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The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid - page 4
Keywords: The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid
By Carlitob10 on 04/11/2006 11:57:07
Level: A Level (Year 13)
Page Number: 4 of 8 pages: 1 2 3 4 5 6 7 8the tile with an ‘X’ and place flask Y over it
5. At a convenient time pour the acid from flask X into flask Y and start the stopwatch.
6. Stir the solution well with a glass rod and watch the ‘X’ through the solution in flask Y.
7. Stop the clock when the ‘X’ on the paper just disappears.
8. Record the time in the results table.
9. Repeat the experiment twice
10. Repeat the procedure for the rest of the mixtures in the table below.
Flask X Flask Y
Volume of HCl (cm3) Volume of Na2S2O3 (cm3) Volume of water (cm3)
5 40 0
5 35 5
5 30 10
5 25 15
5 20 20
5 15 25
5 10 30
Varying the concentration of HCl:
Follow a similar procedure similar to that the first part, but keep the volume of thiosulphate solution constant at 20.0 cm3 and vary the volume of hydrochloric acid as shown in the table below.
Flask X Flask Y
Volume of HCl (cm3) Volume of Na2S2O3 (cm3) Volume of water (cm3)
25 20 0
20 20 5
15 20 10
10 20 15
5 20 20
2.5 20 22.5
1.25 20 23.75
Rate of reaction and determining orders of reaction graphically
From the results I will work out the average time for the ‘X’ to disappear for each of the concentrations of the sodium thiosulphate and hydrochloric acid. The rate of reaction for each of the concentrations will be worked out by the following equation:
Rate of reaction = 1/time
For many reactions, rate is proportional to concentration of reactants (i.e. doubling concentration doubles rate). In this experiment, 1/time is a meaningful calculation of rate because the amount of reaction is the same each time. Since 1/time is proportional to the concentrations of the reagents, it is easy to see the relationship between them two when graphs of rate of reaction against concentration are plotted.
Zero-Order Reaction:
For a zero-order reaction, the rate of reaction is a constant. When the limiting reactant is completely consumed, the reaction abruptly stops.
Rate: R= k
The rate constant, k, has units of mole L-1 sec-1.
First-Order Reaction:
For a first-order reaction, the rate of reaction is directly proportional to the concentration of one of the reactants.
Rate: R = k [A]
Second-Order Reaction:
For a second-order reaction, the rate of reaction is directly proportional to the square of the concentration of one of
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