(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
what are the observations and quation for adding :
2) To a 1cm3 of glacial
ethanoic acid, add 1cm3
ethanol and 2 drops
conc. sulfuric acid.
Warm in a water bath
then tip onto a saturated
solution of Na2CO3 in a
small beaker. Smell
cautiously.
Equation for reaction
Exothermic before heating, effervescence on pouring onto Na2CO3
fruity smell
CH3COOH + CH3CH2OH —-> CH3COOCH2CH3 + H2O Ethyl ethanoate
Exothermic due to adding conc H2SO4 to aqueous solutions Effervescence as acids are neutralised Esters smell sweet/fruity Ester formed from reaction of carboxylic acid and alcohol So carboxylic acid present
what are the observations and quation for adding :
The following reaction is
not a test but a useful
reaction to know.
To 10 drops dilute
ethanoic acid add
NaOH(aq) drop by drop
to excess. Describe the
CHANGE in smell.
Equation for reaction:
Evaporate to dryness
cautiously. Describe the
appearance of the
substance left and identify
it.
Exothermic Vinegar smell disappears
CH3COOH + NaOH —> CH3COO-Na+ + H2O Sodium ethanoate produced
If evaporated to dryness a white solid remains If HCl added —> vinegar smell
CH3COO-Na+ + HCl —> CH3COOH + NaCl
what happens when you mix a carboxilic acid with PCl5
what happens when you mix AgNO3 with the product
what happens when you put conc ammonia near it
effovecence and steamy fumes
white ppt , carboxilic acid has to be in excess though
white smoke NH4Cl
what happens when you mix R-OH with PCl5
give the equation
R-Cl + POCl3 + HCl (steamy fumes)
what happens when you mix R-COOH with PCl5
give the equation
R-COOH + POCl3 + HCl (steamy fumes)
give the equation for ethanoyl chloride with water
and conditions
CH3COCl + H2O —-> CH3-CHOOH + HCl
the water acts as a nuclio phile
room temp
give the equation for ethanoyl chloride with an alcohol (ethanol)
conditions :
CH3COCl + CH3CH2OH —-> H3CCOOCH2CH3 + HCl
creates an ester
room temp anhydrys conditions
give the equation for ethanoyl chloride with conc ammonia
conditions :
CH3COCl + NH3 —-> H3C-CONH2 + HCl
excess amonia results in NH3 + HCl —-> NH4Cl
room temp , anhydris conditions
give the equation for ethanoyl chloride with C2H5NH2
conditions :
CH3COCl + C2H5NH2 —-> CH3CONHCH2CH3 + HCl
product name N-ethyl ethanamide
conditions : anhydris conditions , room temp
