Question

Find how many moles of atoms are there in:
i) 2 g of nitrogen. ii) 23 g of sodium iii) 40 g of calcium.
iv) 1.4 g of lithium v) 32 g of sulphur.

Answer 1

To calculate the number of moles, we use the following formula ( to find how many moles of ATOMS )
No of moles=given mass/atomic mass

(i) atomic mass of Nitrogen=14g
No. of moles = 2/14
Approximately 0.143moles of
Nitrogen (ii) atomic mass of Na = 23g
No. of moles = 23/23
= 1 mole of Na

(iii) atomic mass of Ca= 40g
No. of moles =40/40
=1 mole of Ca

(iv) atomic mass of Li = 7g
No. of moles = 1.4/7
= 0.2 moles of Li

NOTE: don't forget to mention the name of the atom with the answer when calculating the number of moles

Answer 2

We know n=w/M.

i) Atomic mass number of Nitrogen / N2 is 14.

So, the number of moles in 2g of Nitrogen is = (2 X 1) /14 = 0.14 moles.

ii) Atomic mass number of Sodium / Na is 23.

So, the number of moles in Sodium is = (23 X 1) / 23 = 1 mole.
 

iii) The atomic mass number of calcium / Ca is 40.

So, the number of moles in Ca is = (40 X 1) / 40 = 1 mole.

iv) The atomic mass number of Lithium / Li is 7.

As per question there is 1.4 g of lithium.

So, the number of moles in lithium is = (1.4 X 1) / 7 = 0.2 moles.

v) The atomic mass number of Sulphur is 32.

So, the number of moles in Sulphur is = (32 X 1) / 32 = 1 mole.