# Help please!! I got a test today on Moles.. 😖

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#1
In the mark scheme, for Q3 part (a)(v) why did they multiply by 10 x 40. I've seen them using 10x40 in similar questions like this one and idk why :/ i know they are multiplying to get the concentration of ethanol but why 10x40 like where did the 10 and 40 come from? can someone please explain me
Last edited by Aleksander Krol; 1 month ago
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#2
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1 month ago
#3
i think its because concentration has to be moles per dm3 so you have to find out the number of moles in 1000 cm3. They've multiplied it by 10 and 40 to scale up the number of moles to 1000 cm3- beforehand they had worked out the number of moles in 2.5 cm3 (I think), so multiplying it by 10 and 40 finds the number of moles in 1000cm3.
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1 month ago
#4
(Original post by strawberrygemini)
i think its because concentration has to be moles per dm3 so you have to find out the number of moles in 1000 cm3. They've multiplied it by 10 and 40 to scale up the number of moles to 1000 cm3- beforehand they had worked out the number of moles in 2.5 cm3 (I think), so multiplying it by 10 and 40 finds the number of moles in 1000cm3.
Yeah this is it
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#5
(Original post by strawberrygemini)
i think its because concentration has to be moles per dm3 so you have to find out the number of moles in 1000 cm3. They've multiplied it by 10 and 40 to scale up the number of moles to 1000 cm3- beforehand they had worked out the number of moles in 2.5 cm3 (I think), so multiplying it by 10 and 40 finds the number of moles in 1000cm3.
omg really i appreciate your reply you're a life saver thanks again btw❤️✨
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