Introduction to Titration
Introduced| English |
|---|
| titration/taɪˈtreɪʃn/ |
| equivalence point/ɪˈkwɪvələns pɔɪnt/ |
Finding strength drop by drop
- How much acid is really in this vinegar?
- Add a known base, one careful drop at a time.
- The moment it neutralizes, an indicator flips colour.
- That exact volume reveals the unknown concentration.
What a titration does
- A titration 滴定 finds an unknown concentration.
- You add a known solution until the reaction is just complete.
- The volume added tells you the unknown amount.
A titration is used to find...
You add a known solution to determine an unknown concentration.
In a titration you slowly add a solution of ____ concentration.
The titrant has a known concentration; the analyte is unknown.
The equivalence point
- The equivalence point 等当点 is where the moles exactly match the reaction ratio.
- An indicator changes colour near it, marking the endpoint.
- Read the volume of titrant added at that moment.
The equivalence point is where...
At equivalence the reactants are present in the exact ratio.
Working out the concentration
- At the equivalence point, moles of acid match moles of base (for a 1 : 1 reaction).
- $M_a V_a = M_b V_b$ lets you solve for the unknown.
- Rearrange it to find whichever concentration you need.
Run a titration
Add base to acid and watch the pH rise through the steep equivalence point.
A good indicator changes colour at the equivalence point.
The endpoint should match the equivalence point.
$M_1V_1 = M_2V_2$ works directly only for a 1-to-1 mole ratio.
Other ratios need the coefficients from the balanced equation.
$25\ \text{mL}$ of acid is neutralized by $20\ \text{mL}$ of $0.1\ \text{M}$ base (1 : 1).
- $M_a V_a = M_b V_b$ gives $M_a (25) = (0.1)(20)$.
- $M_a = 2/25 = 0.08\ \text{M}$.
$30\ \text{mL}$ of acid is neutralized by $15\ \text{mL}$ of $0.2\ \text{M}$ base (1 to 1). The acid's molarity (in M)?
$M_a(30) = (0.2)(15) = 3$, so $M_a = 0.1\ \text{M}$.
The endpoint (the indicator's colour change) should match the equivalence point, so pick an indicator that flips there. $M_1V_1 = M_2V_2$ holds only for a 1 : 1 mole ratio; otherwise include the ratio from the balanced equation. And measure volumes carefully -- the whole method depends on precise readings.
A titration finds an unknown concentration by adding a known solution until the reaction is complete. At the equivalence point the moles match the reaction ratio, marked by an indicator. For a 1 : 1 reaction, $M_a V_a = M_b V_b$ solves for the unknown.