Magnesium hydroxide [Mg(OH)2] is an ingredient in some antacids. How many grams of Mg(OH)2 are needed to neutralize the acid in 158 mL of 0.106 M HCl(aq)? It might help to write the balanced chemical equation first.

1.95g of Mg(OH)2 are needed

Explanation:

Mg(OH)2 reacts with HCl as follows:

Mg(OH)2 + 2 HCl → MgCl2 + 2H2O

Where 1 mole of Mg(OH)2 reacts with 2 moles of HCl

To solve this question we must find the moles of acid. Then, with the chemical equation we can find the moles of Mg(OH)2 and its mass:

Moles HCl:

158mL = 0.158L * (0.106mol / L) = 0.01675 moles HCl

Moles Mg(OH)2:

0.01675 moles HCl * (2mol Mg(OH)2 / 1mol HCl) = 0.3350 moles Mg(OH)2

Mass Mg(OH)2 -Molar mass: 58.3197g/mol-

0.3350 moles Mg(OH)2 * (58.3197g / mol) =