Question

Milk of magnesia (maalox) contains magnesium hydroxide. magnesium hydroxide can be reacted with hydrochloric acid to form magnesium chloride and water, as seen in the reaction below. using this reaction, how many grams of hydrochloric acid are needed to fully react 355g magnesium hydroxide?

Answer 1

The chemical reaction described by the question:

$Mg(OH)_{2} + 2HCl = MgCl_{2} + 2H_{2}O$

Then for finding the number of moles of magnesium hydroxide Mg(OH)$_{2}$

number of moles = mass (grams) / molecular mass (g/mole)

number of moles of Mg(OH)$_{2}$ = 355 / 58 = 6.12  

From the chemical reaction:

1 mole of Mg(OH)$_{2}$ reacts with 2 moles of HCl

6.12 moles of Mg(OH)$_{2}$ reacts with x moles of HCl

x = (6.12×2)/1 = 12.24 moles of HCl

And now we can determine the mass of hydrochloric acid HCl

mass (grams) = number of moles x molecular mass (grams/mole)

mass of HCl = 12.24 × 36.5 = 446.76 g