The Rate and Extent of Chemical Change Flashcards
Explain why measuing the mass change during a reaction is the most accurate method of measuring rate.
The mass balance used is very accurate.
A student investigated the change in mass when hydrated cobalt chloride was heated. This reversible reaction produces anhydrous cobalt chloride + water.
Suggest why the test tube and contents were heated until the mass did not change. [1 mark]
Paraphrased from June 2022 paper 2 test.
Got 0/1 marks in Easter holiday.
(so that) the reaction was complete
allow (so that) no more water (vapour) was produced
A student investigated the effect of changing the concentration of sodium thiosulfate box solution on the rate of the reaction.
Apparatus used: https://cdn.discordapp.com/attachments/1062056354874937405/1225493397310148761/image.png?ex=662154aa&is=660edfaa&hm=c795dbd812417a07519dad2c8f4c4ac09d52c4e0da601d057380a134ec5ac6c4&
The percentage of light reaching the light sensor decreases by 1% when 7.1 × 10−5 moles of sulfur is produced.
Determine the rate of reaction in mol/s for the production of sulfur at 30 seconds.
You should draw a tangent on Figure 7. [5 marks]
Figure 7: https://cdn.discordapp.com/attachments/1062056354874937405/1225492778264559636/image.png?ex=66215416&is=660edf16&hm=e22e9c56e1c69ac13855958a1b1dac6340cfb7e77b112a7feb0c7dd8b3970735&
Got 5/5 marks with an unconventional method in the Easter holidays.
- correctly drawn tangent at 30 s
- correct values for x step and y step from tangent
- (ratio =) value for y step / value for x step
- correct calculation of ratio
- (conversion rate = ratio × 7.1 × 10-5)
correct evaluation of rate (mol/s)
