Investigating How a Change of Concentration Affects Rate of Reaction

Investigating How a Change of Concentration Affects Rate of Reaction

Plan

In this investigation, I am changing the concentration of the sodium

thiosulphate to see whether it affects the rate of reaction between

sodium thiosulphate and hydrochloric acid. The reaction is said to

have finished, once the black cross underneath the conical flask has

disappeared. The precipitation of sulphur causes the black cross to

disappear from view. The equation below shows what will happen when

the sodium thiosulphate reacts with the hydrochloric acid in the

conical flask.

[IMAGE][IMAGE]Na2S2O3 + 2HCl S + 2NaCl + SO2 + H2O

Theory

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High Concentration

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Medium Concentration

[IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE] The theory behind this

investigation is the collision theory. If the concentration of the

thiosulphate is doubled, this means there are twice as many particles,

meaning there are twice as many collisions therefore the reaction time

is halved. The diagram below shows the collision theory.

[IMAGE][IMAGE] = Sodium thiosulphate =hydrochloric acid

Variables

There are many variables in this investigation and to make sure it is

a fair test, many of the variables must be kept the same apart from

the independent variable and the dependent variable. The concentration

of the sodium thiosulphate is an independent variable and the rate of

reaction is the dependent variable. The controls, the things that stay

the same, in this investigation are the volume of liquid in the

conical flask, 45cm3, the volume of hydrochloric acid, 5cm3, the

temperature will stay constant, the same apparatus will be used (see

list below), same person observing the black cross to see when it

disappears, which will be observed from the same height, the same

bottle of distilled water, hydrochloric acid and sodium thiosulphate

will be used.

Prediction

I predict that as the concentration of the sodium thiosulphate

increases, the rate of reaction will increase. If the concentration

increases, there are more particles, therefore there is a higher

potential for collisions brings the reaction time down.