Acid-Base Titration
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flagWhat you'll discover
- arrow_forwardCarry out the full titration procedure in the correct order, including rinsing the burette with the titrant
- arrow_forwardRead a burette to 0.05 mL and record initial and final readings properly
- arrow_forwardApproach the endpoint dropwise and recognise the indicator colour change
- arrow_forwardRepeat trials until two concordant titres (within 0.2 mL) are obtained
- arrow_forwardCalculate the unknown concentration using M₁V₁ = M₂V₂ for a 1:1 reaction
Why every step of the procedure exists
Titration finds an unknown concentration by reacting it exactly with a standard solution. Each preparation step kills a specific error. The burette is rinsed with the acid it will hold — rinsing with water would leave droplets that dilute the titrant. The pipette is rinsed with the alkali it will measure. The conical flask, however, is rinsed only with distilled water: extra water changes neither the moles of NaOH in the flask nor the titre.
After filling, the jet below the tap must be checked for air bubbles — a bubble that escapes mid-titration counts as fake volume. Readings are taken at eye level from the bottom of the meniscus, with the burette vertical. The first titration is always a rough trial run quickly to locate the endpoint; accurate trials then approach it dropwise.
The endpoint: one drop decides
In this experiment the flask holds 25.0 mL of NaOH with phenolphthalein, which is pink in alkali. As 0.10 M HCl runs in, the reaction NaOH + HCl → NaCl + H₂O consumes the alkali. Near the equivalence point a single drop (about 0.05 mL) swings the solution from alkaline to acidic, and the pink colour vanishes — that decolourisation is the endpoint.
The skill is anticipation: when the pink starts fading slowly where the acid lands, you are within a millilitre. Slow to single drops, swirl after each, and wash the flask walls with distilled water so every drop reacts. If you overshoot, the trial is not wasted — record it as rough and use it to plan the next one. Methyl orange works too (yellow in alkali → red in acid, orange at the endpoint), but its change is harder to judge by eye.
Concordance and the calculation
A single titre proves nothing — the examiner wants concordant results: two accurate titres agreeing within 0.2 mL. Their mean is the reliable titre V. For this 1:1 reaction the calculation is M(NaOH) × 25.0 = 0.100 × V, so M(NaOH) = 0.100 × V / 25.0.
Sources of error worth quoting in your report: air bubble in the burette jet (titre too high), reading the top of the meniscus, overshooting the endpoint, rinsing the burette with water instead of acid (titre too high because the acid is diluted), and using a wet measuring flask for the pipetted solution. Each links a physical mistake to the direction of the error — exactly the reasoning the practical viva tests.