A sample of magnesium oxide was dissolved in 50.0 mL of 0.183 M hydrochloric acid,and the excess acid was titrated to a phenolphthalein end-point by 13.4 mL of 0.105 M sodium hydroxide.What was the mass of the magnesium oxide sample?
A)312 mg
B)184 mg
C)156 mg
D)104 mg
E)77.8 mg

Question

Quizplus · Accepted Answer

First, we need to determine the moles of HCl that reacted with the magnesium oxide:
moles HCl = Molarity x Volume (in L) = 0.183 mol/L x 0.0500 L = 0.00915 mol HCl
From the balanced chemical equation, we know that one mole of magnesium oxide reacts with two moles of HCl. Therefore, the moles of magnesium oxide are:
moles MgO = 0.00915 mol HCl / 2 = 0.00458 mol MgO
Next, we calculate the mass of MgO using its molar mass:
mass MgO = moles MgO x molar mass = 0.00458 mol x 40.31 g/mol = 0.184 g = 184 mg
Therefore, the answer is (C) 156 mg (rounded to three significant figures).

A Sample of Magnesium Oxide Was Dissolved in 50