What Happens in Reaction?

Reaction of nitric acid and sodium thiosulphate - The reaction ...

A Reaction

The exact same question is to be found on this link

http://www.thestudentroom.co.uk/showthread.php?t=378508

And taken from another site.

The reaction between nitric acid and sodium thiosulphate

Nitric acid reacts with sodium thiosulphate solution according to the following equation:

2H+(aq) + S2O3

2-(aq) % S(s) + H2O(l) + SO2(aq)

The sulphur dioxide remains in solution and the insoluble sulphur causes the solution to become opaque. The initial

rate of reaction can be determined by measuring the time taken for enough sulphur to be produced that it obscures

a cross drawn on a piece of paper placed below the reaction vessel.

Requirements

1.0M sodium thiosulphate solution

0.1M nitric acid

distilled water

3 burettes and funnels

150cm3 beaker

test tube

stopclock

cross drawn on a piece of paper

Safety

Lab coats and safety glasses

should be worn

Procedure

a) Using a burette, add 2.0cm3 of sodium thiosulphate solution to the

beaker

b) Using another burette, add 8.0cm3 of distilled water to the same beaker

c) Using a third burette, add 10.0cm3 of nitric acid to a test tube

d) Start a stopclock as you add the nitric acid from the test tube to the

beaker

e) Swirl the beaker gently to mix the contents and place over the cross

f) Note the time taken for the cross to be obscured by the precipitate of

sulphur

g) Repeat for different quantities of each solution as shown in the results

table

Results

Volume (cm3)

Experiment

1.0M Na2S2O3 0.1M HNO3 H2O

Time, t, for cross

to be obscured (s)

Rate of reaction,

1/t (s-1)

1 2.0 10.0 8.0

2 4.0 10.0 6.0

3 6.0 10.0 4.0

4 8.0 10.0 2.0

5 10.0 10.0 0.0

6 6.0 6.0 8.0

7 6.0 8.0 6.0

8 (same as 3) 6.0 10.0 4.0

9 6.0 12.0 2.0

10 6.0 14.0 0.0

Analysis

1. Plot a graph of t-1 on the vertical axis against the volume of sodium thiosulphate solution (which is directly

proportional to [S2O3

2-] as the total volume is 20cm3 in each case) on the horizontal axis for experiment 1-5

and then plot another graph of rate of reaction against the volume of nitric acid (which is directly proportional

to [H+]) for experiments 6-10.

2. Inspect your graphs and use them to deduce, with explanations,

a) the order of reaction with respect to thiosulphate ions

b) the order of reaction with respect to H+

c) the overall order of the reaction

3. Write an expression for the rate equation for this reaction.

4. What does this suggest about the rate-determining step of the reaction?

5. Comment on the accuracy of your experiment and the reliability of your conclusi