Preliminary Summary: I placed a 10cm magnesium strip in 3 different concentrations of Hydrochloric acid. I then calculated how long it took for 100cm of Hydrogen gas to be given off in the shortest time. Here are my results:
0.5 molar – 3 mins for 55cm gas
1 molar – 85.4 seconds for 100ml gas
2 molar – 19.06 seconds for 100ml gas
This proves the collision theory correct and I now have a starting point for my experiment.
Method: I will draw a cross on a piece of paper and place a beaker in the centre over the middle of the cross. I will then place 50cm3 of Sodium Thiosulphate in the beaker. I will measure out 10cm3 Hydrochloric acid and tip this into the beaker when I start a timer. When the cross has disappeared (when the reaction has created a large amount of precipitate to cover the cross) I will stop the timer. I will repeat this 3 times with each concentration of Sodium Thiosulphate. To alter the concentration I will exchange 5cm3 of Sodium Thiosulphate for 5cm3 of water. This will decrease the concentration allowing me to compare the different results.
Diagram:
Equipment list:
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10cm3 Measuring Cylinder
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100cm3 Measuring Cylinder
- Beaker
- Paper
- Black Marker
- Timer
Results
Conclusion: From my experiment I can see that the higher the concentration of the solution the higher the speed of the reaction. I have highlighted the two anomalous results. There are 3 main reasons for these anomalies:
- The beaker I used in the experiment became/was contaminated with other chemical substances
- The reactants I used were mixed/impure
- Human judgement resulting in error in the calculating of when the experiment was complete
- Delay between saying stop and stopping the timer.
I will now look into how I could improve these areas.
To decrease the risk of contamination I would need to totally clean out the beaker using boiling, soapy water, rather than cold water. This would totally clean the beaker of any previous chemicals.
To decrease the risk of the chemicals becoming contaminated I would need to use a brand new batch of chemicals and use a totally clean beaker. This would rule out the chance that the reactants had been mixed with other substances.
In this experiment the way I collected my results was not very accurate as I could only use my own judgement on when the cross could not be seen. To rule out the chance that my judgement could be wrong I would need to use an electronic device;
The radiation box would send out a small ray of beta radiation, when the solution was clear the senor will be able to detect the radiation so the timer will stay on. But when the solution has become ‘cloudy’ the sensor will not be able to detect the radiation so will turn the timer off. This will give me an accurately timed set of results.
My results have proved my hypothesis correct. I now know that concentration affects the rate of reaction.
If I wanted to further my work I could see how temperature, volume and catalyst’s affect the rate of reaction.
