Question

b) Find the molecular weight of the following compounds: i) Urea (CON2H4) ii) Sugar (C12H22O11) iii) Ammonium phosphate (NH4)3PO4

Answer 1

To find the molecular weight, simply add up the mass numbers of all the atoms in the molecule.

Atomic masses of some atoms :

C = 12 g/mole

O = 16 g/mole

N = 14 g/mole

H = 1 g/mole

P = 31 g/mole

i) Urea = $\sf CON_2H_4$

Molecular weight of urea = 12 + 16 + 14(2) + 1(4)

⇒ 28 + 28 + 4

⇒ 60 g/mole

ii) Sugar = $\sf C_{12}H_{22}O_{11}$

Molecular weight of sugar = 12(12) + 1(22) + 16(11)

⇒ 144 + 22 + 176

⇒ 166 + 176

⇒ 342 g/mole

iii) Ammonium Phosphate = $\sf (NH_4)_3PO_4$

⇒ (14 + 1(4))(3) + 31 + 16(4)

⇒ (18)(3) + 31 + 64

⇒ 54 + 31 + 64

⇒ 149 g/mole