Rate of reaction

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Chemistry Coursework

William Lavelle-Bowden
Candidate number: 7108

Aims: To investigate rates of reaction.

I have been given different reactants to choose from as a suitable reaction to change variables is needed to investigate our rates of reaction.  The reactants I have at my disposal are:

-Hydrochloric Acid (HCl)
-Magnesium Ribbon (Mg)
-Calcium Carbonate Chips (CaCo
Sodium Thiosulfate (Na2S2O3)

From these reactants I had a number of reactions to choose from, such as:

1) Hydrochloric Acid + Sodium Thiosulfate  Sodium Chloride + Sulphur  Dioxide + Sulphur + Water
  (HCl+ Na2S2O3
 Nacl +NaO2 + H2O)

2) Hydrochloric Acid + Magnesium
 Magnesium Chloride + Hydrogen
  (HCl + Mg
 MgCl2 + H2)

3) Hydrochloric Acid + Calcium Carbonate
 Calcium Chloride +  Carbon Dioxide + Water
  (HCl + CaCo3
 CaCl2 + CO2 + H2O)

From this I had to choose one reaction to start changing variables. The variables I have to use are:

-Surface Area

As we did not have sufficient laboratory equipment we were not able to asses variables such as pressure and surface area. A catalyst could also not be used as these were forbidden in school.


Deciding which reactants to use

Experiment One 

For the first experiment I chose to use calcium carbonate chips and hydrochloric acid. I used 50 ml of hydrochloric acid and 3 calcium carbonate chips and recorded how long it took for the reaction to take place. This took 23 minutes and 43 seconds.

Experiment Two

For the second experiment I made a sodium thiosulphate solution, by placing sodium thiosulphate crystals into a beaker with a measured amount of water in it. This created for example a 0.5m solution of sodium thiosulphate. After this we placed the solution on to a white tile with a black cross marked on it in the centre so we could see it clearly looking from a birds-eye view over the beaker. The final part to this experiment was placing 20ml of hydrochloric acid into the beaker and timing how long it was until the solution became to cloudy to see the cross through. This was then repeated 3 times and an average was taken for each concentration we tested.

Experiment Three

For the third experiment I decided to use the simplest way of collecting gas from a reaction – Downward Displacement. The reactants I used were hydrochloric acid and magnesium ribbon, I was looking for how much hydrogen gas was given off and how long it took. The equipment I used were as follows:

1. Water Trough
2. Test Tube        
3. Measuring cylinder
4. Rubber Delivery Tube
5. Delivery Tube Stopper
6. A Clamp Stand And Clamp        
7. 2g Of Magnesium (Mg)        
8. 20ml of Hydrochloric Acid 0.5 Molar (HCL)

This process works by gas from the reactants collecting in the conical flask, pushing water into the trough – Downwards Displacement.
Firstly the water trough is filled with water, after this we placed the measuring cylinder in the trough completely filling it with water, and then flipped it over so no air was in the cylinder. To secure it in this position we clamped it. We then slipped the delivery tube into the cylinder with someone on the other end ready to place it over the test tube. This person placed 20 ml of hydrochloric acid into the test tube to react with the 2g of magnesium. Immediately after this is done the rubber stopper is placed over the test tube securely.

Deciding which method to use

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I will use cross and tile method because I feel it is quite simple practically so allows reliable data to be collected as there is less room for error. In my prelim work I investigated changing the concentration and the temperature of the sodium thiosulphate. I found that changing the concentration gave me more reliable results so I think I will investigate this variable. I realised that this method is not perfect and I need to consider all the improvements I can make to control variables such as room temperature, timing, observing, measuring of volume etc.


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This is an average practical investigation. There seems to be more emphasis placed on the preliminary part of the investigation than the main part. The preliminary part should only be used to inform the main part of the practical. The evaluation was good and the data collected was of a sound quality. There are more specific improvements suggested throughout.