ChemistryChapter 18: Alcohol
Oxidation (dichromate School)
Acidified K2Cr2O7 (orange) is the school oxidant.
Learning objectives
- Explain oxidation (dichromate school) in simple chemical language.
- Connect 1. primary with 2. 2 and 3 using equations, observations, or trends where needed.
- Answer a short Federal Board question with the correct terms and a clear reason.
Definition
Acidified K2Cr2O7 (orange) is the school oxidant. Primary alcohol -> aldehyde (distil out) -> carboxylic acid (reflux excess). Secondary -> ketone (stops). Tertiary: no easy oxidation (no H on C-OH). Colour orange to green (Cr6+ to Cr3+). Meaning: the product depends on class and on whether you distil or reflux. Tollens later sorts aldehyde from ketone. No illicit oxidation routes. Primary -> aldehyde then carboxylic acid if excess oxidant; secondary -> ketone; tertiary resistant. Primary alcohols need distillation to stop at aldehyde; dichromate colour change should be stated.
Important terms
- OXIDATION (DICHROMATE SCHOOL)
- Acidified K2Cr2O7 (orange) is the school oxidant.
- 1. PRIMARY
- Distil: catch aldehyde before it becomes acid.
- 2. 2 AND 3
- Propan-2-ol -> propanone, then stop.
Overview
Distil vs reflux, then class:
Primary
Distil: catch aldehyde before it becomes acid. Reflux with excess oxidant: acid. Ethanal vs ethanoic from ethanol. Smell names if the book uses them. Acidified K2Cr2O7 orange to green Cr3+ — colour change observation.
Examples Distil aldehyde · Reflux acid · Orange -> green
2 and 3
Propan-2-ol -> propanone, then stop. Tert-alcohol: remains, dichromate stays orange (school). Fehling/Tollens negative for ketones. Distillation stops at aldehyde; reflux continues to acid.
Examples Ketone · 3 no reaction · Green only if oxidised
WHAT — OXIDATION (DICHROMATE SCHOOL)
Acidified K2Cr2O7 (orange) is the school oxidant. Primary alcohol -> aldehyde (distil out) -> carboxylic acid (reflux excess). Secondary -> ketone (stops). Tertiary: no easy oxidation (no H on C-OH). Colour orange to green (Cr6+ to Cr3+). Meaning: the product depends on class and on whether you distil or reflux. Tollens later sorts aldehyde from ketone. No illicit oxidation routes. Primary -> aldehyde then carboxylic acid if excess oxidant; secondary -> ketone; tertiary resistant. Primary alcohols need distillation to stop at aldehyde; dichromate colour change should be stated.
WHY — Why this topic matters
OXIDATION (DICHROMATE SCHOOL) is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.
HOW — How it works
PRIMARY: Distil: catch aldehyde before it becomes acid. Reflux with excess oxidant: acid. Ethanal vs ethanoic from ethanol. Smell names if the book uses them. Acidified K2Cr2O7 orange to green Cr3+ — colour change observation. Examples: Distil aldehyde; Reflux acid; Orange -> green. 2 AND 3: Propan-2-ol -> propanone, then stop. Tert-alcohol: remains, dichromate stays orange (school). Fehling/Tollens negative for ketones. Distillation stops at aldehyde; reflux continues to acid. Examples: Ketone; 3 no reaction; Green only if oxidised. Exam primary oxidation: distil: aldehyde (ethanal from ethanol) reflux excess: carboxylic acid (ethanoic) K2Cr2O7 orange -> green
In simple words
School dichromate. No chromate waste-dump, no illicit synth.
Key points
- 1 -> al then acid
- 2 -> ketone
- 3 no
- time in the oxidant
- H on C-OH needed
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Oxidation (dichromate School)
Sticky Notes · Quick Revision
Core Idea
- Acidified K2Cr2O7 (orange) is the school oxidant. Primary alcohol -> aldehyde (distil out) -> carboxylic acid (reflux excess). Secondary -> ketone (stops). Tertiary: no easy oxidation (no H on C-OH). Colour orange to green (Cr6+ to Cr3+). Meaning: the product depends on class and on whether you distil or reflux. Tollens later sorts aldehyde from ketone. No illicit oxidation routes. Primary -> aldehyde then carboxylic acid if excess oxidant; secondary -> ketone; tertiary resistant. Primary alcohols need distillation to stop at aldehyde; dichromate colour change should be stated.
1. PRIMARY
- Distil: catch aldehyde before it becomes acid. Reflux with excess oxidant: acid. Ethanal vs ethanoic from ethanol. Smell names if the book uses them. Acidified K2Cr2O7 orange to green Cr3+ — colour change observation.
- Distil aldehyde
- Reflux acid
- Orange -> green
2. 2 AND 3
- Propan-2-ol -> propanone, then stop. Tert-alcohol: remains, dichromate stays orange (school). Fehling/Tollens negative for ketones. Distillation stops at aldehyde; reflux continues to acid.
- Ketone
- 3 no reaction
- Green only if oxidised
Exam Example
- Exam primary oxidation:
- distil: aldehyde (ethanal from ethanol)
- reflux excess: carboxylic acid (ethanoic)
- K2Cr2O7 orange -> green
Common Misconceptions
- Do not confuse 1. PRIMARY with 2. 2 AND 3; state the difference before giving an example.
- Writing only “1 -> al then acid” is not enough. Explain what it means in a complete sentence.
FBISE Exam Check
- Explain oxidation (dichromate school), compare its two main parts, and include the correct chemical evidence.
- School dichromate. No chromate waste-dump, no illicit synth.
60-second revision
- Acidified K2Cr2O7 (orange) is the school oxidant.
- 1. PRIMARY: Distil: catch aldehyde before it becomes acid.
- 2. 2 AND 3: Propan-2-ol -> propanone, then stop.
- Exam reminder: Exam primary oxidation: distil: aldehyde (ethanal from ethanol) reflux excess: carboxylic acid (ethanoic) K2Cr2O7 orange -> green
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