Rate Of Reaction

G.C.S.E Practical Investigation

KS4 Sc. 3 Chemistry

Rate Of Reaction

The aim of this investigation is to find out what controls the rate of reaction. The key factors that control this are:

Concentration
Temperature
Surface Area
Catalysts

In this investigation I am going to look at the temperature factor. The effect of temperature on the rate of reaction should be that it effects the speed of the reaction. So if the temperature is 40C, the reaction should be twice as fast as a reaction that takes place at 20C. The reason for this is that the molecules will gain twice as much energy and will therefore move around twice as fast. The chance of the molecules colliding will be greatly increased due to this.

To help me with my practical, I conducted a preliminary test. The reason for this was to help me find an appropriate temperature range and chemical combination.

To test the temperature range, I listed temperatures, going up in tens, starting at 20C and ending at 80C. This is because I wanted a range using six temperatures but I was unsure of whether to use a high temperature or a lower temperature. So, I then took the lowest temperature and the highest temperature and tested them to see how fast they reacted.

First of all I tested 20C. I heated hydrochloric acid and sodium thiosulphate to this temperature and poured them into a conical flask. Underneath the conical flask was a piece of paper with a large black cross on it. When the two chemicals react, they form a cloudy liquid which means you cannot see the black cross through the liquid. So I timed how long it took for the black cross to disappear and it took 28 seconds. I then repeated this process but I heated the two chemicals to 80C instead. It took 5 seconds for the cross to disappear this time. When I looked at these results it occurred to me that if I used 20C as one of the temperatures, it would take up a large amount of my allocated time in which I had to conduct my practical. I therefore decided to use 80C in my experiment.

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To test the concentrations that would work best for my experiment, I first of all chose three different hydrochloric acid concentrations, 1M, 1.5M and 2M. I then chose three different sodium thiosulphate concentrations, 20g/l, 60g/l and 100g/l. I then reacted each concentration with its corresponding chemical. For example: 1M with 20g/l and 1.5M with 60g/l. I compared the results of each of each reaction and found that the speed of 1.5M and 60g/l was ample for my practical.

After conducting my preliminary tests I decided to use a temperature range of 30C - 80C and use the chemicals 1.5M ...

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After conducting my preliminary tests I decided to use a temperature range of 30C - 80C and use the chemicals 1.5M hydrochloric acid and 60g/l of sodium thiosulphate.

The apparatus I intend to use for my practical is:

Conical flask
2 boiling tubes
beaker filled with water
Bunsen, tripod, gauze and heatproof mat
Hydrochloric acid
Sodium Thiosulphate
Stop clock
Thermometer
Two measuring cylinders
Goggles
Paper with a black cross on it

To begin my practical I set out all my apparatus first. I half-filled a beaker with tap water and placed it over a Bunsen burner. I then measured 20ml of 60g/l sodium thiosulphate into a measuring cylinder and 20ml of 1.5M hydrochloric acid into a different measuring cylinder. I then poured each of them into separate boiling tubes and put the boiling tubes into the beaker of water. After placing a thermometer in the beaker with the boiling tubes I began to heat them with the Bunsen burner. When the water reached 30C, I removed the boiling tubes from the water and poured them into the conical flask. Using the stop-clock, I timed how long it took for the black cross to disappear. I recorded the time on the stop clock into my exercise book. I then washed the two boiling tubes and the conical flask.

I repeated this method for each temperature, recording the results as I went along. Each time I increased the temperature by 10C until I reached 80C.

To make results accurate I will use exactly the same chemicals and amounts. I will keep my method the same and I will wash out the conical flask and the boiling tubes after each test.

By doing the above, my practical will also be a fair test. I will need to make sure that each factor is kept the same and that the only factor that will be changed is the temperature of the chemicals.

To make sure that my practical is safe at all times, I will need to wear goggles throughout the practical, use test tubes holders to pick up the boiling tubes when they have been heated and I must make sure that my Bunsen burner is never left unattended.

To help me with my practical, I used the text book “Chemistry For You” and I also used my exercise book. The information I got from these sources helped me to decide on a method for my practical and they gave me safety guidelines too.

These are the results I collected from my practical. The rate of reaction column in my table shows how long it took in seconds for the black cross to disappear.

Experiment 1:

Experiment 2:

Experiment 3:

I will now work out the averages of my results. To do this I will add each result from the same temperature together and then divide the total by three.

Averages:

I have drawn a graph using my average results. After looking at my results to see if I could find a pattern, I could not find a specific one. However there was a general trend in my results. Each result was lower than the previous result. This trend shows that when the temperature is higher, the rate of reaction is faster because it takes less time to react. The reason for this trend is that the molecules in both chemicals will gain more energy with a higher temperature and will move around faster. This will increase the chance of the molecules colliding with each other and so the reaction happens faster. My results agree with my prediction that I made at the start. This is because I predicted that the temperature would speed up the rate of reaction. My results show that this is true.

When analysing my results I found that I had an odd result. The odd result I found was in my second experiment for 70C. Instead of being lower than the previous result it was higher. I am unsure how I got this odd result but it may have something to do with the temperature of the chemicals in the boiling tubes. To improve my experiment so that this won’t happen again, I could put the thermometer into the boiling tube instead of the beaker with water in it. This will help me make sure that the temperature of the chemicals is the same as the temperature of the water. This will also help me make sure that the chemicals are at the correct temperature.

Even though I had an odd result, my results were good enough to form a firm conclusion. I know this because the trend in my results showed me that my prediction was correct and it can be supported with my scientific knowledge. This means that I can confidently say that my experiment helped me prove that the rate of reaction can be increased if the temperature of the substances used is increased.

To make sure that my results were reliable I compared them with a similar experiment. By doing that I found that my results were reliable because they were very similar to the results of the other experiment.

To back up my results I could have done some extension work. I could have done another experiment, this time using a different method or using different chemicals. For example I could have reacted hydrochloric acid with magnesium ribbon. I could have heated the hydrochloric acid and measured the amount of gas that is produced from the reaction using a gas syringe and timing how long it took for the amount of gas to be produced.