Video: Calculating the Volume of Mg(OH)₂ Solution of Known Concentration Required to Neutralize a Given Volume of H₂SO₄ Solution of Known Concentration

What is the volume of 0.1-molar Mg(OH)2 required to neutralize 100 milliliters of 0.2- molar H2SO4? [A] 50 milliliters [B] 100 milliliters [C] 200 milliliters [D] 300 milliliters [E] 400 milliliters


Video Transcript

What is the volume of 0.1-molar Mg(OH)2 required to neutralize 100 milliliters of 0.2- molar H2SO4? (A) 50 milliliters, (B) 100 milliliters, (C) 200 milliliters, (D) 300 milliliters, or (E) 400 milliliters.

This question mentions a neutralization reaction, which is the reaction of an acid with a base to form salt and water. Mg(OH)2 or magnesium hydroxide is the base in this reaction. And H2SO4 or sulfuric acid is the acid in this reaction. We can write the balanced equation for the neutralization reaction as follows. H2SO4 aqueous plus Mg(OH)2 aqueous gives us MgSO4 aqueous plus 2H2O liquid. The salt produced is magnesium sulfate. Magnesium sulfate is a soluble salt. The mole ratio of the balanced equation is the ratio of stochiometric coefficients in front of each substance. One H2SO4 reacts with one Mg(OH)2 to produce one MgSO4 and two waters. We can see that the reactants react with each other in a ratio one as to one.

Let’s write the data that we have for each reactant underneath the formula. The concentration of magnesium hydroxide is 0.1 molar. Molar is the same as a unit of moles per liter. Sulfuric acid has a concentration of 0.2 moles per liter. When concentration is expressed in a unit moles per liter, we can refer to concentration as the molarity of the solution. So the molarity of magnesium hydroxide is 0.1 moles per liter. And the molarity of sulfuric acid is 0.2 moles per liter.

We are given a volume for sulfuric acid. We need to convert this volume in milliliters into liters. Converting from milliliters to liters, we divide by 1000. And we get a volume in liters of 0.1 for sulfuric acid. Now, we can use the concentration and volume of sulfuric acid to calculate the number of moles of sulfuric acid present. And we get a value of 0.02 moles. We know that sulfuric acid and magnesium hydroxide react in a mole ratio of one as to one. So for every mole of sulfuric acid that reacts, one mole of magnesium hydroxide will also react.

Similarly, for every 0.02 moles of sulfuric acid that reacts, 0.02 moles of magnesium hydroxide will react. 0.02 as to 0.02 is the same as one as to one. In other words, 0.02 moles of magnesium hydroxide will neutralize 0.02 moles of sulfuric acid. Let’s now use the concentration and number of moles of magnesium hydroxide to determine the volume of magnesium hydroxide that will neutralize the given amount of sulfuric acid.

Substituting the number of moles and concentration into the formula for volume, we get a volume of magnesium hydroxide equal to 0.2 liters. The last step is to convert this value into a milliliter unit. Converting liters to milliliters, we multiply by 1000, and we get an answer of 200 milliliters. So answer (C), 200 milliliters, is the volume of 0.1-molar Mg(OH)2 required to neutralize 100 milliliters of 0.2-molar H2SO4.

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