# A-level chemisty : moles! i need some serious help :(Watch

Thread starter 8 years ago
#1
i have a question : calculate the number of atoms of O2 in 0.37 mol of KMnO4??

so far i have done: 6.02x10^23 x 0.37... but now what? do i multiply by 4??

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8 years ago
#2
Wrong forum. Try here:

http://www.thestudentroom.co.uk/forumdisplay.php?f=130
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8 years ago
#3
Shouldn't the question be asking for the number of molecules of O2?
Anyway, in each mole of the KMnO4, there are two moles of O2, shown by the "O4" in the molecular formula. So, in 0.37 moles of KMnO4, there'll be 0.37 x 2 = 0.74 moles of O2. Then just multiply that by Avogradro's constant, and you've got the number of molecules of O2.
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Thread starter 8 years ago
#4
so if the question had the formula KMnO2 for example, i wouldnt have to times by 2?
and sorry if this is the wrong forum, i literally just joined and have no idea what im doing, but thanks for directing me the right way
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8 years ago
#5
(Original post by emily00flowerpot)
so if the question had the formula KMnO2 for example, i wouldnt have to times by 2?
and sorry if this is the wrong forum, i literally just joined and have no idea what im doing, but thanks for directing me the right way
No; that'd mean that, in every mole of KMnO2, there was 1 mole of O2; so in 0.37 moles of KMnO2, then there'd be 0.37 moles of O2, due to the 1:1 ratio.
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Thread starter 8 years ago
#6
(Original post by Revolution is my Name)
No; that'd mean that, in every mole of KMnO2, there was 1 mole of O2; so in 0.37 moles of KMnO2, then there'd be 0.37 moles of O2, due to the 1:1 ratio.
so i go by the molar ratio?
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8 years ago
#7
(Original post by emily00flowerpot)
so i go by the molar ratio?
Well, yes, how many moles of the substance being asked about are in each mole of the substance you're being given information about, which is the only way to do it really.
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Thread starter 8 years ago
#8
(Original post by Revolution is my Name)
Well, yes, how many moles of the substance being asked about are in each mole of the substance you're being given information about, which is the only way to do it really.
ahh thank you so much
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