4.2 Alcohols, Haloalkanes And Analysis

Question 1

Why is the boiling point of alcohols higher than that of their corresponding alkane?

Answer 1

-as their are hydrogen bonds between the alcohol molecules
-this is the strongest type of intermolecular bond
-more energy is needed to overcome this intermolecular force than the London intermolecular forces in alkanes

Question 2

Why are alcohols less volatile than their corresponding alkane?

Answer 2

-due to the hydrogen bonding in alcohols that is not present in alkanes

Question 3

Describe water solubility in an alcohol

Answer 3

-water molecules are polar and so is the alcohol functional group
-meaning some alcohols (methanol,ethanol and propanol) are soluble in water
-their molecules form hydrogen bonds with the molecules, sometimes described as miscibility

Question 4

What happens to the solubility of an alcohol as their alkyl chain length increases?

Answer 4

-the solubility of an alcohol decreases
-because the aliphatic chain cannot form hydrogen bonds and this becomes the larger part of the molecule

Question 5

What happens if you oxidise a primary alcohol with K2Cr2O7 with gentle heating?

Answer 5

-the alcohol group loses its hydrogen and is partially oxidised to an aldehyde-the alcohol must be distilled immediately to prevent any further reaction
-colour change from orange to green

Question 6

What happens if a primary alcohol is heated under reflux with excess K2Cr2O7?

Answer 6

-full oxidation occurs to form a carboxylic acid
-colour change from orange to green

Question 7

How do you form a ketone ?

Answer 7

-oxidise a secondary alcohol by heating it under reflux with K2CrO7 (acidified potassium dichromate (VI)
-colour change from orange to green

Question 8

Are tertiary alcohols oxidised by acidified potassium dichromate (VI)?

Answer 8

-no tertiary alcohols are very resistant to oxidation and are not oxidised by common oxidising agents

Question 9

What is the esterification of alcohols

Answer 9

-making an ester by reacting an alcohol with a carboxylic acid
-conditions:
.sulfuric acid as a catalyst
.80 degrees Celsius

Question 10

How are alkenes formed from alcohols?

Answer 10

-this is an elimination reaction(H2O is eliminated)
-conditions:
.in the presence of an acid catalyst (H2SO4 -sulfuric acid)
.170 degrees Celsius

Question 11

What makes haloalkanes?

Answer 11

-a substitution reaction with halide ions in the presence of an acid (such as concentrated sulfuric acid) mixture is warmed

Question 12

Define a nucleophile?

Answer 12

An electron pair donor

Question 13

What is the test for an unsaturated hydrocarbon (alkene)?

Answer 13

-add a few drops of bromine water to the sample and shake
-bromine water decoloursises the sample

Question 14

What is the test for the haloalkanes?

Answer 14

-add silver nitrate, ethanol and water
-white precipitate indicates chloro-
-cream precipitate indicates bromo-
-yellow precipitate indicates iodo-

Question 15

What happens if you add acidified potassium dichromate to carbonyls?

Answer 15

-ketones- no change
-aldehyde - orange turns green

Question 16

What happens if you add fehling’s solution to carbonyls?

Answer 16

-ketones-no change
-aldehydes- silver mirror

Question 17

What happens if you add Tohlen’s reagent to carbonyls?

Answer 17

-ketones-no silver mirror
-aldehydes -no silver mirroe

Question 18

What is the pH of a carboxylic acid?

Answer 18

-pH of a weak acid

Question 19

What observation can you see if you add a reactive metal like Mg to a carboxylic acid?

Answer 19

-effervescence (hydrogen)

Question 20

What observation can you see if you add a metal carbonate to a carboxylic acid?

Answer 20

-effervescence (carbon dioxide)

Question 21

How can you test for the OH functional group of an alcohol?

Answer 21

-warm with an equal volume of carboxylic acid and a few drops of H2SO4
OBSERVATION- the sweet smell of an ester after a short time

Question 22

What is the link between infrared radiation and global warming?

Answer 22

-as we release more greenhouse gases into the atmosphere more infrared radiation can be absorbed this leads to global warming
-this has influenced governments to introduce policies that encourage the use of technologies and energy resources that do not release greenhouse gases into the environment

Question 23

What does infrared radiation do to covalent bonds?

Answer 23

-it causes covalent bonds to vibrate more and absorb energy