The method and the results are on the oxidation of alcohols lab. Do the analysis yourself first, then check the answers below.
Quick answer: Primary alcohols are oxidised to aldehydes and then carboxylic acids, secondary alcohols to ketones, and tertiary alcohols resist oxidation; acidified dichromate turns from orange to green. These answers go with the Chemistry 11-12 lab on oxidation of alcohols: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Also, the model answers use the sample table. Also, each identification must follow from at least one observation. In addition, equations should balance and use [O] correctly, and the silver calculation uses a 1 : 2 ratio of aldehyde to silver.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.3.5
Both are oxidised, but A gives an aldehyde (DNPH precipitate and mirror) while B gives a ketone (precipitate only). Primary gives a mirror; secondary does not.
Question 3 Why C stays orange
C is a tertiary alcohol: the carbon bearing OH has no hydrogen, so dichromate is not reduced and stays orange.
Question 4 D and E with dichromate
D is an aldehyde and is easily oxidised to a carboxylic acid. E is a ketone, with no hydrogen on the carbonyl carbon, so it resists oxidation.
Question 5 Equation
CH₃CH₂CH₂OH + [O] → CH₃CH₂CHO + H₂O; with excess oxidant under reflux the final product is propanoic acid.
Question 6 Silver from propanal
n = 0.58 / 58.0 = 0.0100 mol; n(Ag) = 0.0200 mol; mass = 0.0200 × 107.9 = 2.16 g.
Question 7 Safety and improvement
On standing, it can form explosive silver compounds, so it is made fresh and destroyed with acid. Improvement: recrystallise the DNPH derivatives and compare their melting points with a data table to confirm each identity.
