[sueannew]

Hi, i am doing an investigation on the effect of concentration on the rate of reaction. My teacher hinted that there is another graph i can make apart from the graph showing the concentration (%) against time (s).
50cm3 of sodium thiosulphate reacts with 10cm3 of hydrocloric acid. the time is taken for the preticipate of sulphur to obscure a cross underneathe. the concentration of sodium thiosulphate is varied using distilled water in precentages.

So, i am wondering is if there is a different graph i can do (btw is it possible to measure the rate of reaction? hint from my teacher!!)
GCSE

[mike]

This depends on what you are trying to determine, reaction order, rate constant etc.

If you are trying to show that the reaction rate increases with initial concentration then maybe plot rate versus concentration. Your rate is the inverse time (1/t).

reaction orders and rate constant need some more experimental information.

[sueannew]

IS it possible to do a graph based on 1/time against concentration of thiosulphate?
If so, how do you plot it?

[sdekivit]

IS it possible to do a graph based on 1/time against concentration of thiosulphate?
If so, how do you plot it?

if the reaction is 2nd order in thiosulphate, a graph between 1/[S2O3(2-)] versus 1/t is possible.

[Borek]

if the reaction is 2nd order in thiosulphate, a graph between 1/[S2O3(2-)] versus 1/t is possible.

Graph is always possible, the question is whether it is linear.

[sdekivit]

absolutely

[sueannew]

Okay so i did another graph this time with concentration(%) on the x-axis and 1/time (s) on the y-axis.

i.e. 1/time taken for cross to disappear, so for my results e.g. i did 1/35.42 = 0.028 and plot tht on the graph.
Is that correct? I got a straight linear line.

[mike]

Cool, what does a graph of ln[concentration] (y-axis) vs ln(rate) (x-axis) look like?

ln = natural log

The slope of this graph will give you the order of the reaction with respect to the thiosulfate.

Have you written a rate equation for the reaction?

[sueannew]

No i havent Im only in yr11!

[mike]

OK then you have done well. Good work.

So what have you concluded from the experiment then? Is rate dependent on the concentration? Does your graph show that as you increase the concentration you increase the rate?

Also you could use your graph to predict what the rate of the reaction at a different concentration from the ones you did might be.

Keep up the great chemistry work!