Rates of Reactions
Rates of reactions can depend on four things:
- Temperature, concentration or pressure, catalyst, size of the particles involved or surface area.
Measuring Rates of Reactions:
1) Precipitation (when a precipitate is produced)
- Put the beaker on some paper with a mark on then time how long it takes for the solution to go cloudy enough that the mark is no longer visible (when it has made the precipitate)
2) Change in mass (gas given off)
- Put the beaker on weighing scales and record how fast the mass drops. This is the reactants reacting then turning into a gas and leaving the flask.
3) Volume of gas given off
- A glass gas syringe is used to see how much gas is given off from the reaction.
Rate of Reaction Experiments
1) Reaction of Hydrochloric Acid and Marble Chips:
- Use a glass gas syringe to collect the CO2 that is given off.
- The reaction happens more quickly if the marble chips are smaller because they have a larger surface area so more can react at one time.
2) Reaction of Magnesium with Hydrochloric Acid:
- Use a set of scales and a timer to see how quickly the reaction loses mass (gas escaping).
- The mass that is lost represents the amount of hydrogen gas that has been given off.
3) Reaction of Sodium Thiosulphate and Hydrochloric Acid:
- Both chemicals are colourless but when mixed, they produce sulphur - a precipitate.
- Use the cross on paper method to see how quickly the precipitate is produced.