Question

A sample of pure lithium carbonate contains 18.8% lithium by mass. what is the % lithium by mass in a sample of pure lithium carbonate that has twice the mass of the first sample?

a.9.40 %
b.18.8 %
c.37.6 %
d.75.2 %

Answer 1

18.8%.
The component percentage of a pure compound does not vary with the mass of the sample.

Answer 2

The correct answer is option (a).

Step-by-step explanation:

The molecular formula of lithium carbonate is
`Li_2CO_3`

Percentage of lithium in lithium carbonate = 18.8 %

Molar mass of the lithium carbonate = M

Atomic mass of lithium = 7 g/mol

`18.8\%=(2* 7 g/mol)/(M)* 100`

M = 74.46 g\mol

Mass of pure lithium carbonate is twice the mass of first sample:
`2* 74.46 g/mol =148.92 g/mol`

Percentage of lithium in pure lithium carbonate sample:

`\%=(2* 7 g/mol)/(148.92 g/mol)* 100=9.40\%`

The correct answer is option (a).