chemistry a level partial pressure question

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hj!gz
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found a question on chemsheets that i disagree with the worked solution for. I'll upload a picture...
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hj!gz
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hj!gz
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you use algebra,
so a change in moles = -/+ x
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hj!gz
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hj!gz
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that's their markscheme!

i get x = 0.025 instead, with a different method
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harleyh4
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I agree with the worked solution. It doesn't give the moles of each substance but A = 0.278, B = 0.278 and C = 0.444.

Chemsheets is notorious for having wrong questions, wrong answers, etc. so I may have done something wrong
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hj!gz
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i don't agree with their use of algebra
that's mathematically incorrect, to completely square root like that, I think!

i created a quadratic equation, even though it says you don't need to, and i solved it for 0.022
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harleyh4
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(Original post by hj!gz)
i don't agree with their use of algebra
that's mathematically incorrect, to completely square root like that, I think!

i created a quadratic equation, even though it says you don't need to, and i solved it for 0.022
Nah that is mathematically correct. e.g. if you were square rooting 4/9 you would get 2/3.
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harleyh4
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I did it again with a quadratic and got 0.22

End up with the quadratic 1.45x^2 + 2.55x - 0.6375 = 0. Put it into my calculator and got the 0.22. I still think the worked answer is right, regardless of method.
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charco
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(Original post by hj!gz)
i don't agree with their use of algebra
that's mathematically incorrect, to completely square root like that, I think!

i created a quadratic equation, even though it says you don't need to, and i solved it for 0.022
16 = 64/4

square root both sides

4 = 8/2
------------------------------------------
4 = 144/36

square root both sides

2 = 12/6
------------------------------------------
it's not mathematically incorrect
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hj!gz
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nvm, might just be my own mistake

thank you, both of you!
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