Module 4.2 Flashcards Preview

Chemistry OCR A Level > Module 4.2 > Flashcards

Flashcards in Module 4.2 Deck (80)
Loading flashcards...
1

Give an overview of alcohols

- Aliphatic
- General formula = CnH2n+1OH

2

Describe the polarity of alcohols

The electronegative oxygen from the OH (of the alcohol) draws electron density from hydrogen making it slightly positive (delta-positive). This slightly positive hydrogen can attract the lone pair of an oxygen from a neighbouring molecule (such as water) forming hydrogen bonds with it.

Therefore, alcohols are polar.

3

What bonds to alcohols form with water? (and between what atoms)

Alcohols can form hydrogen bonds with water.

Between H( (H must have a delta positive charge on it) and O (O must have a delta negative charge on it and a lone pair)

4

Explain in terms of hydrogen bonding, the solubility of alcohols compared with alkenes

- When you mix an alcohol, with water, hydrogen bonds are formed.

If it's a small alcohol, hydrogen bonding lets it mix freely with water. Therefore, small alcohols are soluble in water.

However, in larger alcohols, most of the molecule is NON-POLAR. So there is less attraction for the polar water molecules. This means that as alcohols increase in size, their solubility decreases.

5

Explain in terms of hydrogen bonding, the relatively low volatility of alcohols compared with alkenes

Alcohols have a relatively low volatility because the hydrogen bonds require so much energy to break.

Another saying for this is : Alcohols don't evaporate easily to gas because the H bonds require so much energy to overcome.

6

What are the 3 types of alcohol?

Primary
Secondary
Tertiary

7

Define a primary alcohol

An organic compound, with an OH group, in which the OH group is at the end of a carbon chain.

8

Define a secondary alcohol

An organic compound, with an OH group, in which the OH group is attached to a carbon atom that is attached to 1 hydrogen

9

Define a tertiary alcohol

An organic compound, with an OH group, in which the OH group is attached to a carbon atom which is attached to no hydrogen groups

10

Give examples of a primary alcohols

Ethanol
Butanol
Hexanol
Propan-1-ol
Pentan-1-ol

11

Give examples of secondary alcohols

Propan-2-ol
Butan-2-ol
Hexan-2-ol
Pentan-2-ol

12

Give examples of tertiary alcohols

2-methylpropan-2-ol
2-methylbutan-2-ol
3-methylpentan-3-ol

13

What are the products in the complete combustion of an alcohol?

Carbon Dioxide and Water

14

How do you balance the reaction between an alcohol and oxygen?

- First balance the hydrogen
- Then balance the carbon
- Lastly balance the oxygens

15

What does the sign [O] represent?

An oxidising agent

16

Describe the oxidation of primary alcohols to form aldehydes (Give the reagents, conditions, the observation, a generic equation and an example equation)

Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Distillation
Generic = R-CH2-OH + [O] → R-CHO + H2O
Example = CH3CH2OH + [O] → CH3CHO + H2O
Colour change - Orange to Green

17

Describe the oxidation of primary alcohols to form carboxylic acids(Give the reagents, conditions, the observation, a generic equation and an example equation)

Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Reflux
Generic = R-CH2-OH + 2[O] → R-COOH + H2O
Example = CH3CH2OH + 2[O] → CH3COOH + H2O
Colour change - Orange to Green

18

State the functional group and location of aldehydes

CHO Functional Group
Location = End of the chain

19

What do aldehydes end in?

-al

20

State the functional group and location of carboxylic acids

COOH Functional Group
Location = At the end of the chain

21

What do carboxylic acids end?

- oic acid

22

Describe the oxidation of secondary alcohols to form ketones
(Give the reagents, conditions, the observation, a generic equation and an example equation)

Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Reflux
Generic = R-CH(OH)-CH3 + [O] →R-C(O)-CH3 + H2O
Example = CH3CH2CH3 + [O] → CH3COCH3 + H2O
Colour change - Orange to Green

23

Describe the resistance of oxidation of tertiary alcohols

Tertiary alcohols cannot be oxidised using an oxidation agent such as acidified potassium dichromate because in order for oxidation to occur, the -OH must be attached to a carbon that has at least ONE hydrogen attached to it. For tertiary alcohols, this is not the case

24

Describe the dehydration of water from alcohols to form alkenes
(Give the reagents and conditions)

Reaction name = Dehydration
Regeants = CONC sulphuric acid OR CONC phosphoric acid
Conditions = Reflux, 180 degrees celsius
Products = Alkene + Water

25

Describe the substitution of nucleophiles to go from a haloalkane to a alcohol

Reaction name = Nucleophilic Substitution of haloalkanes
Regeants = Halide ions (from HX)
Conditions = CONC sulphuric acid OR CONC phosphoric acid and ROOM Temperature

26

Describe the hydrolysis of haloalkanes in a substitution reaction by aqueous alkali

Reaction name - Nucleophilic sub
Conditions = Reflux (heat) in aq solution
Regeant = NaOH
Nucleophile used = OH- ion (from NaOH)
Product = Alcohol + X-

27

How can we experimentally compare the rates of hydrolysis of different C-X bonds in terms of precipitation formation?

React the different C-X bonds (C-F,C-Cl,C-Br and C-I) with silver nitrate and ethanol to see how fast each precipitate forms.

The faster the precipitate forms, the faster the rate of hydrolysis

28

What C-X bond forms a precipitate the quickest? What does this us about the rate of reaction

The C-I (Iodine bond) bond takes the least amount of time to for a ppt. This means that it has the fastest rate of reaction.

Iodine the fastest rate of reaction

29

What colour is the precipitate formed by Chlorine?

White

30

What colour is the precipitate formed by Bromine?

Cream