Safety: During the investigation, we will try to be as safe as possible. We will wear an overall and eye goggles to protect our clothes and eyes from the hydrochloric acid. We must make sure that stools and bags are kept under the bench to prevent accidents. We will make sure the apparatus is kept in the centre of the bench to avoid breakages and spillages. If there was a spillage, we would make sure the teacher was informed and that it was wiped up completely.
Fair Test: We will make my experiment as fair as possible by only changing one variable. We will keep the mass of the limestone the same at 5 grams and use the same type of limestone in each experiment, whether that be powdered, large chips or small chips. We will also keep the total amount of liquid the same at 50 ml. We will use the same equipment in each experiment. We will not vary the type of acid. We will also try to keep the temperature of the acid the same (room temperature), however, if the experiment has to be done of two days, the temperature might change because of the weather and there is nothing that can be done about that. We will start and stop the experiment at the same time – from the first bubble and when we reach 25 ml in the measuring cylinder. We will also use the same units in each experiment.
Changes: The only variable we will change in our experiment is the concentration of the hydrochloric acid, so we can get our results and draw a firm conclusion.
Measurements and Trials: In our experiments, we will change the concentration of the acid five times. The measurements will be 100% acid, 80% acid and 20% water, 60% acid and 40% water, 40% acid and 60% water, 20% acid and 80% water. We shall try to do three trials at each different concentration and finally we shall have five sets of results to allow me to plot a graph of averages. By having a lot of results, we will be able to tell whether the result is truly anomalous or correct. If we had only one or two sets of results, it would be hard to tell whether the result was anomalous.
Prediction: I predict that the limestone will react quicker in pure acid than in dilute acid. If a reaction was to take place, the reactive particles of the acid and reactive particles of the limestone must collide with each other with a lot of energy. Acid concentration affects this. For example, in pure acid all the particles are reactive. This means that there are a lot more collisions of acid and limestone particles. If the acid concentration was 20%, this means only 20% of the acid particles are reactive so there is a much less chance of a collision with a reactive limestone particle. The reaction will slow down over time because as the reaction goes on, there will be less reactive acid and less reactive limestone particles, so the reaction will slow down. The speed of the reaction is dependant upon certain things. For example, the temperature of the acid can affect the rate of reaction – if the acid is very cold the reaction will be very slow whereas if the temperature is very hot the reaction will take place very quickly. Another example is the surface area of the limestone. In our experiment, we have three different sizes of limestone: small, large and powdered. I predict that because the powdered limestone has the largest surface area, that reaction will happen very quickly, whereas the large limestone chips have a small surface area, that reaction will happen a lot slower.
Particle Diagrams:
100% Concentration 80% Concentration
60% Concentration 40% Concentration 20% Concentration
Apparatus: In our experiment, we will use a chemical balance to weigh the limestone, a measuring cylinder to measure out the water and acid accurately, a conical flask – where the reaction will take place, a delivery tube to allow the carbon dioxide to travel from the conical flask to the measuring cylinder, a trough of water which the measuring cylinder will be lying in. We will also use a stopwatch to time the rates of reaction.
Displaying Results: This is how we will show our results.
Diagram:
Bubbles of CO2 Gas
Delivery Tube Measuring Cylinder
Conical Flask Water
Hydrochloric Acid
Limestone Trough
Method:
- We set up the apparatus as shown above.
- We measured 5 grams of limestone using a spatula.
- We placed the limestone into the conical flask.
- We poured on the hydrochloric acid and water solution, and then placed the bung in the flask quickly.
- When the measuring cylinder was filled with 25ml of gas, we stopped the stopwatch quickly.
- We recorded the results and repeated the experiment for the different concentrations.
Results:
