Variables:- We had four variables to choose from, Temperature, Concentration, Surface area/Pressure and Catalyst. If we were to use temperature we would measure how much quicker the reaction would go if the acid and calcium were heated together, but we would have to keep the temperature at a constant heat as it wouldn’t be a fair test if the reactants were getting hotter and colder. If we were to use a catalyst it would be used to speed up the reaction, but this would be unfair because we wouldn’t be able to measure how much extra speed is being put in by the catalyst. Or we could change the surface area of the reactant, this would give the acid more of a area to act on, to measure this we would have to weigh the calcium first then expose it to the acid for a certain time and then take it out and weigh it, making sure we use the same concentration of acid each time to make it a fair test. We decided to use Concentration, for this we would change the strength of concentration each time and take a volume of gas that is given off every ten seconds.
From choosing the variable – Concentration we can measure the rate of gas that is being given of, this could be useful because we could work out how much gas per minute is being given off, from that we can then predict how much gas is being given off for any time you need to find.
Prediction:- I think that as the strength of the acid goes up the rate of reaction will go up.
Collision Theory:- I think this will happen because the higher the strength of the solution the more particles there are in the solution, which means more collisions more frequently. The acid will hit the calcium carbonate, if there is enough energy in the acid the calcium and acid will react together to give off Carbon Dioxide. The more the particles collide the faster they react. I have made a predicted graph, showing what I think the graph will look like. I have drawn in the lines of best fit showing the steepness of the line.
This diagram shows how the acid particles collide with the marble chip to give off a gas.
Method:- Set up apparatus as shown above.
- Measure out desired amount of marble chips.
- Measure out desired amount of hydrochloric acid – 0.25 mole first, then when all experiments with 1 mole have been completed go onto 0.5 mole then 1 mole then 1.5 and finally 2 mole.
- Fill up the water bowl.
- Fill measuring cylinder with water up to 100 ml.
- Holding hand over the top of the measuring cylinder quickly turn it upside down and place it under the water (as shown above). If the water comes out refill the cylinder and try again.
- Place tube so one end is coming up in the cylinder under water.
- Put the marbles in the chronicle flask.
- Pour in the hydrochloric acid and quickly affix the top with the tube coming out of it into the chronicle flask.
- Decide at what time you will measure how much gas is given off. We decided to take a reading every 10 seconds, we also decided to start taking the readings at 30 seconds. You measure how much gas is given off by the water dropping in the measuring cylinder. E.g. 10 mls given off in the first 30 seconds.
- Take these readings for 100 seconds using a stop watch to be precise.
I am going to take 3 repeats, I am doing 3 because I can get a fair average from these 3 results. From the averages I will plot a graph to compare the different strength acids.
Analysis:- (Graphs). From my graphs I clearly show the variable of different strengths of acids. As I used higher strength acids, the time in which the gas was produced got much faster.
As the acids get stronger the lines become more inline. Whereas the 0.5 points were all over the place.
From my results I can see that my prediction was correct “I think that as the strength of the acid goes up the rate of reaction will go up”. I could see that from my results the strength of acid went up and the speed it took to make the gas went down.
This links to the collision theory, that is that as the strength of the acid went up there were more particles to collide on the marble, which meant that more gas was given of due to more particles in the small mixture.
The higher the strength of acid the more accurate the results became, we can see this because the range bars get smaller as the strength of the acid gets stronger. From the predicted graph I can see a difference in the results graph. The 1 mole strength acid has taken longer than the 0.5 mole acid to produce the gas. I will explain the possible reasons for this more in my evaluation.
Evaluation:- The main difficulty we faced was with the 2 mole strength acid because it reacted so fast we barely had time to read the times precisely. This may have meant we had unfair results.
The main anomalous results were the 1 mole results, because from the information we have (collision theory) it tells us that it is stronger than the 0.5 mole which means it should be lower than on the graph than 0.5. But it isn’t. This may have been because the results were read wrong, the acid we used may have been slightly too strong or the marble chips we used may have been smaller which means it is easier for the acids to break down.
To improve the accuracy we could use a burette, which are far more accurate than a measuring cylinder or a gas cylinder.
Gas Syringe Burette
Computer data collectors are a very accurate way of registering the time, also if you were to use a camera recorder so you could look back at it and pause it when it got to the times when you needed to record a time.
The results would never be the same because sometimes the measurement of marble chips maybe slightly more or less, or the accuracy of reading the time would be slightly out etc.
As I said earlier in my investigation the results seemed to become more reliable as the strength of acid went up. Although it should be less accurate to measure the time as the acid strength went up it seemed to be more accurate.
