Changing the concentration of the reactants - This would affect the results of the experiment because the concentration is a measure of the number of particles per unit volume. As the concentration of a solution increases, there are more reactant particles in the same volume and this increases the chances of particles colliding with each other. This increases the rate of reaction as there are more successful collisions per second while a lower concentration would decrease the rate of reaction.
Changing the surface area of a solid reactant – This would affect the results of the experiment because the surface area is the measure of how much exposed area a solid has, in square units. By increasing the surface area, more particles are exposed to the other reactant and are more likely to collide with each other. This increases the rate of reaction as there are more successful collisions per second while decreasing the surface area would decrease the rate of reaction.
Introducing a catalyst to the solution could affect the results of the experiment because a catalyst is a substance that changes the rate of a reaction and doesn’t get changed up or used in the process.
I have chosen to change the concentration of sodium thiosulfate because I am unable to change the surface area of the reactants, as there is no solid in the reactants. A catalyst would be difficult to find and changing the temperature would be difficult to change, as we would need to use a water bath and it would mean we o he experiment on one day. So I have decided to change the concentration of the sodium thiosulfate.
Hypothesis – I will measure the how long it takes for the sulphur to form, or in other words, how long until we cannot see the cross. I will do this by adding different concentrations of sodium thiosulfate and I think, the higher the concentration, the faster the rate of reaction.
Hydrochloric acid + sodium thiosulfate sodium chloride + sulfur dioxide + sulfur + water.
HCl(aq) + Na2S2O3(aq) NaCl(aq) + SO2(g) + S(s) + H2O(l)
Prediction – When the concentration is higher, it will take a less time for the reaction to happen, and therefore the rate of reaction is faster. If we double the concentration of sodium thiosulfate, the rate of reaction will be doubled and therefore the time taken will be half.
Equipment
- Conical Flask – To put the solution of sodium thiosulfate, water and acid into.
- Two Measuring Cylinders (one 10ml)(one 25ml) – Each used to accurately measure how much sodium thiosulfate, water and acid are used in the experiment.
- Pipette – Used to put small amounts of acid into a measuring cylinder to receive an accurate measurement.
- Digital Stop clock – Used to time how long it took for the solution to turn cloudy and it’s a more precise reading than an analogue clock as they are nearest to hundred to the second.
- Paper marked with ‘X’ – Used to see whether the solution is cloudy enough to make the ‘X’ not visible.
Method –
- Draw an ‘X’ on a piece of paper and place under a conical flask – We will be measuring how long it takes for the cross to disappear, so it should be clear, bold, and easily seen before the experiment starts.
- Add 5ml of hydrochloric acid in the measuring cylinder using a pipette and add the solution into the conical flask
- Add 25ml of sodium thiosulfate into the conical flask and immediately start the stop clock.
- Swirl the conical flask around, observing carefully
- When you can no longer see the cross, stop the stop clock and record the time
- Repeat this with the other concentrations of sodium thiosulfate.
