Investigate the factors that affect the rate of reaction between Hydrochloric Acid and Sodium Thiosulphate.

Aim- I am going to investigate how changing the concentration of the Hydrochloric Acid affects the rate of reaction between Hydrochloric Acid and Sodium Thiosulphate.

Sodium + Hydrochloric → Sodium + Sulphur + Sulphur + Water

Thiosulphate Acid Chloride Dioxide

Scientific Variables.

Temperature- Increasing the temperature of a solution causes particles to move faster, with more energy. The particles will collide more often and with greater energy. This will mean more successful collisions per second and so a faster rate of reaction.

Catalyst- By using a catalyst the particles will only require moderate energy to collide and react. This means more successful collisions are likely within the same amount of time. More collisions create a faster reaction.

Concentration- Increasing the concentration of a reactant simply means there are more particles in the volume of a solution. Therefore there are more particles, which can collide and so react. More collisions mean a faster reaction.

Fair test- To ensure that the investigation is a fair test the only thing that should be changed is the variable being investigated, in this case the concentration of the Hydrochloric Acid. The volumes of each chemical should be the same for each attempt, the conical flask should be made from the same material each time. When timing the reaction I must start and stop the timer at the same stage of the reaction each time so that the results I collect are reliable.

Method-

Draw a cross on a piece of white paper and place a conical flask on the cross.
Pour 20ml of 2 mouler Hydrochloric Acid into the conical flask.
Measure 20ml of Sodium Thiosulphate and add it to the Hydrochloric Acid.
As soon as all of the Sodium Thiosulphate has been added begin timing the reaction.
When you can no longer see the cross on the paper through the solution stop timing.
Record the time the reaction has taken.
Do the experiment 2 more times so you can work out an average time.
Repeat the experiment ...

This is a preview of the whole essay

Method-

Draw a cross on a piece of white paper and place a conical flask on the cross.
Pour 20ml of 2 mouler Hydrochloric Acid into the conical flask.
Measure 20ml of Sodium Thiosulphate and add it to the Hydrochloric Acid.
As soon as all of the Sodium Thiosulphate has been added begin timing the reaction.
When you can no longer see the cross on the paper through the solution stop timing.
Record the time the reaction has taken.
Do the experiment 2 more times so you can work out an average time.
Repeat the experiment using 1.50 mouler Hydrochloric Acid. Again have 3 attempts so that you can work out an average for the time the reaction took.
Complete the investigation by doing the experiment using each remaining concentration of Hydrochloric Acid (1.00m, 0.75m, 0.50m)

Always remember to:

Use 20ml of Hydrochloric Acid and 20ml of Sodium Thiosulphate on each attempt

Have 3 attempts with each concentration.

Ensure the only variable that changes is the concentration of the Hydrochloric Acid.

Wear safety goggles and do not sit down whilst carrying out the investigation- if any chemicals fall you will not be able to move out of the way as quickly.

Equipment.

1 Conical flask- for the reaction of Sodium Thiosulphate and Hydrochloric acid to take place in.

2 measuring cylinders- one for measuring Sodium Thiosulphate and another to measure Hydrochloric Acid.

5 different concentrations of hydrochloric acid- to enable us to investigate the variable-concentration.

Sodium Thiosulphate- to react with the different concentrations of Hydrochloric Acid.

Paper with a cross- to mark the end of the reaction (when the cross is no longer visible.)

Prediction.

I predict that the higher the concentration of the Hydrochloric Acid, the faster the rate of the reaction will be. I think this will be so because when the concentration of a solution is increased there are more particles within the same volume of solution. The particles will be closer together and so more successful collisions are likely which will speed up the reaction.

Results.

Analysis.

The line of best fit on the attached line graph shows us that as the concentration of the hydrochloric acid is increased the time the reaction takes decreases. This matches with my prediction. Increasing the concentration of the hydrochloric acid means there are more particles within the same volume. This leads to more particles being able to collide, break bonds and so react. With more successful collisions taking place, the reaction time was reduced

The result table shows that the fastest reaction time was 26.11 seconds when using a concentration of 2.00 mol acid. The slowest reaction time was 45.54 seconds, when using a concentration of 0.50 mol acid. This tells us that the reaction time was speeded up by 19.43 seconds when using 2.00 mol hydrochloric acid instead of 0.5 mol.

The line of best fit does not show any major anomalies in the results.

In conclusion, changing the concentration of hydrochloric acid will change the rate of reaction. The higher the concentration, the quicker the reaction will be.

Evaluation.

Results have demonstrated that a change in the concentration of Hydrochloric Acid does directly affect the rate of the reaction time. This can be seen in the results where a concentration of 0.50 mol dm of hydrochloric acid reacts with the Sodium Thiosulphate in 44.74 (ave) seconds to give Sodium Chloride where as 2.00 mol dm of hydrochloric acid reacts with Sodium Thiosulphate in 27.46 (ave) seconds to give sodium chloride. This confirms that a greater concentration of acid means that there are more particles of acid occupying the same space so they have a greater and faster chance of colliding with the particles of Sodium Thiosulphate. If the particles collide at a faster rate (as the results show) then sodium chloride will be made quicker, which was demonstrated by the quicker disappearance of the cross which was used as a marker for the reaction. This change in reaction rate could only have been due to a change in concentrate volume as no other variables were altered.

Errors in the results could have been caused by:

Timing reaction- human error, may have not reacted at exactly the moment the reaction finished ie. The clock was not stopped at exactly the right moment on each attempt. Judging the reaction with the naked eye is not as reliable as a machine might be.
Concentrate (ie. Small amount) could have been in the tube already if the equipment had not been cleaned properly, making the amount of acid slightly out.

The reliability of the results depended on the human hand (working stop clock) and eye (watching cross). This procedure for this experiment could be improved by if possible, using a machine more reliable that the human eye or hand. This would erase human error when collecting results and improve reliability. If it is not possible to use a machine a greater number of readings could be taken for each concentration of Hydrochloric Acid to produce a more comprehensive average. More concentrations of Hydrochloric Acid could be used ie. 0.2, 0.4, 0.6, 0.8, 1.0 mol dm3. By increasing the number of different concentrations used, a more accurate graph can be plotted. This would highlight and anomalies more obviously and also show more clearly, and patterns in the results.

To further investigate reaction times involving Sodium Thiosulphate and Hydrochloric Acid a catalyst could be used. A catalyst is a substance that increases the rate of reaction without being used up. By lowering the amount of energy needed and providing a surface for the reacting molecules to attach to, the chance of the molecules bumping into each other is greater.

However to investigate Sodium Thiosulphate and hydrochloric acid without the influence of a catalyst, the affect of temperature on the rate of reaction could be investigated. The concentration of Hydrochloric Acid used will remain the same throughout the experiment to ensure a fair test but the temperature at which the reactants come together could be altered gradually. A beaker of water could be heated on top of a tripod and gauze over a Bunsen burner and the temperature tested using a thermometer. When the water reaches the desired temperature, the beaker could be removed and the Sodium Thiosulphate and Hydrochloric Acid added to a flask and immediately place over the flame. The cross method could be used again placed on top of the gauze, under the flask. This could be carried out at a number of different temperatures. This would be a good experiment, as the reactant times would highlight whether concentration or temperature has a greater affect. A range of temperatures could be used with 2.00 mol dm, 1.00 mol dm and 0.5 mol dm to also see how heat affect varies with the different concentrations. The Sodium Thiosulpahte and Hydrochloric Acid could also be added together at room temperature with no heat as a control.