To investigate the effect of Concentration on the rate when mixing Dilute Hydrochloric Acid and Sodium Thiosulphate Solution.

The collision theory has a part to play in the experiment. It states that if a reaction is going to take place the particles (Ions, Molecules or Atoms) must collide with each other. Not all collisions end in a reaction though. For the particles to make a reaction though there must be a minimum energy. Basically this is the speed at which the particles travel. If the particles reach the minimum speed, the result is a reaction. This minimum energy (speed) is called the activation energy. For this experiment therefore the greater the concentration the greater the amount of collisions therefore the quicker the rate. I predict that also from this theory that if I double the concentration I will double the rate. If the prediction I make is true there should be a straight line graph theorem.

The collision theory can also be used in the same way for Surface Area and Temperature.

VARIABLES

There could be many input variables for this experiment which are listed below:

1. The concentration of the solution used.
2. The temperature of the solution.
3. The volume of the solutions.
4. The light concentration of the solutions.
5. The catalysts used to see how the reactions speed up.

The variables used in the experiment that must be kept the same all the time though are:

1. The temperature – as this variable will effect the reaction the most as it has the biggest effect on rate.
2. The position from which your eye views the cross. If the distance is higher or lower than the height you said the time could differ as the further back the longer the reaction time.
3. The time at which I stop the clock must be the same i.e. as soon as the x disappears as otherwise for obvious reasons the time will change.
4. Every time the flask must be shaken equally so the collision theory can take place.
5. If sulphur deposits appear to be shown in the flask they must be removed with a brush as otherwise the test becomes unfair.

PREDICTION

From the collision theory and collecting all other information from background information I have decided to predict that the greater the concentration i.e. 100% the quicker the rate. This is because of the collision theory and as if there are more particles of the Thiosulphate solution in the mixture then the more the reactions can take place. This is because in the 50% concentration for example the other 50% in this case water will not react with the HCl so only half the solution i.e. the Thiosulphate will react with the HCl.    

APPARATUS AND CHEMICALS + DIAGRAM

Below is the list of apparatus I shall be using and the quantities.

1 x Conical Flask

1 x Paper with Cross on

1 x 5cm3 measuring cylinder

1 x 50cm3 measuring cylinder

1 x Stopwatch

1 x Thermometer

1 x Brush

Below is the list of chemicals I shall be using in the experiment:

Hydrochloric Acid (HCl)

Sodium Thiosulphate Solution (Na2S2O3)

Water (H20)

METHOD

First of all I shall set out the equipment so it is all laid out accordingly and so it can be accessed easily. Here is the order in which I shall do things:

1. I shall first measure 50cm3 of Sodium Thiosulphate solution in a measuring cylinder (If the concentration is 100% the solution shall be 50cm3 Sodium Thiosulphate and 0cm3 water but for 90% the solution would be 45cm3 Sodium Thiosulphate and 5cm3 water). Then I shall pour it into a conical flask. I shall make sure that the Thiosulphate measuring cylinder is only used for that and that only otherwise a reaction may occur in the measuring cylinder.
2. Then on a piece of white power I shall draw a cross which I shall then put the conical glass on top of it (see diagram)
3. Measure 5cm3 of dilute hydrochloric acid from a measuring cylinder. Remembering that this cylinder is only for HCl.
4. The next thing to do has to be done as quick as possible so that more reliable results are taken.

1. Add the 5cm3 of acid into the Thiosulphate solution
2. Swirl the flask
3. Start the stopwatch
4. Read the thermometer and record

5. Watch the cross from the position shown in the diagram. Once the cross has not become visible to the naked eye because of the sulphur deposits, stop the stopwatch and record the time
6. Measure the temperature again to see if it has risen or fallen and record.
7. Get rid of the solution quickly as it gives off harmful fumes and then wash it out.
8. Repeat the same one three times and then move on to the next concentration level using the same method.

FAIR TEST

To make sure I keep a fair test throughout though I am going to have to consider the following points:

1. Make sure you observe the cross from the same angle and height
2. Keep the cross in the same place throughout and make sure you use the same cross as if you change you may alter the thickness/size.
3. Make sure if any sulphur deposits on any of the flasks or cylinders are removed using washing out and brushing it out.
4. Keep the temperature as close as you can every time so that it shall not differ as this would give unreliable results
5. I shall repeat each test 3 times taking the middle result each time as the actual one as if there is an odd result and I average it shall still come out different.
6. All measurements must be made using the appropriate cylinders

SAFETY

This test could be quite hazardous if the following procedures are not applied

1. Wear safety goggles
2. Wear Lab Coat
3. Make sure the solution of Sodium Thiosulphate and Hydrochloric Acid is disposed of as soon as possible after all results are recorded
4. If spillages of any chemical onto flesh, it should be washed straight away especially HCl, as it is corrosive.
5. Do not drink any chemicals or play about with them.

RESULTS TABLE