Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide: CaO (s) + H₂O (l) → Ca(OH) ₂(s)
A 3.50 g sample of CaO is reacted with 3.38 g of H₂O.How many grams of water remain after completion of reaction?

Question

Quizplus · Accepted Answer

First, we need to determine the limiting reactant in the reaction. To do this, we can use stoichiometry and convert both reactants to moles of calcium hydroxide produced:

For CaO:
3.50 g CaO x (1 mol CaO/56.08 g CaO) x (1 mol Ca(OH)2/1 mol CaO) = 0.0625 mol Ca(OH)2

For H2O:
3.38 g H2O x (1 mol H2O/18.02 g H2O) x (1 mol Ca(OH)2/1 mol H2O) = 0.1875 mol Ca(OH)2

Since CaO produces the smaller amount of Ca(OH)2, it is the limiting reactant. This means that all of the CaO will react and be converted to Ca(OH)2, while some of the water will remain unreacted.

To determine the amount of water remaining, we can use stoichiometry again and calculate how much water is required to react with 0.0625 mol of CaO (the amount originally present):

0.0625 mol CaO x (1 mol H2O/1 mol CaO) x (18.02 g H2O/1 mol H2O) = 1.125 g H2O

Since we started with 3.38 g of water and only 1.125 g was required for the reaction, the remaining amount is:

3.38 g - 1.125 g = 2.255 g

Therefore, the answer is choice C: 2.25 g.

Calcium Oxide Reacts with Water in a Combination Reaction to Produce