Video: Calculating the Amount of Acid from the Number of Equivalents

In a complete neutralization reaction involving H₂SO₄, 0.10 equivalents are consumed. How many moles of H₂SO₄ are consumed? [A] 0.025 mol [B] 0.05 mol [C] 0.2 mol [D] 0.1 mol [E] 98 mol

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Video Transcript

In a complete neutralization reaction involving H₂SO₄, 0.10 equivalents are consumed. How many moles of H₂SO₄ are consumed? A) 0.025 moles, B) 0.05 moles, C) 0.2 moles, D) 0.1 moles, or E) 98 moles.

Commonly, a neutralization reaction is the reaction of an acid and a base producing salt plus water. This reaction might look something like this, where we have HA reacting with a base that contains hydroxide ions, forming XA, the salt, and H₂O. We can simplify this even further by focusing on the hydrogen ion and the hydroxide ion, coming together to form the water molecule. When the question says complete neutralization reaction, in this context, all that means is that it’s a reaction where we’re using all the H⁺ ions. H₂SO₄, otherwise known as sulfuric acid, has two H⁺ ions per unit.

We’ve been told in the question that we have 0.10 equivalents of acid. But what does that really mean? An equivalent of an acid is the amount in moles that contains one mole of H⁺ ions. We’ve already seen that we generate two H⁺ ions per unit of sulfuric acid. Therefore, we’ll generate two moles of H⁺ ions per one mole of sulfuric acid. We can turn that the other way up. We have one mole of sulfuric acid per two moles of H⁺ ions. If we multiply that by one mole of H⁺ ions per equivalent, we get 0.5 moles of H₂SO₄ per equivalent. What this means is that one equivalent of H₂SO₄ is the same as 0.5 moles of H₂SO₄ because 0.5 moles of sulfuric acid have the potential to generate exactly one mole of H⁺ ions.

All we need to do now is multiply this by the number of equivalents that are consumed in the neutralization, giving us 0.05 moles of sulfuric acid, H₂SO₄. We can do a quick check by just reversing the formula. The amount in moles of our acid multiplied by the number of hydrogen ions that we can generate per unit of the acid is the same as the number of equivalents. The amount of sulfuric acid in moles is 0.05. We multiply that by two hydrogen ions per unit. And that gives us the number of equivalents we started with, 0.10.

So in a complete neutralization reaction, where 0.10 equivalents of sulfuric acid are consumed, 0.05 moles of sulfuric acid are consumed.

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