Questions & Answers

Question

Answers

(A) 1.0

(B) 2.0

(C) 3.0

(D) 4.0

(E) 5.0

Answer
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$Cao + H_2O \rightarrow Ca(OH)_2$

We can see that one mole of CaO gives 1 mole of calcium hydroxide,\[{\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}\].

Now, we need to find the molar mass of calcium hydroxide.

For that, we need to know the atomic mass of Calcium, oxygen and hydrogen that is the constituent atoms of calcium hydroxide.

Atomic mass of Calcium = 40 g/mol

Atomic mass of oxygen = 16 g/mol

Atomic mass of hydrogen = 2 g/mol

Molar mass of Calcium hydroxide = 40 + 2(16 x 1) = 74 g/mol

Therefore, 1 mole of calcium hydroxide has 74g.

⟹ 74 grams of calcium hydroxide = 1 mole

⟹ 370 grams of calcium hydroxide = x moles

⟹ x = $\dfrac{{{\text{370}}}}{{{\text{74}}}}{\text{ = 5}}{\text{.0}}$ moles

Hence, 5.0 moles of CaO are required to react with an excess of water to form 370 grams of calcium hydroxide.

\[{\text{Number of moles = }}\dfrac{{{\text{Number of particles}}}}{{{\text{Avogadro Number}}}}\]

Given- Mass = 370g; Molar mass of calcium hydroxide = 74g/mol

Number of moles, n = $\dfrac{{{\text{Given Mass}}}}{{{\text{Molecular mass}}}} = \dfrac{{370}}{{74}} = 5{\text{ moles}}$