Titration Questions: Finding the Concentration
When you mix an acid and a base, there is a neutralization reaction. We use titrations to determine HOW MUCH of one thing (like an acid) is in a mixture by adding another thing (like a base) and knowing how many of one reacted with how many of the other. Here's what I mean:
You need 24.55 mL of 0.1 M NaOH to titrate 25.00 mL of H2SO4 to its equivalence point. What is the concentration of the HCl?
You can use a formula for this, but I want you to UNDERSTAND what's going on, step by step:
- We're adding n = CV = (0.1 mol/L)(0.02455 L) = 0.002455 mol of NaOH. Each of these has one OH- on it.
- One OH- will react with 1 H+ from the acid.
- So we need 0.002455 mol of H+ to be produced.
- Each acid molecule (H2SO4) has TWO H+s on it, so we only need 0.0012275 mol of H2SO4 (half the number of moles)
- Since this is the amount found in exactly 25.00 mL, the concentration must have been C = n/V = (0.0012275 mol)/(0.0250 L) = 0.0491 M