Question

Tasks
5) 1.25 g of calcium is added to 25 cm3 of water. Calculate the
concentration of the calcium hydroxide solution and volume of
hydrogen produced in cm3.
Ca(s) + 2H2O(1) + Ca(OH)2(aq) + H2(g)
6) Chlorine reacts with sodium hydroxide as follows:

Answer 1

Concentration Ca(OH)₂ : 1.25 M

Volume of H₂ : 0.75 L

Further explanation

The reaction equation is the chemical formula of reagents and product substances  

A reaction coefficient is a number in the chemical formula of a substance involved in the reaction equation. The reaction coefficient is useful for equalizing reagents and products  

Reaction

Ca(s) + 2H₂O(1) ⇒ Ca(OH)₂(aq) + H₂(g)

• mol of Ca :

$\tt mol=\dfrac{mass}{MW}=\dfrac{1.25}{40}=0.03125$

• concentration of Ca(OH)₂ :

mol Ca = mol Ca(OH)₂ = 0.03125

V = 25 cm³ = 0.025 dm³(L)

$\tt M=\dfrac{n}{V}=\dfrac{0.03125}{0.025}=1.25~M$

• volume of  H₂ produced

Assume At RTP (room temperature and pressure),  1 mol gas = 24 L

mol H₂ = mol Ca = 0.03125

volume :

$\tt 0.03125\times 24=0.75~L$