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Rate experiments: marble chips and catalysts
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Two classic practicals: marble chips with acid, and testing catalysts for hydrogen peroxide.
Marble chips and hydrochloric acid
CaCO3 + 2HCl → CaCl2 + H2O + CO2
Measure either the volume of carbon dioxide in a gas syringe, or the mass lost from a flask on a balance (with a cotton wool plug to stop acid spray).
To test surface area, use the same mass of large and small chips. To test concentration, change the acid concentration but keep its volume, the chip size and the temperature the same.
Measure either the volume of carbon dioxide in a gas syringe, or the mass lost from a flask on a balance (with a cotton wool plug to stop acid spray).
To test surface area, use the same mass of large and small chips. To test concentration, change the acid concentration but keep its volume, the chip size and the temperature the same.
Catalysts for hydrogen peroxide
2H2O2 → 2H2O + O2
Add the same mass of different solids (such as manganese(IV) oxide or copper(II) oxide) to the same volume and concentration of hydrogen peroxide.
Collect the oxygen in a gas syringe and compare the volume after a set time. The best catalyst gives the most oxygen fastest.
To show a solid is a catalyst: filter it off, dry it and weigh it. Its mass is unchanged.
Add the same mass of different solids (such as manganese(IV) oxide or copper(II) oxide) to the same volume and concentration of hydrogen peroxide.
Collect the oxygen in a gas syringe and compare the volume after a set time. The best catalyst gives the most oxygen fastest.
To show a solid is a catalyst: filter it off, dry it and weigh it. Its mass is unchanged.
Using the results
mean rate = amount of product ÷ time, such as cm3/s.
On a graph, a steeper curve means a faster rate. The curve levels off when a reactant is used up.
Smaller chips (larger surface area) and more concentrated acid both give steeper curves.
On a graph, a steeper curve means a faster rate. The curve levels off when a reactant is used up.
Smaller chips (larger surface area) and more concentrated acid both give steeper curves.
60 cm3 of oxygen is collected in 30 s. What is the mean rate?
- rate = volume ÷ time
- 60 ÷ 30
Answer: 2 cm3/s
Marble chips and hydrochloric acid: measure carbon dioxide volume or mass loss; smaller chips and stronger acid react faster. Hydrogen peroxide: compare oxygen volumes with different solids; a catalyst's mass is unchanged. Mean rate = amount ÷ time.
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