If one antacid tablet contains 0.10g of magnesium hydroxide how many grams of stomach acid does this tablet neutralize?

0.1252 g of HCl

Antacid acts to neutralize excessive acid in the stomach.

The stomach contains hydrochloric acid, HCl.

Therefore; a reaction of antacid (magnesium hydroxide) and HCl will be;

Mg(OH)₂(s) + 2HCl(aq) → MgCl₂(aq) +2 H₂O(l)

We are given;

Mass of magnesium hydroxide as 0.10 g

We can calculate the mass of HCl neutralized by the acid using the following simple steps;

Step 1 : Number of moles of Mg(OH)₂

Number of moles is calculated by dividing the mass of a compound with the relative formula mass of the compound.

Relative formula mass of the compound = 58.32 g/mol

Therefore;

Number of moles of  Mg(OH)₂ = 0.10 g ÷ 58.32 g/mol

                                                  = 0.001715 mol

Step 2: Number of moles of HCl neutralized by 0.10 g of Mg(OH)₂

Moles of Mg(OH)₂ = 0.001715 mol

But, from the equation 1 mole of Mg(OH)₂  reacts with 2 moles of HCl

Thus;

0.001715 moles Mg(OH)₂ will neutralize;

 = 0.001715 × 2

 = 0.003430 moles HCl

Step 3: Mass of HCl neutralized

Mass is calculated by multiplying the number of moles by the relative formula mass of a compound.

Molar mass of HCl = 36.5 g/mol

Therefore;

Mass = 0.003430 mol × 36.5 g/mol

        = 0.1252 g HCl

Therefore; 0.10 g of Mg(OH)₂ neutralizes 0.1252 g of HCl

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