Output-The time of reaction is also expected to vary due to changes in concentration
Controlled-These are unrelated factors, which could possibly effect the results. They are kept constant to minimize their effects on the outcome.
Fair testing:
An test must be fair to produce accurate results. To make this experiment a fair test a number of factors must be controlled.
Firstly the volume of hydrochloric acid and sodium thiosulphate must always be the same .An failure to do so will make it impossible to compare the rate of reaction with repeated experiments.
In this test we are attempting to find out how concentration affects rate of reaction. As we are working with two chemicals one concentration must be kept the same strength while the other is varied. Therefore I have changed the concentration of hydrochloric acid and kept the sodium thiosulphate as the constant.
I had to make sure the stopwatch was started as soon as the hydrochloric acid was added into the beaker, in order to get the most accurate times possible. As soon as the black cross disappeared the stop clock had to be stopped. This is far easier if 2 people work together: whilst one keeps the hand on the stop clock the other watches while the cross disappears. It is also necessary that the cross on the paper is the same colour and size.
Finally the beaker should be cleaned out thoroughly to remove the maximum amount of solution deposited before another experiment is attempted.
Prediction:
Therefore the cross will disappear quickly due to the cloudiness of the solution. This is because the more hydrochloric particles there are, the more likely chance of successful collisions with sodium particles in the beaker. If the strength of the concentration is doubled the rate of reaction is twice as fast.
I believe the concentration of a solution effects the rate of reaction as the rate of reaction relies on how often the molecules of the reacting substance collide. The more concentrated a substance is, the more the number of molecules it contains. The frequency of collisions is greater, as there are more molecules about, and the reaction will therefore happen more rapidly.
Method
Draw a black cross on a white piece of paper
Place cross under conical flask
Measure and add 50 ml of sodium thiosulphate into the beaker
In a test tube add hydrochloric acid and water depending on the concentration
Add dilute hydrochloric acid to beaker
Start the stopcock, immediately as soon as the hydrochloric acid is added to the beaker
Stop the time when the cross is no bigger
Record your results
Repeat test 3 times for every concentration
Safety
Health and safety had to be carried out before and whilst during the experiment. Both the sodium and hydrochloric acid are corrosive. So care had to be taken when handling the chemicals. If the substance contacts with your skin it must be washed off immediately as it will harm your skin. Long hair must be tied back and goggles must be worn in case any acid gets into the eye. Finally leftover products from the reaction must not be poured down a sink. The beaker and conical flask has to be washed out before another test is done.
Equipment
Measuring cylinder
Water
Sodium thiosulphate
Hydrochloric acid
Stopwatch
Conical flask
Beaker
Cross on paper
Diagram
OBTAINING EVIDENCE
EVALUATION:
I have studied the collision theory and have discovered how it takes part in this experiment. I have revealed substances with higher concentrations contain more molecules which means rate of reaction will be quicker according to the collision theory.
The pattern in the groups seem to show higher concentration levels of hydrochloric acid affect the rate of reaction. The more molars the faster the reaction takes place.
Also the graphs show a fine curve of best fit which outlines the pattern of the results taken, where the less the concentration the more time it takes to react.
In conclusion, from primary and secondary sources; I have learnt that the concentration does have an effect on the rate of reaction.
From the readings taken I found the average by working out the mean. After plotting these points on a graph the correlation can clearly be seen, the higher the concentration the faster the reacting time. However as I predicted that double the strength of a concentration would make the rate of reaction go twice as fast, this ended up being untrue as my evidence proves.
All results I got from the experiment were exactly as I expected them to be like. The graphs back up my prediction as well as the table. I got good results as I concentrated on the task at hand and carefully measured all solutions.
I did not encounter any anomalies which means the data taken was flawless and I avoided mistakes when creating my table and graph.
To improve this experiment next time I should use a more accurate measuring cylinder, which measures to the micro litre, and use the same cross under the beaker all the time. Also I must be much more careful when it comes to watching the exact moment the cross is disappeared and stopping the clock.
