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

Answer:

The correct answer is option (a).

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

$18.8\%=\frac{2\times 7 g/mol}{M}\times 100$

M = 74.46 g\mol

Mass of pure lithium carbonate is twice the mass of first sample:$2\times 74.46 g/mol =148.92 g/mol$

Percentage of lithium in pure lithium carbonate sample:

$\%=\frac{2\times 7 g/mol}{148.92 g/mol}\times 100=9.40\%$

The correct answer is option (a).