* The stopwatch used will be the same for all replicas.

* Thickness of Glassware will be kept the same by using the same glassware for all replicas.

Pilot Study

I needed to find out what sort of range of values would be best to use to show the best range of results without being to hard to measure.

I used the same method as the main experiment. I did four experiments both with different variables; my results are below:

Experiment

Amount of Acid/cm3

Amount of Calcium Carbonate/g

Concentration Of Acid/mol/dm3

Size of particles of Calcium Carbonate

Time Taken to displace 30cm3 of Water/secs.

A

5

2

Small

55.99

B

5

5

2

Small

9.66

C

3

3

2

Large

72.04

D

3

2

Powder

5.44

I looked at my results. I thought that using 5cm3 of acid and 3g of calcium carbonate would work well for the first half of the experiment and again 5cm3 of acid but this time only 1g of calcium carbonate. I chose to use small chips for the first experiment and 2 molar acid for the second experiment. I chose these values because at the both extremes of the experiments the reaction would be neither to fast to measure nor take so long that time would be wasted.

Apparatus

i. 1x 50cm3 measuring cylinder

ii. 1x 10cm3 measuring cylinder

iii. 1x 250cm3 conical flask

iv. 1x Empty plastic ice cream tub

v. 1x Tubule connected to rubber bung to be attached to conical

vi. 1x Stopwatch

Method

Experiment Safety

GOGGLES MUST BE WORN WHEN HANDELING ACIDS

A- Concentration

i. Set up the apparatus as shown below.

ii. Add the 5cm3 of 2 molar acid into the conical flask.

iii. Insure that the tubule leads to the 50cm3 measuring cylinder. Also insure that the measuring cylinder is full of water.

iv. Add 3g of small calcium carbonate chips and immediately start the stopwatch.

v. Observe the water level decrease as it's displaced by the carbon dioxide given off in the reaction. Stop the stopwatch as soon as 30cm3 of water has been displaced. Note down the time.

vi. Repeat the same experiment 3 times.

vii. Repeat the experiment with 1.5, 1 and 0.5 molar acids.

viii. To create these concentrations, dilution is required. For 1.5 molar 75% acid and 25% water etc...

ix. Before repeating the experiment create 50cm3 of each of the different concentrations of acid required. The table below shows how much acid is required and how much water:

Concentration/ mol/dm3

Amount of Water/ Cm3

Amount of Acid/ Cm3

.5

37.5

2.5

25

25

0.5

2.5

37.5

x. I created these concentrations and then repeated the experiment at these concentrations again doing 3 replicas.

xi. After completing go on to the second experiment, surface area.

B- Surface Area

i. The general method is the same. Again set up the apparatus as the diagram.

ii. Add the 5cm3 of 2 molar acid into the conical flask.

iii. Insure that the tubule leads to the 50cm3 measuring cylinder. Also insure that the measuring cylinder is full of water.

iv. Add 1g of large calcium carbonate chips and immediately start the stopwatch.

v. Observe the water level decrease as it's displaced by the carbon dioxide given off in the reaction. Stop the stopwatch as soon as 30cm3 of water has been displaced. Note down the time.

vi. Repeat the same experiment 3 times.

vii. Repeat the experiment with mid-size chips, small chips and powder again doing 3 replicas.

Results

Concentration Of Calcium Carbonate/ Mol/dm3

2

.5

0.5

Time Taken to Displace 30cm3 of Water/ Seconds

Replica A

8.18

30.09

50.12

260.07

Replica B

20.13

38.12

56.04

240.94

Replica C

6.7

38.91

54.34

221.34

Average

8.3

35.7

53.5

242.12

Surface Area Of Calcium Carbonate

Large Chips

Mid-Size Chips

Small Chips

Powder

Time Taken to Displace 30cm3 of Water/ Seconds

Replica A

21.07

87.42

55.99

4.44

Replica B

12.97

83.67

49.4

1.02

Replica C

28.44

85.26

38.4

1.94

Average

20.83

85.45

47.93

2.47

Analysing Data

I have found out two clear patterns from my results:

> The reaction performs quicker at higher concentrations.

> The reaction performs quicker when there is a larger surface area.

I found that the lower concentrations of acid caused the rate of reaction to be largely reduced as from the higher concentrations. This was a definite trend. The gap between the average reaction time for 0.5 and 1 molar is much larger than the gap between the average reaction times between 1 and 2 molar. There is a clear exponential rise in the rate of reaction as the concentration increases.

There were almost identical trends in the surface area experiment. As the surface area got larger the reaction time got a lot quicker. The rate of reaction for powder was lightning fast.

My graphs illustrate how the rate of reaction increases with both concentration and surface area.

My results strongly support both of my predictions.

> The rate of reaction was higher at higher concentrations. This is because:

More particles in the same space.

?More collisions

?More successful collisions and a faster reaction.

> The rate of reaction was higher when the surface area was greater. This is because:

More surface for collisions to occur

?More collisions

?More successful collisions and a faster reaction.

Overall Conclusion

The overall conclusion I draw from this practical is that a higher concentration or a greater surface area of a reactant will raise the rate of reaction.

Graphs

I did two graphs, one for each experiment. I used a line graph for the concentration experiment and a bar chart for the surface area experiment. In my line graph I use a line of best fit because the results were very unlikely to be 100% accurate. The graphs are on the next two pages.

Evaluation

I think that it is impossible for my results to be 100% accurate but I think that they are fairly reliable. There is too much room for error in measurement, which makes extremely difficult to get very accurate results. I think that I measured very well in all aspects. I measured and checked everything I did.

There were not any real unexpected results or anomalies to the patterns and trends discovered. The only result that was the individual replica results for was the 0.5 molar concentration experiment. The difference between replicas a and c was nearly 40 seconds. I am not too surprised with this result however because for the slower reactions the gaps between replicas tend to become larger. The longer an experiment goes on the less accurate it is likely to be.

If I were to redo the experiment I would do more replicas of experiments to try to make it more accurate. I would also use a greater range of concentrations and surface areas to increase my range of results. This would make graphs more accurate and there would be more results to compare.

I think that my results are strong enough to give a firm conclusion that an increase of either surface area or concentration will increase the rate of reaction.

If I were to do further work I would do similar experiments using a catalyst and varying temperature to see the affects they cause on the rate of reaction. I would expect to find similar results, that they both increase the rate of reaction.

Raj Purewal Chemistry SC1 2001 Page 1 of 10