Test
Aim;
To test the affect of concentration of sodium Thiosulphate on the rate it’s of reaction with hydrochloric acid.
Variables;
Variables to change-
- The concentration of Thiosulphate
Variables to keep the same-
- Concentration of hydrochloric acid
- Volume of sodium Thiosulphate
- Volume of hydrochloric acid
- Temperature
- No catalysts
Accuracy;
Things to control to get accurate results-
- Same person timing
- Same person measuring reactants
- Same measuring cylinder
- Same stop watch
- Same cross on paper (see method)
- Repeat results and take an average
- Make sure lowest point on meniscus lines up with measuring mark
Safety;
Things to control to keep my test safe-
- Wear safety goggles to protect eyes
- Wear overall to protect clothes and skin
- Rinse apparatus after use
Explanation;
I chose to test the affect of concentration because you cannot change the surface area or pressure because the reactants are liquids, not gases. Temperature is very difficult to control when using a Bunsen burner and using a water bath would take too long.
Concentrations;
The concentration I will use are-
-
0.1M (50cm3 sodium thiosulphate)
-
0.08M (40cm3 sodium thiosulphate + 10cm3 water)
-
0.06M (30cm3 sodium thiosulphate + 20cm3 water)
-
0.04M (20cm3 sodium thiosulphate + 30cm3 water)
-
0.02M (10cm3 sodium thiosulphate + 40cm3 water)
Method;
Na2S2O3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+SO2(aq)+S(s)
1. Measure out and make the five concentrations of sodium thiosulphate you are going to use.
2. Add 50cm 3 of 0.1M sodium thiosulphate to 5cm 3 of hydrochloric acid to a flask that is over a piece of piece of white paper with a black cross on it.
3. Start the stop clock as soon as the two reactants are in the flask together. Time how long it takes until you can no longer see the cross through the bottom of the flask (because of Sulphur forming on the bottom of the flask).
4. Repeat steps 1-3 twice more for 0.1M sodium thiosulphate
Repeat steps 1-4 for the other four concentrations.
Equipment List;
- Measuring cylinders-one for hydrochloric acid, one for sodium thiosulphate
- Flasks for sodium thiosulphate concentrations
- Stop clock
- Paper with cross on
- Flask for reaction to take place in
Prediction;
I predict that the stronger the concentration the faster the rate of reaction. I think this will happen because there will be more thiosulphate particles to the same volume of solution in the 0.1M solution than in the 0.02M solution, therefore there will be a higher chance of collision and more collisions per second. See below-
0.08M Sodium Thiosulphate Solution (thio:water=4:1)
Water particles: 10
Sodium thiosulphate particles: 40
Hydrochloric acid particles: 5
0.08M Sodium Thiosulphate Solution (thio:water=4:1)
Water particles: 40
Sodium thiosulphate particles: 10
Hydrochloric acid particles: 5
I have also previously performed an experiment reacting magnesium with hydrochloric acid-
Mg+2HCl→MgCl2+H2
I varied the concentration of the hydrochloric acid and my results showed the stronger the concentration of the acid the faster the rate of reaction
Other Sources say;
“The number of collisions per unit time can be expected to grow with the number of molecules of the reactants available” The University of Delaware
“The more concentrated (the reactants) the faster the rate (of reaction)” Dr Clive Buckley
“As you increase the concentration… you increase the rate of reaction” Chemistry for You
Results;
Analysis and conclusion;
There were no anomalous results. I have found from my graph (see page attached) that the more concentrated the sodium thiosulphate was the shorter time taken to obscure the cross. My prediction was correct as I predicted that therefore an increase in concentration causes an increase in rate of reaction. This is because there were more thiosulphate particles in 50 cm3 of 0.1M solution than in 50 cm3 of 0.02M solution, therefore there was a higher chance of collision in the more concentrated solution and more collisions per second. See below;
0.08M Sodium Thiosulphate Solution (thio:water=4:1)
Water particles: 10
Sodium thiosulphate particles: 40
Hydrochloric acid particles: 5
0.08M Sodium Thiosulphate Solution (thio:water=4:1)
Water particles: 40
Sodium thiosulphate particles: 10
Hydrochloric acid particles: 5
Evaluation;
Improvements I could make to the concentrations experiment-
Accuracy in Timing
The human eye is not a very accurate measuring device; everyone’s eyes are different and are affected by changes in light and sometimes look away from what they are supposed to be watching. If I used a light sensor to time how long it takes for the sodium deposit to become opaque it would be much more accurate;
Accuracy in Measurement
When making up concentrations and measuring out acid there are two ways in which I could make my measurements more accurate. Firstly I could use a water level sensor
like those found in washing machines. The computer is programmed to stop filling the container when it senses that the water has reached the level;
Also I could use the weight of a liquid to determine its volume more accurately. The container is set on some electronic scales that are interfaced with a computer. The scales are set at zero with the flask on them, and then it is filled by a source controlled by the computer. When the computer senses through the scales that the container has a certain weight of liquid that it knows is the weight of the desired volume it shuts off the liquid source.
Other experiments I could try-
The affect of Temperature
The reason I did not investigate the affect of temperature on rate of reaction was that it would be too difficult to control with a Bunsen burner and I would have had very inaccurate results. However, if I used a water bath to regulate the temperatures of the Sodium Thiosulphate this experiment would probably be quite successful. I would test it a 20 0C, 30 0C, 40 0C, 50 0C and 60 0C. I predict that an increase in temperature would cause an increase in rate of reaction, as the atomic particles would have more energy and move around faster, causing them to collide more often.