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Moles help

M.M.HUSSAIN

Hi,

I have two questions, can you tell me how to answer them please by giving a method

Calculate how many atoms in 26g of Ag

Calcuate how many molecules there are in 90g of H2O

Thanks

Reply 1

AvengeNedStark

oh I was thinking this would be about the skin blemishes. I don't care about maths, carry on.

Reply 2

MM17

Use the equation No. of moles = mass in g/relative atomic (or molecular) mass (Also called molar mass).

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Reply 3

SaFa1237

Q1) 26/107.9= 0.241

0.241* (6.022*10^23) = 1.45*10^23

q2) 90/18= 5

5* 6.022*10^23 = 3.011*10^24

The equation n= m/mr
That will give you the number of moles. To then get the number of atoms/molecules, multiply by avogadro's number. This is 6.022*10^23.

Hope that helps. :smile:

(edited 10 years ago)

Reply 4

MM17

So for 26g of Ag it would be: No. of moles = 26/108 = 0.24 mols. (2dp)

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Reply 5

MM17

And for 90g of H2O it would be: No. of moles = 90/(2x1 + 16) = 90/18 = 5 mols.

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Reply 6

Veqz

Original post by MM17

So for 26g of Ag it would be: No. of moles = 26/108 = 0.24 mols. (2dp)

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And then multiply it by Avogadro's constant!

Reply 7

MM17

Yes good point, I read the question too quickly! Make sure you multiply by avogadro's constant!

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Reply 8

Dylann

Original post by Veqz

And then multiply it by Avogadro's constant!

You don't need to multiply it by Avogadro's constant. Writing "5 moles of molecules" is perfectly acceptable, as is "0.241 moles of Ag atoms".

Reply 9

Borek

Original post by Dylann

You don't need to multiply it by Avogadro's constant. Writing "5 moles of molecules" is perfectly acceptable, as is "0.241 moles of Ag atoms".

I wonder if it would get accepted by the teacher. But you are perfectly right.

Reply 10

Dylann

Original post by Borek

I wonder if it would get accepted by the teacher. But you are perfectly right.

The whole concept of moles were first created to simplify Avogadro's number, this question is a prime example of why moles are much easier to write and use than just writing the amount of atoms.