Answer is: mass of slaked lime is 6.92 grams.
Balanced chemical reaction: Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2NH₃ + 2H₂O.
m(NH₄Cl) = 10 g; mass of ammonium chloride.
M(NH₄Cl) = 14 + 1·4 + 35.5 · g/mol.
M(NH₄Cl) = 53.5 g/mol; molar mass of ammonium chloride.
n(NH₄Cl) = m(NH₄Cl) ÷M(NH₄Cl).
n(NH₄Cl) = 10 g ÷ 53.5 g/mol.
n(NH₄Cl) = 0.187 mol; amount of ammonium chloride.
From balanced chemical reaction: n(NH₄Cl) : n(Ca(OH)₂) = 2 : 1.
n(Ca(OH)₂) = 0.093 mol.
m(Ca(OH)₂) = n(Ca(OH)₂) · M(Ca(OH)₂).
m(Ca(OH)₂) = 0.093 mol · 74.1 g/mol.
m(Ca(OH)₂) = 6.92 g.
