3.2Unit 3. Practical Skills in Chemistry I
Inorganic & Organic Chemistry Core Practicals — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 4 parts Lesson 2 of 2 1 quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Lesson summary
3.2 Inorganic & Organic Chemistry Core Practicals — halogenoalkanes, chlorination, oxidation and ion tests — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Describe and analyse Core Practicals 5 to 8: halogenoalkane hydrolysis, chlorination of 2-methylpropan-2-ol, oxidation of propan-1-ol…
- Carbonate and hydrogencarbonate
- Nucleophile
- Distillation
- Separating funnel
- Drying agent
- Qualitative analysis
Section 1 of 4More from the specification
Hydroxide
- A compound containing the OH− ion, formed by Group I metals with water.
Pipette
- Apparatus measuring a fixed volume such as 25.0 cm³.
Ionic equation
- An equation showing only the ions that react.
Carbon dioxide
- A gas that turns limewater cloudy.
Section 2 of 4Key terms
| Term | Meaning |
|---|---|
| Hydrolysis | Breaking a bond by reaction with water or hydroxide ions. |
| Nucleophile | A species with a lone pair that attacks an electron-deficient carbon. |
| Reflux | Heating with a vertical condenser so vapour returns to the flask. |
| Distillation | Heating a mixture so the most volatile component vaporises and is condensed and collected. |
| Separating funnel | Apparatus used to separate two immiscible liquid layers. |
| Drying agent | An anhydrous salt, e.g. MgSO4, that removes water from an organic liquid. |
| Qualitative analysis | Tests that identify which ions or functional groups are present. |
Section 3 of 4Syllabus checklist
1
Hydrolysis with aqueous NaOH or KOH is very slow at room temperature, so the mixture is warmed.
2
The rate depends on the halogen.
- The stronger the C-X bond, the slower the reaction: bond enthalpy C-F > C-Cl > C-Br > C-I.
- Fluoroalkanes do not react; iodoalkanes react very quickly.
3
OH− is a better nucleophile than water because it carries a full negative charge, whereas oxygen in water has only a partial charge.
4
If NaOH(aq) is used, acidify with HNO3 before adding AgNO3.
1
Put equal volumes of ethanol and acidified silver nitrate into three test tubes in a 50 °C water bath.
2
Add a few drops of a chloroalkane, a bromoalkane and an iodoalkane, one to each tube.
3
Start the stopwatch immediately.
4
Time how long each precipitate takes to appear.
Core Practical 5: measuring the rate
Water acts as the nucleophile: R-X + H2O → R-OH + H+ + X−, then Ag+ + X− → AgX(s).
Ethanol is the common solvent so the halogenoalkane and aqueous silver nitrate mix.
| Halogenoalkane | C-X bond enthalpy (kJ mol−1) | Precipitate | Rate |
|---|---|---|---|
| Chloro | about 346 | White AgCl | Slowest |
| Bromo | about 290 | Cream AgBr | Medium |
| Iodo | about 228 | Yellow AgI | Fastest |
- Bond enthalpy, not polarity, controls the rate; tertiary halogenoalkanes react faster than primary ones.
- Reaction(CH3)3COH + HCl → (CH3)3CCl + H2O at room temperature.
1
Place 8 cm3 of 2-methylpropan-2-ol in a separating funnel.
2
In a fume hood add 20 cm3 of concentrated HCl in 2–3 cm3 portions, releasing the pressure after each.
3
Leave for 20 minutes, gently shaking every 2 minutes.
4
Let the layers separate and run off the lower aqueous layer.
- The chloroalkane forms the upper organic layer.
1
Add sodium hydrogencarbonate solution in small portions, shaking and releasing pressure, to remove acidic impurities.
2
Run off the aqueous layer.
3
Pour the organic layer into a dry conical flask and add two spatulas of anhydrous magnesium sulfate until the liquid is clear.
4
Decant into distillation apparatus.
5
Distil and collect the fraction at 47–53 °C.
- A fume hood is essential because concentrated HCl is volatile and gives off hydrogen chloride gas;
- the window must not be above the safety line.
- Propan-1-ol oxidises to propanal (aldehyde) and then to propanoic acid.
1
Add 20 cm3 of acidified potassium dichromate(VI) to a pear-shaped flask and cool it in iced water.
2
Set up reflux apparatus and add anti-bumping granules.
3
Add 1 cm3 of propan-1-ol dropwise through the condenser.
4
Remove the ice bath and warm to room temperature.
5
Heat in a water bath or with an electric heater for 20 minutes.
6
Purify the product by distillation.
1
Distilling off the product at once gives propanal; heating under reflux with excess oxidant gives propanoic acid.
2
Boiling points: propanal 49 °C, propan-1-ol 97 °C, propanoic acid 141 °C.
3
Cr2O72− (orange) is reduced to Cr3+ (green).
4
Aldehydes give a silver mirror with Tollens' and a red precipitate with Fehling's; carboxylic acids fizz with NaHCO3.
1
Alcohols such as propan-1-ol, butan-1-ol and pentan-1-ol are flammable and harmful: keep them away from naked flames and use electric heating.
2
Avoid skin contact and breathing the vapour; use a fume cupboard for harmful alcohols.
3
Potassium dichromate is a strong oxidising agent and must be handled with care.
4
Mop up spillages straight away with plenty of water.
Core Practical 8: tests for ions
Dissolve a solid in deionised water before testing.
Ammonium
- Ammonium warm with NaOH(aq) in a water bath; NH4+ + OH− → NH3 + H2O.
- Damp red litmus paper turns blue in the NH3.
Carbonate and hydrogencarbonate
- Carbonate and hydrogencarbonate add dilute HCl and pass the gas into limewater.
- 2H+ + CO32− → CO2 + H2O and H+ + HCO3− → CO2 + H2O.
- The limewater turns milky.
Sulfate
- Sulfate acidify with dilute HCl, then add BaCl2(aq); a white precipitate of BaSO4 forms.
- HCl first removes carbonates that would also give a precipitate.
Halides
- Halides acidify with HNO3, add AgNO3 and test the precipitate with ammonia.
- (white AgCl, cream AgBr, yellow AgI)
1
Dip a nichrome or platinum wire loop in concentrated acid and hold it in a blue flame until no colour shows.
2
Dip the loop in the solid sample.
3
Hold it at the edge of the blue flame without letting the wire glow red.
4
Record the colour (Li+ red, Na+ yellow, K+ lilac, Ca2+ orange-red).
- Only one type of ion must be present, otherwise the colours mix.
| Test for | Method | Positive result |
|---|---|---|
| C=C | Shake with bromine water | Orange to colourless |
| -OH group | Add PCl5 | Steamy fumes of HCl |
| Primary/secondary alcohol, aldehyde | Warm with acidified K2Cr2O7 | Orange to green |
| Tertiary alcohol | Warm with acidified K2Cr2O7 | No change |
Section 4 of 4Exam technique
1
Forgetting to acidify with nitric acid before silver nitrate when NaOH was used — the hydroxide would give a false precipitate.
2
Using polarity to explain hydrolysis rate — the C-X bond enthalpy decides.
3
Heating organic liquids with a Bunsen burner — use an electric heater or water bath.
4
Not releasing pressure in the separating funnel — CO2 builds up when NaHCO3 meets acid.
5
Adding BaCl2 without acidifying first — carbonates also give a precipitate.
Marked practiceQuizzes for this lesson
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