Rate Of Reaction In Sodium Thiosulphate And

HCl Essay, Research Paper

Plan We

must produce a piece of coursework investigating the rates of reaction, and the

effect different changes have on them. 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 is five factors which 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

catalysts. I have chosen to investigate the effect temperature and

concentration have on a reaction. This is because they are the most practical

to investigate . it would take longer to prepare a solid in powdered and

unpowdered form, and it is difficult to get accurate readings due to the

inevitabilities of human errors, and as gas is mostly colourless it is difficult

to gauge a reaction changing the pressure, and if a substance is added to give

the gas colour, it may influence the outcome of the experiment. Similarly the

use of a catalyst complicates things, and if used incorrectly could alter the

outcome of the experiment.

Aim: –

To see the effects of a change in temperature and concentration on the rate of

a reaction. The reaction that will be used is:

Sodium Thiosulphate + Hydrochloric Acid

Na2S2O3 (aq) + 2HCl (aq)

Sodium Chloride + Water + Sulphur Dioxide +

2NaCl (aq) + H2O (l) + SO2 (g) +

Sulphur

S (s)

Two series of experiments will be carried out . one changing the temperature

(while everything else remains constant) and one varying the concentration

(while keeping everything else constant). Both the sodium thiosulphate and the

Hydrochloric acid are soluble in water, so the concentration of either can be

changed. However I have chosen to vary the sodium thiosulphate as it is

available in larger amounts, and various concentrations are prepared. When the

temperature is constant room temperature will be used as the temperature as it

more practical and will not need to be monitored. When the temperature is being

varied a water bath will be used to heat up the acid and thiosulphate to the

necessary temperature.

I decided which temperatures and concentrations to use during my preliminary

series of experiments .

1 mol/dm3 of HCl (acid concentration will be fixed)

10-35g/dm3 of sodium thiosulphate (all of these concentrations will be tested

in turn going up in steps of 5g/dm3)

20-70°C temperature (all of these temperatures will be used going up in steps

of 10°C)

Concentrations of 5, and 40 g/dm3 of thiosulphate were available to me but my

preliminary work showed that the 5 g/dm3 and 40g/dm3 were too slow and fast

respectively in reacting to be worth testing. Similarly any temperature below

20°C reacted too slowly, and 80°C and 90°C reacted too quickly to be worth

including in my final results.

Using my preliminary experiments I decided on using the following apparatus:

1 thermometer

1 beaker

2 measuring cylinders

1 conical flask

1 tripod

1 gauze

1 heatproof mat

1 stopwatch

1 Bunsen burner

X board

1 pair of tongs

1 pair of goggles

1 apron

Method: –

Experiment 1 – Changing the concentration

5 cm3 of HCl (at concentration 1 mol./dm3) and 15 cm3 of sodium thiosulphate

(at varying concentrations . 10 to 35 g/dm3) are poured out into two measuring

cylinders and then poured into a conical flask, which is placed on top of a

board marked with letter X. The stopwatch will now be started. When the mixture

has turned sufficiently cloudy so that the letter X can no longer be seen the

stopwatch will be stopped and the time will be recorded. The experiment is

repeated with all the concentrations. The whole procedure is then repeated.

Experiment 2 . Changing the temperature

5 cm of HCl (at concentration 1 mol./dm3) and 15 cm of sodium thiosulphate (at

varying concentrations . 10 to 35 g/dm3) are poured out into two measuring

cylinders. A beaker is half filled with hot water from a tap. The water is

placed on top of a Bunsen on a blue flame and the two measuring placed inside

the water bath. The water is heated to the necessary temperature (30°C to 70°C)

then the two measuring cylinders are taken out and the contents of both are

poured into a conical cylinder. The time it takes for the X to disappear is

timed and recorded. The experiment is repeated using all the temperatures. The

entire procedure is the repeated.

Repeat results and averages will be taken to improve the credibility of the

findings, and present solid grounding for the final conclusion. The repeat

results will help to iron out any anomalies and the average will g

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