Carboxylic acids Flashcards
(26 cards)
Give one use for carboxylate salts. [1]
Soap
Outline how you would carry out a simple laboratory process to show that the recrystallised product is a pure sample of N-phenylethanamide. [3]
Measure melting point
Use oil bath
Sharp melting point
Suggest the most likely impurity to have caused a lower melting point than the data-book value and an improvement to the method so that a more accurate value for the melting point would be obtained in the recrystallisation of crude products. [2]
- Water
- Press crystals between filter paper
Suggest why the student should not use this sample of paracetamol for the purposes of pain relief. [1]
May still be small amounts of impurities
Explain why the melting point of an organic solid is lower when impurities are present.
- Impurities distort the regular tightly bound lattice structure
- Particles are less tightly packed
- Less energy needed to break the bonds between particles
State three uses of glycerol.
- Cosmetics
- Glue
-Food
Why is ethanoic anhydride used to make aspirin over ethanoyl chloride?
More expensive
Violent reaction
Produces HCl fumes
Using what two molecules can you form aspirin?
acid = ethanoic anhydride
alcohol = 2-hydroxybenzoic acid
How do carboxylic acids react with metal carbonates?
React to form CO2H2O and a salt
Write an equation to represent esterification. What is the catalyst for this reaction?
Carboxylic Acid + Alcohol <–> Ester + Water
strong acid catalyst e.g H2SO4
What are the uses of esters?
Food flavourings
Perfumes
Solvents (polar/volatile)
Plasticizers - added to plastics, to increase fluidity
Recall the hydrolysis of esters in acidic conditions.
Warm under reflux
Dilute HCl
Ester + Water -> Carboxylic Acid + Alcohol
Recall the hydrolysis of esters in basic conditions.
- Heat under reflux
- Dilute NaOH / KOH base
- Ester + OH- -> (salt ion of acid) + Alcohol
Why are small chain carboxylic acids soluble in water?
able to form H bonds with water molecules
between lone pair on O and delta positive H atom
Recall the reaction, reagent and conditions for the formation of esters.
Condensation reaction between -OH and -COOH to form ester + water
Strong acid catalyst e.g H2SO4
Under reflux
Why are carboxylate ions stable?
Negative charge delocalised across two oxygen atoms
Stable ions are more likely to form
Why does the solubility of -COOH decrease with increased chain length?
Polar group becomes less significant
What is saponification?
production of carboxylate ion via base hydrolysis
Why can carboxylate salts of long chain -COOH used as soaps?
they have hydrophilic and hydrophobic regions
Recall the process of saponification.
Base hydrolysis of vegetable oils and animal fats to give soap and glycerol.
How are biodiesels produced?
reacting vegetable oils (tryglycerides) with methanol in the precense of KOH (catalyst)
What is biodiesel?
Mixture of methyl esters of long-chain carboxylic acids
State why the burning of biodiesel may be classed as carbon neutral.
CO2given off would be equal to the CO2extracted from the air by photosynthesis when the plants grew
CO2given off would be equal to the CO2extracted from the air by photosynthesis when the plants grew
- React violently at room temperature with nucleophiles.
- 2 electronegative atoms (O and Cl) means Catom is very δ+
