Sodium Thiosulphate and Hydrochloric Acid Reaction

Laura Curnock

11SKs

28/04/2007

Sodium Thiosulphate and Hydrochloric Acid Reaction

Plan

For Sodium Thiosulphate and Hydrochloric acid to react their particles need to collide with sufficient energy. There are three ways I can speed up the reaction, these are:

Increasing the temperature, this causes the particles to move faster, there for the particles collide move often and with sufficient energy, so the particles react.

Adjusting the concentration; to alter the concentration of the hydrochloric acid water is substituted for acid. This makes the acid weak and so you start with weak acid and gradually add acid to it, making it stronger.

A Catalyst; a catalyst works by giving the reacting particles a surface to stick to where they can bump into each other more often which increases the collisions and speeds up the reaction.

In my experiment to speed up the reaction between Sodium Thiosulphate and Hydrochloric acid, I am going to increase the temperature until I can see the rate of reaction go up. I have decided to use the temperature increase because it can be easily controlled and readings can be taken simply. I intend to take 5 readings at a range of temperatures at 22,24,29,38,47°C. I may need to repeat my readings so I can see if they are accurate, and also to calculate the average.

The equipment I plan to use for my experiment will be:

A small conical flask
50cm³ of Sodium Thiosulphate solution
10cm³ of Hydrochloric acid
A sheet of printed paper
A Bunsen burner
A tripod
A gauze
A thermometer
A timer

Method

This is a preview of the whole essay

The equipment I plan to use for my experiment will be:

A small conical flask
50cm³ of Sodium Thiosulphate solution
10cm³ of Hydrochloric acid
A sheet of printed paper
A Bunsen burner
A tripod
A gauze
A thermometer
A timer

Method

I will put about 50cm³ of Sodium Thiosulphate solution into a conical flask. I will then put the conical flask onto a gauze and tripod, next I’ll heat the Sodium until it is at the temperature needed e.g. 22°C. I will then quickly take the flask off the tripod and place it on a flat surface with the printed-paper underneath. I would have to do this quickly so no heat is lost. As soon as the printed-paper is underneath the flask I will pour 10cm³ of dilute hydrochloric acid into the flask and then start the timer. As soon as the solution reacts I will no longer be able to see the printed-paper, so I stop the clock, and record my results. I repeat this about 5 times, each time I start with new un-heated solution and heat it a bit higher than the previous solution.

The safety precautions that I will take are:

Wear safety goggles when near solution
Keep the solution in a flask
Dispose of the solutions safely

I plan to make my experiment a fair test by:

Using the same volume of both solutions.
Using the same concentration for all experiments.
I will only ever change the temperature.
Using the same printed paper
Start the clock as soon as the acid is poured into the flask

Predictions

I predict that the higher the temperature the faster the solution will react so for example when the solution is at 30°C it will take 20 seconds for the solutions to react, and when the solution is at 40°C it will take 10 seconds for the solutions to react. I predict this because I know that when a solution is at a high temperature it’s particles move faster causing the solution to react quicker.

Analysis

On my results when the temperature is at 22°C the two solutions take 39 seconds to react and make the solution cloudy. This shows that the higher the temperature the faster the chemicals react. This rise in temperature causes the two solutions to react quicker because; reactions only happen if the particles collide with sufficient energy. At a high temperature there will be more particles colliding with enough energy to make the reaction happen. This initial energy is known as the activation energy, and it’s needed to break the initial bonds.

Here are my results:

If I compare my results with my predictions I will find that I was generally right, the higher the temperature of the solution is the faster it reacts.

I did my experiments a second time so I can see if they are accurate, and also so I can calculate the average. On the first experiment the solution took 31 seconds to go cloudy, and on the second experiment it took a lot longer at 37 seconds. I repeated this experiment at the same temperature a third time so I could see which experiment was correct.

Rate

The rate is twice as fast by every 10°C, so it takes half the time each 10°C. Hence if you increase a solution by 10°C it will react twice as fast as it would of 10°C lower.

Therefore double the molecules double the speed in which it takes react.

Evaluation

I think my results are reliable and accurate because the second results were very much the same. However one of my results was anomalous, which I believe was due to faults in the reading, for example maybe I set the time wrong. I also may have got the quantities of hydrochloric acid or Sodium Thiosulphate wrong.

To improve my accuracy measure of Sodium Thiosulphate or hydrochloric acid, instead of pouring the solutions into a measuring flask. To make my experiment even more accurate I could have checked the conditions in which I was doing the experiment. Some things that could of affected the speeds of my experiment are:

Room temperature ~ If I did my experiment in a hot room temperature the solution would take longer to cool down, than if it was in a cool room temperature. So I need to make sure the room temperature is the same for every experiment.

Amount of Sodium Thiosulphate/Hydrochloric acid ~ There may have been inaccurate measurements of the solutions, so this wouldn’t of been a fair test. If there was more acid the reaction would of happened quicker. I could use burettes or pipettes to measure more accurately, and get the same amount for each experiment.

Time ~ The time between heating the solution and pouring it in to the flask, and starting the time maybe different for each experiment, thus making it an unfair test. To overcome this problem, I could have made sure the room temperature was the same at every reading, also I could have had a set time between removing the Bunsen, and starting the timer e.g. 5 seconds.

Overall the experiment I did proved that increasing the temperature speeds up reactions. I have learnt to be more accurate with experiments and plan them out carefully thinking about every aspect.