Question

Check your self:- 1. Define Molar mass. 2. Calculate the mass of 0.5 mole of N2 (Nitrogen gas). ( atomic mass of N =14u) 3. Calculate the Molar mass of HCl. (atomic mass of H =1u; Cl = 35.5u) 4. Calculate the number of moles in 48g of helium (atomic mass of He= 4u ) 5. Calculate the Molar Mass of C2H6. (atomic mass of H =1u; and C=12u)

Answer 1

Molar mass refers to the mass of a single mole of an element.

• It can also be described as the ratio of the sample of mass of an element to the number of moles in the sample.
• Mathematically it can be summarized as

Molar mass (M)

$= \frac{mass}{no \: of \: moles}$

$= \frac{m}{n}$

The mass of 0.5 mole of N2 (Nitrogen gas) is:

• The molar mass of N is 14u

No of moles = 0.5 Mol

mass = ?

mass = Molar mass × number of moles

mass = 14 × 0.5

mass = 7g

The Molar mass of HCl is:

• The addition of the atomic masses if H amd Cl

H = 1u

Cl = 35.5 u

HCl = 1 + 35.5

= 36.5 u

The molar mass of HCl is 36.5 u

The number of moles in 48g of helium (atomic mass of He= 4u):

No of moles =

$\frac{mass}{molar \: mass}$

mass = 48g

molar mass = 4u

no of moles = 48÷4

= 12

• 12 moles of Helium are present

The Molar Mass of C2H6:

• There are 2 moles of C =

2 × 12 = 24

• There are 6 moles of H =

6 × 1 = 6

• The molar mass of C2H6 is:

24 + 6 = 30u

The molar mass of C2H6 is 30u

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