Alcohols, Haloalkanes and Analysis

Question 1

What is a primary alcohol?

Answer 1

An alcohol where the carbon attached to the hydroxyl group is only attached to one other carbon

Question 2

What is a secondary alcohol?

Answer 2

An alcohol where the carbon attached to the hydroxyl group is attached to two other carbons

Question 3

What is a tertiary alcohol?

Answer 3

An alcohol where the carbon that is attached to the hydroxyl group is attached to 3 other carbons

Question 4

Why are short chained alcohol molecules soluble in water?

Answer 4

The OH group forms hydrogen bonds with the water molecules, this enables dissolve in water. Larger alcohol molecules aren’t soluble in water as the alkyl chain becomes too long and disrupts the hydrogen bonding of the OH group with the water molecules

Question 5

What are the products of complete combustion?

Answer 5

Carbon dioxide and water

Question 6

What are the products of incomplete combustion

Answer 6

Carbon monoxide and water

Question 7

Which alcohols can be oxidised by an oxidising agent?

Answer 7

Primary and secondary alcohols

Question 8

What does the oxidisation of a primary alcohol produce?

Answer 8

An aldehyde and then a carboxylic acid, partial oxidation produces an aldehyde, reflux produces a carboxylic acid

Question 9

What does the oxidisation of a secondary alcohol produce?

Answer 9

A ketone, heat under reflux

Question 10

What is the oxidising agent used to oxidise primary and secondary alcohols?

Answer 10

Acidified potassium dichromate, K2Cr2O7 / H+

Question 11

Describe the process of reflux

Answer 11

• Add the pre weighed potassium dichromate to a pear shaped flask using a funnel
• Slowly add 20cm^3 of 3.0 moldm-3 sulfuric acid to the pear shaped flask using a funnel
• Add a few anti-bumping granules (to make the mixture boil more calmly) and swirl the flask to dissolve the solid
• Cool the solution by swirling the flask in an ice water bath for 2-3 minutes until the solution is cooler than 10 degrees
• Carefully add 0.5cm^3 of ethanol to the flask drop wise while swirling the flask in ice water
• Continue to swirl the mixture in ice water and monitor the temperature of the reaction with a thermometer
• Clamp the flask by the neck, position in your heating apparatus and arrange the condenser above the flask in a reflux setup, turn on the condenser water flow
• Heat the reaction mixture under reflux for around 20 minutes

Question 12

Write the equation of the oxidation of propan-1-ol to propanal

Answer 12

C3H7OH + [O] → CH3H6O + H2O

Question 13

Write the equation of the oxidation of propan-1-ol to propanoic acid

Answer 13

CH3H7OH + 2[O] →CH2H5COOH + H2O

Question 14

Write the equation of the oxidation of a butan-2-ol to butanone

Answer 14

C4H9OH + [O] →CH3COC2H5 + H2O

Question 15

What is the observation in the oxidation of any class of alcohol?

Answer 15

Colour change from orange to green

Question 16

What is the trend in reactivity of haloalkanes?

Answer 16

• Going down the halogen group the reactivity of the haloalkanes increases, with fluoroalkanes being the least reactive and iodoalkanes being the most reactive
• As you go down the halogen group, the atomic radius increases in size and therefore their bonding electrons experience a greater shielding effect and a weaker nuclear attraction, this means bonds that these electrons form have lower bond enthalpies than bonds formed by bonding electrons of elements further up the group
• The lower bond enthalpy means that the C-X bond is easier to break and therefore the haloalkanes of elements further down the group are more reactive

Question 17

What is the order of reactivity of the haloalkanes?

Answer 17

Most reactive- Iodoalkanes, bromoalkanes, chloroalkanes, fluoroalkanes -Least reactive

Question 18

Will there be a faster rate of hydrolysis using water or an aqueous alkali such as NaOH?

Answer 18

An aqueous alkali as it fully dissociates meaning it releases more OH- ions at a faster rate than water

Question 19

Write the mechanism for the decomposition of ozone by chlorine radicals

Answer 19

Propagation- Cl. + O3 → ClO. + O2
- ClO. + O3 → Cl. + 2O2
Overall- 2O3 → 3O2

Question 20

Write the mechanism for the decomposition of ozone by NO radicals

Answer 20

NO. + O3 → NO2. + O2
NO2. + O → NO. + O2
Overall- O3 + O → 2O2

Question 21

What is the molecular formula of a typical CFC?

Answer 21

C2F2Cl2

Question 22

Does potassium dichromate change colour at low temperatures when added to a ketone?

Answer 22

No, tit will only react with aldehydes at low temperatures, this is a way to determine what product you have formed

Question 23

What is the half equation for the reduction of Cr2O7^2-?

Answer 23

Cr2O7^2- + 14H+ + 6e- → 2Cr3+ + 7H2O

Question 24

What is the half equation for the oxidation of an aldehyde?

Answer 24

3RCHO + 3H2O → 3RCOOH + 6H+ + 6e-

Question 25

What is the overall equation for the oxidation of an aldehyde?

Answer 25

• 3RCHO + Cr2O7^2- + 8H+ → 2Cr3+ + 3RCOOH + 4H2O

- Or simplified: RCHO + [O] → RCOOH