Topic 6 - Organic Chemistry I

Question 1

what is a halogenoalkane?

Answer 1

an alkane with at least one halogen atom in place of a hydrogen atom

Question 2

what can halogenoalkanes be classed as?

Answer 2

primary
secondary
tertiary

Question 3

what are primary halogenoalkanes?

Answer 3

a halogenoalkane where the halogen is attached to a carbon which is attached to 1 alkyl group

Question 4

what are secondary halogenoalkanes?

Answer 4

a halogenoalkane where the halogen is attached to a carbon which is attached to 2 alkyl groups

Question 5

what are tertiary halogenoalkanes?

Answer 5

a halogenoalkane where the halogen is attached to a carbon which is attached to 3 alkyl groups

Question 6

what is a nucleophile?

Answer 6

an electron rich species that can donate a lone pair of electrons to form a covalent bond

Question 7

halogenoalkanes can be hydrolysed to form what?

Answer 7

alcohols

Question 8

halogenoalkanes are hydrolysed to form alcohols in what reaction?

Answer 8

a nucleophilic substitution reaction

Question 9

what is the bond between a carbon and a halogen?

Answer 9

a polar bond as halogens are more electronegative than carbon. this creates an uneven distribution of atoms causing the carbon atom to be partially positively charged (causing it to become a target for nucleophiles) and the halogen atom to be partially negatively charged.

Question 10

what are the steps in a nucleophilic substitution reaction?

Answer 10

1. a nucleophile is attracted to the partially positive carbon atom on the halogenoalkane
2. the nucleophile donates its lone pair of electrons to the carbon atom forming a new covalent bond
3. the original bond between the partially positive carbon and the halogen breaks heterolytically (the halogen atom takes both shared electrons)
4. The halogen departs as a halide ion being replaced by the nucleophile

Question 11

what do halogenoalkanes react with in a nucleophilic substitution reaction to form alcohols?

Answer 11

hydroxide ions, use warm aqueous potassium hydroxide and perform the reaction under reflux (the hydroxide ions acts as a nucleophile)

Question 12

what happens when aqueous silver nitrate solution in ethanol is added to a halogenoalkane?

Answer 12

the water in the solution acts a s a nucleophile leading to the break down of the halogenoalkane releasing halide ions into the solutions, the halide ions then react with the silver ions from silver nitrate to form silver precipitates

Question 13

what and how does halogenoalkanes react with in a nucleophilic substitution reaction to from nitriles?

Answer 13

potassium cyanide in ethanol is heated under reflux (cyanide ion acts as the nucleophile) with a halogenoalkane to form nitriles

Question 14

what happens to the carbon chain during the formation of a nitrile

Answer 14

it is extended by adding another carbon

Question 15

how do you form amines from a halogenoalkane?

Answer 15

when halogenoalkanes are heated under pressure with excess concentrated ethanolic ammonia (ammonia in ethanol), it undergoes nucleophilic substitution to form primary amines

Question 16

Why is an excess of ammonia used in the formation of a primary amine?

Answer 16

to prevent further substitution reactions (since the primary amine is a nucleophile and can react with more halogenoalkanes to form secondary, tertiary amines etc..) using excess ammonia ensures there is more ammonia than halogenalkane so the halogenoalkane will react with the ammonia and not the primary amine limiting further substitution

Question 17

what is the nucleophile in the formation of primary amines?

Answer 17

ammonia - NH3

Question 18

what does halogenoalkanes react with to produce alkenes? what type of reaction is this?

Answer 18

an alkali (e.g. KOH - potassium hydroxide) dissolved in ethanol, (hydroxide ion acts as a base) reaction must be heated under reflux, elimination reaction

Question 19

What happens as a result of heating the halogenoalkane under reflux to form an alkene?

Answer 19

The C-X bond breaks heterolytically, forming an X- ion and leaving an alkene as an organic product

Question 20

what colour is the precipitate when silver nitrate reacts with a halogenalkane depending on the halide

Answer 20

silver chloride (AgCl) - white precipitate
silver bromide (AgBr) - cream precipitate
silver iodide (AgI) - yellow precipitate

Question 21

what is the general trend of reactivity in halgenoalkanes?

Answer 21

reactivity increases down the group
(iodo > bromo > chloro > fluoro)
and depends on the class
tertiary > secondary > primary

Question 22

what is the reason for the tertiary >secondary >primary reactivity trend in halogenoalkanes?

Answer 22

tertiary - form the most stable carbocations due to increased electron-donating alkyl groups, which stabilise the positive charge
secondary - form less stable carbocations than tertiary but more stable than primary
primary - form the least stable carbocations as they have the least number of electron-donating alkyl groups

Question 23

explain the trend in reactivity of halogenoalkanes going down the group

Answer 23

the bond enthalpy decreases down the group because the atomic radius of the halogen increases so the carbon-halogen bond length increases so the electrostatic attraction between bonding electrons and nuclei decreases so the amount of energy needed to break the longer, weaker bonds decreases and therefor they get more reactive as you go down the group

Question 24

what is bond enthalpy?

Answer 24

the energy required to break 1 mole of a type of bond in a gaseous molecule under standard conditions

Question 25

what can alcohols be classed as?

Answer 25

primary secondary tertiary depending on which carbon atom the OH group is bonded to

Question 26

what is the functional group and general formula of an alcohol

Answer 26

OH group - hydroxyl group Cn H2n+1OH

Question 27

What is an alcohol called when there are 2 hydroxyl groups present?

Answer 27

A diol

Question 28

what is produced when an alcohol combusts in excess oxygen?

Answer 28

it reacts with the oxygen to form carbon dioxide and water, releasing energy

Question 29

how are chloroalkanes made?

Answer 29

by reacting an alcohol with PCl5 (phosphorous pentachloride) or an alcohol with hydrochloric acid (HCl)

Question 30

the reaction between alcohol and hydrochloric acid is fastest when______ and slowest when_____

Answer 30

fastest when it is a tertiary alcohol slowest when it is a primary alcohol

Question 31

how do you produce bromoalkanes what reaction is this?

Answer 31

1.you react potassium bromide (KBr) and 50% concentrated sulfuric acid (H2SO4) to produce HBr 2. HBr reacts with the alcohol, the Br replaces the OH group producing bromoalkane a nucleophilic substitution reaction

Question 32

how do you produce iodoalkanes and what reaction is this?

Answer 32

1. you reflux the alcohol with the red phosphorus and iodine to form PI3 (phosphorus triiodide) 2. PI3 reacts with the alcohol removing the OH group and I taking its place a nucleophilic substitution reaction

Question 33

what does [O] represent in equations?

Answer 33

the oxidising agent

Question 34

how do you form aldehydes from primary alcohols?

Answer 34

you gently heat the primary alcohol with acidified potassium dichromate, use distillation to remove the aldehyde as it forms to prevent further oxidation

Question 35

what do aldehydes form when further oxidised?

Answer 35

carboxylic acids

Question 36

how do you obtain carboxylic acids from a primary alcohol?

Answer 36

heat the alcohol with an excess of potassium dichromate under reflux conditions

Question 37

what is the role of dilute sulfuric acid in the oxidation of a primary alcohol?

Answer 37

dilute sulphuric acid is used to activate the potassium dichromate by providing the acidic conditions essential for the reaction to take place

Question 38

how do you test for aldehydes?

Answer 38

aldehydes can be further oxidised but ketones cannot fehlings solution/benedicts solution (contains Cu2+ ions - blue) - warm the aldehyde with the feelings solutions positive result: aldehyde - blue solution -> brick red precipitate (Cu2O) negative result: ketone - remains blue

Question 39

how do you form a ketone?

Answer 39

refluxing secondary alcohols with acidified potassium dichromate

Question 40

can secondary alcohol be oxidised further?

Answer 40

no

Question 41

describe and explain the colour change when acidified potassium dichromate (VI) is used to oxidise alcohols

Answer 41

green -> orange potassium dichromate contains Cr6+ (chromium ions) that gives the solution its bright orange colour when the dichromate oxidises an alcohol it gains electrons so the chromium is reduced to Cr3+ which are green proving that the alcohol had been oxidised

Question 42

can tertiary alcohols be oxidised?

Answer 42

no

Question 43

what does the dehydration (removal of water) of alcohols produce?

Answer 43

alkenes through an elimination reaction

Question 44

what catalyst is used in the dehydration of alcohols to form alkenes and what is the condition?

Answer 44

a phosphoric acid catalyst (H3PO4) heated under reflux

Question 45

what can happen when complex alcohols undergo dehydration?

Answer 45

elimination can occur from different positions along the carbon chain resulting in a mixture of alkene positional isomers as products

Question 46

what is a reflux reaction?

Answer 46

technique used to heat chemical reactions for an extended time without losing any volatile substances (using a condenser) volatile - has a low boiling point

Question 47

why is refluxing used in some organic reactions?

Answer 47

many organic substances are volatile meaning that when heated in an open vessel they can evaporate before the reaction takes place so heating under reflux condenses the evaporated organic vapours that then drip back into the flask refluxing allows organic substances to be heated to their boiling point, speeding up the reaction without losing material

Question 48

what equipment is used when refluxing and what do they do?

Answer 48

round bottomed flask - holds the mixture condenser - cools the vapour back into a liquid to prevent loss of volatile substances anti-bumping granules - helps mixture to boil smoothly (prevents large bubbles and splashing

Question 49

what is the purpose of the cold water flowing through the condenser?

Answer 49

to condense evaporated vapours back into a liquid to drip back into the flask /(reaction vessel)

Question 50

how is the organic mixture usually heated under reflux?

Answer 50

heating is usually done electrical rather than an open flame which could cause flammable vapours to ignite

Question 51

what is separating funnel used for?

Answer 51

used to separate 2 liquids with different densities

Question 52

what is solvent extraction?

Answer 52

a method using a solvent to remove a desired organic product from a reaction mixture

Question 53

What features do solvent used in solvent extraction need to have?

Answer 53

Immiscible (doesn’t mix) with the solvent containing the desired organic product The desired organic product should be much more soluble than the added solvent

Question 54

how do you carry out extraction with a solvent using a separating funnel?

Answer 54

Place the reaction mixture in a separating funnel and add the chosen solvent forming a separate layer Place a stopper in the neck of the funnel Gently shake the contents for a while Allow the contents to settle into 2 layers Remove the stopper and open the tap, allowing the lower layer to drain into a flask remove the lower layer pour remaining layer into a clean dry conical flask add 2 spatulas of magnesium sulphate (it should be added until there is no further clumping)

Question 55

What will magnesium sulfate do to the organic layer in solvent extraction?

Answer 55

remove the water

Question 56

what does distillation do?

Answer 56

separates substances with different boiling points

Question 57

how does distillation work?

Answer 57

The mixture is gently heated, vapours evaporate in order of increasing boiling point, and are condensed back into liquid to be collected

Question 58

What is the role of the thermometer in distillation?

Answer 58

To monitor the boiling point of the vapour, helping identify the substance being distilled

Question 59

How do you know when to collect the desired product during distillation?

Answer 59

Begin collecting when the thermometer shows the boiling point of the desired product

Question 60

How does distillation help prevent further reaction of a product?

Answer 60

The product evaporates and is removed from the mixture as it's formed, preventing it from reacting with leftover reactants

Question 61

what is added to the organic product after seperation and what is its purpose?

Answer 61

anhydrous salt (e.g.magnesium sulfate MgSO4) - a drying agent it is used to remove water from the product by binding to it

Question 62

how can you remove the drying agent from the product after used?

Answer 62

filteration

Question 63

How can a liquids purity be measured?

Answer 63

By measuring its boiling point

Question 64

What will impurities present in liquid do its boiling point?

Answer 64

Raise it

Question 65

how can you determine the boiling point of an organic liquid?

Answer 65

Set up a distillation apparatus with the liquid sample Gently heat the liquid while monitoring the temperature using a precise thermometer placed at the top of the apparatus Record the temperature at which the liquid begins to distill - This is the boiling point. Continue heating and note any temperature range over which the liquid boils Repeat the process to confirm the accuracy of the boiling point or range obtained Compare the observed boiling point or range with known literature values to assess the purity of the organic liquid A boiling point that closely matches the literature value suggests high purity In contrast, a boiling point that is significantly different to the literature value or a wide boiling range indicates the presence of impurities.