Question

Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide. A 4.50-g sample of CaO is reacted with 4.34 g of H2O. How many grams of the excess reagent remain after the reaction is complete

Answer 1

2.88 g

Step-by-step explanation:

First, let us look at the balanced equation of the reaction:

`CaO(s) + H_2O (l) --> Ca(OH)_2(s)`

From the equation, 1 mole of CaO reacts with 1 mole of H2O to produce 1 mole of
`Ca(OH)_2`.

mole = mass/molar mass

4.50 g of CaO = 4.50/56.08 = 0.08 mole

4.34 g of H2O = 4.34/18.02 = 0.24 mole

The ratio of moles of CaO and H2O should be 1:1, hence, H2O is in excess.

Excess mole of H2O = 0.24 - 0.08 = 0.16 mole

mass of 0.16 mole of H2O = mole x molar mass = 0.16 x 18.02 = 2.88 g

Therefore, 2.88 g of the excess reagent (water) would remain after the reaction is complete.