How to find moles from mass?

Let us consider this definition :

1 mole of a substance can be defined as relative atomic or mollecular mass expressed in grams. it is at the S.I unit for amount of substance

In the light of this definition,

Mole = given mass of substance ÷ atomic mass (in grams)

Now, condisering this Question,

Find No. Of moles in 100 g of NaCl.

Firstly molar mass of NaCl =23+35.5=58.5

Now using the formula,

Moles = 100÷58.5

Moles = 1.71

Simply, 100g of NaCl is equal to 1.71 moles of NaCl.

Ex.2= Moles in 36 g of Carbon,

Since C = 12,

Moles = 36÷12

Moles = 3.

36g of carbon have 3 moles.

Hope you understood

To find the number of moles you have you understand what element you are looking at.

Lets say we are given 2 grams of NaCl,

1. First find the molar mass of NaCl (58.44 g/mol)

2. Now set up the equation 2 grams NaCl * (1 mole of NaCl / 58.44 grams) = moles of NaCl; then simple math, 2 times 1, divided by 58.44 grams

3. The moles for this example would be 0.0342 moles of NaCl

The equation : number of moles = mass of element being looked at ÷ mass of the element on the periodic table

Actual form of equation : n= m ÷ M