# Investigation: How does channging the concentration of a substance affect the rate of reaction?

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• Published: May 3, 2004

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A chemical reaction is the process by which atoms or groups of atoms are redistributed, resulting in a change in the molecular composition of substances.

The reaction rate is how quickly a reaction occurs. I will be using the reaction rate during my investigation to see how the concentration of acid effects the reaction rate. To do this I will be using the following reaction

Hydrochloric + Calcium Ü Calcium + Carbon + Water

Acid Carbonate Chloride Dioxide

powder

2HCl + CaCO3 Ü CaCl2 + CO2 + H2O

I will be using these substances because I know from my research and previous experiment that these two substances react well together. So, I will be able to have quick and efficient experiments.

I will be using the following equipment and setting the equipment up as shown in the diagram.

2. Gas Syringe

3. Rubber plug

4. Stop Clock

5. Top Pan Balance

6. Heat Proof mat

7. Clamp and Boss

8. Clamp Stand

I will be testing to see how the concentration of the hydrochloric acid effects the reaction rate. I will be able to see this by measuring the gas using the gas syringe. As carbon dioxide is released during the experiment, I will measure how much carbon dioxide will be produced in certain amounts of time. I will then draw a graph to show how much carbon dioxide had been produced in several time intervals. I will then take the gradient at one point in the graph where each line is straight.

This will show me the reaction rate of each experiment. I will use five different concentrations of acid. Below are the different concentrations I will be using.

Quantity of HCl (ml) Quantity of H20 (ml)

50 0

45 5

40 10

35 15

30 20

25 25

From this information, I can work out what molar, the acid is. I will do this by using a special formula, the formula is:

Volume of acid X 2

Total volume of solution

Dividing the volume of acid by the volume of gas will show how much of the solution is made up of acid. However you have to multiply this answer by two, this is because I will be using a two molar acid as my original hydrochloric acid, which I will then add water to.

I can now work out the molars of each solution. They will be:

Quantity of acid (ml) Quantity of Water (ml) Molar (M)

50 0 2.0

45 5 1.8

40 10 1.6

35 15 1.4

30 20 1.2

25 25 1.0

I have decided to use 50 ml of acid as my upper limit, because it should give me a relatively quick reaction, so the experiment will take only a short amount of time. I will use 25 ml of acid as my lower limit if I start taking readings below that measurement, the reactions will start to get very slow and so take up a long amount of time. I will be able to see the general pattern, as I would already have six readings. I am using six readings because it will be enough to draw a good line of best fit.

This should hopefully give me a clear result of what effect the concentration of acid has on the reaction rate. For each experiment I will use 5 grams of calcium carbonate. I will take readings from the gas syringe every 30 seconds. The amount of gas produced every 30 seconds shows how quickly the reaction has taken place.

Before my main experiment I will perform a trial experiment to make sure I can complete the experiment in time, make sure I am using the right quantities of each substance, so that I can see any other problems that might occur during my experiment. For the trial experiment I will test the two extreme quantities to check that they are suitable for the experiment. So I will be using

Quantity of HCl (ml) Quantity of H2O (ml)

50 0

25 25

I hope for each experiment to last over one minute, so my results are more accurate. After my trial I will change the quantities if they are wrong so that each experiment lasts over one minute.

In order to make my experiment safe I will use goggles when I handle acids or alkalis. I will also make sure that if I decide to use any...