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# Question on gasses (unit 5 specimen paper) Tweet

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1. Question on gasses (unit 5 specimen paper)
This question is from the specimen paper for AQA unit 5 Nuclear and Thermal Physics:

Exam paper
Mark scheme

There is 3.5x10-4 m3 of air space in the bottle and the volume of the pump chamer changes from zero at the beginning of the up-stroke to 6.5 x 10-4m3 at the end of the up-stroke. The initial pressure of the air in the bottle is that of the atmosphere with a value of 99 kPa.

Assuming the process is a constant temperature, calculate the pressure in the bottle after one up-stroke of the pump.

My calculations were as follows:

before: Pv = (99)(3.5) = 346.5

after: 346.5/(3.5+6.5) = 34.65

Pressure is 34.65 kPa.

However the mark scheme gives the answer as 83.5 KPa

Can anyone help me out?
2. Re: Question on gasses (unit 5 specimen paper)
Check your units, the volume of the pump chamber changes from zero to 6.5 x10^-5 not x10^-4. (will give correct answer)

Also, it is good practice to do these equations in SI units, (pa and m^3) rather than kpa and x10^-4 m^3. It doesn't make a difference in this case, but can give you the wrong answer if you're not careful of your units in some questions (part b for example).
Last edited by Jambre; 24-06-2011 at 20:22.
3. Re: Question on gasses (unit 5 specimen paper)
I am aware that this is an old thread, but it appears on Google and I have something to add!

It seems that old versions of the specimen paper contain an error - they have it as when the answers seems to assume it is , as is given in the corrected paper above.

I also got the answer of 35 kPa. If you've done the paper, give yourself the mark for that
4. Re: Question on gasses (unit 5 specimen paper)
(Original post by Xero Xenith)
I am aware that this is an old thread, but it appears on Google and I have something to add!

It seems that old versions of the specimen paper contain an error - they have it as when the answers seems to assume it is , as is given in the corrected paper above.

I also got the answer of 35 kPa. If you've done the paper, give yourself the mark for that
Hi, please could you tell me why you are supposed to plus the 3.5x10-4 and 6.5x10-5, I thought you would have to subtract the two? Thanks in advance!
5. Re: Question on gasses (unit 5 specimen paper)
(Original post by Topcat94)
Hi, please could you tell me why you are supposed to plus the 3.5x10-4 and 6.5x10-5, I thought you would have to subtract the two? Thanks in advance!
Adding them gives the total volume of the bottle plus pump chamber, which is the volume taken up by the gas.