What the OH carbon decides

Science · Chemistry · ages 16-17

Name ______________________ Date ____________

What colour change shows an alcohol oxidised by acidified dichromate?
- Green to orange
- Orange to green
- Colourless to black
An alcohol has two carbons joined to the C-OH carbon. Which class is it?
- Primary
- Tertiary
- Secondary
What happens to a tertiary alcohol with warm acidified dichromate?
- It gives a ketone
- Nothing; it stays orange
- It gives a carboxylic acid
Butan-2-ol and 2-methylpropan-2-ol are each warmed with acidified dichromate. What happens?
- Both give ketones
- One gives a ketone
- Both resist oxidation
How do you stop the oxidation of a primary alcohol at the aldehyde?
- Reflux the mixture
- Add extra oxidiser
- Distil it off
Dehydration of an alcohol needs only cold dilute acid.
Circle one: True False
A student refluxes a primary alcohol and expects only aldehyde. What is the error?
- Reflux pushes on to the acid
- Reflux stops all oxidation
- Primary alcohols cannot form aldehydes at all
Why do alcohols boil far higher than alkanes of similar mass?
- Alkanes hydrogen bond more strongly
- Hydrogen bonds beat London forces
- Alcohols are always heavier molecules

Answer key

For grown-ups. Fold this page away before handing over the rest.

Orange to green · Orange to green marks the chromium reduced as the alcohol oxidises.
Secondary · Two neighbours means secondary.
Nothing; it stays orange · Tertiary alcohols resist oxidation.
One gives a ketone · Secondary oxidises to a ketone, tertiary has no room to oxidise.
Distil it off · Removing the aldehyde by distillation stops further oxidation.
False · It needs heat with concentrated sulfuric acid or hot aluminium oxide.
Reflux pushes on to the acid · Reflux keeps the aldehyde in contact with oxidiser, so it oxidises further.
Hydrogen bonds beat London forces · Stronger forces between molecules need more energy to break.