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Chemistry IAL EDEXCEL A-Level > Unit 5- Topic 20 > Flashcards

Unit 5- Topic 20 Flashcards

1
Q

Test and notes on alkenes

A

Functional group= C=C
Test: add bromine water (Br2 (aq))
Observation: bromine decolourises immediately

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2
Q

Reaction bromine water with aldehydes and ketones

A

Bromine water is decolourised very slowly

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3
Q

Test and observation of halogenoalkanes (R-X) where X= Cl, Br or I

A

Test: warm with NaOH (aq) and then add dilute HNO3, followed by a few drop of AgNO3(aq)
Observations: R-Cl= produces white ppt. Ppt is insoluble in dilute NH3
R-Br= produces cream ppt. Ppt is insoluble in dilute NH3 but soluble in concentrated NH3
R-I= produces yellow ppt. Ppt is insoluble both dilute NH3 and concentrated

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4
Q

Test and observation of hydroxy group

A

Functional group= -OH
Test= add solid PCl5
Observation= misty fumes
Both alcohols and Carboxylic acids produce misty fumes, but not phenols

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5
Q

Test and observations of primary alcohols

A

Functional group= (RCH2OH)
Test= add acidified K2Cr2O7 solution and warm
Observation= solution turns from orange to green
The organic product of this reaction produces a silver mirror with Tollen’s reagent

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6
Q

Test and observation of secondary alcohols

A

Functional group= (R2CHOH)
Test=add acidified K2Cr2O7 solution and warm
Observation= solution turns from orange to green
Notes= the organic product does not produce a silver mirror with Tollen’s reagent

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7
Q

Test and observation for carbonyls

A

Functional group: (C=O)
Test: add 2,4-DNPH
Observation: orange precipitate
Notes:both aldehydes and ketones produce and orange ppt

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8
Q

Test and observation for aldehydes

A

Functional group=(RCHO)
Test= add Tollen’s reagent and warm
Observation= silver mirror forms
Notes= Fehling’s solution can also be used. Ketones do not react with Tollen’s or Fehling

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9
Q

Test and observation for CH3- C=O- R or CH3- CHOH - R

A

Test= add alkaline solution of iodine and warm
Observation= yellow ppt forms
Notes= known as triiodomethane or iodoform test

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10
Q

Test and observation for carboxylic acids

A

Functional group= R-COOH
Test= add NaHCO3 or Na2CO3 and warm if necessary
Observation= bubbles of gas

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11
Q

Test and observation for phenol

A

Functional group= benzene- OH
Test= addd bromine water
Observations= bromine immeaditely decolourises and a white precipitate forms
Notes= phenylamine produces same results.
Phenol is soluble in NaOH but insoluble in dilute HCl.
Phenylamine is insoluble in NaOH but soluble in dilute HCl

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12
Q

State the four ways of extending an existing carbon chain by one or more atoms

A

1- Reacting a halogenoalkane with a cyanide ion forms a nitrile with one more carbon atom that the halogenoalkane
2- the addition of hydrogen cyanide to a carbonyl compound
3- the alkylation of benzene, which introduces an alkyl group into a benzene ring
4-the use of Grignard reagents

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13
Q

What are the Grignard reagents

A

They are organometallic compounds containing magnesium. They are made by heating under reflux the chosen halogenoalkane with magnesium in a solvent of dry ether. Bromoalkanes are the preferred halogenoalkane. Grignard reagents contain magnesium covalently bonded to both the alkyl group and the halogen. General equation:
R - Br + Mg —> R - Mg - Br
Grignard reagents react with water so they are made nd used in a solvent of dry ether

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14
Q

Grignard reactions

A

RMgBr + CO2 -> RCOOH, grignard + carbon dioxide -> carboxylic acid
RMgBr + CH2O -> RCH2OH, grignard + methanal -> primary alcohol
RMgBr + R’CHO -> RR’CHOH, grignard + aldehyde -> secondary alcohol
RMgBr + R’COR’’ -> RR’R’’COH, grignard + ketone -> tertiary alcohol
After the reaction is complete, dilute acid is added to obtain the desired organic product

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15
Q

How can functional groups influence the behaviour of compounds that contain them

A

-can affect if the compounds is going to act as nucleophilic or electrophile
-if they are susceptible to addition reactions or substitution
-if they are easily oxidised or easily reduced

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16
Q

How to approach a ‘plan to a reaction scheme with intermediate’ questions

A

-check is carbon chain length has increased or decreased
-by looking at final product and working back to the starting compound
-by looking at the starting compound and thinking of types of reactions it can undergo

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17
Q

Reaction: alkene to halogenoalkane

A

Equation: CH2=CH2 + HX -> CH3CH2X
Reagent: hydrogen halide
Conditions: mix the gases at room temperature

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18
Q

Reaction: halogenoalkane to alcohol

A

Equation: RX + NaOH —> ROH + NaX
Reagent: aqueous sodium hydroxide
Conditions: heat under reflux

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19
Q

Halogenoalkane to nitrile

A

Equation: RX + KCN —> RCN + KX
Reagent: alcoholic potassium cyanide
Conditions: heat under reflux

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20
Q

Reaction: halogenoalkane to amine

A

Equation: RX + 2NH3 —> RNH2 + NH4X
Reagent: aqueous ammonia
Conditions: heat under reflux

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21
Q

Reaction: alcohol to chloroalkane

A

Equation: ROH + PCl5 —> RCl + HCl + POCl3
Reagent: phosphorus (V) chloride
Conditions: room temperature

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22
Q

Reaction: alcohol to bromoalkane

A

Equation: ROH + HBr —> RBr + H2O
Reagent: 50% concentrated sulfuric acid and potassium bromide
Conditions: warm

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23
Q

Reaction: alcohol to iodoalkane

A

Equation: 3ROH + PI3 —> 3RI + H3PO3
Reagent: red phosphorus and iodine
Conditions: heat under reflux

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24
Q

Reaction: primary alcohol to aldehyde

A

Equation: RCH2OH + [O] —> RCHO + H2O
Reagent: potassium dichromate (Vl) and dilute sulfuric acid
Conditions: add the reagent to hot alcohol and allow the aldehyde to distil off as it is formed

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25
Q

Reaction: primary alcohol to carboxylic acid

A

Equation: RCH2OH +2[O] —> RCOOH + H2O
Reagent: potassium dichromate (VI) and dilute sulfuric acid
Conditions: heat under reflux

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26
Q

Reaction: secondary alcohol to ketone

A

Equation: RCH(OH)R’ + [O] —> RCOR’ + H2O
Reagent: potassium dichromate (VI) and dilute sulfuric acid
Conditions: heat under reflux

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27
Q

Reaction: aldehyde to primary alcohol

A

Equation: RCHO + 2[H] —> RCH2OH
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature

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28
Q

Reaction: ketone to secondary alcohol

A

Equation: RCOR’ + 2[H] —> RCH(OH)R’
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature

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29
Q

Reaction: aldehyde to 2-hydroxynitrile

A

Equation: RCHO + HCN —> RCH(OH)CN
Reagent: potassium cyanide in dilute sulfuric acid
Conditions: 10-20 ºC

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30
Q

Reaction: ketone to 2-hydroxynitrile

A

Equation: RCOR’ + HCN —> RR’C(OH)CN
Reagent: potassium cyanide in dilute sulfuric acid
Conditions: 10-20 ºC

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31
Q

Reaction: carboxylic acid to primary alcohol

A

Equation: RCOOH + 4[H] —> RCH2OH + H2O
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature

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32
Q

Reaction: carboxylic acid to ester

A

Equation: RCOOH + R’OH —> RCOOR’ + H2O
Reagent: alcohol and concentrated sulfuric acid
Conditions: heat

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33
Q

Reaction: acyl chloride to carboxylic acid

A

Equation: RCOCl + H2O —> RCOOH + HCl
Reagent: water
Conditions: room temperature

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34
Q

Reaction: acyl chloride to ester

A

Equation: RCOCl + R’OH —> RCOOR’ + HCl
Reagent: alcohol
Conditions: room temperature

35
Q

Reaction: acyl chloride to primary amide

A

Equation: RCOCl + 2NH3 —> RCONH2 + NH4Cl
Reagent: aqueous ammonia
Conditions: room temperature

36
Q

Reaction: acyl chloride to secondary amide (N-substituted amide)

A

Equation: RCOCl + R’NH2 —> RCONHR’ + HCl
Reagent: amine
Conditions: room temperature

37
Q

Reaction: nitrile to primary amine

A

Equation: RCN + 4[H] —> RCH2NH2
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature

38
Q

Reaction: nitration of benzene

A

Equation: C6H6 + HNO3 —> C6H5NO2 + H2O
Reagent: concentrated nitric acid and concentrated sulfuric acid
Conditions: heat under reflux between 50 and 60 ºC

39
Q

Reaction: sulfonation of benzene

A

Equation: C6H6 + H2SO4 —> C6H5SO3H + H2O
Reagent: fuming sulfuric acid
Conditions: 40 ºC

40
Q

Reaction: bromination of benzene

A

Equation: C6H6 + Br2 —> C6H5Br + HBr
Reagent: liquid bromine with iron (to form iron (III) bromide)
Conditions: dry and room temperature

41
Q

Reaction: alkylation of benzene

A

Equation: C6H6 + RX —> C6H5R + HX
Reagent: halogenoalkane
Conditions: dry, in the presence of anhydrous aluminium halide

42
Q

Reaction: acylation of benzene

A

Equation: C6H6 + RCOCl —> C6H5COR + HCl
Reagent: acyl chloride
Conditions: dry, in the presence of anhydrous aluminium chloride

43
Q

What does the hazard of a chemical relate to

A

Relates to the inherent properties of each substance

44
Q

What is a hazard

A

A property of a substance that could cause harm to a user

45
Q

What is a risk

A

The possible effect that substance may cause to a user, and this will depend on factors such as concentration and apparatus. The level of risk in controlled using control measures.

46
Q

What is a chemical that is a health hazard mean

A

It could cause skin rashes, eye damage and harm if ingested

47
Q

What is a chemical that is corrosive mean

A

It can cause skin burns and permanent eye damage

48
Q

What is a chemical that is flammable mean

A

Can catch fire if heated or comes into contact with a flame

49
Q

What is a chemical that has acute toxicity mean

A

It can cause life-threatening effects, even in small quantities

50
Q

Why is heating under reflux needed

A

Because some organic compounds are volatile, so there is a risk that they will escape from the reaction mixture during heating. Refluxing ensures that all the vapours rising from the reaction mixture during heating enter the condenser and change back into liquids.

51
Q

Why are anti-bumping granules used in heating under reflux

A

It helps to make the boiling smooth

52
Q

State the three methods of separation

A

Simple distillation
Steam distillation
Fractional distillation

53
Q

What is simple distillation used for

A

It is used to obtain a liquid product from a reaction mixture that has a boiling temperature much lower than the other substances in the reaction mixture

54
Q

State how does the apparatus of simple distillation work

A

Distillation of an impure liquid involves heating it in a flask connected to a condenser. The liquid with the lowest boiling temperature evaporates or boil off first and passes into the condenser first, and so can be collected in the receiver separately from another liquid that may evaporate later

55
Q

Why is a thermometer used in simple distillation

A

It is used to monitor the temperature of the vapour as it passes into the condenser. If temperature remains steady, this indicates that one compound is being distilled. If after a while the temperature begins to rise, this indicates that a different compound is being distilled

56
Q

Advantages and disadvantages of simple distillation

A

Advantages: it is easier and quicker to set up than fractional distillation
Disadvantages: it does not separate the liquids as well as fractional distillation . It should only be used if the boiling temperature of the liquid being purified is very different from th other liquids in mixture.

57
Q

What is steam distillation used for

A

Used to separate an insoluble liquid from an aqueous solution.

58
Q

what does steam distillation involve

A

Passing steam into a reaction mixture that contains an aqueous solution and a liquid that forms a separate layer. The agitation of the liquid caused by the steam bubbling through the mixture ensures that both the insoluble liquid and the aqueous solution are on the surface of the mixture and so can form part of the liquid that evaporates

59
Q

Advantage of using steam distillation

A

The insoluble liquid is removed from the reaction mixture at a temperature below its normal boiling temperature

60
Q

Apparatus used in fractional distillation

A

Uses the same apparatus as simple distillation but with a fractionating column between the heating flask and the still head

61
Q

How is the fractionating column prepared for fractional distillation and why

A

The column is usually filled with glass beads. These act as surfaces on which the vapour leaving the column can condense, and then be evaporated again as more hot vapour passes up the column. The vapour experiences several repeated distillations as it passes up the column, which provides a better separation

62
Q

Advantages and disadvantages of fractional distillation

A

It takes longer than simple distillation.
Provides a better separation than simple distillation

63
Q

when is fractional distillation used

A

Used when the difference in boiling temperatures is small and when there are several compounds to be separated from a mixture

64
Q

What is solvent extraction used for

A

Used to remove the desired organic product from other substances in the reaction mixture using a solvent

65
Q

What does the solvent choice depend on in solvent extraction

A

-solvent added must be immiscible with the solvent containing the desired organic product
-the desired organic product should be much more soluble in the added solvent than in the reaction mixture

66
Q

Method for solvent extraction

A

-Place the reaction mixture in a separating funnel, and then add the chosen solvent -it should form a separate layer
-place the stopper in the neck of the funnel and gently agitate the contents of the funnel for a short while
- allow the contents to settle into two layers
- remove the stopper and open the tap to allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask
-when te desired organic product has been separated, simple or fractional distillation is used to separate the desired organic product from the solvent used

67
Q

In solvent extraction, how should the solvent be added

A

In small portions because this is more efficient- removes more of the desired organic product.

68
Q

What is washing used for

A

Used to remove impurities from a solid or liquid. It could involve water or the use of sodium carbonate solution, to remove excess acid

69
Q

Method for washing

A

An impure solid is stirred in some of the solvent, then the mixture is filtered.
A liquid would be mixed with a solvent chosen so that it will not dissolve the liquid to be purified. The mixture is then shaken in a separating funnel. After allowing the two liquid layers to separate, the tap is opened to allow each layer to drain into a separate container

70
Q

Technique used to dry organic solids

A

There is no special technique- it just needs to be left in a warm place or a desiccator with a suitable drying agent

71
Q

Features of drying agents in drying

A

-drying agents do not react with the organic liquid
-most common are anhydrous metal salts: (CaCl2, MgSO4, Na2SO4)
-they form hydrated salts- when they come in contact with water, they absorb water. As water of crystallisation

72
Q

Method of drying

A

The drying agent is added to the organic liquid and the mixture is gently agitated or shaken, and then left for a period of time. Before use, drying agent is powdery, after absorbing water it looks more crystalline. If drying agent is added and it remains powdery, the liquid is dry. Liquid goes from cloudy to clear when water removed.

73
Q

How is the drying agent removed after drying

A

By decantación or filtration

74
Q

When is recrystallisation used

A

To purify. A solid compound is dissolved in a suitable solvent that can dissolve all or most of any impurities but very little of the compound being dissolved

75
Q

Method for recrystallisation

A

-Add the impure solid to a conical flask
-Add some of the chosen solvent and warm until the mixture nears the boiling temperature of the mixture
-if there is still some undissolved solid, add further solvent and warm until the mixture boils again
-continue adding further solvent and heating until all of the soluble solid has dissolved
-If insoluble impurities are present, then hot filtration could be done using fluted filter paper in a heated funnel
-Allow the liquid to cool until crystals of the organic solid have formed
-More crystals can be obtained by cooling the solution below room temperature in an ice bath
-The mixture is then filtered to remove soluble impurities using a Buchner funnel or a Hirsch funnel
-The crystals are washed with a small amount of ice cold solvent and then dried in a desiccator or warm oven

76
Q

Why does the impure solid need to be dissolved in minimum volume of hot solvent in recrystallisation.

A

To make sure that the pure solid will crystallise when the solution is cooled

77
Q

Why is hot filtration used in recrystallisation

A

To ensure the pure solid does not crystallise at this stage

78
Q

Why do the crystals of the pure solid crystallise in rerystallisation

A

Because the solid is less soluble in the cold solvent than in the hot solvent

79
Q

why are the crystals washed with a small amount of ice-cold solvent after recrystallisation

A

To remove any soluble impurities, to make sure that very little of the pure solid dissolves

80
Q

How can you test for purity

A

If a compound is a solid, then its melting point can be measured.
If a compound if a liquid, then its boiling temperature can be measured.

If it is pure it should be sharp rather than over a range of temperatures

81
Q

How to test for purity by the determination of the melting point

A

Impurities reduce the melting point. By measuring the mp, you can compare it to a known value. Place some of the solid in a small capillary tube attached to the bulb of a thermometer and then place the assembly in a liquid that has a boiling temperature above that of the melting temperature of the solid

82
Q

How to test for purity by determining the boiling temperature

A

For liquids, impurities raise the boiling temp. Compare the data measured with a known value to calculate the percentage purity.
The apparatus used to determine depends on the volume of liquid available and whether it is toxic or flammable. Apparatus for simple distillation can be used in most cases.

83
Q

What disadvantages does testing thee purity by determining the boiling temperature have

A

-test may not be enough proof since you may not be able to measure the boiling point of the organic compound accurately enough
-thermometer may read too low or too high so you may wrongly assume that your compound is pure after comparing an inaccurate measured value to te known value.
-different organic compounds have the same boiling temperature

Chemistry IAL EDEXCEL A-Level (7 decks)

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