Question

Green plants use light from the Sun to drive photosynthesis, a chemical reaction in which liquid water and carbon dioxide gas form aqueous glucose and oxygen gas. Calculate the moles of oxygen produced by the reaction of of carbon dioxide. Be sure your answer has a unit symbol, if necessary, and round it to the correct number of significant digits.

Answer 1

The question is missing the number of moles of carbon dioxide that will react with water.

I will work the problem with an arbitrary amount of carbon dioxide to show how to solve it.

For this, I will take 2.40 moles of carbon dioxide.

Answer:

• The number of moles of oxygen atoms produced is equal to the number of moles of carbon dioixide that react: 2.40 moles of oxygen.

• 2.40 has 3 significant figures.

Explanation:

1) Word equation:

• carbon dioxide gas + liquid water (in the presence of light) → aqueous glucose + oxygen gas

2) Balanced chemical equation

• 6CO₂ (g) + 6H₂O (l) → C₆H₁₂O₆ (aq) + 6O₂(g)

3) Mole ratios

• 6 mol CO₂ (g) : 6 mol H₂O (l) : 1 mol C₆H₁₂O₆ (aq) : 6 mol O₂(g)

4) Set a proportion:

It is assumed that there is plenty liquid water (excess reactant), so you can set a proportion with the number of moles of carbon dioxide:

• 6 mol CO₂ / 6 mol O₂ = 2.40 mol CO₂ / x

From which, x = 2.40 mol O₂

So, the number of moles of oxygen produced is equal to the number of moles of carbon dioxide that react.

Since the number of moles of reactant has 3 significant figures, and the stoichiometric coefficients are considered exact, the answer also has 3 significant figures.