Question

Many computer chips are manufactured from silicon, which occurs in nature as SiO2. When SiO2 is heated to melting, it reacts with solid carbon to form liquid silicon and carbon monoxide gas. In an industrial preparation of silicon, 155.8 kg of SiO2 is allowed to react with 79.0 kg of carbon to produce 66.1 kg of silicon.

1. Determine the limiting reactant for the reaction (SiO2 or C)

2. Determine the theoretical yield for the reaction

3. Determine the percent yield for the reaction

Answer 1

The reaction is SIO2+2C----> Si+2CO

Atomic weight of Silica= 28, C=12 and O= 16

Molecular weights :SIO2= 28+32= 60 Molecualr weight of Oxygen =32

Moles of SIO2= mass of SIO2/Molecular weight= 155.8/60=2.59 moles

Moles of C = 79/12= 6.58 Molar ratio of SIO2 :C =1 :2 ( This is the theoretical ratio of reactants)

Actual ratio ' 2.59: 6.58= 1: 6.58/2.59= 1:2.3

This suggest C is supplied in excess (2.3 for 1 mole of SIO2 as against 2

Limitnng reactant is SIO2

As per the reaction, 1 mole of SIO2 gives rise to 1 mole of SI

2.59 moles give rise to 2.59 mole of Si

Mass of Si= 2.59*28=72.52 gms . This is the theoretical yield.

Percent yield= 100* actual yield/ Theoretical yield= 100*66.1/72.52=91.14%