Mandatory Student Experiment No. 14A
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What is studied in this experiment?
The effect of concentration on the reaction rate using sodium thiosulfate solution and hydrochloric acid
Describe the 7 steps of this experiment
• A conical flask is placed on a sheet of white paper which has been marked with an ‘X’ • 100 cm cubed of a 0.1 M sodium thiosulfate solution is added to the conical flask • 10 cm cubed of 3M hydrochloric acid is added to the conical flask of sodium thiosulfate solution and is swirled • A stopclock is started • The clock is stopped once the X can no longer be seen through the solution and record your results • Calculate the the rate as the inverse of time (1/time) • Repeat the experiment using 80, 60, 40 and 20 cm cubed of sodium thiosulfate made up to 100 cm cubed with deionised water
What is the conical flask placed on during this experiment?
It is placed on a sheet of paper marked with a cross
What M of sodium thiosulfate solution is used in this experiment?
0.1 M
How much 0.1 M sodium thiosulfate solution is placed into the conical flask during the first round of the experiment?
100 cm cubed is added
What M of hydrochloric acid is used in this experiment?
3 M
How much hydrochloric acid is used in each run of this experiment?
10 cm cubed is used
What is immediately done when the acid has been added to the sodium thiosulfate solution?
The conical flask is swirled A stopclock is started The flask is placed on top of the cross
When is the reaction considered to be over?
When the cross is no longer visible through the solution
How does one calculate the rate as the inverse of time?
1/time
Why does the solution become milky or change from colourless to a creamy yellow colour?
As sulfur is created during this reaction which does not dissolve in water and instead remains in suspension in the water
What colour change occurs in this experiment?
Colourless to a creamy yellow colour / solution becomes milky
What type of graph is obtained when the rate as the inverse of time (1/time) is plotted against the concentration of sodium thiosulfate?
A straight line graph is obtained which passed through the origin