Rates of Reaction.

Sara Rider

Rates of Reaction.

Introduction:

During the reaction between sodium thiosulphate and hydrochloric acid I know that a solid sulphur will be formed and also that the solution of the two will turn cloudy before going completely opaque, also during this a poisonous gas is also given off called sulphur dioxide.

For the reaction to take place I know that the particles of these two reactants must make successful collisions and that if during the reaction more particles collide successfully then the reaction will go faster, but if reacted alongside water then the reaction will be diluted slightly the rates of reaction will be lowered.

From this first evidence I can make an primary prediction that doubling the concentration of the chemicals will double the rate of reaction.

I predict this because if there is double the concentration then there will be double as many particles meaning that there will be a higher chance of successful collisions.

Preliminary Experiment:

Measure out 30cm3 of sodium thiosulphate and 5cm3 of hydrochloric acid.
Pour the Sodium thiosulphate into a conical flask and place on a piece of paper on which a thick cross has been drawn.
Get the stopwatch ready and start timing as soon as the Hcl touches the sodium thiosulphate, continue to time until the cross is no longer visible.
Do this twice so that the result is sure to be accurate.

The results I got from doing this preliminary experiment were,
30cm – 1min 29 sec’s

1 min 28 sec’s
10cm – 4 min’s 2 sec’s

4 min’s 5sec’s

From looking at my graph I can see that as the volume of the concentration increases the time decreases, like I said in my initial prediction that if the concentration is doubled then the rate of reaction would be doubled, from my graph above I can now see that this is slightly wrong and if the concentration is doubled then the rates of reaction is more then doubled. During this experiment I have made a conscious descion that the HCl should be kept constant and that the Sodium thiosulphate was variable.

Plan:

I must plan and produce a piece of coursework investigating the rate of reaction between Hydrochloric acid and Sodium thiosulphate.

The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by dividing 1 by the time taken for the reaction to take place.

There are five main factors that affect the rate of a reaction, according to the collision theory of reacting particles: temperature, concentration (of solution), pressure (in gases), surface are (of solid reactants), and ...

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Plan:

I must plan and produce a piece of coursework investigating the rate of reaction between Hydrochloric acid and Sodium thiosulphate.

The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by dividing 1 by the time taken for the reaction to take place.

Concentration means the amount of reactant particles in a GIVEN AREA. When you INCREASE the concentration you INCREASE the number of particles in that are therefore there is a higher possibility of SUCCESSFUL COLLISIONS. If the solution is diluted with (e.g. water) there are more non reactant particles for the reactant particles to collide with - therefore DECREASING THE NUMBER OF SUCCESSFUL COLLISONS

I have chosen to investigate the effect concentration will have on a reaction.

Aim:

The Aim of my investigation is to find out how the rate of a chemical reaction is affected by the concentration of chemicals.

Hypothesis:

I predict that this reaction has a definite end point (when the cross on the test tube ‘disappears’). The faster the cross ‘disappears’ the faster the reaction and by timing how long this takes we can establish the rate of reaction.

There are various factors affecting the rate of reaction that we need to take into consideration, these are:

Temperature - I will conduct all the tests at room temperature (hopefully on the same day) because temperature has an effect on the rate of the reaction.

Shaking or stirring – I will try to keep jogging of the solutions to a minimum so as not to alter the rate of reaction.

Catalysts speed up reactions.

I predict that the greater the concentration of Sodium Thiosulphate (hydro) in the solution the faster the chemical reaction will take place. Therefore, the cross will disappear more quickly due to the cloudiness of the solution. But only up to a point after this the solution will not react within a reasonable time (i.e. under 30 min). On a graph I predict it would be a plateau.

I think that the concentration of a solution effects’ 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 successful collisions is greater, and the reactions happen faster.

Fair Test:

In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 15 cm3 All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful.

Method:

Firstly I will need:

Hydrochloric acid

Thiosulphate

Stopwatch

Conical flask

Measuring cylinder

Pipette

Water

Cross board

I am going to measure how changing the concentration of sodium thiosulphate affects the reaction time between it and hydrochloric acid. Every time I will add 20 ml of hydrochloric acid that is 2 molar to that I will add 20 ml of a thiosulphate and water solution.

By varying the amount of water in the thiosulphate solution I will vary the concentration. I will first put the hydrochloric acid in a test tube with a cross on the back. Then I will add the hypo and will start the stop clock immediately. As soon as the cross disappears I will stop the timer. This means that the reaction has ended. I will repeat the experiment varying the amount of water each time.

Safety:

To conduct my experiment safely I will follow normal laboratory rules, which include:

The wearing of safety goggles to protect my eyes from chemical splashes.
Standing up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals.
Taking care when handling chemicals, particularly Hydrochloric acid and Sodium Thiosulphate because they are irritants. I will not touch my eyes or mouth until I have thoroughly washed my hands.
Taking care when using glassware to prevent injury.

Variable Control:

To make this experiment a fair test I will only vary one thing – the concentration of the Sodium Thiosulphate solution.

I will conduct all the tests at room temperature because temperature has an effect on the rate of the reaction. I will try to conduct all of the experiment on the same day because the temperature will change from one day to the next and this may effect the accuracy of my results and possibly making it harder to construct a table.

The measures of Hydrochloric acid will all be the same (5cm). The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock.

Analysis:

From looking at my graph I can see that as the concentration is increased the rates are also increased by a considerable amount, although I followed all of the fair test rules I think my graph look slightly in-accurate as 6 results under the line of best fit. My graph suggests that if I double the concentration from 0.5 to 1.0 then the rates of reaction change from 1.4 to 2.1. I feel that this is also inaccurate because before we found that if then concentration is doubled then the rates are more then doubled. The reasons that concentration effected the rates are: -

If there are more particles then there will be more collisions between them.
That if the particles are colliding then the reaction will be more successful
Increasing the concentration will increase the rate/speed of the reaction.

I had predicted earlier that if I doubled the concentration then the rates should be more than doubled. However my results prove this very and this was an unexpected thing to happen in my experiment.

However I feel that some of my results are slightly or very much inaccurate and I would not like to use them to make any further predications