To neutralize an acidic substance with the basic solution, the number of moles should be equal. First, we calculate for the number of moles of KHP.
molar mass of KHP = (1 mol K)(39.1 g K/1 mol K) + (1 mol H)(1 g H/1 mol H) + (1 mol P)(30.97 g P / 1 mol P) = 71.07 g KHP/ mol
number of moles KHP = (0.4218 g KHP) x (1 mol KHP / 71.07 g KHP)
n = 0.0059 moles
Let M be the molarity of the solution and equating the number of moles,
0.0059 moles = (18.68 mL)(1 L/1000 mL)(M)
M = 0.32 moles/L
ANSWER: 0.32 M
