Question

Silica (also known as silicon dioxide) reacts with hydrofluoric acid to produce silicon tetrafluoride and water vapor.

Answer 1

The problem is solved by balancing the reaction equation as shown below. The stoichiometry of the reaction is now applied in solving the question.

The balanced reaction equation is:

SiO2 + 6HF → H2[SiF6] + 2H2O

Using stoichiometry

The amount of silicon dioxide reacted = 12.5 g/60.08 g/mol = 0.21 mole

1 mole SiO2 yields 2 moles of H2O

0.21 mole of SiO2 yields 0.21 * 2/1 = 0.42 moles of H2O

The amount of HF reacted = 24.6 g/20.01 g/mol = 1.23 moles of HF

6 moles of HF yield 2 mole of H2O

1.23 moles of HF yields 2 * 1.23/6 = 0.41 moles of H2O

Hence HF is the limiting reactant.

Theoretical yield of H2O = 0.41 moles of H2O * 18 g/mol = 7.38 g

The percentage yield of the water is = actual yield/theoretical yield * 100

Hence;

% yield = 2.50 g/7.38 g * 100 = 33.9%

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Answer 2

Answer:

a) 4HF(aq]+SiO2(s]→SiF4(g]↑⏐+2H2O

c) 75%