Question

How do you calculate the moles of a substance?

Answer 1

In order to calculate the moles of a substance, you need to know the mass of the substance and its molar mass. Molar mass is the atomic weight in grams/mol. Utilize the atomic formula to locate the molar mass; to acquire the quantity of moles, partition the mass of compound by the molar mass of the compound communicated in grams

Complete step by step answer:
To calculate moles of copper sulfate, $Ca(OH)_2$ in 250.0g $Ca(OH)_2$?
Molar Mass of $CuSO_4$
Subscript x molar mass =
$1{\text{ }}*{\text{ }}40.078$ g/mol Ca = $40.078$ g/mol Ca
$1{\text{ }}*{\text{ }}1.007g$ /mol H = $1.007g$ /mol H
$2{\text{ }}x{\text{ }}15.999$ g/mol O = $31.998$ g/mol O
Total Molar mass of $Ca(OH)_2: 73.083g/mol$
1mol $Ca(OH)_2$ = 73.083g $Ca(OH)_2$ , which gives us two conversion factors:
$\dfrac{{1{\text{mol Ca}}{{\left( {OH} \right)}_2}}}{{73.083{\text{g Ca}}{{\left( {OH} \right)}_2}}}$ and $\dfrac{{73.083{\text{gCa}}{{\left( {OH} \right)}_2}}}{{1{\text{mol Ca}}{{\left( {OH} \right)}_2}}}$

Now multiply the known mass x the conversion factor with moles on top and grams on bottom. This will cancel the grams and leave the moles.

$250.0g{\text{ }}Ca{\left( {OH} \right)_2}$ x$\dfrac{{1mol{\text{Ca}}{{\left( {OH} \right)}_2}}}{{73.083g{\text{Ca}}{{\left( {OH} \right)}_2}}}$ = $\;3.42$ $mol{\text{ }}Ca{\left( {OH} \right)_2}$

Note:
The mole is spoken to by Avogadro's number, which is $6.022 \times {10^{23}}$ particles or atoms per mol.
Mole : The measure of substance of a framework that contains the same number of rudimentary elements as there are molecules in $12{\text{ }}g$ of $carbon - 12$ .
In order to calculate the molar mass of a substance you should take the approx value.
Example: -
Take molar mass of $Ca$ =$40$ g/mol in the place of $40.078$ g/mol
Take molar mass of $H$ =1 g/mol in the place of 1.007 g/mol
Take molar mass of $O$ = 16 g/mol in the place of 16 g/mol