An experiment was previously done to determine the effect of concentration on the rate of reaction using hydrochloric acid and a magnesium ribbon. The results showed that at a higher concentration the rate of reaction between hydrochloric acid and magnesium was higher.
The reaction that will be investigated is between hydrochloric acid and sodium thiosulphate.
The reaction as shown in the equation below:
Preliminary Results
A preliminary experiment was done to find out what volume and concentration should then be used to get the optimum results. The concentration of the Sodium Thiosulphate that was used in the preliminary experiment was 0.003M which was weak; the volume of the sodium thiosulphate and the hydrochloric acid was too low.
All the results that were obtained took over 2 minutes so from this the volume of both the hydrochloric acid and the sodium thiosulphate were increased and the concentration the sodium thiosulphate made stronger. The original volume of sodium thiosulphate that was used was 10cm3 which was too small a quantity so in the final investigation the volume would have to be increased to 35cm3. The concentration of the sodium thiosulphate was so a concentration of 0.015M will be used instead of 0.003M.1 result was taken down for each of the concentrations. In the final investigation each concentration must be repeated so valid conclusions can be drawn and an average would be taken for accuracy. A range of results and repeats would have to be taken to identify any anomalies.
Prediction
I predict that as the concentration increases in strength the rate of reaction will be faster. The reason why I think this is because if the concentration of the hydrochloric acid is increased there are more reactant particles in the same volume of the substance. The more reactant particles there are the higher the frequency there will be of successful collisions. So if there are more collisions the rate of reaction will increase. After taking all this into consideration I have drawn up a predicted graph.
As you can see for the graph I have predicted, the line of best fit is straight not curved because it is not changing the volume of the hydrochloric acid but I am changing the concentration of it and so the results would be directly proportional.
Variables
Input Variable: Concentration of Hydrochloric Acid
Output Variable: Amount of time taken
Controlled Variable: Volume of both the Hydrochloric Acid and the Sodium Thiosulphate
Concentration of the Sodium Thiosulphate
Ph of both acids
Temperature
Apparatus
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100 cm3 Conical Flask
- Burette
- 2x Test Tube Rack
- 10x Test Tubes
- Stopwatch
- 2x Beakers
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50 cm3 Measuring Cylinder
Method
Before starting anything, make sure that the area at which the experiment will take place is clean. This is so if a spillage takes place none of the other equipment would get dirty.
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Carefully pour 15cm3 of hydrochloric acid into the burette, making sure that none of the acid spills. MAKE SURE THE BURRETE IS CLOSED BEFORE POURING IN THE HYDRCHLORIC ACID.
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Take out 5cm3 of Hydrochloric acid into one of the test tubes. In another test tube put 4cm3 of hydrochloric acid. In another test tube put 3cm3 of hydrochloric acid. In another test tube put 2cm3 of hydrochloric acid. In the final test tube put 1cm3 of hydrochloric acid. Put all the test tubes in the test tube rack.
- Wash out the burette to make sure none of the hydrochloric acid is left. If it is not thoroughly washed some results can be contaminated.
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Once this is done put 10cm of water into the burette and fill up 5 test tubes, one with 4cm3 another with 3cm3 then 2cm3 then 1cm3 and finally leave the last one empty. Once this is done the burette can be moved to the side as it won’t be used till the next repeat.
- Now take the first set of test tubes containing hydrochloric acid and mix then with the new set which contain water to change the concentration of hydrochloric acid. Here is a table to show what concentration is being made and which volumes of hydrochloric acid and water are to be mixed together.
- Once this is done the 5 empty test tubes can be washed. It is crucial that they are washed thoroughly as they will be used again in repeats.
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Using the measuring cylinder measure out a total of 35cm3 of sodium thiosulphate, once this is done pour the solution into the conical flask. Get a piece of paper and draw an X shape onto it, then attach it to the bottom of the conical flask.
- Now take one of the test tubes with the concentrated hydrochloric acid and pour it into the conical flask ( already full of sodium thiosulphate ), the reaction will start as soon as the hydrochloric acid is poured into the conical flask so ensure the timer is started promptly.
What can be observed is that the solution turns a cloudy yellow colour because sulphur is being produced, a bad smell is given off which is caused by the sulphur dioxide which his given off.
Safety
In the investigation safety precautions must be taken:
Not Running – During the investigation there will be people walking around with acids and glass. If running an incident may take place in which others may get injured.
Clean Up Spills – If something is spilt it must be cleaned up as quickly as possible to prevent injuries to others and yourself.
Wear Goggles – You must always wear goggle in this investigation, hydrochloric acid is corrosive so can burn if made contact with the eyes.
Handling Glassware – When glassware is handled always make sure that it is held with a proper grip so that it may not fall and break. If glassware does break always report it.
Washing – Once the investigation is finished make sure the glassware and any other equipment used is washed.
Results
All my results are to the nearest millisecond to give us more precise results. The reason why I have done 3 repeats for each concentration is so that once I have collected all my results I can tell if there are any anomalies within them.