Question

Iron (III) oxide chunks contain 80 ppm silica (SiO2). What is the concentration of this impurity in mass%?

(a) 0.008%

(b) 0.080%

(c) 0.800%

(d) 8.000%

I had been asked this question in exam.

I would like to ask this question from Expressing Concentration of Solutions topic in chapter Solutions of Chemistry – Class 12

Answer 1

The correct choice is (a) 0.008%

Best explanation: 80 ppm silica means there are 80 mg of silica is 10^6 mg (or 1 kg) of iron (III) oxide and silica mixture. The mixture can be regarded as 10^6 mg (or 1 kg) of iron (III) oxide since 80<<10^6

Mass% = (mass of impurity/mass of total mixture) x 100%

Mass% = (80mg/10^6mg) x 100% = 0.008%.