Acids, Bases, Esters, Aldehydes and Ketones Flashcards
Carboxyl functional group
COOH
Nomenclature of carboxylic acids
Alkane + oic acid
Why are carboxylic acids weak
- There is low dissociation of H+ ions
- There is a higher concentration of carboxylic acid than H+
- The equilibrium lies towards the carboxylic acid
What is an oxonium ion
When an acid is added to water it donates a proton to a water molecule which forms a dative covalent bond
How does a base act in water
It accepts one of waters protons causing the formation of a hydroxide ion (OH-)
What is dissociation
The breaking of the bond between a hydrogen atom and a electronegative atom by heterolytic fission to leave a proton and a negative ion
What is a conjugate base
The anion formed after an acid dissociates e.g. Cl- from HCl
What makes an acid strong or weak
An acid gets stronger the higher the percentage of their atoms dissociate, this is not affected by concentration
What is the acid dissociation constant formula
Ka =[H+][A-]/[HA]
What is pKa and its formula
- Its the constant for weak acids
- pKa = -log10 Ka
- The bigger the Pka the weaker the acid
Why do different molecules have different amounts of dissociation
- The stronger the O-H bond the weaker the acid as its harder to donate a proton
- Sulfuric acid has lots of electronegative oxygen atoms which withdraws electrons away from th O-H so it is easier to break
What is the formula for pH
pH = -log10 [H+]
What is the trend in boiling points for carboxylic acids
As the length increases so does the boiling point due to more induced dipole-induced dipole attractions
What is a titration curve
Its the plotting of the change in pH of a titration. The pH is plotted against the volume of alkali added
What is the equivilance point
The middle of where there is a large change in pH but small addition of alkali it can also be called the neutralisation point
What do the 4 different titration curves look like
- A strong base and a weak acid will have a small vertical portion from about 3 to 8 which is high up
- A weak base and weak acid will have a very shallow change so indicator will be hard to determine
- A weak base and a strong acid will have a medium vertical portion from around 4 to 11
- A strong base and strong acid will have a long vertical portion from around 2 to 10
What are the indicators and their ranges
Litmus = 5-8
Methyl orange = 3.1-4.4
phenolphthalein = 8.3-10
How to get carboxylic acids from esters
The ester is refluxed with a dilute acid or alkali
How to get carboxylic acids from amides
Reflux them with a dilue acid or alkali
What is esterification
The production of an ester by refluxing a carboxylic acid with an alcohol in the presence of an acid, an equilibrium mixture is produced
What are acyl chlorides
Carboxylic acids with their OH group replaced by a Cl
Nomenclature of acyl chlorides
The oic acid is replaced by an oyl chloride
Why are acyl chlorides useful
The carbon is very susceptable to nucleophilic attack due to the highly elecronegative chlorine atom
How are acyl chlorides produced
Carboxylic acids react with sulfuryl chloride or phosphorus chloride
Nomenclature of esters
They are split into a carboxylic acid section and an alcohol section, yl and oate e.g. methyl ethanoate
Formula for the equilibrium constant
Kc =[C]^y[D]^z
——-
[A]^w[B]^x
Where wA + xB = yC + zD
What does a high equilibrium constant mean
That at equilibrium the concentration of products is alot higher than the reactants
How are esters hydrolysed
- Water reacts with the carbonyl carbon eliminating the alcohol
- This can be made quicker with a base, boiling an ester with soduim hyroxide forms the salt of the acid and the alcohol
What mechanism do acyl chlorides undergo
An addition-elimination reaction
- A nucleophile e.g. water attacks the carbonyl carbon
- The C=O bond is broken and the electrons are transfered to the oxygen
- The hydrogens are rearranged
- The electrons from the O-H bond are transfered to the C=O reforming the double bond
- The chlorine is lost
- HCl is formed as a product
Nomenclature for amides
- Carbonyl with NH2 attached
- The suffix amide to the chain e.g. ethanamide
Reaction of ammonia with acyl chlorides
- Ammonia attacks the carbonyl carbon
- Double bond is broken and oxygen become negative
- Hydrogen transfered to the O-
- O-H bond electrons transfered to form a C=O and Cl bond broken
Nomenclature of nitriles
A chemical with CN will be called its alkane and end in nitrile e.g. ethanenitrile
Preperation of amides
- Reaction cyanide ions with halogenalkanes
- Reacting HCN with aldehydes or ketones
Hydrolysis of nitriles
- Very slow in water
- Faster in acidic or basic conditions
- When done in acid a carboxylic acid and ammonium salt is produced
- When done in a base a carboxylate and ammonia is formed
Reduction of nitriles
an be reduced using a strong reducing agent to form a primary amine
How to work out [H⁺]
[H⁺] = log^pH
What does the carbonyl functional group contain
C=O
Whats the difference between Aldehydes and Ketones
- Aldehydes contain the carbonyl at the beginning or end
- Ketones have the carbonyl group in the middle
How are aldehydes and ketones formed
Aldehyde - Oxidisation of a primary alcohol
Ketone - Oxidisation of a secondary alcohol
Potassium dichromates with sulphuric acid is the oxidising agent
Formation of carboxylic acids
Heating primary alcohols under reflux
Tollens test
- Tollens reagent has [Ag(NH3)2]- ions
- Add ammonium
- When warmed with the reagent an aldehyde will be oxidised
- The silver will solidify and become reflective
- A ketone wont be oxidised so the silver wont solidify
Fehlings test
- Copper(II) ions act as an oxidising agent
- If an aldehyde is warmed with it the Cu(II) ions get reduced to Cu+ ions
- The colour changes from blue to red if a aldehyde is present
- The colour change is not observed with a ketone
Oxidisation of primary and secondary alcohols
- Done by potassium dichromate
- An orange to green colour change is observed
- Primary -> Aldehyde
- Secondary -> Ketone
Addition of HCN to carbonyls to form nitriles
- The cyanide attacks the carbon
- The electrons from the Pi bond are transfered to the oxygen making it negatively charged
- The negative oxygen bonds to the H+
The general mechanism with both aldehydes and ketones
- A nucleophile attacks the carbon
- The Pi bond is broken giving its electrons to the oxygen making it negatively charged
- The oxygen attracts a H+
