carboxylic acids Flashcards
what is the functional group of carboxylic acid?
-COOH
draw out the functional group of carboxylic acids
-C-O-H
II
O
what is vinegar in relation to ethanoic acid?
vinegar is an aqueous solution containing ethanoic acid
how are carboxylic acids formed?
it is formed by the oxidation of the corresponding alcohols, e.g., ethanoic acid is formed when ethanol is left in the air or oxidised using potassium dichromate (VI) in dilute sulfuric acid
what is the molecular formula of methanoic acid?
CH2O2
what is the molecular formula of ethanoic acid?
C2H4O2
what is the molecular formula of propanoic acid?
C3H6O2
what is the molecular formula of butanoic acid?
C4H8O2
what is the structural formula of methanoic acid?
HCOOH
what is the structural formula of ethanoic acid?
CH3COOH
what is the structural formula of propanoic acid?
CH3CH2COOH
what is the structural formula of butanoic acid?
CH3CH2CH2COOH
draw out the displayed formula for methanoic acid, ethanoic acid, propanoic acid, butanoic
check in p.294
what type of acid is carboxylic acid?
they are weak acids?
what are weak acids?
acids with a pH of about 3-5 depending on conc. of solution.
A weak acid is an acid that only partially dissociates into ions in water, producing a relatively small number of hydrogen ions (Ht). Weak acids have a relatively low pH value.
how does ethanoic acid react with water?
it reacts the same way other dilute acids react but MORE SLOWLY.
metal + acid -> salt + hydrogen
metal hydroxide/oxide + acid -> salt + water
metal carbonate + acid -> salt + carbon dioxide
what happens when ethanoic acid reacts with magnesium?
lots of fizzing. salt and hydrogen formed. the salt is called magnesium ethanoate
what is the name of salts that contain ethanoic, methanoic etc., acids in them?
methanoate
ethanoate
propanoate
butanoate
what is an ethanoate ion?
part of a salt containing athanoic acid
it looks like CH3COO-
is an ethanoic acid is weak?
it only partially dissociates in solution
what is the equation for ethanoic acid and sodium hydroxide? word
ethanoic acid + sodium hydroxide-> sodium ethanoate + water
what is the equation for ethanoic acid and sodium hydroxide? symbol (structural)
2CH3COOH + NaOH -> 2CH3COO-Na+ + H2O
what is the equation for ethanoic acid and magnesium ? word
magnesium + ethanoic acid -> water + magnesium ethanoate
what is the equation for ethanoic acid and magnesium ? symbol
CH3COOH + Mg -> (CH3COO)2Mg + H2O
how are carboxylic acids formed?
they are formed by the oxidation of their corresponding alcohols
e.g., ethanoic acid is formed when ethanol is left in the air or oxidise
how do you oxidise ethanol?
- a few drops of ethanol are added to a solution containing a solution containing the orange mixture of dilute sulphuric acid and potassium dichromate (VI).
- the test tube is heated in a hot water bath.
- the solution turns green and now contains a very dilute solution of ethanoic acid together with the other products
- the green colour indicates the presence of Cr3+ ions, which are formed when potassium (VI) dichromate is reduced
(wear goggles in case reaction is vigorous and spits out)
what is the word equation for the oxidation of ethanol?
ethanol + potassium dichromate (VI) in dilute sulphuric acid -> ethanoic acid + water
heat under reflux
what is the oxidising agent in the oxidation of ethanol?
acidified potassium dichromate (VI) aka potassium dichromate (VI) in dilute sulphuric acid
write out the symbol equation for the oxidation of ethanol
structural formula
CH3CH2OH + 2[O] -> CH3COOH + H2O
across the arrow: reflux and K2Cr2O7/H2SO4
what conditions are required for oxidation?
you must heat under reflux, meaning you stop the vapour from escaping
draw out, in displayed fromula, the oxidation of ethanol
what is the oxidising agent in the oxidation of the oxidation of an alcohol?
acidified potassium dichromate (VI)
what happens to the dichromate in the oxidation of an alcohol?
what colour change takes place?
Cr2O7 (charge:2-) -> Cr (charge:3+)
charge on Cr (oxidation no): 6+ -> 3+
colour changes from orange to green
what happens in the reaction between magnesium and dilute ethanoic acid? what is the equation?
Mg (s) + 2CH2COOH (aq) -> (CH3COO)2MG (aq) + H2 (g)
lots of fizzing and a salt+ hydrogen produced
state 2 observations for the oxidation of the alcohold in the presence of acidified potassium dichromate (VI) solution
colour change: orange to green
product smells acidic (like vinegar)
how can you show that an alcohol has been oxidised and an acid has fromed?
universal indicator
why does old alcohol have an acidic taste?
it is exposed to oxygen and it oxidises in the air due to bacteria/yeast and ethanoic acid is made
what happens when a metal carbonate and a carboxylic acid reacts?
metal carbonate + acid -> co2+ h2o + salt (e.g., sodium ethanoate)
what is the charge of ‘ethanoate’ ions. draw out the displayed and structural formula of an ethanoate ion
CH3COO -
how do different metals react with carboxylic acids?
they react more/less vigorously depending on their position on the reactivity scale e.g., sodium is dangerously reactive , whereas zinc produces bubbles of hydrogen more slowly than it does with HCl
what can you observe when sodium carbonate or calcium carbonate reacts with an ethanoate?
lots of fizzing and a colourless solution containing the salt
The colour of bromine water is orange.
State the final colour of the mixture after bromine water is shaken with:
an unsaturated fat
and a saturated fat
unsaturated - colourless
saturated - orange
Which type of fat contains a double carbon to carbon (C C) bond?
unsaturated fats
