carboxylic acids

Question 1

explain boiling points of carboxylic acids

Answer 1

higher in carboxylic acids than in corresponding alkanes
carboxylic acids have intermolecular van der waals and also hydrogen bonds between molecules which are stronger
stronger than corresponding alcohol because each carboxylic acids is help together by 2 hydrogen bonds and can form dimers

Question 2

explain solubility of carboxylic acids

Answer 2

soluble in water due to their ability to form hydrogen bonds with the water
long chain hydrocarbons hinder formation of hydrogen bonds

Question 3

equation for reaction with metal

Answer 3

metal + acid -> salt + hydrogen

Question 4

reaction with base

Answer 4

base + acid -> salt + water

Question 5

reaction with carbonates

Answer 5

metal carbonate + acid -> salt + water + carbon dioxide

Question 6

reaction with ammonia

Answer 6

acid + ammonia -> ammonium salt

Question 7

method for reaction of carboxylic acids than with sodium carbonate, sodium hydroxide solution and aqueous ammonia

Answer 7

• place 1cm3 of carboxylic acid in boiling tube
  -record pH using pH paper
  -add spatula measure of sodium carbonate and record observations
  -record pH using pH paper
  -repeat using 1cm3 of sodium hydroxide solution and then repeat again with ammonia instead of sodium carbonate

Question 8

what happens when di or tribasic acids react

Answer 8

in EXCESS all groups react

Question 9

reactions of carboxylic acids with PCl5

Answer 9

eg. ethanoic acid
CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl(g)
(products are ethanoyl chloride, phosphorus trichloride and hydrogen chloride
conditions: room temperature
observations: mixture warms up, steamy misty fumes of hcl solid dissapears

Question 10

reduction with lithal LiAlH4

Answer 10

reduced to corresponding aldehydes which cam be further reduced to corresponding primary alcohol in prolonged conditions

Question 11

preparation of carboxylic acids than

Answer 11

conditions: reflux with acidified potassium dichromate (vi) solution
Cr2O7 2- + 14H+ + 6e- -> Cr3+ + 7H2O
orange > green solution

Question 12

method of purification

Answer 12

• add conc sulfuric acid to water in a pear shaped flask
• swirl solution and cool in cool waterbath to dissipate head to prevent spitting
  -add potassium dichromate (vi) solution and swirl flask
  -add anti bumping granules
  -attach a vertical condenser
  -add primary alcohol slowly, down condenser to acidified potassium dichromate solution, cooling reaction in cold warer bath
  -heat mixture under reflux for 30 mins
  -distill off acid and rearrange for simple distillation

Question 13

why is yield not 100%

Answer 13

organic liquid sticks to apparatus, loss in transfer and loss in distillation
some side reactions are also formed

Question 14

method for purifying organic liquid

Answer 14

-place impure organic liquid product in a beaker/conicle flask
-add a spatula of a suitable drying agent such as calcium chloride and swirl
-add more of drying agent until cloudy-> clear
-decant/filter off liquid

Question 15

acid catalysed hydrolosis

Answer 15

esters undergo acid hydrolysis on refluxing with dilute hydrochloric acid forming a carboxylic acid and an alcohol

Question 16

base catalysed hydrolysis

Answer 16

-reaction is not reversible
-products are easier to separate

by reaction with ester and sodium hydroxide a sodium salt and alcohol are formed
carboxylic acid is liberated by reaction of a dilute mineral acid at room temp

Question 17

acid catalysed hydrolysis of nitrile

Answer 17

dilute hcl
CH3CH2CN + 2H2O + HCL -> CH3CH2COOH +NH4CL

Question 18

base hydrolysis of nitriles

Answer 18

nitrile heated under reflux with sodium hydroxide solution
liberate with dilute mineral acig eg HCL