I will be looking at the concentration of acid (hydrochloric) and seeing what effect it has on the speed of a reaction of calcium carbonate (limestone)
CaCO3 + 2HCL CaCI2 + CO2 + H2O
You can tell a reaction is taking place as gas is given off.
Prediction
With this knowledge, I predict that the higher the concentration of acid, the faster the reaction, (as there are more particles to collide with).
I have thought, that perhaps there is a relationship between the time it takes to lose a certain amount of mass)
My guess is that for each percentage, the reaction takes off 0.2grams of mass.
For example, if 100% is 1.7g, 50% would be 1.5g
I will be working on how much mass the limestone loses over 7 minutes
In dilute acid, there are not so many acid particles. This means they have less chance of an acid particle hitting a Limestone atom.
Here the acid is more concentrated, and there are more acid particles in it. There is now more chance of a successful collision occurring.
The Collision Theory can be used to explain this.
- Chemical reactions happen when particles of the reactants collide with each other.
- They must collide with a minimum energy, called the “activation energy”.
Apparatus
Distilled Water
Acid (various concentrations)
Limestone
Conical Flask
Stop clock
Cotton wool
Scales
Measuring cylinder
Fair Test
The same value of limestone (6g) will always be used.
The only thing to change is the Acid concentration
Method
- Put goggles on for safety
- Measure dilution of acid needed.
100% is 60ml pure acid.
75% is 45ml acid (15ml distilled water)
50% is 30ml acid (30ml distilled water)
25% is 15ml acid (45ml distilled water)
10% is 6ml acid (54ml distilled water)
- Weigh out 6g of limestone on the scales
- Pore the dilution used into a conical flask
- Put the conical flask on the scales with cotton wool in the top then zero the scales
- Take the cotton wool out of the flask and get ready to press start on the stop clock
- Put limestone in the conical flask, press start, and put cotton wool in the neck of the flask
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Observe and record results at 2nd, 3rd, 4th, 5th, 6th, 7th minutes
- At 7 minutes stop the stop clock
- Repeat the experiment 3 times then average the results
- Repeat above steps for the other concentrations of acid
Results
Minutes Timed
Average Results
Analysis
I have produced a graph. It shows that, as I explained in my prediction, the lower the concentration, the less mass it would lose (and the slower the rate of reaction.)
For example, for 100% the average total mass lost was 0.7g
For 10% a total of 0.3g of mass was lost.
This is because there are more acid molecules in 100% concentration and in 10% concentration there are less.
The reason this is is because the particles are closer together, hit each other more often, and so will react quicker.
Evaluation
There is no clear difference in the numbers, as they were all as accurate as I could get them. For this reason it was a very accurate test, although the results were all rounded off to one decimal place, more attempts should have been made to obtain evidence (to make averages more accurate.) The limestone was not the same size each time and the room was not the same temperature. These factors we could not control, would have affected the results considerably. Future tests could be made with more percentages, using the same methods but using closer percentages such as 5% intervals or with much higher percentages, such as 100% 4M acid.
