Rates of Reaction Investigation.

Rates of Reaction Investigation

Introduction

In this investigation I am going to investigate how fast the chemicals Hydrochloric Acid and Sodium Thiosulphate react. The four main variables that affect rate are:

Temperature – if the reactants are heated/cooled they have more/less energy. If they have more energy there is greater chances of successful collisions meaning the reaction occurs faster.
Concentration – if the solution is more concentrated there are more reactants there is a greater chance of successful collisions.
Surface Area – if one reactant has more surface area there is greater chance of a successful collision as there is more area for the reaction to occur on.
Catalysts – a catalyst is a chemical that speeds up a reaction without changing itself during the reaction. An example of this is an enzyme.

In this investigation however I am only going to investigate how concentration affects rate of reaction as the other methods of increasing the rate of reaction are not easily controlled and I do not know of a catalyst that will speed up the reaction.

Preliminary Work

In this preliminary work I am going to investigate the two extreme possible measurements.

In this preliminary work I placed 20cm³ of Hydrochloric acid and 20cm³ of Sodium Thiosulphate into a conical flask over a cross on a piece of paper. I then measured the time for it to no longer be visible when viewed from above. I also did 1cm³ of hydrochloric acid, 19cm³ of water and 20cm³ of Sodium Thiosulphate.

As the concentration 0.01M took such a long time I may not repeat it in my actual experiment although I believe it may be an anomalous result.

Prediction

I believe that the higher the Molar/concentration the faster the reaction will occur. I believe this will be the case because of the higher concentration of reactive particles in the hydrochloric acid increasing the chances of a successful collision. I also predict that the lowest concentration of hydrochloric acid will take the longest time to react, as there are less particles of hydrochloric acid thus decreasing the chance of a

successful ...

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As the concentration 0.01M took such a long time I may not repeat it in my actual experiment although I believe it may be an anomalous result.

Prediction

successful collision. I have made this prediction as this is what was indicated in my

preliminary work.

Also I predict that if I halve the concentration that the reaction will take twice

the amount of time and so on and so forth.

Method

Plan

Set up equipment as shown.
Measure the amount of time for the cross to no longer be visible.
Change the liquids, using appropriately gauged measuring equipment, and repeat.
To change the concentration of the acid mix it with a calculated

amount of water to lower the concentration. The higher the amount of water the lower the concentration.

Variables

The variables in this experiment are:

Amount of Hydrochloric Acid – the more acid the faster the reaction will take place as there will be more.
Amount of Water – the more water in the solution the less concentrated the acid will be thus slowing down the reaction.
Amount of Sodium Thiosulphate – if there is less sodium thiosulphate there will be not as many molecules for the hydrochloric acid to hit thus reducing the rate of reaction.

Time Taken for reaction to occur

I have not included some variable that could not possible be controlled in a classroom environment.

Safety

As we are using hydrochloric acid we will be wearing safety goggles at all times and also as we are using hydrochloric acid we will be careful to not get any on our hands and if we do we will wash our hands immediately.

Fair Test

In order to make my experiment a fair test I am going to:

Keep all variables the same by carefully measuring all liquids and using finely scaled measuring equipment.
Take evenly spaced measurements.

Reliability

To minimise the occurrence of an anomalous result I will:

Keep all variables the same by carefully measuring all liquids.
Use appropriately sized measuring equipment to allow for maximum accuracy
Use the same cross for each experiment.
If an anomalous result occurs I will repeat that concentration
Use the same person to evaluate when the cross has disappeared
Use the same shape of beaker each time
Use the same size of beaker

Results

See next PageAnalysis

I can see that as the concentration increases the rate of reaction increases because as the concentration increases there is a higher percentage of reacting molecules, meaning that the reaction between Sodium Thiosulphate will occur faster as there are more of these reacting particle increasing the chances of a successful collision between them. This is shown on the graph by an ascending straight line. This supports the main part of my initial prediction totally. The reason the rate of reaction increases in higher concentrations because there are more molecules of hydrochloric acid increasing the chance of a successful collision.

The results do support most of my initial prediction as I predicted that as I increased the concentration the rate of reaction will increase and vice-versa. This is because as I said previously in higher concentrations there are more reactive molecules of Hydrochloric acid and Sodium Thiosulphate increasing the chance of successful collisions thus increasing the rate of reaction.

However my prediction that halving the concentration will double the time taken is not conclusive so further investigation would be required.

Evaluation

There is only one anomalous result in my experiment and this is labelled on the graph. This may have occurred due to foreign chemicals entered the solution or we may have measured the Concentration wrong. Therefore I believe that my results are sufficient to support a firm conclusion. This conclusion is that rate of reaction does increase with concentration

I believe that my experiment was suitable in the most part however it could have been improved if I had a method of controlling the temperature of the solution constantly so that the reaction speeds up or slows down due to the concentration and not due to the temperature.

I could improve accuracy by using mechanical pipettes to measure the liquids. Also I could repeat the experiment further so that I could get even more reliable results.

Possible experiments that could be done to further support my theories are perhaps repeat the experiment but this time change the concentration of the sodium sulphate. Also I could do the experiment in a situation where I can control all of the undependable variables, which I could not control in a classroom such as the temperature of the Sodium Thiosulphate/Hydrochloric Acid/Water.

Rates of Reaction Investigation.