(YELLOW) Carboxylic acids Flashcards
(YELLOW) Carboxylic acids
Solubility decreases with increasing chain length. Explain why (in carboxylic acids)
The length of the non polar part increases therefore increased London forces between them and increased amount of energy needed to separate them. Not energetically compensated for by the new hydrogen bonds formed between the acid and water. Energy required to overcome h bonds in liquid water is also not compensated for.
What is the appearance of benzoic acid
White powder/crystals
Comment benzoic acid solubility in hot water and in cold
Explain the difference using intermolecular forces
Insoluble in cold water
Dissolves in hot water to give a colourless solution, crystallises out as solution cools.
H-bonding with water is not enough when cold to overcome the considerable London forces and H-bonding between benzoic acid molecules. When hot these forces can be overcome and benzoic acid forms H-bonds with water.
hydrolysis of a nitrile
how do you go from a nitrile to a carboxilic acid
give reagents , and conditions , and an general equation ( of the two types )
reagents : dil HCl ( + water and H+ catalyst )
donditions : heat under reflux
CH3CN + H2O + HCl —–> CH3COOH + NH4Cl
or with just water:
CH3CN + H2O —–> CH3COOH + NH3
hydrolysus of an amide
how do you go from an amide to a carboxilic acid
give reagents , and conditions , and an general equation
reagents : water and H+ catalyst
conditions: heat under relux (probs does not say)
CH3CHONH2 + H2O –(H+ catalyst)—> CH3COOH + NH3
write out the reaction between ethanoic acid and KOH
CH3CO2H(l) + KOH —–> CH3COO-K+ + H2O
write out the reaction between ethanoic acid and sodium
CH3CO2H(l) + Na —-> CH3COO-Na+ + ½ H2(g)
write out the reaction between propanoic acid and potassium hydroxide
CH3CH2CO2H (l) + KOH(aq) —> CH3CH2COO-K+ (aq) + H2O
write out the reaction between methanoic acid and sodium carbonate:
2H2COOH + Na2CO3 —> 2H2COO-Na+ + CO2 + H2O
write out the reaction between ethanoic acid and sodium hydrogencarbonate:
CH3COOH + NaHCO3 –> CH3CO O–Na+ + H2O + CO2
info card
- Weak acids when compared to nitric, sulphuric and hydrochloric acids.
- Stronger acids than alcohols, which are considered to be neutral.
- Take part in typical acid reactions – with metals, carbonates and bases to form salts.
- Salts formed from carboxylic acids are known as carboxylates.
are short chain carboxilic acids soluable in water
yes as they can form hydrogen bonds
rank on order of boiling points :
Butane , Butan-1-ol , Butanoic acid
explain why using intermolecular forces
Butane<Butanoic acid<Butan-1-ol
/ butane has only weak london forces therefore lowest b.p
/ butan-1-ol and butanoic acid both have h-bonding and london forces
/butanoic acid has more e- so stronger london forces and can form more extensive hydrogen bonds therefore more energy is required to break the intermolecular forces
why are carboxilic acids acids while alcohols are not
The reason why carboxylic acids are more acidic than alcohols is as follows. In addition to the O-H…the C=O group pulls electrons away from the –OH group making the H atom more d+. The equilibrium is shifted further to the right compared to their corresponding alcohols, favouring the deprotonated salt.
when a proton (H+ ion ) is lost , a pi bond is formed over the C-O atoms (COO-)
the negative charge is shared (delocalised) between the 3 atoms
this stabalisise the carboxilate ion
alcohols do not have this delocalisation so they do not readily lose protons
what are the observations and quation for adding :
1) To a 1cm3 of dilute ethanoic acid, add a
small quantity of a solid
carbonate (e.g. CaCO3).
Equation for reaction:
Collect the gas evolved
into a teat pipette and
bubble through a small
volume of fresh lime-
water.
Effervescence Test tube became warm
2CH3COOH + CaCO3 —-> (CH3COO-)2Ca2+ + H2O + CO2
Lime water —-> white ppt
