Question

7.

A mineral contains lithium chromate and other

inert compounds.

In order to

find out

what

the percent

mass of

lithium chromate is in the mineral you dissolve 6.294g of the

mineral

in water

and add iron(III) nitrate to the solution. A solid forms

and

you continue to

add

iron(III) nitrate until the solid stops forming. You filter the solution, dry the solid

you

obtained and

measure that the mass of

solid

formed is 1.596 g. What is the percent mass

of lithium chromate

in the

mineral?

Answer 1

The reaction that occurs is:

3 Li2CrO4 + 2 Fe (NO3) 3 = 6 LiNO3 + Fe2 (CrO4) 3

The compound that precipitates is Fe2 (CrO4) 3, the initial mass of Li2CrO4 is calculated:

m Li2CrO4 = 1,596 g Fe2 (CrO4) 3 * (1 mol Fe2 (CrO4) 3/460 g) * (3 mol Li2CrO4 / 1 mol Fe2 (CrO4) 3) * (130 g Li2CrO4 / 1 mol) = 1,353 g Li2CrO4

The percentage in the mineral is calculated:

% Li2CrO4 = g Li2CrO4 * 100 / g mineral = 1,353 * 100 / 6,294 = 21.50%

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