If 42.8 ml of 0.204 m hcl solution is needed to neutralize a solution of ca(oh)2, how many grams of ca(oh)2 must be in the solution?

Hey There!

At neutralisation moles of H⁺ from HCl  = moles of OH⁻ from Ca(OH)2  so :

0.204 * 42.8 / 1000  => 0.0087312 moles

Moles of Ca(OH)2 :

2 HCl + Ca(OH)2 = CaCl2 + 2 H2O

0.0087312 / 2 => 0.0043656 moles (  since each Ca(OH)2 ives 2 OH⁻ ions )

Therefore:

Molar mass Ca(OH)2 = 74.1 g/mol

mass = moles of Ca(OH)2 * molar mass

mass =  0.0043656 * 74.1

mass = 0.32 g of Ca(OH)2

Hope that helps!