Question

05. (a) Calculate the mass of 3 moles of C,H,OH. [ Atomic mass of C=12u, H=1u, 0-16u)
(b) How many moles of molecules are there in:
(i) 18 g of hydrogen H2
(ii) 54 g of H2 O​

Answer 1

Answer:

(a) the mass of 3 moles of C = 3 × atomic mass of C

= 3 × 12

= 36u

the mass of 3 moles of H = 3 × atomic mass of H

= 3 × 1

= 3u

the mass of 3 moles of OH = 3 × atomic mass of OH

= 3× 16×1

= 3× 16

= 48u

(b)

1. no.of moles = given mass / molecular mass

= 18/2

= 9 moles

2. no.of moles = given mass/ molecular mass

= 54/18

= 3 moles

Explanation:

molecular mass of H2O = 2 × atomic mass of H + 1× atomic mass of O

= 2 × 1 + 1 × 16

= 2+16

= 18g

molecular mass of H2 = 2× atomic mass of H

= 2 × 1

= 2g