Hydrochloric acid and sodium Thiosulphate Investigation

Introduction: for this experiment/investigation I want to find out how long it takes for two different solutions to react togeather, these are;

Hydrochloric acid and sodium Thiosulphate.

I will change the concentration of the sodium thiosulphate to see whether this affects the rate of the reaction. Other things that may affect the rate of a reaction are temperature, catalysts, size of bits and surface area, but were just testing the concentration area.

A reaction goes quicker if the temperature rises. This is because of the increase in kinetic energy, which enables the particles to collide more quickly.

A powdered substance reacts more quickly than one with larger bits. This is because the powder has much bigger surface area, so more reacting particles come into contact.

Concentration is the number of particles there are in a given volume; this is measured in Molarity.

I will use 0.15 M of sodium thiosulphate.

For these two chemicals to react (sodium thiosulphate and hydrochloric acid) they will need to create Ions, and these need to collide so the more there are the more chance of them colliding and the quicker the reaction will be. If there’s an increase in concentration there will be and increase in Ions and this increases the chance of a successful collision.

COLLISON THEORY: (picture on separate sheets)

Collision theory is the theory that explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called fruitful collisions. The fruitful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more fruitful collisions, increasing the rate of reaction. When a catalyst undergoes collision with the reactant molecules, less energy is required for the chemical change to take place, and hence more collisions have sufficient energy for reaction to occur. The reaction rate therefore increases.

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Catalysts are any chemical added which makes the reaction take place quicker without being used up it’s self, it helps other chemicals meet and join up more quickly.

Activation energy may play a part to; this is the energy required in order to start a chemical reaction. Some elements and compounds will react together merely by bringing them into contact (spontaneous reaction). For others it is necessary to supply energy in order to start the reaction, even if there is ultimately a net output of energy. This initial energy is the activation energy.

Before we started any thing we ...

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Catalysts are any chemical added which makes the reaction take place quicker without being used up it’s self, it helps other chemicals meet and join up more quickly.

Before we started any thing we had a class demonstration which was our preliminary work and during this we decided to not go below the concentration of 0.03 because it took far to long, here’s the table of results:

That table shows our demo preliminary work in time and seconds and also shows why we didn’t go below 0.3 concentration. (Take far too long)

Method: when I start off I will have too collect all the apparatus that I will require when doing this experiment- these are:

Measurement cylinders x2c

Small conical flask

Paper with black cross on

0.15m sodium thiosulphate

2m hydrochloric acid

Goggles

Stop watch

Next I will measure 10 cm of hydrochloric acid using a measurement cylinder then place in a conical. Flask- once this is done place it on the black cross. When putting the hydrochloric acid in the measuring cylinder I will use a pipette to get the exact amount of solution. This is all so it will be accurate. And also I will use separate measuring cylinders and put the black X into a plastic wallet so that when I was out the cylinders they wont smudge the the X’s and wont ruin the test and the X’s will be the same colour all the way through the test.

Measure out 10 cm of sodium thiosulphate and add it to the acid in conical flask. AS SOON as you do this start the stopwatch and record how long it takes for the black cross to disappear.

Repeat all this two more times so we can be sure the results are accurate.

Then do it again changing the concentration of sodium thiosulphate, using the table shown below

Prediction: My prediction is that the reaction between sodium thiosulphate and hydrochloric acid will get slower as the sodium thiosulphate is diluted with water. If the concentration of the thiosulphate decreases, the rate of reaction also decreases because there has to be enough of the sodium thiosulphate Ions for the hydrochloric acid to react with.

I also think that the concentration is proportional to the rate of reaction so if I doubled the concentration the time in which it takes for the reaction to take place will double too.

E.g.- 0.03 may take 1200 seconds so I think that 0.06 would take 600 seconds (just an example)

Or concentration x 2 = rate of reaction /2c

I also think I will get a graph that looks like this so I think that as the concentration of the reactant increases time will decrease or concentration of reactant decreases with time.

Now I am going to carry out the experiment as I said I would above in my method.

I also have all these results on a graph.

Analysis: I have found that the lower the concentration of sodium thiosulphate the longer it takes and the higher the concentration of sodium thiosulphate the quicker the reaction is.

I have also noticed that also noticed that if I double the concentration it will double the rate of reaction, just like I said in my prediction.

On the double concentration, double rate of reaction theory can be proved because At 0.3 the average time was 1207 and at 0.6 the average time was 603 which is more or less directly proportional to the concentration, if I double 603 and half 0.6 that would equals 1206 and 0.3.which is very close the actual result which is 1207. This also works for the rest of the results (as shown in this table)

So in theory you have to double the concentration then half the average time for that concentration that you doubled and you should get the next result.

As the concentration got bigger the reaction took longer to take place or as the concentration increases the rate of the reaction. (Time it took) decreases. This is shown on this graph that I thought I would get and I stated this in my prediction.

When I did this experiment I believe that the reactant particles began to collide, but only a certain amount of the total collisions that began to take place caused chemical change; these are called fruitful collisions. The fruitful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more fruitful collisions, increasing the rate of reaction. This is what I believe to have happened in my experiment because the “collision Theory” tells us this is what happens.

I think that a couple things could have affected my results and they are Temperature and concentration.

Temperature could have, because we did it on different days and we know that the temperature can affect the rate of a reaction, if the temperature is increased, it will bring about more collisions increasing the chance of more fruitful collisions and this increases the rate of a reaction.

Concentration, because when we were doing the experiment we had to measure out the liquids in measuring cylinders, this process may not have been accurate 100% of the time, and also when we had measured out the solution, we had to rinse out the measuring cylinder. But then again this may not have been done correctly as well, there could have been still some solution left in it. Therefore this would have affected the rate of reaction.

My results completely support my prediction because I said that that the reaction between sodium thiosulphate and hydrochloric acid will get slower as the sodium thiosulphate is diluted with water. If the concentration of the thiosulphate decreases, the rate of reaction also decreases.

When the concentration was only 0.3 it took 1207 seconds and at 0.15 it took 72 seconds, so yes when I increased the amount in which in was diluted by water it did get slower. And my graph cam out as I predicted, I got no strange results. They were pretty good, BUT if I was to this investigation again I would use different measuring cylinders for each measurement I make, I would try to do it all on the same day and at the same temperature because these both could have affected the results I got. I would also consider doing the experiment more than 3 times for each solution, just to check and I would maybe go higher than the concentration of 0.15, so I can see how quickly it is possible for it to take. Then I could fully test the theory of if I double the concentration, will the rate of the reaction always be half?