A chemist investigates the rate of reaction of four different magnesium pellets with dilute sulfuric acid. Each pellet has a different surface area.
They add each pellet to 30 cm330\text{ cm}^330 cm3 of dilute sulfuric acid and measure the time taken for the pellet to completely react (dissolve). The table shows their results.
| Pellet | Surface area of pellet (cm2\text{cm}^2cm2) | Volume of pellet (cm3\text{cm}^3cm3) | Surface area to volume ratio | Time taken to completely react (seconds) |
|---|---|---|---|---|
| P | 2.4 | 0.5 | 4.8 : 1 | 140 |
| Q | 2.7 | 0.6 | 155 | |
| R | 3.6 | 0.4 | 9.0 : 1 | 75 |
| S | 4.0 | 0.4 | 10.0 : 1 |
Calculate the surface area to volume ratio of pellet Q.
Surface area to volume ratio = __________ : 1
Complete the sentence to describe the relationship between the surface area to volume ratio and the time taken to completely react.
As the surface area to volume ratio __________, the pellet will take __________ time to completely react.
The chemist thinks that pellet S will react the slowest in the acid. Explain why the chemist is incorrect.
The chemist performs paper chromatography on solutions of compounds extracted from the reaction mixtures.
The spots on the chromatogram are colourless. State one method the chemist could use to make the spots visible.
After using a method to see the spots, the chromatogram for Sample Y is shown below.
Calculate the RfR_fRf value for the spot seen from Sample Y.
RfR_fRf value = __________
Controlling reactions Questions
Practise OCR GCSE Chemistry Controlling reactions with exam-style questions for Foundation and Higher tier. 56 questions, matched to the OCR GCSE Chemistry (J248) specification and written in Paper 1 and Paper 2 (Foundation Tier) or Paper 3 and Paper 4 (Higher Tier) style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.