Describe the observations and inferences for a chemical reaction experiment involving sodium thiosulphate and hydrochloric acid, and explain how changes in concentration and temperature affect the rea

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• OBSERVATION: The solution gradually becomes cloudy and a cross marked below the beaker becomes invisible.
• INFERENCE: Sulfur is formed as a precipitate, indicating the progress of the reaction. The time taken for the cross to disappear is used to determine the reaction rate.

Part (i)

• OBSERVATION: Volume of sodium thiosulphate solution taken = 40 cm³
• INFERENCE: Time taken for the cross to disappear = 25 seconds (This information is already provided and correct.)

Part (ii)

• OBSERVATION: Volume of water added = 10 cm³
• INFERENCE: Concentration of thiosulphate is lower, reaction is slower. (The original inference was incorrect. Adding water dilutes the solution, decreasing the concentration and thus slowing down the reaction.)

Part (iii)

• OBSERVATION: Volume of dilute HCl added = 10 cm³
• INFERENCE: A pale yellow precipitate of sulphur is formed. (This information is already provided and correct.)

Part (iv)

• OBSERVATION: Temperature of the mixture = 30°C
• INFERENCE: Rate of reaction increases with temperature. (This information is already provided and correct.)