Mole ConceptHard

Question

To determine soluble (free) SiO2 in a rock, an alkaline extraction was carried out, as a result of which there was found 1.52% of SiO2 in the extract and also 1.02% of Al2O3. Considering that, apart from the free SiO2, the extract also contained the SiO2 that had passed into it from Kaolin (2SiO2·Al2O3), the percentage of free SiO2 in the rock being analysed is (Si = 28, Al = 27)

Options

A.1.20
B.0.32
C.0.50
D.1.52

Solution

Al2O3⋅2SiO2 = 102 + 2 × 60

∴ SiO2 in combined state = $\frac{120}{102} \times 1.02$ = 1.20 g

Hence, percentage of free SiO2 = 1.52 – 1.20 = 0.32%

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