RATES OF REACTION - CONCENTRATION / PRESSURE

Joanna investigates the reaction between sodium thiosulphate and hydrochloric acid.

A pale yellow solid is made during the reaction.

Look at the diagram.

Joanna looks down at the cross. As the pale yellow solid is made, the liquid in the beaker gets cloudy.

After a time she cannot see the cross.

She records the time taken for cross to disappear in seconds .

She does the experiment five times.

She uses five different concentrations of sodium thiosulphate solution (A, B, C, D and E).

All the experiments are carried out at 20 oC.

The table shows Joanna's results.

concentration
taken for cross to disappear in seconds
A
142
B
55
C
124
D
63
E
13

  1. Look at the table.
    1. Which concentration of sodium thiosulphate gave the slowest reaction?
    2. Choose from A, B, C, D or E. [1]
    3. Which is the most concentrated solution of sodium thiosulphate?
    4. Choose from A, B, C, D or E. Explain your answer. [2]
  2. Changing the concentration changes the speed of the reaction. Mention two other ways of speeding up this reaction. [2]
  3. Look at the equation for the reaction.
    sodium thiosulphate
    		 +
    hydrochloric acid
    sodium chloride
    		 +
    sulphur dioxide
    		 +
    sulphur
    		+
    water
  4. Write down the name of
    1. one reactant. [1]
    2. the yellow solid made in this reaction? [1]
    3. the gas produced in this reaction [1]
  5. Eventually the reaction will stop. Explain why. [1]
  6. This reaction happens quite slowly. Other reactions go much much faster. Write down one very very fast reaction. [1]

I