alcohols chp 14

Question 1

what gives alcohols there physcial and chemical properties

Answer 1

The Hydroxyl group (-OH)

Question 2

what are some difference between the characteristic of alcohols and alkanes

Answer 2

• they have higher melting/boiling points
• they have greater water solubility (than there corresponding alkanes)

• The differences become smaller as chain length increases

Question 3

Descibe and explain what effect the polarity of alkanes has on its characteristics

Answer 3

• non-polar due to electronegativity similarity bonding elements
• intermolecular forces between non-polar molecules are very weak London forces leads, to low melting and boiling points
• insoluble in polar solvents
• soluble in non-polar solvents

Question 4

Descibe and explain what effect the polarity of alcohols has on its characteristics

Answer 4

• alcohols are polar due to presence of OH group making them soluble in some polar solvents
• higher melting and boiling points than respective alkanes

Question 5

what does the trend in boiling points between alcohols and alkanes look like

Answer 5

Question 6

define Volatility

Answer 6

how easily a substance will vaporize

volatile liquids have a low boiling point

Question 7

what alcohols if any are soulble in water and explain why they are

Answer 7

alcohols such as methanol and ethanol are completely soluble in water as hydrogen bonds form between the polar OH groups of the alcohols and the water molecules

Longer chain are less soluble due to the effect of the OH group becomeing less prevelant with increasing chain length

Question 8

what is a primary alcohol

Answer 8

• OH group in alcohol attached to carbon attached to 2 hydrogens and a single carbon
• 3 hydrogens in methanol case

Question 9

what is a secondary alcohol

Answer 9

The alcohol is OH group is attached to a carbon atom that is attached to 1 hydrogen atom and 2 alkyl groups

Question 10

what is a tertiary alcohol

Answer 10

The OH group is attached to a carbon atom that is attached to no hydrogen atoms and 3 alkyl groups

Question 11

can alcohols be oxidised, if so which alcohols

Answer 11

• Primary and secondary alcohols can be oxidised (using [o], acidfied potassium dichromate(VI) K2Cr2O7/H+)
• Tertiary alcohols cannot be oxidised

Question 12

what colour change occurs when alcohols are oxidised

Answer 12

orange to green

Question 13

what are primary alcohols oxidised into

Answer 13

-Primary alcohols can be oxidised to either aldehydes or carboxylic acid
-The product of the oxidation depends on the reaction conditions used (aldehydes are themselves oxidised to carboxylic acids)

Question 14

how do you obtain aldehydes from alcohols

Answer 14

• distill primary alcohols with acidified potassium dichromate

Question 15

• how do you obtain a carboxylic acid from an alcohol
• write reaction

Answer 15

• reflux primary alcohol with excess acidified potassium dichromate (VI) (ensures all alcohol is oxidised)
• reflux ensures any aldehyde formed undergoes oxidation to form carboxylic acid.

Question 16

what are secondary alcohols oxidised into

Answer 16

They are oxidised into ketones (it is not possible to further oxidise ketones using acidified dichromate ions)

Question 17

what is the process to obtain a ketone from a secondary alcohol

Answer 17

you heat the secondary alcohol under reflux with excess acidified dichromate ions

-you heat under reflux to ensure that all alcohol has been reacted - you add excess to ensure that the all the alcohol is allowed to react -There will be a colour change from orange to green

Question 18

what is a dehydration reaction

Answer 18

dehydration is any reaction in which a water molecule is removed from the starting material

Question 19

whats the process to dehydrate an alcohol

Answer 19

• heat alcohol under reflux in presence of acid catalyst conc H2SO4, or conc (phosphoric acid) H3PO4.
• produces alkene

Question 20

what are the products of a dehydration reaction with an alcohol

Answer 20

water + alkene

Question 21

what type of reaction is a dehydration reaction

Answer 21

An elimination reaction

Question 22

what is a substitution reaction

Answer 22

an atom, ion, or group of atoms or ions in a molecule is replaced by another atom, ion, or group

Question 23

What is an example of a substitution reaction that alcohols can undergo

Answer 23

alcohols react with hydrogen halides to form haloalkanes

Question 24

what is the process to produce a haloalkane from an alcohol

Answer 24

• alcohol is heated under reflux with sulphuric acid and a sodium halide,
• ^hydrogen halide is formed which reacts with alcohol to produce a haloalkane, salt and water

Question 25

what does the hydrogen halide reaction with the alcohol chemical equation look like

Answer 25