RP: Rates of reactions

Question 1

What are the chemicals involved in the “disappearing cross” experiment?

Answer 1

• sodium thiosulfate solution + hydrochloric acid –> sulphur (is one of products.)
• SULPHUR turns the solution cloudy when reaction is complete!

Question 2

What are the 8 steps in “the disappearing cross” experiment?

Answer 2

1.) Use measuring cylinder to measure 10cm³ of sodium thiosulfate solution into a conical flask.
2.) Place the conical flask onto a printed black cross.
3.) Add 10cm³ of hydrochloric acid to the conical flask.
4.) Swirl the solution and start a stopwatch.
5.) Look down through the top of the conical flask.
6.) Stop the stopwatch when you can longer see the black cross.

Repeat the experiment with lower cocnentrations of sodium thiosulfate solution.

Repeat the whole experiment and calculate mean values for different concentrations of sodium thiosulfate.

Question 3

What is the issue with “the disappearing cross” experiment?

Answer 3

• Experiment may not be reproducible.
• As people have different eyesight, so some people may see the black cross for longer than others.
• BY USING THE SAME SIZE BLACK CROSS WE REDUCE THIS ISSUE.

Question 4

What is the method for investigating how different concentrations of reactants affect the volume of gas produced?

Answer 4

1.) Place 50cm³ of hydrochloric acid into a conical flask.
2.) Attach the conical flask to a bung that is attached to a gas syringe.
3.) Add a strip of magnesium to the conical flask and start a stopwatch.
4.) Every 10 seconds, measure the volume of hydrogen produced in the gas syringe.
5.) Repeat until no more gas is given off.
6.) Repeat the experiment with different concentrations of hydrochloric acid.