Investigating the rate of reaction of hydrochloric acid with calcium carbonate

Variables

There are 4 variables that will change the rate of reaction in my experiment:

.Temperature - The more thermal energy in the experiment will give the particles more speed. This will result in the particles colliding more frequently and increasing the speed of the reaction. Also when they have more energy there will be more chance of the collisions being successful because the activation energy will be attainable.

2.Concentration of acid (pressure for gases) - to change the concentration of the acid we will add water to dissolve it. The higher the concentration of acid the more reactant particles will be introduced in the same space. Reaction rate will therefore increase with concentration

3. Surface Area - There are 3 types of chips we can use. They all have a varied surface area, the largest surface area being the powder form, then the small chips, and finally the smallest surface area being the large chips. The rate of a reaction involving a solid is proportional to the surface area of the solid. By increasing area we increase the rate of the reaction. This is because there is more particles exposed in the reaction and reaction will thus increase. Smaller particles have a bigger surface area than larger particle for the same mass of solid. There is a simple way to visualize this. Take a loaf of bread and cut it into slices. Each time you cut a new slice, you get an extra surface onto which you can spread butter and jam. The thinner you cut the slices, the more slices you get and so the more butter and jam you can put on them. This is "Bread and Butter Theory". By chewing your food you increase the surface area so that digestion can go faster.

4. Amount of acid or marble-It is important to get the right amount of marble and acid if one them is in too small amount then there will be an incomplete reaction. Keeping this in mind I have decided to use excess quantities of acid to insure there is a complete reaction.

*Note: Another variable would be the use of a catalyst. The reaction will be faster but the catalyst will not be used up during the reaction. When the activation rate is lower not much energy is needed to make the reaction successful. But we are not going to use a catalyst in this experiment so it is not a factor needed to be considered.

Controlled variable: I will test change the concentration of the experiment to see if this affects

Prediction

I predict that if the concentration of the HCl is doubled then the experiment will happen twice as fast. This is because twice as many HCl particles will be present than previously and there will be twice as much chance of the calcium carbonate chips colliding with the concentrated hydrochloric acid. Therefore when the concentration is double the time take for the reaction should be halved. With the acid being very dilute, many of these collisions will be with harmless water molecules, which play no part in the reaction; therefore it may be a while before the appropriate particles collide.

Previous experiments on rate of reaction

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A previous experiment we have done which involves the rate of reaction between Sodium Thiosulphate + Hydrochloric acid. The equation for this is:

2HCL (aq) + Na2S2O3 (aq) --> 2NaCl (aq) + H2O (l) + SO2 (g) + S (s)

In this experiment timed how long it took for a cross underneath the flask to disappear. We change the concentration of the acid to see what effect it had on the rate of the reaction. This is the apparatus we used to record results

The results we got were then plotted showed that rate is direction proportional to concentration.

Other experiments we could of done would have been magnesium with acid. We could have measured for the reaction to be completed by measuring the gas given off. Equation for this reaction is:

Mg (s) + 2HCL (l) --> MgCl2 (l) + H2 (g)

Method

Trial experiment

To test the rate of the reaction in my experiment I have decided to measure the gas given off over a set amount of time. Our first experiment has to try out some trial masses and concentrations to decide suitable ones for our experiment.

We used a measuring cylinder and a test tube to measure off the amount of gas given off. We also timed how long it took for the reaction to be completed. We mixed the amount of marble and concentration of acid so we could see which would be suitable. The marble was in the form of powder, which means we had a large surface area. The mean room temperature was about 22o throughout the experiment. Equipment we used were:

measuring cylinder

conical flask

bowl of water

delivery tube with bung

acid (HCL)

calcium carbonate (CaCO3)

clock

clamp

boss

We set out the equipment into the following arrangement:

The results we record are shown below:

Concentration of Hydrochloric acid

Mass of Calcium carbonate

Time for reaction to complete

Verdict

2.00 mol/dm3

2.00g

3.59 seconds

Much too fast

2.00 mol/dm3

.00g

7.12 seconds

Much too fast

.00 mol/dm3

.00g

25.66 seconds

Too fast

.00 mol/dm3

0.50g

67.77 seconds

Still relatively fast, but will work for the highest concentration.

0.50 mol/dm3

0.50g

83.00 seconds

Good length

0.01 mol/dm3

0.50g

Over 2 minutes

Too slow

The results show the reaction went too quickly or too slowly to record results. It also was difficult to read the results as the measuring cylinder needed to be turned upside down in the experiment meaning the label we read from to record results were also upside down.

For the experiment we re-decided that the mass of the marble to be only 0.5g but to keep the marble in its powdered form. Powdered marble is easier to measuring out than larger lumps that would be varied masses. Both the form and the mass of marble would remain a constant variable throughout the experiment. New improvements to the apparatus now meant that we would use a gas syringe instead of the measuring cylinder that was harder to use. Are input variable (the acid) would be measured from 0.2 mols to 1 mol at 0.2 mol intervals.

Experiment

The apparatus we are using are similar to the experiment using magnesium ribbon. We found this to be the most success apparatus to record accurate results with so far. The apparatus were as follows