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Rates of Reaction Experiment HCl and Sodium Thiosulphate

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The rate of reactions is how fast something changes from its reactants to its products. For a reactions to occur, the particles must strike with enough energy. At the start of the practical only some of the reactions will have enough energy to strike with each other and create energy for the reaction to happen.

We can increase the rate of reaction by changing specific conditions in order to increase the rate of collision what will happen is that one of the things what can change it is the temperature because it provides the reactant with more energy. So this means the particles will be moving around more and therefore they are more likely to collide with each other. Another one is the concentration because by increasing the concentration of a reactant we are increasing the number of particles in a certain volume.

This means there is more likely to be more collisions because they is more particles with in a small space. Another one could be pressure because by increasing the pressure we are decreasing the space in what the practices can move about in. so this means the practices will be more likely to collide with each other because there is less space for them to move around. Another one could be a catalyst because this is a lower activation energy required by particles to start a reaction and provides another route for the reaction to occur, thus speeding up the reaction.

In the reaction what I will carry out the equation is:

Hydrochloric acid + sodium thiosulfate sodium chloride + sulphur dioxide +

Sulphur + water

2HCl (aq) + Na2s2o3 (aq) 2Nacl (aq) + SO2 (g) + S (s) + H2O (l)

On this experiment we will be changing the concentration of the hydrochloric acid. So if we change the concentration of the experiment we are increasing the number of practices inside the reactions.


Based on the information’s what I put about the rate of reaction I think as the concentration increase the rate of reactions will increase as well because they will be more practical inside the experiment so they will be colliding with each other more so the rate of reaction will increase.


* Measuring cylinders- so we could measure how much of the chemical we was using when we did the experiment

* Test tube-so we could pour the chemicals into

* Test tube holder- so then when we are waiting for the test to finish we don’t have to hold the measuring cylinders we can just put them in the rack.

* Hydrochloric acid- so we have a chemical to react with sodium thiosulphate.

* Sodium thiosulphate- so then we have something to react with hydrochloric acid

* Sodium carbonate- to put the finish produce in because after the reaction the mixer starts to smell.

* Stop watch- to time the time taken for the reaction to finish.

* Paper and marker- so we have something to look for on the other side of the test tube to test the rate of reaction

* Goggles- so aware eyes always stayed protected when we are doing the experiment


An independent variable is hydrochloric acid solution. Dependent variables is how long the reaction takes. The dependent variable was the rate of reaction. The controlled variable was the amount of hydrochloric acid contraction must be the same. If you don’t have any controlled variables then this experiment wouldn’t have worked.


My limitations could have been:

Human error – I could have stopped the stop watch a second after the ‘X’ had disappeared, thus causing outliers in my work.

The stop watch could have been faulty – the button might not have been working well and may not have stopped the timer when I pressed it.

Some chemicals may have been left behind in the measuring cylinder/ test tube.

Distractions – I may have been distracted by something such as a loud noise and I might have looked away at the exact moment that the X disappeared.

The equipment that I used might have been contaminated if it wasn’t washed out properly the last time it was used. This could have caused a faster reaction because of any other unwanted chemicals still inside the equipment

Lastly, there could have been a mistake in the measuring. This could have happened if I didn’t have the measuring cylinder at eye level when I poured in the chemicals.


The first thing that I did was prepare myself and the area around me for the practical. I pushed all stools and bags under the desk so there is no risk of anyone tripping. So that me and my classmates where safe.

The next thing that I did was gather up all of my equipment/reactants and lay them out on the table. I made sure that I had everything before I started. This makes sure that my experiment runs smoothly.

Then, I drew a large “X” on the white paper using the marker pen. This was important because it would help to finding out the rate of reaction

Next we measured out 2cm3 of hydrochloric acid solution and sodium thiosulphate in separate measuring cylinders.

Then place them two in the same beaker and put the paper with the cross on it on the back with the cross facing towards you.

Then when can no longer see the cross stop the stopwatch and listed down the time in your result table. Then pour the finished substance into sodium carbonate because the reaction will start to smell after a while so this chemical will help prevent the bad smell.

Do this 3 times so it is easier for you to find out the average time taken for the cross to disappear.

Then you change the concentration of sodium thiosulphate to 0.4cm3 and 1cm3 and repeat the experiment for them to concentrations and do it 3 times for both of these concentration. So then you can see if different concentration will make the rate of reaction change.

Fair test

To make the investigation is a fair test I made sure:

• The same person observe the reaction because different people have different eyesight so keeping the same person to observe the ‘X’ disappear is better.

• Use the same ‘X’ as a darker or bigger ‘X’ can increase the time it takes for it to disappear.

• The temperature is kept the same.

• Same volume of solution – total volumes need to be the same.

My results

HcL concentration

1st time taken

2nd time taken

3rd time taken

Average time taken

0.4 cm3















You work out the rate of reaction by 1/average time taken

So for HcL the rate of reaction was:

HcL concentration

Rate of reaction







Analysis and Evaluation

By using my results it does show that as the concentration level goes up the time of reaction goes down. On my result I think we had a limitation because for the first 2 test of 2cm3 didn’t go with the rest of the results so they are ………… so I think we went wrong with that concentration. So for all the other results they matched what the scientific information said in my introduction so that show this experiment still went well even though we went wrong on them two results. The scientist said as the concentration goes up the rate of reaction will increase as well and the second table would show this but because of the 2cm3 results it doesn’t quite work out but for 1cm3 and 0.4cm3 this does go with what the scientist where saying. If I did this experiment again I would make sure that the test tubes where clean because I think we didn’t wash them out properly so it affected aware results because we did 0.4cm3 and then we did 1cm3 so I think so of the substance was still left other and it affected the 2cm3 results. This would make it better because then I think the results will show what they should show because no reactants where left other.



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