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chemistry

How to solve the problems of avogadro constant????
Here is one problem of mine:
Calculate the total number of atoms in 8.5g of CH2Cl2. Molar mass of CH2Cl2 is 85 g/mol
Avogadro constant 6.0*10^23

Reply 1

nyxnko_

the equation for avogadro's constant is

number of moles \times avogadro constant = number of molecules/atoms

so you can calculate the number of moles coz you've got the mass (8.5g) and you've got the molar mass (85g/mol)
then just sub it into the equation and you're good :smile:

Spoiler

Reply 2

madmahin

Thx,
So you wanted to say that we need to multiply moles with avogadro constant which is equal to number of molecules divided by atoms.

Reply 3

nyxnko_

Original post by madmahin

Thx,
So you wanted to say that we need to multiply moles with avogadro constant which is equal to number of molecules divided by atoms.

no, it's equal to the number of molecules OR atoms

Reply 4

madmahin

Answer is not matching

Reply 5

nyxnko_

you have to go through a step first using the
mass = Mr x moles
equation first. you have the mass (8.5g) and you have the Mr/molar mass (85) so in order to find the number of moles, you'll have to divide the mass by the Mr.
then you multiply by Avogadro's constant to find the number of molecules or atoms.

Reply 6

lordmasterlu

So Avogadro's constant is the number of atoms or molecules in 1 mole of substance. If you have 2 moles of substance, the number of atoms you have would be double Avogadro's constant --> #moles * Avogadro's constant = # of atoms or # of molecules

First you gotta determine the number of moles you have of CH2Cl2: so (8.5g)/(85g/mol) = 0.1mol
Then multiply your answer by Avogadro's constant: 0.1 * 6.022*10^23 = 6.022*10^22 molecules in 8.5g of CH2Cl2

Hope that helps :smile:

Reply 7

Pigster

Original post by lordmasterlu

= 6.022*10^22 molecules in 8.5g of CH2Cl2

The OP asked about the number of atoms in 8.5 g, NOT the number of molecules.

There are 5 atoms (1xC, 2xH & 2xCl) in each molecule of CH2Cl2, hence there will be 5 x 6.02x10²³.

Reply 8

lordmasterlu

Original post by Pigster

The OP asked about the number of atoms in 8.5 g, NOT the number of molecules.

There are 5 atoms (1xC, 2xH & 2xCl) in each molecule of CH2Cl2, hence there will be 5 x 6.02x10²³.

Oops you're right, my bad :smile:

(edited 6 years ago)

Reply 9

alow

Original post by nyxnko_

the equation for avogadro's constant is

number of moles \times avogadro constant = number of molecules/atoms

so you can calculate the number of moles coz you've got the mass (8.5g) and you've got the molar mass (85g/mol)
then just sub it into the equation and you're good :smile:

Spoiler

The

\LaTeX

Reply 10

nyxnko_

Original post by alow

The

\LaTeX

sorry? it's really bad, isn't it?

Reply 11

alow

Original post by nyxnko_

sorry? it's really bad, isn't it?

In general when you're writing text in LaTeX it should be upright, this means on TSR you have to use \text{...}. Also to do a displayed fraction, use \dfrac{numerator}{denominator}.

Reply 12

nyxnko_

Original post by alow

In general when you're writing text in LaTeX it should be upright, this means on TSR you have to use \text{...}. Also to do a displayed fraction, use \dfrac{numerator}{denominator}.