AS Chemistry AQA Unit 2 Flashcards Preview

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Flashcards in AS Chemistry AQA Unit 2 Deck (80):
0

Le Chatelier's principle

If a system in equilibrium is disturbed, the point of equilibrium will shift to counteract the change

1

Enthalpy change

Heat energy transferred in a reaction at constant pressure

2

Mean bond enthalpy

Average value for a bond enthalpy over the range of compounds it is found in

3

Enthalpy change of a reaction

Total energy absorbed - Total energy released

4

Standard enthalpy of reaction

The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, with all reactants and products in their standard states and under standard conditions

5

Standard enthalpy of formation

The enthalpy change when one mole of a product is formed from its elements, under standard conditions with all reactants and products in their standard states

6

Standard enthalpy of combustion

The enthalpy change when one mole of a substance is completely burned in excess oxygen, under standard conditions, with all reactants and products in their standard states

7

Measuring enthalpy change

q = mcΔt
q= heat change, m=mass of solution heated, c=specific heat capacity of water (4.18) Δt= change in temp
standard enthalpy change = q/n

8

Activation energy

The energy required for a reaction to start

9

Catalyst

Increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy

10

Steam Hydration of ethene

C2H4 + H2O <--> C2H5OH

11

Conditions for steam hydration of ethene

6000-7000kPa (60-70 atm)
Temperature of 300 degrees
SOLID phosphoric acid catalyst

12

Methanol production

2H2 + CO <---> CH3OH

13

Conditions for methanol production

5000-10000 kPa (50-100 atm)
250 degrees
Mixture of catalysts: copper, zinc oxide, aluminium oxide

14

Uses of ethanol

Alcoholic beverages
Fuel

15

Uses of methanol

Fuel
Mainly used to produce other chemicals

16

Redox reaction

Reaction in which oxidation and reduction occurs simultaneously

17

Oxidation state of oxygen

-2 except for peroxides, where it is -1

18

Oxidation state of hydrogen

+1 except for in metal hydrides, where it is -1

19

Half equations

Electrons and ions, and element
Show reduction or oxidation

20

Halogen boiling point trend

Increase down group

21

Halogen electronegativity trend

Decrease down group (shielding, atomic radius)

22

Reaction: Bromine water and potassium iodide

Iodine is displaced; brown solution

23

Reaction: Chlorine water and potassium bromide

Bromine is displaced; orange solution

24

Making bleach

2NaOH + Cl2 ---> NaClO + NaCl + H2O
Sodium hydroxide + Chlorine= Sodium chlorate(l) + Sodium chloride + water

25

Disproportionation

The oxidation and reduction of the same element in a redox reaction

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Reaction: Chlorine and water

Cl2 + H2O <---> HClO + HCl

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Risks of chlorine

Irritate respiratory system
Chemical burns
Chlorinated hydrocarbons are carcinogenic

28

Equation: Conc. sulphuric acid and sodium chloride/fluoride

H2SO4 + NaCl ---> NaHSO4 + HCl
Steamy fumes of HCl as it meets moisture in air
HCl or HF cannot reduce sulfuric acid; reaction ends

29

Equation: Conc. sulphuric acid and sodium bromide

H2SO4 + NaBr ---> NaHSO4 + HBr
Steamy fumes of HBr
HBr is stronger reducing agent than HCl or HF; reduces sulfuric acid
2HBr + H2SO4 ---> SO2 + Br2 + 2H2O

30

Equation: Conc. sulfuric acid and sodium iodide

H2SO4 + NaI ---> NaHSO4 + HI
Steamy fumes of HI
HI is strong reducing agent; reduces sulfuric acid
2HI + H2SO4 ---> SO2 + I2 + 2H2O
HI continues to reduce SO2
6HI + SO2 ---> H2S + 2H2O + 3I2

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Observations: Conc sulfuric acid and sodium chloride/fluoride

Steamy fumes of HCl or HF

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Observations: conc sulfuric acid and sodium bromide

Steamy fumes of HBr, choking fumes of SO2, orange fumes of Br2

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Observations: conc sulfuric acid and sodium iodide

Steamy fumes of HI, choking fumes of SO2, purple fumes of I2, bad egg smell of H2S, black solid (iodine)

34

Test for halides

Silver Nitrate test;
Add nitric acid to remove carbonate ions (ions that interfere)
Add silver nitrate
White ppt indicates chloride, cream ppt indicates bromide, yellow ppt indicates iodide
Dissolves in dilute ammonia=chloride, dissolves in conc ammonia=bromide, doesn't dissolve in conc ammonia=iodide

35

Melting point of group 2 metals

Decrease down group; blip at magnesium bc crystal structure

36

Group 2 metal reactions with water

Form metal hydroxide and hydrogen

37

Group 2 hydroxide solubility

solubility increases down group

38

Group 2 sulphate solubility

solubility decreases down group

39

Test for sulfate ions

Barium ions, e.g. barium chloride (acidified with HCl)

40

Test for hydroxide ions

Magnesium ions, e.g. magnesium chloride

41

Slaked lime

Ca(OH)2 calcium hydroxide used to neutralise acidic soil

42

Extracting metals from sulfide ores

1. Turn into oxide; roast in air
2.Reduce oxide

43

Roasting

Heating in plenty of air

44

Reducing iron(lll) oxide

Blast furnace, over 700 degrees
Carbon or carbon monoxide reducing agent
2Fe2O3 + 3C ---> 4Fe + 3CO2
Fe2O3 + 3CO ---> 2Fe + 3CO2

45

Reducing manganese(lV) oxide

Blast furnace, 1200 degrees
Carbon or carbon monoxide
MnO2 + C ---> Mn + CO2
MnO2 + 2CO ---> Mn + 2CO2

46

Reducing copper carbonate

heat with carbon, or decompose into oxide and reduce with carbon

47

Malachite

contains CuCO3, iron ore

48

Extracting tungsten

Hydrogen
Furnace, above 700 degrees

49

Extracting aluminium

Electrolysis; remove impurities, bauxite dissolved in molten cryolite, pure aluminium collects as molten metal

50

Bauxite

Al2O3, aluminium ore

51

Cryolite

Na3AlF6 reduces aluminium melting point

52

Extracting titanium

Carbon and chlorine to form titanium chloride
React with more reactive metal eg sodium to get pure metal

53

Evaluation recycling metals

+ ores are a finite resource - saves raw materials; saves energy; reduces landfill waste; mining damages landscape
-collecting and sorting metals is expensive and hard; purity of metal varies; recycling may not produce consistent supply

54

Using scrap iron

Dissolve copper ores in acidified water, scrap iron added. Iron dissolves and reduces copper ions; copper precipitate forms

55

Synthesis of chloroalkanes

free radical substitution; react alkane with halogen with UV

56

Ozone layer

O2 breaks down into O radicals under UV
O2 + O' ---> O3
ABSORBS UV IN THIS WAY

57

Ozone breakdown by CFCs

CCl3F ---> CCl2F' + Cl'
Cl' + O3 ---> ClO' + O2
ClO' + O3 ---> 2O2 + Cl'
OVERALL: 2O3 ---> 3O2

58

CFC uses

propellant in aerosols, coolant gas in fridges

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Nucleophile

Electron pair donor

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Electrophile

Electron pair acceptors

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Nucleophilic substitution

Nucleophile attacks polar molecule, replaces it

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Examples of nucleophiles

:NH3, :CN-. :OH-

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Synthesising amines

Warm haloalkane with ethanolic ammonia (ammonia dissolved in ethanol)
Ammonia swaps with halogen; NUCLEOPHILIC SUBSTITUTION

64

Synthesising nitriles

Warm haloalkane with ethanolic potassium cyanide
NUCLEOPHILIC SUBSTITUTION

65

Hydrolysis of haloalkanes

Warm aqueous sodium hydroxide and haloalkane

66

Nucleophilic sub vs elimination

React haloalkane with water, under reflux = nucleophilic sub, not much elimination
React haloalkane with ethanol under reflux= elimination

67

Test for unsaturation

Shake with bromine water- orange to colourless means unsaturation

68

Carbocation

Organic ion containing positively charged carbon atom

69

Hydration of alkenes

React alkene with water, with cold concentrated sulfuric acid
1. alkene and sulfuric acid
2. add cold water and warm; hydrolysed to ethanol

70

Synthesis of bromoalkanes

ELECTROPHILIC ADDICTION
C2H4 + HBr ---> C2H5Br

71

Unsymmetrical alkanes

Br bonds to most stable carbocation (tertiary most stable, primary least stable)

72

Polymerisation

n (H2C=CH2) ---> n(-CH2-CH2-)

73

Polyethene uses

Soft flexible plastic, plastic bags and squeezy bottles

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Polypropene uses

Tough, strong plastic. Bottle crates, rope.

75

Production of ethanol by fermentation

30-40 degrees
yeast
anaerobic conditions
C6H12O6 ---> 2C2H5OH + 2CO2
around 15% alcohol, yeast dies
Fraction distillation increases conc of alcohol

76

Dehydration of ethanol

react with conc sulfuric acid (or phosphoric acid) REFLUX
C2H5OH + H2SO4 ---> C2H5OSO2OH + H2O
C2H5OSO2OH ---> C2H4 + H2SO4

77

Oxidation of alcohols

Acidified potassium dichromate, orange to green
Primary: distilling: Aldehyde reflux: Carboxylic acid
Secondary: reflux: ketone
Tertiary: not oxidised

78

Tollens reagent

Silver mirror with aldehyde, none with ketone
Reduced to silver with aldehyde

79

Fehlings solution

Blue to brick red with aldehyde, not ketone