Concentration* involves adding water to the hydrochloric acid, then adding marble chips to the solution. The more concentrated the acid then the quicker the reaction will take place, because there will be more acid particles than water particles for the marble chips to collide with and therefore reacting faster. More collisions between the two reactants will take place resulting in a quicker time for the reaction. This is the easiest variable to measure.
The variable marked with a * is the one that will be varied, the others will be kept constant so the tests are fair. I intend to find out how long it takes to fill a test tube full of carbon dioxide.
This reaction produces a gas and I can measure how quickly this forms using different concentrates of acids.
Aim: to find if changing the concentration of an acid will increase or decrease the rate of reaction. I will measure it by the time (seconds) it takes to fill a beaker full of carbon dioxide.
Making it a fair test:
To ensure that my experiment is fair there are many aspects I have to consider. Firstly the apparatus that I use will not be exactly the same, for example I will use a different side armed test tube on one lesson than I did on the last lesson. Also I will be using a different sample of hydrochloric acid than I had done the lesson before. All though they are important factors there is not much I can do to prevent them. Instead I will try and concentrate on the more common aspects. I will try and keep the marble chips as near to the same size as possible. I will work in the same place as I had done the last lesson in case there is a dramatic temperature change. I will always have the same amount of solution in the beaker each time. I will only change one variable and always collect the same amount of CO2 each time.
Also to ensure my test is accurate I will repeat it three times.
Method
Apparatus needed:
-
side armed test tube
- bung
- hydrochloric acid
- stop clock
- calcium carbonate (marble chips)
- trough
- test tube
- water
- measuring cylinder
- The apparatus was set up as shown.
- fill the test tube with water and place over the delivery tube (as shown)
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Add the selected amount of HCl and H2O (is applicable) to the side armed test tube.
- Add the marble chips, put on the bung and start the stop watch.
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Collect the amount of CO2 needed through displacement of water.
- as soon as the test tube is filled with gas the stopwatch is stopped and time recorded
- The acid is poured away and marble chips washed for the next use.
- The above steps are repeated for each concentration of acid. Then the whole investigation is repeated for accuracy.
Test for CO2 : lime water goes cloudy
Rough trial
Using the method above the following rough trials were carried out so as to determine the best range of concentration. For these rough trials I decided to use 15cm3 of liquid in total.
From these results, I decided to keep the total liquid the same as the trail and use concentrations from 15cm3 to 5cm3 any lower and it would take to long. I will time how long it takes to fill a whole test tube full of carbon dioxide gas and will record the results. To make my results as reliable as possible I will repeat them as many times as possible and find the average.
For safety:
- Goggles will be worn at all times
- Acid is kept away from skin and eyes if possible. If it comes in contact with eyes or skin it will be washed thoroughly.
- An overall will be worn.
- A first aid kit will be in the class room
Predictions
I predict that the higher the concentration of acid, the shorter time taken to fill a test tube with carbon dioxide, and therefore a larger and faster rate of reaction. I know this because there will be more acid particles than water particles for the marble chips to collide with and therefore reacting faster. More collisions between the two reactants will take place resulting in a quicker time for the reaction.
Predicted graph shape:
Results
(Simple graph)
Analyzing the evidence
Analyse
My results show that with an increase in concentration and increase in the rate of reaction occurs. It shows that the amount of concentration has a very big effect on the rate in which the marble chips react with the acid. When the acid increases the rate of reaction quickens, when the water increase the rate of reaction slows.
Conclusion
As predicted, the rate of reaction increased as the concentration increased this is because The higher the concentration of acid, the shorter time taken to fill a test tube with carbon dioxide, and therefore a larger and faster rate of reaction. I know this because there will be more acid particles than water particles for the marble chips to collide with and therefore reacting faster. More collisions between the two reactants will take place resulting in a quicker time for the reaction, as it was stated in the conclusion.
We are now able to answer our main hypothesis : “how does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate” The answer to that is more and less gas would be produced depending on whether the concentrations where more or less.
Obtaining the evidence
During the experiment, I kept as many things as I could constant (i.e. the amount of liquid) I used a stop clock to time my experiment to produce the results and I always watched the experiment to see if any irregularity occurred. I collected the results after repeating them twice and found the average. The results shown are the average results. I think my results are fairly reliable but a few mistakes did occur:
- I spilt a bit of hydrochloric acid over the side of the test tube
- my measuring skill may not have been always accurate
- The temperatures might have been changed.
I believe that I uses the apparatus correctly and safely and my produced results where a good outcome. The experiment was as fair as I could make it but I could have made it more reliable by repeating it a few more times. All the evidence collected was from the using the equipment.
- To have made my results really accurate I could have done more re tries and found the average
- To make my experiment more through I could have changed the concentration by every cm3 rather than every two three.
- If there was and odd results (which there wasn’t I could have redone them to make sure it wasn’t a mistake.
- I have tried to record my results neatly and easy to read.
Evaluating my evidence
Comment on the produced results
I think my experiment went very well. All the results where planned out nicely on the graph making it very easy to read. From looking at my results there was no major error but I repeated the set below:
This is because the second set of results is not very close to the first set. When it was repeated it came out almost the same so i decided to leave the results as they were. There might have been a temperature change or I could have used a different acid.
The method was easy and practical. It was very easy to follow and produced nice results. To improve it you could have had the concentrations all ready made up for you so everybody’s measuring was the same or you could have had two people doing it so that the timing was correct as it was hard to put on the bung, add the marble chips and start the timer all at once.
If you had wanted further evidence I could have had a wider range of tests and I could have repeated them more times but over all the experiment was very conclusive.
