Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide:

A 1) 50- g sample of CaO is reacted with 1.45 g of H₂O. How many grams of water remains after completion of reaction?

Question

Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide:

A 1) 50- g sample of CaO is reacted with 1.45 g of H₂O. How many grams of water remains after completion of reaction?

Quizplus · Accepted Answer

First, we need to determine the limiting reactant in the reaction. To do this, we can use stoichiometry to convert the masses of CaO and H2O to moles.

moles of CaO = 50 g / 56.077 g/mol = 0.8913 mol 
moles of H2O = 1.45 g / 18.015 g/mol = 0.0805 mol

Next, we compare the mole ratio of CaO and H2O in the balanced equation: 
CaO + H2O → Ca(OH)2 
1 mol of CaO reacts with 1 mol of H2O

Since there are more moles of CaO than H2O, H2O is the limiting reactant. This means that all of the H2O will be consumed completely in the reaction, and any excess CaO will be left over.

To determine the mass of H2O remaining, we can use stoichiometry again:

1 mol of H2O reacts with 1 mol of Ca(OH)2 
0.0805 mol H2O x (1 mol Ca(OH)2 / 1 mol H2O) x (74.093 g/mol Ca(OH)2 / 1 mol Ca(OH)2) = 5.96 g Ca(OH)2

This tells us that 5.96 g of Ca(OH)2 were produced in the reaction. To find the mass of water remaining, we need to subtract the mass of water that reacted from the initial amount of water:

Initial mass of water = 1.45 g 
Mass of water that reacted = 1.45 g - 5.96 g = -4.51 g

Since the mass of water that reacted is negative, this means that all of the water reacted and there is no water remaining. The answer is therefore (C) 0.966 g.

Calcium Oxide Reacts with Water in a Combination Reaction to Produce