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Investigate a factor which affects the rate of reaction in the reaction between sodium thiosulphate and dilute hydrochloric acid.

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Introduction

Aim- To investigate a factor which affects the rate of reaction in the reaction between sodium thiosulphate and dilute hydrochloric acid. When sodium thiosulphate and hydrochloric acid react they produce a cloudy Solution. The two chemicals are both clear solutions and will react together to form a yellow precipitate of sulphur. As the solution will turn cloudy, we can observe the rate of reaction by placing a black cross underneath the beaker and seeing how long it takes for it to disappear by timing it. The reaction happens because of the collision theory. Every atom vibrates and depending on the circumstances the strength of the vibrations might increase or decrease. When two substances are placed together, they will vibrate and often collide. When the two atoms collide a certain amount of energy is needed for the reaction to take place. The minimum amount of energy that is needed for a reaction to take place is called the activation energy (See Fig.1 and Fig.2). Key - - Atom - Direction atom is moving As you can see in Fig.1 the atoms are about to collide, in Fig.2, you can see that the top pair of atoms did not react, that is because not enough energy was produced so they did not react instead they bounced off each other and moved along in another direction. Whereas the bottom two atoms reacted together because the activation energy was reached. ...read more.

Middle

Prediction I predict that the higher the concentration of the sodium thiosulphate becomes and the amount of water goes down the rate of the reaction would increase. Preliminary investigation The reason that I have done the preliminary investigation is to determine what the interval between the tests should be. Method for preliminary investigation 1. Set up the apparatus 2. Work out the suitable concentration for the sodium thiosulphate to start the experiment to start with. 3. Measure the amount of sodium thiosulphate and water 4. Measure the amount of hydrochloric acid. 5. Add them together 6. Start timing 7. Stop timing when the cross disappears. After doing the preliminary investigation I have collected the correct information on how to make this experiment as fair as possible and how to get the most accurate results. These are the following * The correct equipment that I will have to use. * The same cross will have to be used throughout the experiment to make it a fair test. * The same amount of hydrochloric acid must be used in all the tests to make it fair. * What the interval should be between the tests. * How many times the experiment should be done to get an accurate result. The apparatus This is a list of all the apparatus that I will use in the experiment- * 1 x Ajar of hydrochloric acid * 1 x A jar of sodium thiosulphate * 1 x Conical flask * ...read more.

Conclusion

In my first and third attempts I got 38.02 seconds and 45.6 seconds. This means that the second attempt was probably incorrect. This could have been caused by any number of things such as: * Measuring- the actual measuring of the chemicals is difficult because of the meniscus of the liquid and the accurateness of the measuring cylinders. Also, the human eye causes errors such as this * The eye could also have made mistakes in judging whether or not the cross had actually completely disappeared * Again human error could have occurred. If the same person watching the reaction was working the timer, errors could occur in their co-ordination. We could remove these errors by: * Using a burette or a to measure. This would remove the measuring errors associated with measuring cylinders, using a burettes are a far more accurate way of measuring the correct amounts. * Use light sensors to detect when the cross is no longer visible. A light sensor would be placed underneath the conic flask and would be connected to a timer. The light sensors will detect when there is no light shining through the substance. This would automatically stop the timer and therefore make the experiment fairer and more accurate. To further investigate this experiment, I could use a wider range of times. I could have done the experiment at intervals of 5ml up to 100ml, this would give me more results, which would mean I could plot more results in my graph. This would be even more accurate. Rumel Ahmed 3873 Page 1 of 6 ...read more.

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