I have chosen to use the concentration of the acid as my factor that I will change. I chose this because several different concentrations can be made. There will be several different concentrations of acid, which will give me a wide range of results, which will be reliable.
Question
My question is to see that if the concentration of the Hydrochloric acid is changed for each experiment I will see an increase or decrease in the rate of reaction between Hydrochloric acid and Magnesium ribbon.
Prediction
My prediction is that the higher the concentration of the acid then the higher the rate of the reaction will be. I am predicting this because of the collision theory. The higher the concentration of acid then the higher the number of acid particles present per 25 cm3 of acid. This means that there will be more collisions per second, so the rate of reaction will increase. If I double the concentration of the acid from 0.3M hydrochloric acid to 0.6M hydrochloric acid then I will expect to see the rate of the reaction double. This is because there are twice as many acid particles in 0.3M hydrochloric acid than in 0.6M hydrochloric acid, so there will be twice the amount of collisions per second, and because there are twice the amount of collisions per second then there will be twice as many successful collisions per second, increasing the rate of reaction.
Plan
I am intending to make a reaction between a chosen length of magnesium ribbon with a chosen amount of hydrochloric acid. I will measure the rate of reaction by collecting the hydrogen gas that is produced in a measuring cylinder that will be connected, via a piece of rubber tubing and a rubber bung to the conical flask that the reaction will take place. I will quickly drop the length of magnesium into the flask and connect the rubber bung to it. I will then start the stop clock and record the volume of gas evolved every 10 seconds for 160 seconds. I am measuring the initial reaction not the average.
Fair Test
In order to keep my experiment a fair test I will have to make sure that I keep the following factors the same:
· Volume of acid used (cubic centimeters)
· Surface area of the magnesium
· Length of magnesium
I will also need to clean the magnesium to get rid of unwanted chemicals.
The apparatus and chemicals used during my experiment are as follows:
Chemicals
- 1.5g magnesium ribbon
- 0.3M hydrochloric acid
- 0.4M hydrochloric acid
- 1.5M hydrochloric acid
- 0.6M hydrochloric acid
- 0.7M hydrochloric acid
- Distilled water
Apparatus
· Measuring cylinder
· Conical flask
· Safety goggles
· Test tubes
· Thermometer
Safety
The things that I will need to do to keep my experiment a safe one for myself and other students around me are as follows:
· Wear safety goggles as I am using concentrated hydrochloric acid
· Care in using glassware since it is sharp when broken and can cut skin
· Safe disposal of acid
Method
1. Put on safety goggles
2. Collect conical flask and 2 measuring cylinders
3. Collect stop clock
4. Measure out 50 cm3 of 0.0M hydrochloric acid with the measuring cylinder
5. Pour hydrochloric acid into the conical flask
6. Collect thermometer
7. Measure the starting temperature of the hydrochloric acid
8. Measure 1.5g of magnesium ribbon, cleaned to remove unwanted chemicals
9. Drop the magnesium into the conical flask
10. Quickly place the rubber bung into the conical flask
11. Start timing with the stop clock
12. Record the amount of gas evolved every 10 seconds for 160 seconds
13. Measure the temperature of the solution after the reaction is over and measure the temperature change
Results
Conclusion
My results table and graph show me that when I increase the concentration of the hydrochloric acid, the initial rate of reaction also increases.
Altogether I tested 5 different concentrations of hydrochloric acid. 0.3M, which was the lowest concentration of acid that I used had the slowest reaction. 0.7 M hydrochloric acid, which was the highest concentration that I used, produced the fasted rate of reaction. I repeated all 5 concentrations twice to be sure that they were reliable results and in all cases the higher the concentration the higher the rate of reaction. I had stated this in my prediction.
However I also said in my prediction that if I doubled the concentration from 0.3M to 0.6M hydrochloric acid then the rate of reaction will also double. I have discovered that this is not the case.
As you can see from this table as the concentration doubles then the rate of reaction approximately quadruples. My graph also shows that as the concentration doubles, then the initial rate of reaction approximately quadruples.
I therefore conclude that:
The initial rate of reaction increases as the concentration of the acid increases. My original prediction was that the initial rate of reaction would double as the concentration doubles. This was incorrect because it was not based on experimental evidence.
Evaluation
I believe this test was successful enough to show my prediction was correct, but there was still room for improvement. A factor which could have harmed my results was, when I had to quickly place the rubber bung on the conical flask, this meant that different amount of gas could escape quickly. The length of magnesium could have made a difference, it was very hard to keep all the pieces the same size because the magnesium ribbon was different widths and lengths. Some of the magnesium had already started reacting before it went into the flask because, although we had cleaned it there were still some Hydrochloric acid on our hand and desks.
