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Rates of reaction between sodium thiosulphate and hydrochloric acid

Categories: ConcentrationSodium

Tom – this is good, in that it’s all there. But it’s muddled – again, I don’t think you’ve really gone away from it and then come back fresh, and read it through to see if it makes sense. There’s no point submitting work until you have. My comments are in italics

You need to explain the chemistry behind the theory – it will be in your textbook I imagine

Rates of reaction between sodium thiosulphate and hydrochloric acid


The aim is to find the effect of different concentrations on reaction rate.

We have to change the concentration of one solution. This last sentence doesn’t make sense- so what? Why? why not scrap it altogether?


We know that in order for two substances to react, their particles must collide with each other with enough energy for the reaction to be successful. The energy is necessary because…(ie what happens to the particles when they collide with enough energy?).

If we can make the particles collide more often with more energy and therefore make the collisions a lot more successful, then the reaction should go faster. This theory is called Collision Theory.

Reaction being studied.

We have learnt that by halving the concentration, we double the [time of the] rate of reaction. How have we learnt this? you haven’t said anything about the reaction being studied under this heading. Don’t you want to say something like: the reaction being studied is that of hydrochloric acid with… etc??? this is what the heading says

Word equation.

Hydrochloric acid + sodium thiosulphate sulphur + sulphur dioxide + sodium + water

Symbol equation

Na S O + 2HCl S + SO + 2NaCl + H O

Study variable

In this investigation the variable we will study is the effect of changing the concentration on the rate of reaction. In order to do this, we have to make sure that the only thing changing in each experiment is the concentration.

Controlled variables

* The concentration of the distilled water will be kept constant in each experiment. This is the first time I have heard of distilled water, here – shouldn’t you mention it above???

* The concentration of the thiosulphate the same in each experiment.

* And the concentration of the HCl?? no – now that I have read on, I see that you change this but you need to explain it all at the beginning otherwise the reader has the soma confusion that I had

* No catalyst will be used.


I predict that the reaction will go faster with a stronger solution. This is because there is more energy in the reaction. Explain the chemistry of there being more energy there when it is a stronger solution

Trial work

I am going to try to keep the chemicals before the reaction at room temperature. I am keeping the same concentration of thiosulphate but I will change the concentration of the acid by diluting it with water. I will keep the same volumes of each chemical. The amount of thiosulphate will stay at 20ml and the acid and water combined will stay at 50ml throughout the experiment.



* Hydrochloric acid – varied volume

* Sodium thiosulphate – 20ml

* Distilled water – varied volume


* 100ml conical flask

* 3 * 50ml measuring cylinder

* Stop clock

* 3 * 250ml beakers

* Black cross – for testing

* Stopwatch

* Safety goggles


Get three 250ml beakers. Fill one up with acid, one up with sodium thiosulphate, and one up with distilled water. Get three measuring cylinders and [put] assign? a cylinder to each beaker and keep each cylinder [to] with? its beaker so as not to mix the chemicals when measuring them out. Get a piece of paper and draw a thick, black cross onto it. Fill up the cylinders with the required amount of chemicals. Put the acid and (if there is any) water into the conical flask. Then add 20ml of thiosulphate to the beaker and start the stopwatch. After a while the chemicals will start to cloud. When the chemicals are so cloudy that you can’t see the cross, stop the timer. The clouding of the chemicals means that sulphur is forming (See equation, above). You now have to repeat this process whilst varying the chemicals.


When recording the results, make sure that they are written in seconds and ml. Why? To keep the measurements standard

When doing any experiment wear safety goggles.

Keep all measuring cylinders on the desk and read off the measurement from eye level.


Acid (ml)






Water (ml)






Thiosulphate (ml)






Run 1 (secs)






Run 2 (secs)






Run 3 (secs)






The results that I got were the results that I expected to get. The reactions with the most acid in went faster than those with less acid in them. This shows that when a chemical is diluted it [has less energy to react as fast.] it reacts more slowly. This is because… This is useful to know because for example, if you spilt acid onto a table you would now know to mix it with water so that the acid has less of a chance to react. And therefore damage the table.


During this experiment I have found out that when diluted, reactions work a lot slower because there is less energy in the particles. This means that once this has been found out reactions can be slowed down dramatically and by being able to do that we can prevent spillages of acid and other chemicals from affecting whatever they spill on. It also has implications for industry: for instance, there are times when reactions need to work fast as this saves time and therefore money. As we know that they react faster when more concentrated then technologists can design processes using the correct concentration of chemical for the process required. Read why does the solution go cloudy

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Rates of reaction between sodium thiosulphate and hydrochloric acid. (2020, Jun 02). Retrieved from

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