(U2) Alcohols

Question 1

What are miscible liquids?

Answer 1

Liquids which mix in all proportions i.e. form a single layer

Question 2

What is a primary alcohol?

Answer 2

An alcohol which has 1 carbon atom directly bonded to the carbon atom that is bonded to the OH group

Question 3

What is a secondary alcohol?

Answer 3

An alcohol which has 2 carbon atoms directly bonded to the carbon atom that is bonded to the OH group

Question 4

What is a tertiary alcohol?

Answer 4

An alcohol which has 3 carbon atoms directly bonded to the carbon atom that is bonded to the OH group

Question 5

What is the catalyst used to oxidise alcohols?

Answer 5

Acidified potassium (or sodium) dichromate

K₂Cr₂O₇

Question 6

What are the products of oxidation of primary alcohols?

Answer 6

• 1st an aldehyde (for partial oxidation) e.g.
  C₂H₅OH + [O] —> CH₃CHO + H₂O
• 2nd a carboxylic acid (for complete oxidation) e.g.
  C₂H₅OH + 2[O] —> CH₃COOH + H₂O

Question 7

What are the products of oxidation of secondary alcohols?

What is their functional group?

Answer 7

• Ketones
• C=O

Question 8

What are the products of oxidation of tertiary alcohols?

Answer 8

None

Question 9

What is the colour change of acidified potassium dichromate when an alcohol is oxidised?

Answer 9

Orange to green

Question 10

Why can alcohols form hydrogen bonds?

What is the effect of this on the solubility and boiling points of alcohols?

Answer 10

1. Due to the presence of a hydroxyl group (-OH)

• means they are soluble in aqueous solvents and organic solvents
• also means they have far higher b.p.s than alkenes, alkanes etc.

Question 11

What is the general formula of alcohols?

What is the functional group?

Answer 11

• C_nH_2n+1OH
• (-OH)

Question 12

What colour is the flame of alcohol when it burns in pure oxygen?

What would it be in incomplete combustion?

Answer 12

• Clean blue
• Smokey blue

Question 13

What is the general equation for the reaction between alcohols and HBr?

What are the conditions (2)?

Answer 13

1. ROH + HBr —> RBr + H₂O

• anhydrous conditions
• must be heated under reflux (in order for HBr to be prepared in situ - react NaBr and H₂SO₄)

Question 14

What is the general equation for the reaction between alcohols and PCl₅?

What are the conditions (2)?

What are the observations (5)?

Answer 14

1. ROH + PCl₅ —> RCl + HCl + POCl₃

• anhydrous
• room temp

• white solid disappears
• effervescence
• fumes form
• vigorous
• heat released

Question 15

What is the equation for the reaction between ethanol and Na?

What are the observations (4)?

Answer 15

1. 2C₂H₅OH_(l) + 2Na_s —> 2C₂H₅ONa_(alc) + H_{2 (g)}

• solid disappears
• colourless solution formed
• heats up
• effervescence

Question 16

Recall the preparation of alcohols from halogenoalkanes (4)

Answer 16

• place the halogenoalkane in a round bottomed flask
• add dilute NaOH solution
• heat under reflux
• distil off the alcohol