Question

Calculate the molar mass for the following show your work.

1) C₁₀H₂₂

2) Fe₂(SO₄)3

Calculate the number of moles in each sample

1) 450.0 g C₁₀H₂₂

2) 15.65g Fe₂(SO₄)3

Answer 1

Solution:- (a) Molar mass is the sum of atomic mass times subscript of each element.

(1) The given molecular formula is C₁₀H₂₂. It has 10 carbons and 22 hydrogens. Atomic mass of C is 12.01 and that for H is 1.01.

So, molar mass of C₁₀H₂₂ = 10(12.01) + 22(1.01) = 120.1 + 22.22 = 142.32

Unit of molar mass is g/mol. So, for C₁₀H₂₂ , the molar mass is 142.32 g/mol.

(2) Fe₂(SO₄)₃ has two Fe, three S and twelve oxygen.

Atomic mass of these atoms are.......

Fe = 55.85, S = 32.06 and O = 16.00

So, molar mass = 2(55.85) + 3(32.06) + 12(16.00) = 111.7 + 96.18 + 192.0 = 399.88

Hence the molar mass of Fe₂(SO₄)₃ is 399.88 g/mol.

(b)

(1) For grams to moles we divide by the molar mass as molar mass is the mass of 1 mol of the substance we are dealing with. For example molar mass of H₂O is 18.02 g/mol. It means mass of 1 mol of H₂O is 18.02 g.

450.0 g C₁₀H₂₂ x (1mol/ 142.32 g) = 3.162 mol C₁₀H₂₂

(2) 15.65 g Fe₂(SO₄)₃ x (1mol/ 399.88 g) = 0.03914 mol Fe₂(SO₄)₃