carboxylic acids

Question 1

suggest how anti-bumping granules prevent bumping during reflux

Answer 1

• prevents vigorous uneven boiling
• by making small bubbles form instead of large bubbles

Question 2

suggest why an excess of sodium hydroxide is uses in hydrolysis of esters

Answer 2

• to ensure the ester is completely hydrolysed

Question 3

suggest why an electric heater is used rather than a bunsen burner in this hydrolysis

Answer 3

• organic compounds are flammable

Question 4

suggest why reflux is used in this hydrolysis

Answer 4

• reflux prevents reacta vapour from escaping

Question 5

suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water

Answer 5

• sodium benzoate is ionic
• benzoic acid is insoluble because the benzene ring is non polar

Question 6

describe the method the student should use to purify the benzoic acid

Answer 6

• dissolve crude product in hot solvent
• of minimum volume
• filter ( hot to remove insoluble impurities)
• cool to recrystallise
• filter under reduced pressure with Buchner
• wash with cold solvent and dry

Question 7

give the equation for acid + metal

Answer 7

acid + metal > salt + hydrogen

2CH3COOH + 2Na > 2CH3COONa + H2

Question 8

give the equation for acid + alkali

Answer 8

acid + alkali > salt + water

CH3COOH + NaOH > CH3COONa + H2O

Question 9

give the equation for acid + carbonate

Answer 9

acid + carbonate > salt + water + carbon dioxide

2CH3COOH + Na2CO3 > 2CH3COONa + H2O + CO2

Question 10

what is the functional test for carboxylic acids ?

Answer 10

• reaction of carboxylic acids with solid metal carbonate produces effervescence caused by production of CO2

Question 11

what happens when carboxylic acids react with alcohols in presence of a strong acid catalyst

Answer 11

• esters and water is formed

Question 12

give the general equation for acid + alcohol

Answer 12

acid + alcohol >< ester + water

Question 13

what are the downsides of esterification

Answer 13

• reaction is reversible
• the reaction is slow and needs heating under reflux
• low yields are achieved
• acid catalyst is needed

Question 14

what are the downsides of esterification

Answer 14

• reaction is reversible
• the reaction is slow and needs heating under reflux
• low yields are achieved
• acid catalyst is needed

Question 15

what are the main uses of esters

Answer 15

• perfumes and flavourings
• solvents for polar organic substances
• uses for plasticisers for polymers

Question 16

what are the two ways esters can be hydrolysed and split up

Answer 16

• heating with acid
• sodium hydroxide

Question 17

what are the conditions for with acid

Answer 17

• dilute acid (HCL)
• heat under reflux

Question 18

what are the conditions for with sodium hydroxide

Answer 18

• dilute sodium hydroxide
• heat under reflux

Question 19

why is the reaction of esters with sodium hydroxide not reversible

Answer 19

• carboxylic acid salt product is the anion of the carboxylic acid
• anion is resistant to attack by weak nucleophiles such as alcohols