AQA Chemistry exam question from AS paper 2 2021
06.2. In the second experiment, another flask is used for a combustion reaction.
Method
• Remove all the air from the flask.
• Add 0.0010 mol of 2,2,4-trimethylpentane (C8H18) to the flask.
• Add 0.0200 mol of oxygen to the flask.
• Spark the mixture to ensure complete combustion.
• Cool the mixture to the original temperature.
The equation is
C8H18(g) + 12 1
2
O2(g) ⟶ 8 CO2(g) + 9 H2O(l)
Calculate the amount, in moles, of gas in the flask after the reaction.
- I understand how to get 0.0080 moles of CO2 but I am unsure how to get the answer of 0.00155, could someone please explain the reason behind this?
Method
• Remove all the air from the flask.
• Add 0.0010 mol of 2,2,4-trimethylpentane (C8H18) to the flask.
• Add 0.0200 mol of oxygen to the flask.
• Spark the mixture to ensure complete combustion.
• Cool the mixture to the original temperature.
The equation is
C8H18(g) + 12 1
2
O2(g) ⟶ 8 CO2(g) + 9 H2O(l)
Calculate the amount, in moles, of gas in the flask after the reaction.
- I understand how to get 0.0080 moles of CO2 but I am unsure how to get the answer of 0.00155, could someone please explain the reason behind this?
Reply 1
Original post
by Slugzie(:06.2. In the second experiment, another flask is used for a combustion reaction.
Method
• Remove all the air from the flask.
• Add 0.0010 mol of 2,2,4-trimethylpentane (C8H18) to the flask.
• Add 0.0200 mol of oxygen to the flask.
• Spark the mixture to ensure complete combustion.
• Cool the mixture to the original temperature.
The equation is
C8H18(g) + 12 1
2
O2(g) ⟶ 8 CO2(g) + 9 H2O(l)
Calculate the amount, in moles, of gas in the flask after the reaction.
- I understand how to get 0.0080 moles of CO2 but I am unsure how to get the answer of 0.00155, could someone please explain the reason behind this?
Method
• Remove all the air from the flask.
• Add 0.0010 mol of 2,2,4-trimethylpentane (C8H18) to the flask.
• Add 0.0200 mol of oxygen to the flask.
• Spark the mixture to ensure complete combustion.
• Cool the mixture to the original temperature.
The equation is
C8H18(g) + 12 1
2
O2(g) ⟶ 8 CO2(g) + 9 H2O(l)
Calculate the amount, in moles, of gas in the flask after the reaction.
- I understand how to get 0.0080 moles of CO2 but I am unsure how to get the answer of 0.00155, could someone please explain the reason behind this?
You have the balanced equation:
C8H18(g) + 12.5O2(g) ⟶ 8 CO2(g) + 9 H2O(l)
You are told that there is complete combustion, i.e. the oxygen is in excess.
From the stoichiometry, 0.001 mol of 2,2,4-trimethylpentane will produce 0.008 mol of carbon dioxide (water is a liquid and can be ignored)
The oxygen needed is 0.001 x 12.5 = 0.0125
The available oxygen is 0.02, therefore there is an excess of 0.02 - 0.0125 = 0.0075 mol
Therefore the total mol present after reaction = 0.008 + 0.0075 = 0.0155 mol
Reply 2
11
Thank you I understand now
Quick Reply
Related discussions
- Chemsitry aqa gcse 2024
- 2024 A level chemistry paper
- E’s GYG Year 11 GCSES
- A-level Chemistry Study Group 2022-2023
- aqa alevel chem
- Have primrose kitten predicted papers been accurate?
- chemistry vs psychology
- v's year 11 gyg!
- How I Got an A* in (AQA) A-Level Physics With Little To No Worry: A Guide
- ppl who have bought exam predictions before, were they good?
- Do to B in 2 months. Help !!
- Eduqas A-Level Computer Science Component 1 (10th of June 2024)
- do i have enough time to get a decent grade in a-level chemistry?
- grow your grades but everyone has really cool titles but I don't :)
- Year 11 GCSE and Year 13 A-Level Request Your Exam Timetable Thread
- Psychology edexcel
- AQA Biology A2 A* Revision notes
- AQA How to revise organic?
- GCSE Exam Discussions 2025
- The GREAT GCSE Lock-in!!
Latest
Trending
Last reply 3 weeks ago
AQA A level chemistry synthetic routes map - what is the best one to memorise?Last reply 4 months ago
AQA Chemistry Electrode Potentials Conventional Representation QuestionLast reply 6 months ago
OCR B Salters A Level Chemistry 2025 Advanced ArticleLast reply 6 months ago
Help with this chemistry question? (A2, acid-base equilibria)
How The Student Room is moderated
To keep The Student Room safe for everyone, we moderate posts that are added to the site.
