Calcium carbonate Carbon Dioxide
2HCl (aq) + CaCo3 (s) CaCl2 (s) + H20 (l) + Co2 (g)
This will be an exothermic reaction as it will give out heat.
Equipment
Rubber bung
Plastic tubing
Conical flask
100ml plastic measuring cylinder
Plastic bowl
Stopwatch
Measuring beaker
Spatula
6-9mm particle size calcium carbonate
50 ml hydrochloric acid
China beehive
Top pan balance
Diagram
Method
- Set up the equipment as shown in the diagram.
- Weigh out 2.5g of calcium carbonate particles, 6-9mm.
- Measure out the acid concentration, by first adding 50ml of 0.5m acid to the conical flask.
- Put the bung on quickly and start the stopwatch.
- Time for 2 minutes.
- Once the 2 minutes has passed record the amount of gas that has been produced.
- Do this five times, and then go through the other concentrations, repeating each five times.
- Take an average for each concentration, then plot on a graph.
Controls in the Experiment
The rate of reaction between hydrochloric acid and calcium carbonate powder was controlled by changing the following variables:
- Concentration of acid
- Amount of calcium carbonate
- Concentration of calcium carbonate – powder
I kept the amount and concentration of calcium carbonate the same, but changed the concentration of acid.
Prediction
I think that the stronger the concentration of acid the quicker the reaction time will be. This is because with a higher concentration it means that there are more particles, creating more collisions between the acid and the calcium carbonate.
This is due to the collision theory; all matter is made up of particles, and these can be atoms or molecules. All particles move to some extent depending on which state (solid, liquid or gas) they are in. For atoms to react they must collide into each other. To control the speed of a reaction we need to increase the chances of this happening, which can be done in a number of ways using different variables. These are:
- Giving the atoms more energy. This will make the molecules move faster and therefore collide more often - this is achieved by raising the temperature.
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Varying the concentration. A concentrated solution contains more molecules per cm3 than a dilute solution; therefore the molecules collide more often.
- Changing the surface are. A larger surface area, smaller particles/powder exposes more molecules than a large chunk does; this means more collisions which then leads to a faster reaction time.
- Introducing a catalyst. The use of a catalyst will lower the activation energy without being used up itself, once again speeding up the rate of the reaction.
Results Table
Graph
Graph to show the volume of gas produced in 2 minutes when hydrochloric acid is mixed with calcium carbonate
Acids, Bases and Alkalis
To explain this experiment, we need to understand how acids and alkalis react together. There are certain substances that can neutralise acids and these are called bases. Bases are the chemical opposites of acids; acids give out H+ ions whereas bases take H+ ions. Bases include the oxides, hydroxides and carbonates of metals.
Most bases are insoluble in water, but only a few are soluble. These soluble bases are called alkalis, all of which have a pH greater than 7. The commonest alkalis are sodium hydroxide (NaOH), calcium hydroxide (Ca (OH)2) and ammonia (NH3). Sodium oxide and calcium oxide react with water to form the hydroxides, both of which are alkalis.
Calcium hydroxide is much less soluble in water than sodium hydroxide and ammonia. A solution of calcium hydroxide in water is usually called lime water.
Acids have a pH less than 7 and are soluble in water. They react with bases to form salts and water and react with carbonates to produce carbon dioxide.
These reactions are described as neutralisations and this concept is used in everyday life, for example, alkaline indigestion remedies for an acid, upset stomach.
Conclusion
In this experiment I found that as the concentration increased, the rate of the reaction quickened. My graph and results back this up as there is a steady rise in the results. The collision theory has been proved as the results demonstrate that as the concentration of the particles increases there is more possibility for the atoms to hit each other and react.
My conclusion supports my prediction fully; it says how the rate of the reaction will speed up as the concentration of the acid is increased.
Evaluation
My experiment worked as I predicted it would. There was one anomalous result in test 1 when I used 1.75 molar concentration of acid, and this seemed to give a lower result. I recalculated the average ignoring this result and it brought the average up to 134. When the graph was then re-plotted, it showed a straighter line. See below.
This leads me to believe that the line above should be straight, showing a steady increase in gas volume with acid concentration.
One way the accuracy could be improved is to measure the calcium carbonate powder straight into the conical flask on the scales, rather than doing it on filter paper, which would then prevent the loss of some of the powder.
Another way to improve the accuracy of the concentrations of the hydrochloric acid would be to measure it in a burette rather than measure it out in beakers, as these tend to be better calibrated.
I am positive that my experiment is accurate enough for my conclusion to be correct.
If I were to do my experiment again I would keep the method the same, but would introduce the above amendments. It would be interesting to see how other variables would change the rate of the reaction, for example, the temperature could be varied, and the particle size of the calcium carbonate could be varied.
I would also like to try this experiment with other alkalis such as calcium or sodium hydroxide to see if they react the same as the carbonate.