Investigation on reacting sodium thiosulphate with hydrochloric acid.

I will have to use the same cross throughout the whole experiment, because if I used one of different size, it would alter the time it would to disappear.

I will also have to use the same conical flask throughout the whole experiment, because if I used one of a different size, it would alter the time it would take for the cross to disappear.

Experiment 1

Apparatus

Sodium Thiosulphate

Hydrochloric acid

Water

Burette

Retort Stand

Burette clip

Conical flask

Paper with cross on it

Stopwatch

Method

1. Put on a pair of safety goggles and remember to keep them on for the rest of the experiment
2. Measure out the chosen amount of sodium thiosulphate using a burette, into a conical flask.
3. Measure out the chosen amount of water using a burette, into the conical flask.
4. Measure out 10cm3 of hydrochloric acid and place into small beaker.
5. Place the conical flask onto the piece of paper with the cross on it. Make sure you are able to see the cross through the bottom of the flask.
6. Pour the hydrochloric acid into the conical flask and start the stop watch
7. Wait until the cross is no longer visible through the bottom of the flask and stop the stopwatch.
8. For each concentration do this experiment 3 times. This will give you 15 experiments.

Preliminary Experiment

In order to choose my concentrations for my experiment, I carried out a preliminary experiment.

I followed the above instructions with three different concentrations. These were:-

The first experiment took 25 seconds. The second, 150 seconds, and the third took so long I did not have enough time so I stopped the experiment. From these results I decided that the upper bound of my experiment would be 100cm3 of sodium thiosulphate and no water, the lower bound would be 20cm3 of sodium thiosulphate and 80cm3 of water.

The final list of concentrations I will use is: -

Analysis

By examining my graph, I can see that the more concentrated sodium thiosulphate is, the faster it will react with hydrochloric acid. This is because increasing the concentration of thiosulphate will mean there is more chance of collisions between it and the hydrochloric acid.

By examining the graph I can conclude that my qualitative prediction was correct. Increasing the concentration of sodium thiosulphate does decrease the reaction time. When the concentration of thiosulphate was 0.03 molar the reaction time was 160 seconds. When I increased the concentration of thiosulphate to 0.15 molar, the reaction time decreased to 25 seconds.

By examining the graph, I can also conclude that my quantitative prediction was correct. Doubling the concentration of sodium thiosulphate does halve the reaction time. When the concentration of thiosulphate was 0.06 molar, the reaction time was 69 seconds. When I doubled the concentration of thiosulphate to 0.12 molar, the reaction time halved to 34 seconds.

Evaluation

I believe that the experiment worked well because it gave results that were consistent with each other, and were reproducible.

I also believe that my results were of a high quality because I received no anomalous results. However they were not perfect; as you can see in fig 1 not all the points lay on the same line.

A way to improve the experiment would be to use a water bath to keep the temperature constant throughout the whole experiment.

Experiment 2

Apparatus

Sodium thiosulphate

Hydrochloric acid

Water

Burette

Retort Stand

Burette clip

Conical flask

Stopwatch

Water batch

Thermometer

Black marker pen.

Method

1. Put on a pair of safety goggles and keep them on for the rest of the experiment.
2. Set the water batch to about 25ºC
3. Draw a cross with a marker pen on the bottom of a conical flask.
4. Measure out the chosen amount of sodium thiosulphate using a burette, into the conical flask.
5. Measure out the chosen amount of water using a burette, into the conical flask.
6. Measure out 10cm3 of hydrochloric acid and place into small beaker.
7. Wait until the thermometer reads the correct temperature and place the conical flask into the water bath
8. Place the thermometer into the conical flask, and wait until it is the same temperature as the water in the bath.
9. Pour the hydrochloric acid into the conical flask and start the stopwatch.
10. Wait until the cross is no longer visible through the bottom of the flask and stop the stopwatch.
11. For each concentration perform the experiment 3 times. This will give you 15 experiments.

Extension

A way to extend this enquiry would be to investigate the affect of varying the temperature on the rate of reaction between sodium thiosulphate and hydrochloric acid. There are two ways of varying the temperature of a solution. The first would be to use a water bath; the second is to use a Bunsen burner. For this experiment either method would be acceptable, but it is probably easier and more accurate to use a water bath.

Experiment 3

Apparatus

Sodium thiosulphate

Hydrochloric acid

Water

Burette

Retort Stand

Burette clip

Conical flask

Stopwatch

Water bath

Thermometer

Black marker pen.

Method

1. Choose a concentration that does not take to long to react, but is not too slow that if you heat the solution it will be over in a second. I would choose 0.75 molar which is 50cm3 of water and 50cm3 of  sodium thiosulphate.
2. Decide what temperatures to use; barring in mind that the previous experiment was performed at about 20ºC, it would be a good idea for this temperature to be the lower bound of the experiment. About five temperatures will be needed to give results of any meaning, so I would probably go up in steps of 10ºC from 20ºC.
3. Preheat the water bath to the first temperature.
4. Draw a cross with a marker pen on the bottom of a conical flask.
5. Measure out the chosen amount of sodium thiosulphate using a burette, into the conical flask.
6. Measure out the chosen amount of water using a burette, into the conical flask.
7. Measure out 10cm3 of hydrochloric acid and place into small beaker.
8. Place the conical flask into the water bath, and place the thermometer into the conical flask.
9. Wait until the thermometer reads the chosen temperature and take the thermometer out of the conical flask
10. Pour the hydrochloric acid into the conical flask and start the stopwatch.
11. Wait until the cross is no longer visible through the bottom of the flask, and stop the stopwatch.
12. Repeat this experiment twice.
13. Change the water bath to your next chosen temperature and repeat steps 5-13 until you have results for 5 temperatures.