ما هي معادلة الأسترة وكيف يتكون الإستر؟ What is the esterification reaction equation?

تفاعل الأسترة هو تفاعل انعكاسي بين حمض كربوكسيلي وكحول في وجود حمض الكبريتيك المركز كعامل حفاز لنزع الماء: R-COOH + R2-OH ⇌ R-COO-R2 + H₂O، ونواتجه إستر وماء. [الصيغة الرمزية الموزونة: R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O]

6.2Unit 6. Practical Skills in Chemistry II

Advanced Inorganic & Organic Chemistry Core Practicals — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 4 of 14 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision

Curriculum Equation Key Esterification Reaction EquationFast Exam Solution

R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O

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Lesson summary

6.2 Advanced Inorganic & Organic Chemistry Core Practicals: Complex Preparation, Qualitative Analysis and Aspirin — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Carry out and evaluate the core practicals on preparing a transition metal complex, qualitative analysis of inorganic and orga…

Cold ethanol wash
Yield above 100%
Group 2 ions
Ammonium ions
Order for sulfate
Tollens' reagent

Part 1 of 9Core Practical 12: preparing a copper complex

Product

Product dark blue crystals of Cu(NH₃)₄SO₄·H₂O.

Equation

CuSO₄·5H₂O + 4NH₃ → Cu(NH₃)₄SO₄·H₂O + 4H₂O.

Weigh 1.4–1.6 g of copper(II) sulfate by difference using a test tube.

Add 4 cm³ of water and dissolve it in a hot-water bath.

In a fume cupboard wearing gloves, add 2 cm³ concentrated ammonia while stirring, giving deep blue [Cu(NH₃)₄(H₂O)₂]²⁺.

Pour into 6 cm³ ethanol and cool in an ice bath.

Filter under reduced pressure with a Buchner funnel and wash with cold ethanol.

Dry between two filter papers and weigh the crystals.

Part 2 of 9Explaining the complex preparation

Ethanol

Ethanol is less polar than water, so the ionic complex is less soluble and crystallises.

Cold ethanol wash

Cold ethanol wash removes impurities without dissolving the product, which a hot wash would.

Yield above 100%

Yield above 100% shows the crystals are wet or impure.

Losses

Losses come from incomplete reaction and product remaining in solution.

Hazards

Hazards concentrated ammonia is corrosive, toxic and environmentally harmful;
- copper salts are harmful;
- ethanol is flammable.

Part 3 of 9Core Practical 15: tests for positive ions

Core Practical 15: tests for positive ions

Preparation

Preparation a solid sample is first dissolved in deionised water.

Group 2 ions

Group 2 ions add NaOH dropwise to the chloride solutions of Ba, Ca, Mg and Sr, then in excess, and compare the precipitates.

Ammonium ions

Ammonium ions warm the sample gently with NaOH(aq) and hold damp red litmus paper at the mouth of the tube, which turns blue in ammonia gas.

Ion	Test with NaOH(aq)	Observation
Fe²⁺	Add NaOH	Green precipitate that darkens in air
Fe³⁺	Add NaOH	Orange-brown precipitate
Cu²⁺	Add NaOH, then excess NH₃	Blue precipitate dissolving to a deep blue solution

Part 4 of 9Core Practical 15: tests for negative ions

Ion	Test	Positive result
Cl⁻, Br⁻, I⁻	Add dilute HNO₃, then AgNO₃	White, cream and yellow precipitates; dilute or concentrated ammonia then distinguishes them
OH⁻	Red litmus or universal indicator paper	Litmus turns blue, clearly alkaline pH
CO₃²⁻	Add dilute HCl and pass the gas into limewater	Gas turns limewater milky
SO₄²⁻	Add dilute HCl, then BaCl₂(aq)	White precipitate of BaSO₄

Order for sulfate
- HCl is added first to remove carbonate, which would also give a precipitate.

Part 5 of 9Core Practical 15: tests for organic functional groups

Group	Reagent	Positive result
C=C	Bromine water	Orange solution decolourises
–OH	PCl₅	Steamy fumes of HCl at room temperature
Primary or secondary alcohol	Acidified K₂Cr₂O₇ or KMnO₄	Orange to green, or purple to colourless
Carbonyl C=O	2,4-DNPH	Deep orange precipitate
Aldehyde	Tollens' reagent, warmed	Silver mirror
Aldehyde	Fehling's or Benedict's solution, warmed	Brick-red precipitate of Cu₂O
Carboxylic acid	Na₂CO₃(s) or NaHCO₃(aq)	Effervescence of CO₂
CH₃CO– or CH₃CH(OH)–	Iodine and NaOH (iodoform)	Yellow precipitate

Part 6 of 9Interpreting the carbonyl tests

2,4-DNPH

2,4-DNPH the C=O group condenses with it, and the precipitate is purified by recrystallisation and identified from its melting point.

Tollens' reagent

Ag⁺ oxidises an aldehyde to a carboxylic acid and is reduced to silver.

Fehling's solution

Cu²⁺ oxidises an aldehyde to a carboxylic acid and is reduced to Cu⁺ in Cu₂O.

Ketones

Ketones give no reaction with Tollens' or Fehling's because they cannot be oxidised.

Alcohol oxidation

Alcohol oxidation primary and secondary alcohols are oxidised to aldehydes and ketones,
- which can be tested further,
- whereas tertiary alcohols are not oxidised.

Part 7 of 9Core Practical 16: preparing aspirin

Skills
- measuring, heating in a water bath, recrystallising a solid and using melting-point apparatus.

Mix 6.0 g salicylic acid, 10 cm³ ethanoic anhydride and 5 drops of concentrated sulfuric acid catalyst in a conical flask.

Warm in a water bath at about 60 °C for 20 minutes.

Cool and pour into 75 cm³ cold water so aspirin crystallises.

Filter under reduced pressure with a Buchner funnel.

Recrystallise: dissolve in the minimum hot ethanol, pour over 40 cm³ cold water, filter and dry.

Take the melting point of the dry product.

Part 8 of 9Recrystallisation and melting point of aspirin

Recrystallisation

Recrystallisation uses the minimum hot solvent, a hot filtration for insoluble impurities, slow cooling for large crystals and a wash with cold solvent.

Repeating

Repeating gives a purer product but lowers the yield each time.

Purity

Purity pure aspirin melts sharply at 135 °C, whereas impurities lower and broaden the melting range.

Technique

Technique use a dry, finely powdered sample, heat slowly, repeat three times and quote a range.

Part 9 of 9More from the specification

Key terms

Term	Meaning
Recrystallisation	Purifying a solid by dissolving it in the minimum hot solvent, cooling to crystallise and filtering.
Complex ion	A central metal ion with ligands bonded by dative covalent bonds.
Buchner filtration	Filtration under reduced pressure for speed.
Qualitative analysis	Tests that identify which ions or functional groups are present.
Tollens' reagent	Ammoniacal silver nitrate, which gives a silver mirror with aldehydes.
Melting point range	The interval over which a solid melts, which shows purity.

Avoid these mistakes

Using hot solvent to wash crystals — the product dissolves, so use cold solvent.

Adding BaCl₂ before HCl in the sulfate test — carbonate would give a false precipitate.

Quoting a melting point as a single number — give a range and compare it with the data book.

Saying ketones give a silver mirror — only aldehydes react with Tollens' reagent.

Last updated: 15 October 2026