O-LevelChemistryStoichiometry5070/41 · May/June 2023 · Q46 Marks

Baking powder is used to make cakes rise. When water is added to baking powder, carbon dioxide gas is released. The longer the baking powder is stored, the less carbon dioxide it releases when water is added. Plan an investigation to show which of two different samples of baking powder has been stored for longer. Your plan should include the use of common laboratory apparatus, the two samples of baking powder and water. No other chemicals should be used. Your plan should include: • the apparatus needed • the method to use • the measurements to take • the variables to control • how to use the results to determine which sample has been stored for longer. You may draw a diagram to help you answer the question.

(a)Baking powder is used to make cakes rise. When water is added to baking powder, carbon dioxide gas is released. The longer the baking powder is stored, the less carbon dioxide it releases when water is added. Plan an investigation to show which of two different samples of baking powder has been stored for longer. Your plan should include the use of common laboratory apparatus, the two samples of baking powder and water. No other chemicals should be used. Your plan should include: • the apparatus needed • the method to use • the measurements to take • the variables to control • how to use the results to determine which sample has been stored for longer. You may draw a diagram to help you answer the question.[6]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] (1) Apparatus • Balance
[1] (1) Apparatus • Test-tube / conical flask / beaker to hold sample and water
[1] (1) Apparatus • Equipment to measure volume of gas etc. e.g. measuring cylinder with water trough / gas syringe
[1] (2) Method and Measurements • Measures a mass / amount of a sample
[1] (2) Method and Measurements • Adds (excess) water
[1] (2) Method and Measurements • Reweighs or measures volume of gas produced / counts bubbles / measures time to turn limewater milky / (IGNORE one which goes milkier)
[1] (3) Control • Same mass of each sample / amount / volume OR calculate change in mass / volume produced per gram OR same surface area of baking powder
[1] (3) Control • Same temperature
[1] (3) Control • Measure total volume of gas produced when no further change / Measure volume of gas produced in a fixed time / Measure time taken to produce a fixed volume of gas
[1] (4) Use of results • Sample that produces more gas / loses more mass (weight) / has more bubbles / has less time to turn milky / is milker is stored for less time or vice versa

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.