Investigating how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate (marble chips)

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Investigating how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate (marble chips)

Hypothesis:

As the concentration of acid increases, the rate of reaction between marble chips and hydrochloric acid increases.

Explanation:

The higher the concentration of acid, the more often collisions between marble chip particles and hydrochloric acid particles will occur. By increasing the concentration per unit volume of acid, there are more hydrochloric acid particles than water particles so marble chip particles can react frequently therefore increasing the frequency of collisions. This would make it more likely to get successful collisions. These factors would increase the rate of reaction.

According to the collision theory, reactant particles have to collide in order for a reaction to start. However not all the collisions are successful and if there is not sufficient energy, the molecules will simply rebound. I expect the rate of reaction to be proportional to the concentration of acid in the first few minutes if the practical, e.g. doubling the concentrations of the acid should double the rate of reaction; therefore my results should show that the reaction rate at concentration 1.0mol is half the rate of reaction when the concentration of the acid is 2.0mol.

The reaction rate should theoretically decrease as the reaction progresses. This is due to the reaction time increasing as the number of HCl molecules present decreases as they react with calcium carbonate molecules to produce calcium chloride, water and carbon dioxide. Although carbon dioxide escapes into the air, the water produced will dilute the acid, so the concentration of HCl will decrease. There will be fewer successful collisions due to the decrease of HCl molecules.

This reaction is exothermic reaction energy is released to the surroundings because more energy is released making bonds in the products than is needed to break bonds in the reactants.

                                                                                                           

Here is the balanced equation for this reaction:

CaCO3(S) + 2HCl (aq)                              CaCl2 (aq) + H2O (L) + CO2 (G)

Control Variables:

I will keep the temperature constant by keeping the equipment in the same environment before and during the practical. I will carry out the experiment in a specific classroom.

The surface area, size and mass of the marble chips will be fairly constant. The marble chips will be measured out using weighing scales correct to 2 decimal places.

The volume of HCl used will be kept constant. We will measure the HCL using graduated pipettes.

I will ensure all equipment (graduated pipettes, conical flasks, etc) will be thoroughly cleaned after each experiment to ensure that no cross contaminations take place.

Preliminary Experiment For Rates Of Reaction

The aim of my preliminary experiment was to determine the appropriate concentrations of HCL, marble chip sizes, the optimum mass of marble chips and the volume of acid.

To do this, I tested both amounts of marble chips and concentration ranges of HCL acid. I also experimented with different measuring cylinder sizes to see which ones were appropriate for the actual experiment.

Method for preliminary test

  1. Take 2 grams of marble chips which have all been cut down to approximately the same size.
  2. Take the different concentration of HCL acids and pour out 40ml using a measuring cylinder
  3. Prepare 3 different beakers and balances.
  4. Weigh the marble chips and record them
  5. Pour in the hydrochloric acid and the marble chips in each beaker.
  6. Place the beakers containing each solution on top of a balance.
  7. Start the stop clock
  8. Note down the results you obtain per 30 seconds until the reaction has fully completed.
  9. Find the difference in mass between the mass before and after to find how much CO2 was released.
  10. Use this data to identify what you can improve on your actual experiment.

Preliminary Experiment Results

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Safety/ Risks

  1. Be careful when handling the graduated pipette as it is made of fragile glass. If the pipettes are used incorrectly, they may cause injuries. Always handle this equipment with care!
  2. Hydrochloric acid is corrosive and therefore it should be treated with care. Wear gloves! If HCL is spilt, clean the spill up immediately
  3. Safety goggles should be worn at all times.
  4. Tuck in any loose pieces of clothing or hair so they won’t get in the way of the practical.
  5. Any other breakages of equipment should be reported and cleaned up appropriately.

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