Acid & Base Titrations

Pipette

used to accurately measure a known volume of liquid

Procedure for Pipette

1. Rinse with deionised water

2. Rinse with solution it will contain. This done to remove the used while rinsing to avoid diluting the solution

3. Using a pipette filler, fill the pipette with solution until the bottom of the meniscus reaches the calibration mark when read at eye level.

4. Let the pipette drain under gravity. Touch the tip of the pipette against the container to remove the last drop

Burette

used to accurately measure the volume of liquid /solution added

Procedure for Burette

1. Rinse with deionised water

2. Rinse with the solution it’s to contain

3. Clamp vertically

4. Using a funnel, fill the burette above the zero mark

5. Remove the funnel

6. Open the tap to bring the bottom of the zero mark, & to fill the jet below the tap.

Meniscus

is the curve in upper surface of a liquid close to the surface of the container or another object, produced by surface tension

Use for the Meniscus

It will reduce the potential errors in volumetric analysis

Conical Flask

a specially shaped flack that allows swirling without spilling the contnent

Procedure for Conical Flask

Clean with deionised water only

Procedure for Volumetric flask

Clean with deionised water only

Volumetric Flask

a specially shaped flask that holds a specific calibrated volume of liquid

1)Standardise a solution HCL using a standard solution of Na₂CO₃

Theory

The HCL acid that we use in the lab isn’t sufficiently pure to be used as a primary standard. Thus we need to use a primary standard solution to standardise it.

Key Info

Acid: HCL - strong acid

Base: Na₂CO₄ - strong base

Indicator: Methyl Orange = Yellow to Red

Equation: 2HCL + Na₂CO₃ +HO₂ + CO₂ Ratio: 2 HCL :Na₂CO₃

Concentration of Sodium Carbonate = 0.1M Volume used = 25cm³

Rough Titre = 27cm³ Second Titre = 26.6cm³

Third Titre = 26.7cm³ Av. Titre 26.65cm³

Calculation

_Va x Ma_ = _Vb x Mb_

Na Nb

2) (OL) Standardised a prepare solution of Sodium Hydroxide using previous standardised Hydrochloric acid & thus produce a sample of Sodium Chloride salt

Theory

Standardised solution of HCl used to standardise a prepared solution of NaOH. We initially carry out the titration with an indicator. Once the end point is established the titration is repeated with no indicator. The neutral solution will contain Na⁺ & Cl^- ions. When the solvent is evaporated, we are left with NaCl crystal - common table salt

Key Info

Acid: HCl - strong acid

Base: NaOH - strong base

Indicator: Methyl Orange (SASBMO)

Colour change: Yellow to Red

Equation: HCl + NaOH —→ NaCl + H₂O Ratio: 1 HCl:1 NaOH

Concentration of HCl = 0.1M Volume used = 24.15cm³

Concentration of NaOH = xM Volume used = 25cm³

Rough Titre = 24.2cm³ Second Titre = 24.1cm³

Third Titre = 24.2cm³ Average Titre = 24.15cm³

3) To determine the concentration of ethanoic acid in vinegar

Theory

Vinegar is a solution of ethanoic acid (CH₃COOH) in water. Ethanoic acid is a weak acid. The concentration of ethanoic acid in vinegar can be found by a titration with sodium hydroxide. To minimise wastage we dilute the vinegar prior to the titration. We must take the dilution into account when calculation out final concentration.

Key Info

Acid: CH₃COOH - weak acid

Base: NaOH - strong base

Indicator: Phenolphthalein (WASBPH)

Colour change: Pink to Colourless

Equation: CH₃COOH + NaOH —→ CH₃COONa + H₂O Ratio: 1 CH₃COOH :1 NaOH

Note

Vinegar must be diluted beforehead because it’s too concentrated. Make sure to multiply the concentration of the dilute vinegar by the dilution factor to find the concentration of the original vinegar.

Dilution Factor

Volume of Diluted Vinegar

Volume of Original Vinegar

4) To determine the amount of water of crystallisation in washing soda (Hydrate sodium carbonate)

Theory

Hydrated sodium carbonate has the formula Na₂CO₃.xH₂O where x is the number of molecules of water present in the crystalline structure (water of crystalisation)

Key Info

Acid: HCl - strong acid

Base: Na₂CO₃ - weak base

Indicator: Methyl Orange (SAWBMO)

Colour change: Yellow to Red

Equation: 2HCl + Na₂CO₃ —→ NaCl + H₂O + CO₂ Ratio: 2HCl : 1Na₂CO₃

Notes

Same as titration number 1, just with extra calculations.

The crystals are made up of Na₂CO₃.xH₂O

1. The percentage of water of crystallisation

2. The value of x

These calculations can also comes up for other compounds - not just in this experiment. E,g, finding the percentage water of crystallisation & value for x in hydrated copper (II) sulphate, CuSO₄.xH₂O

Percentage water of Crystallisation

water mass x 100

total mass