Lab Report: How Concentration Affects Rates of Reaction

Decomposition of sodium thiosulphate

Aim:

The aim or purpose of this investigation is to explain how concentration affects the rate of reaction (the decomposition of sodium thiosulphate in reaction with hydrochloric).

I will now give a simple definition of what rate of reaction actually is.

Definition:

The rate of a chemical reaction is defined as the change in the concentration of one of the reactants or products in unit time.

I will now display my preliminary work.

Preliminary:

I did a preliminary (trail) test to supply a source and to give a better perspective of the real experiment I am directed to carry out which is the decomposition of sodium thiosulphate.

The table below is a set of data collected from the preliminary (trails) test I carried out.

Temperature (˚,c) Volume of sodium thiosulphate (cm³) Volume of acid (cm³) Volume of water added (cm³) Time taken for x to disappear (sec)

25 20 20 0 42

25 20 20 10 54

25 20 20 20 1:08

25 20 20 30 1:23

25 20 20 40 1:44

25 20 20 50 1:50

In my preliminary I have decided to keep the temperature at room temperature which 25˚,. I also kept the volume of sodium thiosulphate which was 20cm³. However I changed the volume of water added with intervals of 10. I predicted that as you increase the concentrations of hydrochloric acid and add it to the sodium thiosulphate the reaction will increase. By observing my table you can see that my prediction is correct as you dilute the hydrochloric acid the reaction time takes longer.

I will now discuss my variables, both dependent and independent and I will also state the reasons in why some factors need or need not be changed.

Variables:

The independent variable is a variable that you ...

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...wasn't enough to get many of the particles to activation energy levels. In addition, in the solution there were plenty of particles so concentration wasn't important.

The investigation could have been improved by testing the temperature variable on the computer as the stop watch I used could not cope with the speed of the reaction. It would also have helped to test each concentration more than once to ensure that the results were true. When using the light sensor I should have covered the underside of the sensor with black material rather than sticking on paper as this could have let in some light. In addition I should have used an artificial source of light as the natural light in the room was constantly changing as clouds pass in front of the sun. I could also have used a burette to measure out the reactants although the measuring cylinder was quite accurate.