Step-by-step explanation:
The reaction between HCl and Ca(OH)₂ is:
2 HCl + Ca(OH)₂ ----> CaCl₂ + 2 H₂O
First we have to find the number of moles of HCl that were needed to neutralize the Ca(OH)₂ solution. We used 27.5 mL of a 0.125 M solution.
volume of solution in L = 27.5 mL * 1 L/1000 mL
volume of solution in L = 0.0275 L
moles of HCl = 0.125 moles/L * 0.0275 L
moles of HCl = 0.003438 moles
According to the coefficients of the reaction, 2 moles of HCl will neutralize 1 mol of Ca(OH)₂. The molar ratio between them is 2 to 1. We can use this relationship to find the number of moles of Ca(OH)₂ that will be neutralized by 0.003438 moles of HCl.
2 moles of HCl = 1 mol of Ca(OH)₂
moles of Ca(OH)₂ = 0.003438 moles of HCl * 1 mol of Ca(OH)₂/(2 moles of HCl)
moles of Ca(OH)₂ = 0.001719 moles
Finally we can convert these moles into grams using the molar mass of Ca(OH)₂.
molar mass of Ca(OH)₂ = 74.09 g/mol
mass of Ca(OH)₂ = 0.001719 moles * 74.09 g/mol
mass of Ca(OH)₂ = 0.127 g
Answer: the mass of Ca(OH)₂ that must be in the solution is 0.127 g.