Defence11
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Hi I do not get the mark scheme in question 7.7
Question paper http://filestore.aqa.org.uk/resource...84621H-SQP.PDF
Mark scheme http://filestore.aqa.org.uk/resource...84621H-SMS.PDF
Pls explain. Thanks
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Gurdeepthelegend
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#2
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It’s right. Co2 should be collected at the end
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Defence11
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(Original post by Gurdeepthelegend)
It’s right. Co2 should be collected at the end
How does that answer the question
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KR1282
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i think what the mark scheme is saying is that the only thing left at the end of the experiment will be the co2 so it doesn't matter how much air is collected and the amount of air collected will not affect the volume of co2 collected therefore student 2 is correct coz air being collected doesn't affect the amount of co2

i think that makes sense
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BlueCactus16
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basically at the start of each different mass of sodium carbonate, the first few bubbles of gas are air. The mark scheme is saying this doesn't matter because if you look at the end of each mass reacting with acid, not all the carbon dioxide makes it to the measuring cylinder. So the 'extra' air you collected at the beginning basically represents the actual carbon dioxide you lack at the end, as the actual carbon dioxide stays in the flask (only at the end) so these equal each other. Thats why the mark scheme says 'displaced'. hope this helps
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BlueCactus16
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(Original post by KR1282)
i think what the mark scheme is saying is that the only thing left at the end of the experiment will be the co2 so it doesn't matter how much air is collected and the amount of air collected will not affect the volume of co2 collected therefore student 2 is correct coz air being collected doesn't affect the amount of co2

i think that makes sense
no thats not right because the air that isn't carbon dioxide will still contribute to the volume measured. there is nothing outlined in the method which tests for carbon dioxide etc, they just measure what goes through the bung from the flask.
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KR1282
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ok
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BlueCactus16
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(Original post by Defence11)
Hi I do not get the mark scheme in question 7.7
Question paper http://filestore.aqa.org.uk/resource...84621H-SQP.PDF
Mark scheme http://filestore.aqa.org.uk/resource...84621H-SMS.PDF
Pls explain. Thanks
wait why r u going through a paper 1 wth
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Defence11
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(Original post by BlueCactus16)
wait why r u going through a paper 1 wth
What do u mean
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Defence11
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(Original post by BlueCactus16)
basically at the start of each different mass of sodium carbonate, the first few bubbles of gas are air. The mark scheme is saying this doesn't matter because if you look at the end of each mass reacting with acid, not all the carbon dioxide makes it to the measuring cylinder. So the 'extra' air you collected at the beginning basically represents the actual carbon dioxide you lack at the end, as the actual carbon dioxide stays in the flask (only at the end) so these equal each other. Thats why the mark scheme says 'displaced'. hope this helps
How do u know that not all the carbon dioxide makes it to the measuring cylinder
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BlueCactus16
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have u not done ur paper 1 already, we only have paper 2 left and they have different topics
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Defence11
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(Original post by BlueCactus16)
have u not done ur paper 1 already, we only have paper 2 left and they have different topics
Bro I’m in year 10 and I have a paper 1 mock. Any good luck for ur GCSEs. Also pls reply to my question
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Defence11
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(Original post by Defence11)
Hi I do not get the mark scheme in question 7.7
Question paper http://filestore.aqa.org.uk/resource...84621H-SQP.PDF
Mark scheme http://filestore.aqa.org.uk/resource...84621H-SMS.PDF
Pls explain. Thanks
I don’t understand what it means by there was co2 left in the flask at the end
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BlueCactus16
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(Original post by Defence11)
How do u know that not all the carbon dioxide makes it to the measuring cylinder
thats exactly what the first line of markscheme says "carbon dioxide is left in flask at end". remember the flask is where the reaction takes place.
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BlueCactus16
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(Original post by Defence11)
I don’t understand what it means by there was co2 left in the flask at the end
so yk how a new reaction takes place with each new mass of sodium carbonate right. But when each reaction comes to an end, a tiny amount of CO2 gets left in the flask and doesn't make it through the bung, only coz its a small amount.
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BlueCactus16
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(Original post by Defence11)
Bro I’m in year 10 and I have a paper 1 mock. Any good luck for ur GCSEs. Also pls reply to my question
ohh okay and thanks ps im a girl not ur bro aha
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Defence11
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(Original post by BlueCactus16)
so yk how a new reaction takes place with each new mass of sodium carbonate right. But when each reaction comes to an end, a tiny amount of CO2 gets left in the flask and doesn't make it through the bung, only coz its a small amount.
So what if co2 is left in the flask. What does that do
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BlueCactus16
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(Original post by Defence11)
So what if co2 is left in the flask. What does that do
LOOK AT THE APPARATUS WHILE U READ THIS - and read a few times lol

co2 is what we're actually measuring, and the place we measure from is the measuring cylinder, so we would want all the co2 to travel through the tube into the cylinder. however at the end a small amount of co2 is uncontrollably left in the flask, and doesn't actually travel to the cylinder where we would measure it.
so the problem is that we are not able to measure all the co2 in the cylinder bc of some not even travelling to the cylinder (stays in flask). BUT this isn't an issue as the 'air' collected in the beginning has the same volume of the co2 which doesn't make it to the cylinder where we actually measure from.SOO although there is a few bubbles of air which is not co2, this is the same volume of the co2 that doesn't make it to the cylinder to get measured.
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BlueCactus16
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so u are left with an accurate volume
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Defence11
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(Original post by BlueCactus16)
LOOK AT THE APPARATUS WHILE U READ THIS - and read a few times lol

co2 is what we're actually measuring, and the place we measure from is the measuring cylinder, so we would want all the co2 to travel through the tube into the cylinder. however at the end a small amount of co2 is uncontrollably left in the flask, and doesn't actually travel to the cylinder where we would measure it.
so the problem is that we are not able to measure all the co2 in the cylinder bc of some not even travelling to the cylinder (stays in flask). BUT this isn't an issue as the 'air' collected in the beginning has the same volume of the co2 which doesn't make it to the cylinder where we actually measure from.SOO although there is a few bubbles of air which is not co2, this is the same volume of the co2 that doesn't make it to the cylinder to get measured.
Right thanks. So I kinda get it better but why is the air collected have the same volume as the co2 that is left in the flask?
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