Question

23 What is the volume of a sample of octane, C8H18, that contains 8.0 x 1025 hydrogen atoms? The density of octane is 0.703 g/cm'. (A) 6. 7930 x 10 cm (B) 2694.7cm (C) 1197.6 cm (D) 591. 88 cm

Answer 1

1 C8H18 molecule has 18 H atoms.

So,

Number of C8H18 molecules = number of H atoms / 18

= (8.0*10^25) / 18

= 4.44*10^24 molecules

use:

number of mol = number of molecules / Avogadro’s number

number of mol = 4.44*10^24 / 6.022*10^23 mol

number of mol = 7.373 mol

Molar mass of C8H18,

MM = 8*MM(C) + 18*MM(H)

= 8*12.01 + 18*1.008

= 114.224 g/mol

use:

mass of C8H18,

m = number of mol * molar mass

= 7.373 mol * 1.142*10^2 g/mol

= 8.422*10^2 g

Now use:

Volume = mass / density

= (8.422*10^2 g) / (0.703 g/cm^3)

= 1.198*10^3 cm^3

Answer: C