Acids, Bases, Esters, Aldehydes and Ketones

Question 1

Carboxyl functional group

Answer 1

COOH

Question 2

Nomenclature of carboxylic acids

Answer 2

Alkane + oic acid

Question 3

Why are carboxylic acids weak

Answer 3

• There is low dissociation of H+ ions
• There is a higher concentration of carboxylic acid than H+
• The equilibrium lies towards the carboxylic acid

Question 4

What is an oxonium ion

Answer 4

When an acid is added to water it donates a proton to a water molecule which forms a dative covalent bond

Question 5

How does a base act in water

Answer 5

It accepts one of waters protons causing the formation of a hydroxide ion (OH-)

Question 6

What is dissociation

Answer 6

The breaking of the bond between a hydrogen atom and a electronegative atom by heterolytic fission to leave a proton and a negative ion

Question 7

What is a conjugate base

Answer 7

The anion formed after an acid dissociates e.g. Cl- from HCl

Question 8

What makes an acid strong or weak

Answer 8

An acid gets stronger the higher the percentage of their atoms dissociate, this is not affected by concentration

Question 9

What is the acid dissociation constant formula

Answer 9

Ka =[H+][A-]/[HA]

Question 10

What is pKa and its formula

Answer 10

• Its the constant for weak acids
• pKa = -log10 Ka
• The bigger the Pka the weaker the acid

Question 11

Why do different molecules have different amounts of dissociation

Answer 11

• 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

Question 12

What is the formula for pH

Answer 12

pH = -log10 [H+]

Question 13

What is the trend in boiling points for carboxylic acids

Answer 13

As the length increases so does the boiling point due to more induced dipole-induced dipole attractions

Question 14

What is a titration curve

Answer 14

Its the plotting of the change in pH of a titration. The pH is plotted against the volume of alkali added

Question 15

What is the equivilance point

Answer 15

The middle of where there is a large change in pH but small addition of alkali it can also be called the neutralisation point

Question 16

What do the 4 different titration curves look like

Answer 16

1. A strong base and a weak acid will have a small vertical portion from about 3 to 8 which is high up
2. A weak base and weak acid will have a very shallow change so indicator will be hard to determine
3. A weak base and a strong acid will have a medium vertical portion from around 4 to 11
4. A strong base and strong acid will have a long vertical portion from around 2 to 10

Question 17

What are the indicators and their ranges

Answer 17

Litmus = 5-8
Methyl orange = 3.1-4.4
phenolphthalein = 8.3-10

Question 18

How to get carboxylic acids from esters

Answer 18

The ester is refluxed with a dilute acid or alkali

Question 19

How to get carboxylic acids from amides

Answer 19

Reflux them with a dilue acid or alkali

Question 20

What is esterification

Answer 20

The production of an ester by refluxing a carboxylic acid with an alcohol in the presence of an acid, an equilibrium mixture is produced

Question 21

What are acyl chlorides

Answer 21

Carboxylic acids with their OH group replaced by a Cl

Question 22

Nomenclature of acyl chlorides

Answer 22

The oic acid is replaced by an oyl chloride

Question 23

Why are acyl chlorides useful

Answer 23

The carbon is very susceptable to nucleophilic attack due to the highly elecronegative chlorine atom

Question 24

How are acyl chlorides produced

Answer 24

Carboxylic acids react with sulfuryl chloride or phosphorus chloride

Question 25

Nomenclature of esters

Answer 25

They are split into a carboxylic acid section and an alcohol section, yl and oate e.g. methyl ethanoate

Question 26

Formula for the equilibrium constant

Answer 26

Kc =[C]^y[D]^z ------- [A]^w[B]^x Where wA + xB = yC + zD

Question 27

What does a high equilibrium constant mean

Answer 27

That at equilibrium the concentration of products is alot higher than the reactants

Question 28

How are esters hydrolysed

Answer 28

* 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

Question 29

What mechanism do acyl chlorides undergo

Answer 29

An addition-elimination reaction 1. A nucleophile e.g. water attacks the carbonyl carbon 2. The C=O bond is broken and the electrons are transfered to the oxygen 3. The hydrogens are rearranged 4. The electrons from the O-H bond are transfered to the C=O reforming the double bond 5. The chlorine is lost 6. HCl is formed as a product

Question 30

Nomenclature for amides

Answer 30

* Carbonyl with NH2 attached * The suffix amide to the chain e.g. ethanamide

Question 31

Reaction of ammonia with acyl chlorides

Answer 31

1. Ammonia attacks the carbonyl carbon 2. Double bond is broken and oxygen become negative 3. Hydrogen transfered to the O- 4. O-H bond electrons transfered to form a C=O and Cl bond broken

Question 32

Nomenclature of nitriles

Answer 32

A chemical with CN will be called its alkane and end in nitrile e.g. ethanenitrile

Question 33

Preperation of amides

Answer 33

* Reaction cyanide ions with halogenalkanes * Reacting HCN with aldehydes or ketones

Question 34

Hydrolysis of nitriles

Answer 34

* 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

Question 35

Reduction of nitriles

Answer 35

an be reduced using a strong reducing agent to form a primary amine

Question 36

How to work out [H⁺]

Answer 36

[H⁺] = log^pH

Question 37

What does the carbonyl functional group contain

Answer 37

C=O

Question 38

Whats the difference between Aldehydes and Ketones

Answer 38

* Aldehydes contain the carbonyl at the beginning or end * Ketones have the carbonyl group in the middle

Question 39

How are aldehydes and ketones formed

Answer 39

Aldehyde - Oxidisation of a primary alcohol Ketone - Oxidisation of a secondary alcohol Potassium dichromates with sulphuric acid is the oxidising agent

Question 40

Formation of carboxylic acids

Answer 40

Heating primary alcohols under reflux

Question 41

Tollens test

Answer 41

* 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

Question 42

Fehlings test

Answer 42

* 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

Question 43

Oxidisation of primary and secondary alcohols

Answer 43

* Done by potassium dichromate * An orange to green colour change is observed * Primary -> Aldehyde * Secondary -> Ketone

Question 44

Addition of HCN to carbonyls to form nitriles

Answer 44

* 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+

Question 45

The general mechanism with both aldehydes and ketones

Answer 45

* 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+