Silicon dioxide reacts with carbon upon heating to produce silicon carbide (SiC) and carbon monoxide. SiO2(s) + 3C(s) → SiC(s) + 2CO(g)

Question

a.) What mass of carbon is required to react completely with 15.70 g of SiO2?

b.) When 152 g of SiO2 reacts with excess carbon, what mass of SiC is produced?

c.) If 42.2 g of CO were produced by this reaction, what mass of carbon must have reacted?

Answer 1

First, we make sure the chemical equation is balanced, because our equation will be used as a clue to help us get the answer. Next, we find the limiting reagent. Next, we look at the number of moles of each reactant. We see that for every mole of SiO2, 3 moles of C is required to produce our reactants. Based on this 1:3 molar ratio, we can do some math tricks to get to the mass of carbon we need. We'll go backwards, converting the mass of SiO2 used to moles using its molra mass (60.08 g/mol), use our 1:3 ratio to figure out how many moles of Carbon is used in this reaction, and then convert to grams of carbon to get our mass of carbon used in this reaction.

Finding limiting reagent:

1) Convert moles of SiO2 to

1) Convert 15.70 g SiO2 to moles.

Use dimensional analysis to solve this: 15.70 g SiO2 x (1 mole SiO2)/(molar mass of SiO2: 60.08 g) = 0.261318 moles SiO2

2) Multiply the number of moles of SiO2 by our ratio of moles of SiO2 to moles of C.

0.261318 moles SiO2 x (3 moles C)/(1 mole SiO2) = 0.7839 moles C

3) Convert moles of Carbon to grams of Carbon using molar mass of Carbon.

0.7839 moles C * 12 g C/1 mole C = 9.4068 grams Carbon

4) Make sure we are using the correct amount of sig figs: the question uses "15.07 g SiO2". There are four significant figures in this answer and so we will round our answer to 9.407 g Carbon.

1) Convert 152 g of SiO2 to moles of SiO2 by dividing by molar mass of SiO2.

1:1 ratio of SiO2 to SiC, so the moles of SiO2 = moles of SiC.

2) Given the moles of SiC, you can now convert to grams of SiC using the molar mass of SiC.

Part C)

1) Convert 42.2 g of CO to moles of CO by dividing by molar mass of CO.

2) Multiply by ratio: (3 C)/(2 CO)

3) Convert to grams of carbon by multiplying by molar mass of C