3.2.4Physical Chemistry
Practical: Effect of Surface Area on Rate of Reaction — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 7 parts Lesson 12 of 19
Part 1 of 5Aim and variables
Aim
- Aim To find out how changing the surface area of calcium carbonate affects its rate of reaction with dilute hydrochloric acid.
Variables
- Variables Independent variable: the size of the marble chips (large, medium, small or powder).
- Dependent variablethe volume of carbon dioxide produced in a fixed time, for example 30 seconds.
Control variables
- Control variables Keep constant the mass of marble, the volume and concentration of acid, the temperature and the apparatus used.
Part 2 of 5Method
1
Measure a fixed volume of dilute hydrochloric acid with a measuring cylinder and pour it into a conical flask.
2
Fill a measuring cylinder with water, invert it in a trough of water and connect it to the flask with a delivery tube.
3
Weigh a fixed mass of marble chips of one size, drop them into the acid and immediately close the bung. Start the stopwatch.
4
Read the volume of carbon dioxide collected in the measuring cylinder after 30 seconds.
5
Repeat with the same mass of chips of a different size, using fresh acid each time, and repeat each size at least twice to find a mean.
Part 3 of 5The reaction and what to expect
1Equation
- Equation CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
2Smaller pieces
- Smaller pieces Crushing the marble into smaller pieces increases the total surface area of the same mass.
3More exposed particles
- More exposed particles More calcium carbonate particles can be hit by acid particles at the same time.
4Faster rate
- Faster rate Collisions are more frequent, so more gas is collected in 30 seconds.
Part 4 of 5Recording and processing results
| Size of marble chip | Volume of gas in 30 s (cm3), run 1 | Run 2 | Mean (cm3) |
|---|---|---|---|
| Large | |||
| Medium | |||
| Small | |||
| Powder |
Part 5 of 5Conclusion, safety and improvements
Surface area and rate
Conclusion
- Conclusion The smaller the pieces, the larger the surface area and the faster the reaction.
- This is because more particles of marble are exposed to the acid, giving more frequent successful collisions.
Safety
- Safety Wear eye protection.
- Dilute hydrochloric acid is an irritant, so wipe up any spills and avoid pushing the bung in hard.
Improvements
- Improvements Use a gas syringe for more precise readings, take volume readings at regular intervals to plot a graph, and work out the rate in cm3/s.
Sources of error
- Sources of error Some gas may escape before the bung is fitted, and carbon dioxide dissolves slightly in water, so volumes can be a little low.
Key terms
| Term | Meaning |
|---|---|
| Surface area | The total area of the outer surface of a solid that is exposed to a reactant. |
| Independent variable | The variable you deliberately change. |
| Dependent variable | The variable you measure as the outcome. |
| Control variable | A factor kept the same so the test is fair. |
| Rate of reaction | How quickly reactants are used up or products are formed. |
Avoid these mistakes
1
Using the same size of chips but different masses. Mass of marble must be kept constant while size changes.
2
Saying smaller chips 'have more surface' without explaining it is the surface area of the same mass, which leads to more collisions per second.
3
Starting the timer late. Start the stopwatch as the chips go in and the bung is closed.
4
Reusing acid from the previous run, which has lower concentration.
5
Writing that smaller chips make the reaction produce more gas overall. The final volume is the same; it is just reached sooner.
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