Ex 2: Acid + Base titration

Primary standard

a pure, stable substance used to prepare a solution of known concentration.

Equivalence point

the point in a titration where stoichiometrically equal amounts of acid and base have reacted.

Monoprotic

an acid that donates 1 proton (H⁺).

Diprotic

an acid that donates 2 protons (H⁺)

Triprotic

an acid that donates 3 protons (H⁺).

Standardization

the process of determining the exact concentration of a solution using a primary standard.

Weighing by Difference

define: Determining mass by weighing the same container before and after transfer.

weigting by difference method

• Use a clean, dry weighing beaker

• Use a paper strip as a handle (never touch the beaker)

• Weigh to four decimal places

• Transfer solid into flask

• Reweigh the same weighing beaker

• Mass of sample = difference between the two masses

Quantitative Transfer

All of the sample must be transferred — no loss allowed.

Solid transfer

• Pour solid into receiving vessel

• Tap to remove particles

• Rinse weighing paper/boat/beaker with solvent

• Add all rinses to the receiving container

Liquid transfer

• Pour liquid into receiving vessel

• Rinse original container at least 3 times

• Rinse funnel too (if used)

• Add all rinses to receiving vessel

Use of a Burette

Deliver precise, variable volumes (±0.01 mL).

• Read bottom of meniscus at eye level

• Record to 0.01 mL

Titration

Adding titrant until the endpoint colour change occurs.

To determine the unknown concentration (or amount) of a substance by reacting it with a solution of known concentration until the equivalence point is reached.

Pipette

Deliver a fixed, accurate volume.

Volumetric Flask

Prepare a solution of exact concentration.

Acid

• A substance that donates H⁺ (protons) in water

Base

A substance that accepts H⁺ or produces OH⁻ in water

Acid–Base Reaction (Neutralization)

An acid reacts with a base to form:

• Salt + water

Strong acid

• Completely dissociates in water

• Produces 100% H⁺

Strong base

• Completely dissociates in water

• Produces 100% OH⁻

Weak acid

• Partially dissociates

• Produces some H⁺

Strong acid – Strong base

• Reaction goes to completion

Weak acid – Strong base

• Weak acid is not fully dissociated

• Conjugate base forms

Strong acid – Weak base

• Weak base is not fully dissociated

• Conjugate acid forms

Sodium hydroxide (NaOH)

• Strong base

• Fully dissociates in water:

NaOH(aq) → Na+(aq) + OH−(aq)

Oxalic acid (H₂C₂O₄)

• Weak acid

• Diprotic (can donate 2 H⁺)

• Partially dissociates in water

• H2​C2​O4​⇌2H++C2​O42−​

Sulphamic acid (NH₂SO₃H)

• Strong acid (for CHEM 120L purposes)

• Monoprotic (donates 1 H⁺)

• Dissociates essentially completely in water

NH2​SO3​H(aq) → H+(aq) + NH2​SO3−​(aq)

A. Standardization of NaOH with oxalic acid

H2​C2​O4​(aq) + 2 NaOH(aq) → Na2​C2​O4​(aq) + 2 H2​O(l)

B. Titration of sulphamic acid with standardized NaOH

NH2​SO3​H(aq) + NaOH(aq) → NH2​SO3​Na(aq) + H2​O(l)

How Titration Works (in THIS Experiment)

• NaOH concentration is first determined using oxalic acid (primary standard)

• Standardized NaOH is placed in the burette

• Sulphamic acid sample is in the flask

• NaOH is added until the equivalence point is reached

• Volume of NaOH used → moles of acid

• Moles → concentration or mass of sulphamic acid