Question

calculate the number of moles present in:
(1) 3.011 × 10²³ no: of oxygen atoms
(2) 60g of calcium

need full explanation
plz guyzz
important

Answer 1

(1)1 mole of oxygen=6.022 X 10^23 oxygen atoms
given no.of atoms of oxygen= 3.011 X 10^23
6.022 X 10^23 atoms -------------- 1 mole of oxygen
3.011 X 10^23 atoms----------------- ?moles of O2
no. of x moles=(3.011 X 10^23) / (6.022 x 10^23)
= 3.011/6.022
= 1/2
=0.5 moles of oxygen

(2) 40 gm (molecular mass)-------------1 mole of Ca
60 gm ---------------- ? moles of Ca
x moles of Ca= 60/40
= 3/2
=1.5 moles of Ca

Answer 2

Firstly you need know the formula . Which is :

number of moles = given mass÷molar mass

Now calculations : 32 ( oxygen diatomic / O2 ) & 60 g of calcium...so 32÷60g = 0.5 mol.