An experiment to investigate the effect of changing the concentration

An experiment to investigate the effect of changing the concentration

of hydrochloric acid on the rate of reaction with sodium thiosulpahte.

Aim

I am trying to find out how the concentration of hydrochloric acid

affects the reaction time with sodium thiosulpahte.

If a clear solution of sodium thiosulphate is mixed with hydrochloric

acid then a reaction will occur where a creamy-yellow precipitate of

sulphur is produced.

H20

Text Box: + Text Box: + Text Box: + Na2S203 2HCL

Text Box: + 2NaCl SO2 S

Reactants Products

The sulphur takes a while to form and starts to turn the water cloudy

after a short time. You cannot tell when the reaction has stopped so a

cross drawn on a piece of paper in pencil can be sued to do this

experiment. The liquid is placed on top of the cross in a beaker and

it is timed how long it takes for the cross to disappear when viewed

through the liquid.

This experiment can be used to investigate the effects of

concentration and temperature on rate of reaction. This is the

experiment I am going to do because I am trying to see how the

concentration of acid affects the rate of reaction.

Variables

In my investigation I could change:

* Concentration of sodium thiosulphate

* Temperature of solution

* Concentration of acid

* Type of acid

* Volume of thiosulphate

* Volume of acid

I am going to change the concentration of acid.

I will keep all the other variables the same. The independent variable

will change the dependant variable- the rate of reaction.

Prediction

I predict that the less concentrated the acid is then the longer it

will take for the sodium thiosulphate to react.

If you increase the temp, increase concentration, add a catalyst or

the solid reactant is crushed up into smaller bits then the rate of

reaction will always increase.

Apparatus

* Sodium thiosulphate

* Hydrochloric acid

* Measuring cylinder

* Beaker

* Paper

* Pencil

* Distilled water

* Stop watch

* Conical flask

Safety

Goggles should be worn to prevent any of the solution from going into

the eye.

Everyone should behave sensibly to prevent accidents.

Collision theory

The rate of reaction depends on how often and how hard the reacting

particles collide with each other. The particles have to collide hard

enough in order to react. The rate of reaction can be increase...

... middle of paper ...

...2 and 3 only have a

1second difference in time. These results are too close together and

cannot be reliable.

These results aren't adequate for a firm conclusion as it has a few

anomalous results and on the average times they don't have a large

enough gap between them e.g. 34 and 36. The experiment should be

carried out more times for a more accurate result.

The procedure used was suitable but produced quite unreliable results

as the cross on the paper may have not fully disappeared when the

other person was told to stop the timer as this is what we did. If the

person looking at the cross and observing when it disappeared changed

then the person's opinion on when it has disappeared may make it an

inaccurate test so it would have to be kept the same person all the

time.

If I did the experiment again I would probably take more time

measuring out the solutions and it would probably be a better idea for

the person observing to see when the cross can no longer be seen to

have the stop watch so they can stop it at the exact time they can no

longer see it. It could also be improved if the experiment was carried

out more times as a better average could be produced.