The sodium thiosulphate

The size of this activation energy is different for different reactions. I think that the concentration of a solution affects the rate of reaction because ‘the rate of reaction depends on how frequently the molecules of the reacting substances collide. A more concentrated substance has more molecules for a given volume than a more dilute substance because there are more molecules about, the frequency of the successful collisions is greater and the reaction happens faster. ’ I have predicted this through my acquired knowledge of the collision theory.

But I must take into consideration that not all collisions results in a chemical reaction because there is not sufficient energy to overcome activation energy. How does the concentration of Sodium Thiosulfate affect the rate of this reaction? The Main Experiment Safety precautions: Safety is a key aspect to any experiment. There are a lot of safety issues we must abide when performing this experiment. The first safety precaution I used was to make sure I was standing up during my experiment, that way I will be more cautious and aware of my surroundings not causing accidents with equipment I’m using - e.

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g.tipping over my hydrochloric acid and sodium thiosulphate solution.

A key safety aspect was that we covered the top of the conical flask with cotton wool, making sure no gas escapes the air we breathe into as sulphur dioxide; one of the products formed from the experiment is a toxic gas. I also decided to wear goggles to protect my eyes from the acid splashing, squirting or any way entering my eye.

Another precaution to take measure of is wearing gloves to protect your skin as hydrochloric acid is corrosive. Afterwards, when you have done your experiment thoroughly wash away all apparatus used and pour the solution down the sink.

One change I made to my safety procedures is that I said standing during the experiment is better, as you’ll be more cautious and aware of your surroundings. I decided to add this on because as I was doing my preliminary experiment sitting was difficult, standing made it easier to move about while handling the apparatuses; making it less likely for an accident to happen i. e. spillage of chemicals.

Methodology:

1. If you have not already done so, put on your goggles and gloves.
2. Place the paper with an X onto a flat surface and put a conical flask on top.
3. Measure 9 cm3 of sodium thiosulphate using a pipette and put it into a flask. Then measure 1 cm3 of water using a different pipet.
4. Then measure 10 cm3 of hydrochloric acid using a measuring cylinder.
5. Add both the Sodium Thiosulfate solution and acid into the conical flask at the same time, quickly placing a ball of cotton wool on top of the flask to block the formed gas from getting into the air. When acid and water is added, immediately start the timer.
6. Look down at the cross from above the flask. The solution turns cloudy because we get precipitate of sulphur as the solution react. When the cross disappears, stop the timer and note the time, recording it in the table.
7. Repeat this process using different concentrations of sodium thiosulpahte solution with water as shown in the table above.
8. Carefully pour the solution into the sink straight after each test, thoroughly rinsing the measuring cylinders and conical flask with plenty of water each time. I decided to add both the Sodium Thiosulfate Solution and Hydrochloric Acid at the same time, as it makes the outcome of the result more reliable.

Main Experiment Results Table Sodium Thiosulfate Solution

• • Hydrochloric Acid Reading (seconds)
  • Average time taken
  • Rate Volume of water (cm3)
  • Volume of Sodium Thiosulfate (cm3)
  • Concentration (M)
  • Volume of Hydrochloric Acid (cm3)
  • Concentration (M)
  • 1st test 2nd test 3rd test
  • Average rate = 1st+2nd + 3rd/3
  • Rate of reaction = 1/average rate

(I have made some changes to my table. Some of these changes are that I have applied an clear subheading under each row to organise the presentation of the table, making it clear and easier to understand. One of five subheadings I have inserted is ‘Sodium Thiosulfate Solution’, under this are 3 rows of broken down areas of the subject; Volume of water (cm3), Volume of Sodium Thiosulfate (cm3) and Concentration (M).

Another adjustment I have done is added on three readings instead of one as it is one of many factors that show from my table - for my experiment to be reliable.

How to make it a fair test

To make sure my results are accurate and reliable the experiment will be kept as fair as possible by making sure the following things are kept constant:

1. The total volume of solution used in the reaction (10cm3 ).
2. The temperature of all chemicals (room temperature). To ensure this and make it a fair test, the experiment is done in the same room, same time, and same place.
3. The volume of Hydrochloric Acid used in the reaction (10cm3 ).
4. The same paper with the black cross will be used for all tests.
5. Each measurement will be measured accurately, by the same person (as each person has different eye-sights).
6. Different measuring equipment used for HCl and Na2S2O3 to avoid contamination.
7. To ensure this experiment is a fair test, I will follow through certain steps. In this experiment we are trying to find the rate of reaction using concentration as a factor, so there are a number of things we need to make sure we do to keep it a fair test. Firstly I will keep a chemical at a constant concentration.

So in this experiment we have chosen to keep Hydrochloric Acid at a constant concentration (10cm3). I will repeat the experiment of sodium thiosulphate solution and hydrochloric acid, three times. This will make sure no faults or errors are being made – through either the apparatus used, making sure the volume of each concentration is accurate and even human errors etc. By doing my experiment three times it increases the reliability of the experiment. I will also check my results with other students to make sure our results are the same or closely similar, definitely ensuring my tests to be reliable.

I will also make sure that the same person is measuring all the concentrations in each test, because each person has different methods of measuring and may be doing it – differently. Each person also has different eye-sights which may lead to inaccurate recordings. So we chose a person who has good visual perception. I will also make sure that the same person with quick reaction-time is stopping the timer when ‘X’ is not visible because again people have different reaction-times, which may result in odd results if a variation of people are taking turns to stop the clock watch.

I will make sure that the measuring cylinders for Hydrochloric Acid and Thiosulfate will not be mixed up, also in-between each use of the apparatus i. e. the measuring cylinder, is thoroughly washed as I do not want any substances to remain from my previous test, which if not done – will make my solution inaccurate. The concentration of Sodium Thiosulphate in the beakers will be the only factor to change in the experiment. Another thing that must be taken into consideration is that the Hydrochloric Acid and the Sodium Thiosulphate (+Water) must be poured into the conical flask simultaneously.

This ensures a fair test; one more thing is that the stop-clock must be started as soon as the two solutes mix together. Another factor which can affect my results is the conical flask. I must wash it out with water and dry it each time. This is because if there is any remaining solution, then it could alter my results and make my investigation unfair. Therefore I must clean out the flask. One of the most important factors to consider is the temperature of my investigation. From background knowledge I know that the temperature of the reaction will affect the speed of it.