Sodium + Hydrochloric = Sodium + Sulphur + Sulphur
thiosulphate acid chloride dioxide
Prediction
I Think that the higher the concentration, the higher the rate, (the shorter the time for the solution to produce a precipitate of sulphur) the faster the reaction will go. At a higher concentration there is larger proportion of Sodium Thiosulphate molecules to the same amount of space and they are more likely to collide with the Hydrochloric acid, speeding up the reaction as there will be more collisions. I also used the collision theory to help with my prediction, the collision theory is:
In order for any reaction to happen, those particles must first collide. This is true whether both particles are in solution, or whether one is in solution and the other a solid. If the concentration is higher, the chances of collision are greater.
This makes me believe that if you were to double the concentration of sodium thiosulphate you would be doubling the probability for the particles to collide therefore decreasing the length of the reaction by half.
Graph prediction
Variables
I would need a minimum of three different concentrations to plot a graph but I am going to aim for five different concentrations because I can then achieve a wide range of results and see if there is a pattern.
To make the results more accurate I will repeat each concentration twice but if the two readings aren’t within more than a 5 second difference of each other then I will repeat it again.
Preliminary experiment
Diagram
Apparatus
- Beaker x3
- Measuring cylinder (large and small)
- White paper with a thick cross
- Stop clock
- Hydrochloric Acid
- Sodium thiosulphate
- Distilled water
- Goggles x2
Method
Firstly I will get the apparatus on my desk, like the diagram above. I’m planning to do 2 of each concentration as it will make it fair, and If both aren’t with in 5 seconds I will repeat. I will pour from a beaker, the appropriate amount of sodium thiosulphate for the concentration(see observation table) and mix it with the right amount of distilled water in the larger measuring cylinder. I would then pour the solution of sodium thiosulphate and distilled water into the beaker over the cross. Then I would pour, into a smaller measuring cylinder 5cm3 of hydrochloric acid. I do it in a second measuring cylinder to avoid contamination. I then add this to the solution of sodium thiosulphate and my partner starts the clock. I watch until the black cross is completely obscured by a yellow precipitate of sodium then stop the clock and record the time in a table like the one below.
Table
Observations of preliminary work
Analysis and Evaluation
By doing this experiment I have found out that my prediction was correct and that increasing concentration increases the rate of reaction and my results support my prediction. I did notice a problem that will alter my method. When I looked into my concentration of sodium thiosulphate after pouring into the beaker, my partner pointed out that the solution had already started to react as it had started to change colour already. This contamination will have affected my results and in my improved method the changes will prevent this happening again. In my real experiments, to make it more accurate I am going to use separate syringes to make my measurements more accurate. I also had an anomalous result in the 100% concentration; this is because the temperature was lower so the molecules wouldn’t have had as much energy and, therefore, collided less slowing the reaction. Even so I believe this preliminary experiment was carried out swiftly and in a safe and well controlled manner.
Method(improved)
I’m planning to do 2 of each concentration as it will make it fair, and If both aren’t with in 5 seconds I will repeat. Firstly I will get all the apparatus on my desk arranged as in the diagram.
Then I will pour from a beaker, the appropriate amount of sodium thiosulphate for the concentration(see observation table) and mix it with the right amount of distilled water in the larger measuring cylinder. Instead of doing this I am going to draw the sodium thiosulphate from the beaker using a large syringe as they are more accurate. Also, I will have to separate ones of different sizes, one for sodium thiosulphate and water, the other for hydrochloric acid, and as they are different sizes I won’t get them mixed up
I would then pour the solution of sodium thiosulphate and distilled water into the beaker over the cross. I am not going to pour it into the beaker over the cross because the beaker has only been rinsed with water, so contamination could happen and the reaction would of started, when I'm busy doing the hydrochloric acid. So instead I will just leave in the measuring cylinder
Then I would pour, into a smaller measuring cylinder 5cm3 of hydrochloric acid. I do it in a second measuring cylinder to avoid contamination.
I then add this to the solution of sodium thiosulphate and my partner starts the clock. I will not do this either. I will add both solutions to the beaker over the cross at the same time, meanwhile my partner will start the clock.
I watch until the black cross is completely obscured by a yellow precipitate of sodium then stop the clock and record the time in a table like the one below. I will then rinse then start again.
Observations
Secondary data
At the beginning of the reaction, the cross can be seen easily.
As the flask becomes more and more cloudy
the cross gets harder to see.
The investigation could have been improved by testing the percentages imbetween, say 10% 30% etc. also the reaction could be tested more accurately if a light sensor was placed under the flask, instead of a cross. The sensor would be attached to the computer and would be very accurate at telling when no light can pass through