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Chem - A level (units 1 -10) > Elements from the Sea - Unit 3 > Flashcards

Elements from the Sea - Unit 3 Flashcards

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1
Q

What is the apperence of F2 at room temp?

A

Pale yellow gas

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2
Q

What is the apperance of Cl2 at room temp?

A

Pale green gas

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3
Q

What is the appearance of Br2 at room temp?

A

Red liquid

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4
Q

What is the appearance of I2 at room temp?

A

Grey solid

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5
Q

What is the trend in “id-id” effect down halogens, why and what does this mean (group 7)?

A

1 - As you go down the group the “id’id” intermolecular forces get bigger as there are more e- in the compounds as you go down the group

2 -This therefore means the compounds futher down the group have a higher Bpt

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6
Q

What is the solubility of halogens in water?

A

Not very soluble

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7
Q

What is the solubility of halogens in Organic solvents e.g hexane?

A

Very soluble

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8
Q

What are the key features of halogens?

A

Good oxidising agents

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9
Q

What is the equation for the displacement of I2 from KI?

A

Br2(aq) + 2KI (aq)—> I2(s) + KBr (aq)

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10
Q

What are halogens?

A

Group 7 elements

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11
Q

How are the halogens found?

A

They are all found naturally in compounds because they are the most reactive non metals

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12
Q

In a compound what are the two ways in which a halogen atom achieve stability?

A

1 - The halogen atom gains an e- from the metal atom forming a halide ion in an ionic compound

or

2 - The halogen atom shares an e- with a non metal atom to form a covalent compound

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13
Q

What is the trend in reactivity of the halogens and why? (3)

A

1 - Elements further up the group are more reactive

2 - This is because they have fewer no. e- shells and therefore the nucleus is less sheilded

3 - This therefore means there is a larger electrostatic charge between the incoming e- and the nucleus and therefore the atom has a higher electronegativity so gains the e- more easily to form the negative halide ion

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14
Q

What are halides?

A

Group 7 ions or salts

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15
Q

When solid I2 sublimes what is it’s appearance?

A

Purple vapour

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16
Q

What is a spectator ion?

A

Ions that are left out of the ionic equation because they are unchanged

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17
Q

Turn this equation into an ionic equation and state what has happened and why? (3)

Cl2(aq)+ 2Kl-(aq) —> 2KCl-(aq) + I2(aq)

A

Cl2 + 2I- —-> 2Cl- + I2

  • Each Iodine ion loses an e- so is oxidised, the Cl causes this to happen so is the oxidising agent

2I- —-> I2 + 2e-

  • Each Chlorine atom gains an e- so is reduced, the Iodine ions cause this to happen so are the reducing agent

Cl2 + 2e- —> 2Cl-

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18
Q

What type of reaction is this an example of and why? (4)

Br2 + 2I- —> 2Br- + I2

A

redox

Oxidation and Reduction have taken place

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19
Q

When is a reaction a redox reaction?

A

When oxidation and reduction hae occured in the same reaction

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20
Q

What is the equation for precipitation reaction between silver ions and halide ions?

A

Ag+(aq) + X-(aq) —> AgX(s)

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21
Q

What colour precipitate do I, Cl, and Br form in silver ions?

A

Cl - White

Br - Cream

I - Pale yellow

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22
Q

How does adding amonia to silver halide precipitates help to distinguish what compound has been formed? (2)

A

1 - The solubility decreases from Cl, Br and I silver halides

2 - So, when the ammomia is added the compounds can be distingusihed by seeing by how much each has dissolved in the ammonia

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23
Q

What colour is Cl, Br and I when dissolved in water?

A

Cl - Pale green

Br - orange/yellow/

I - brown

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24
Q

What colour is Cl, Br and I when dissolved in cyclohexane?

A

Cl - pale green

Br - orange/brown/red

I - violet

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25
Q

What determines the colour of the cyclohxane or aqueous solution?

A

The diatomic element formed not the ion

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26
Q

What is an example of oxidation?

A

2Br- —-> Br2(aq) + 2e-

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27
Q

What is an example of reduction?

A

Cl2(aq) +2e- —> 2Cl-(aq)

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28
Q

What is the oxidation number for different substances? (6)

A

1 - Elements =0

2 - Simple Ions = It’s charge

3 - Oxygen in compounds (normally) = - 2

4 - Hydrogen in compounds (normally) = +1

5 - In a compound the sum of the oxstates = 0

6 - In a complex ion sum of oxstates = It’s charge

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29
Q

What does it mean if the oxidation goes up/down?

A

Goes up - Been oxidised

Goes down - Been reduced

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30
Q

What does the change in oxidation number tell you?

A

The number of e- either gained or lost

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31
Q

What does the roman numerals represent, using an example?

A

1 - The oxidation state of one of the elements in the compound e.g Nitrate (v) means the N atom has a 5+ charge

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32
Q

How is bromine produced in the laboratory?

A

A chlorine solution is added to a solution containing bromide ions

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33
Q

What happens to oxidising and reducing agents?

A

Oxidising agent are reduced

Reducing agents are oxidised

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34
Q

What are the three things reduction can mean?

A

1 - loss oxygen

2 - Gain e-

3 - Decrease in oxidation number

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35
Q

What are the three things oxidation can mean?

A

1 - Gain oxygen

2 - Loss e-

3 - Increase in oxidation number

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36
Q

What is FeO called, using roman numerals?

A

iron (II) oxide

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37
Q

What is Fe2O3 called, using roman numerals?

A

iron (III) oxide

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38
Q

In potassium nitrate (v) what element has the oxidation stae +5?

A

The nitrogen

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39
Q

What is four in roman numerals?

A

IV

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40
Q

What is an oxyanion?

A

A negative ion with oxygen in it

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41
Q

What formula does the nirate (v) and nirate (III) ions have?

A

Nitrate (V) : NO3-

Nitrate (III) : NO2-

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42
Q

In oxyanions, what do the roman numerals refer to?

A

The oxidation state of the element other than oxygen

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43
Q

What are stoichiometric equations?

A

Balanced equations

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44
Q

What is the rule for loss and gain of e- in redox reactions?

A

The number of e- lost must equation the number of e- gained

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45
Q

How do you structure an answer that asks you to ‘explain the obsevations in the aquaous and cyclohexane layer’ (6)

A

1 - Colour change in the aqueous solution

2 - Colour change in the cyclohexane

3 - The colour is seen because of the halogen that has formed from the halide

4 - What has been oxidised + reduced and oxidising and reducing agents

5 - Ionic equation

6 - Reaction occurs due to trend in reactivity - shells

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46
Q

What observations show that halogens are more soluble in cyclohexane than water?

A

The cyclohexane layer gets most of the colour

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47
Q

Why do halogens further down the group lose e- more readily? (3)

A

1 - They have more e- shells so are bigger and the nucleus is therefore sheiled by more inner e-

2 - Therefore there is a weaker electrostatic attraction between the nuclus and outer e-

3 - Therefore the e- is lost easier

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48
Q

How should you write oxidation numbers?

A

+/-n

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49
Q

What is brine

A

Concentrated solution of NaCl

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50
Q

What substances does the electrolysis of NaCl generate? (3)

A

1 - Chlorine and it’s co - products: hydrogen and sodium hydroxide

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51
Q

What is the chlor-alkali industry and why is it a thing?

A

1 - The pdouction of Chlorine and sodium hydroxide

2 - Because the manufacture of the compounds is directly linked

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52
Q

What are the advantages of the co-products in the electroylsis of brine to podurce chlorine? (2)

A

1 - They can be sold to increase profitability

2 - Reduce waste

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53
Q

What is the overall equation and half equations for the electroylsis of brine and where do they occur?

A

2Cl-(aq) + 2H2O(l) –> Cl2(aq) + 2OH- (aq) + H2(g)

Positive electrode: 2Cl-(aq) –> Cl2(aq) + 2e-

Negative Electrode: 2H2O (l) + 2e- –> 2OH- (aq) + H2(g)

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54
Q

What is electrolysis and how is it able to happen?

A

1 - When electricity is passed through a molton or aqueous ionic compound it is broken down

2 - This is because the charged ions are free to move so move to the oppositly charged electrodes

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55
Q

What happens at the electrodes?

A

e- are lost or gained by ions

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56
Q

Why does electroylsis only work with molton or aqeous ionic compounds?

A

Because the charged ions are free to move and so can carry a current

57
Q

Describe the electroylis of Lead bromide? (4)

A

1 - The positive Lead ions migrate towards the cathode

2 - The Lead ions gain e- to form lead atoms so are reduced

3 - The negative Bromide ions migrate towards the anode

4 - The Bromide ions lose e- to form Bromine atoms so are oxidised

58
Q

What is the cathode

A

Negative electrode

59
Q

What is the anode?

A

Positive electrode

60
Q

What is the product at the cathode of the electrolysis of a molten salt?

A

Metal

61
Q

What is the product at the anode of the electrolysis of a molten salt?

A

non metal - apart from hydrogen

62
Q

Why is it harder to predict what will be produced at the electrodes in the electrolysis of aqueous salt solutions? (3)

A

1 - In the elctrolysis of molten salts there was no competition at the electrodes

2 - Whereas in the electrolysis of solutions water competes with ions in the salt

3 -Water can be oxidised or reduced at the anode and cathode

63
Q

WHy type of electrolysis is easier and why?

A

Electrolysis of aquous salt solutions because some compounds melting points are very high

64
Q

What is the half equation for the reduction of water at the cathode?

A

2H2O(l) + 2e- —> 2OH-(aq)+ H2(g)

65
Q

What is the half equation for the oxidation of water at the anode?

A

2H2O(l) —> O2 (g) + 4H+ (aq) +4e-

66
Q

What happens at the anode

A

Oxidation

67
Q

What happens at the cathode?

A

Reduction

68
Q

What is found at the Cathode in the electrolysis of aqeous salt solutions?

A

Metal ions and water

69
Q

What is possibly formed at the Cathode in the electrolysis of aqeous salt solutions? (3)

A

If metal Group 1,2 of aluminium = hydrogen produced

All other salts = The metal

For acids = Hydorgen

70
Q

What is found at an unreactive anode in the elctrolysis of aqeous salt solution?

A

The negative ions and the water

71
Q

What is formed at an unreactive anode in the elctrolysis of aqeous salt solution? (3)

A

1 - Halides loses e- easier than water so halogen formed

2 - Sulfate or Nitrate - harde to lose e- than water so Oxygen formed

3 - Hydorxides - Oxygen formed

72
Q

What happens at the cathode and reactive copper

anode in the electroylsis of copper sulfate?

A

1 - Anode - The copper anode loses mass because it’s copper atoms are oxidised to copper ions and go into the solution

2 - Cathode - Copper is depsoited. Therefore, althought Copper ions from the anode enter the solution the conentration of Cu ions in the solution remains the same

73
Q

What makes an anode reactive?

A

If its the same metal as the one in the salt

74
Q

What are examples of unreactive anodes?

A

1 - Graphite

2 - Platinum

75
Q

What type of ions does the cathode attract?

A

cations

76
Q

What type of ions does the anode attract?

A

Anions

77
Q

Write the equation fr the production of O2 from the elctroylis of water?

A

2H2O —> O2 +4H+ + 4e-

78
Q

What is the equation for the production of O2 from the elctroylsis of OH-?

A

4OH- –> O2 + 2H2O + 4e-

79
Q

What is the equation for the prouction of hydrogen from acids?

A

H+ + 2e- –> H2

80
Q

What is the equation for the prouction of hydroxide ions and hydrogen from water?

A

2H2O + 2e- –> 2OH- + H2

81
Q

How are bleaches made from chlorine? (3)

A

1 - Chlorine gas is passed through cold Sodium Hydroxide

2 - The Sodium Hydroxide reacts with the Chlroine to form Sodium Chlorate (I)

3 - This is an equilibrium reaction

82
Q

What is a closed system?

A

Where nothing can enter or leave a reaction

83
Q

Explain reversable change? (4)

A

1 - In the gas, the molecules are moving quickly and randomly so collide with molecules on the surface of the liquid

2 - Some gas particles bounce back into the gas phase but some enter the liquid phase

3 - At the same time, lquid molecules are also colliding with eachother and so near the liquid surface some of the molecules escape into the gas phase

4 - This means there are molecules entering and leaving the liquid phase - It is a reversable change

84
Q

What is the forward reaction?

A

reaction going from left to right

85
Q

Describe and expalin the stages of this reaction?

H2 + I2 <–> 2HI (4)

A

1 - The rate of the forward reaction inreases as H2 and I2 react to make 2HI and there concentratiosn decrease

2 - At the start of the reaction, the rate of the reverse reaction will be 0 because 2HI has not yet been produced

3 - The rate of the reverse reaction increases as the concentration of the 2HI increases

4 - The reaction has reached dynamic equilibrium when the rate of the forward and reverse reactions are equal

86
Q

In an equilibirum reaction, what would happen to the colour of the purple I2 and H2 solution as it reacts to make HI? (2)

A

1 - The purple become paler as the iodine concentartion decrease as it reacts to make HI

2 - However the purple colour doesn’t dissapear and once the reaction has reached equilibrium, the colour remains constant

87
Q

What are the three key points in the definiton for dynamic equilibrium?

A

1 - Concentrations of products and reactants remain constant but are not the same

2 - The rate of reverse and forward reaction equal

3 - forward and reverse reactions are happening

88
Q

What factors change Kc?

A

Only temperature

89
Q

What type of reactions are equilibrium reactions?

A

All reactions

90
Q

What does Kc>1 mean?

A

More products than reactants at equilibrium

91
Q

What does Kc stand for?

A

Equilibrium constant

92
Q

What does Kc>>1 mean (greater than 1010)?

A

The reaction has gone to completion

93
Q

What does Kc<1 mean?

A

More reactants than products

94
Q

What does Kc<<1 mean? (less than 1010)

A

the reaction hasn’t occured

95
Q

What is a model way of answering what happens when extra reactant is added at equilibrium when the Kc value is 4? (3)

A

1 - Immediatly after adding more reagant the Kc valus is smaller as there is a higher conc reagnt over product

2 - Therefore, more reactant had to react to produce more product and keep the Kc value constant

3 - So, the equilibrium moved to the right side to re-establish the Kc

96
Q

What does it mean for a reaction to have gone to completion?

A

All the reactants have been converted into products

97
Q

What are the risks of storing and transporting chlorine? (2)

A

1 - Toxic and corrosive - damage skin and eyes and respiratory system

2 - Must be kept away from flammable materials - Is an oxidisng agent so increases fire risk

98
Q

How are the possible effects of chlorine mitigated against during it’s transport?

A

Kept as a liquid under pressure in small cylinders

99
Q

What are the uses of Chlorine? (3)

A

1 - Steralises water

2 - Kills microorganims

3 - Bleach

100
Q

What is the use of Iodine-Sodium Thiosulfate reactions?

A

Finding the concentration of an oxidising agent that is strong enough to oxidise iodine ions

101
Q

How do you titrate iodine with sodum thiosulfate? (6)

A

1 - Add oxidisng agent into a flask and then add excess potassium iodide and sulfuric acid

2 - This will produce iodine by

xO3- + 5I- + 6H+ –> I2 + 3H2O + x

3 - Using a burette, slowly add sodium thiosulfate solution into the flask untill the solution is pale yellow

4 - Then add starch solution which will turn the solution blue

5 - Add sodium thiosulfate slowly untill the blue colour has dissappeared as this means the idoine has been reduced to iodide ions by:

I2 + 2S2O32-→ 2 I− + S4O62-

6 - Then calulate the conecntrtaion of sodium thiosulphate used to reduce the iodine

7 - Then use that to work out the no. moles of iodine + from this, the conc. of the oxidising agent

102
Q

How can you imrpove the accuracy of titrations? (4)

A

1 - Rinse out burette with the solution as water will dilute solution

2 - Read reading from bottom of meniscus at eye level

3 - Wash the flask between repeats

4 - Repeat experimnet untill you get result 0.1cm3 within eachother then take the mean

103
Q

WHat are the specifc erros that could occur in the iodine - sodium thiosulfate titration? (2)

A

1 - The solutions will react slowly with oxygen so they should be made up as freshly as possible

2 - If starch added too soon then idoine will stick to the strach and won;t react as well with the thiosulfate ions so only add starch when solution is pale yellow

104
Q

What is the formula for thiosulpahte ions?

A

S2O32-

105
Q

What’s a by product? (2)

A

1 - produced by another reaction

2 - Not useful

106
Q

What is a co-product?

A

1 - Often useful

2 - Produved by the same reaction alongside the desired product

107
Q

What is the atom economy if you only have one product.?

A

100%

108
Q

What does a greater atom economy mean?

A

Less waste

109
Q

What is the atom economy?

A

The % of reactant atoms forming the desired product

110
Q

What is % yeild?

A

The amount of product obtained in a reaction

111
Q

What halogens are stronger oxidising agents?

A

Halogens further up the group

112
Q

What halogens are stronger reducing agents?

A

Halogens further down the group

113
Q

What are the ways in which hydrogen halides can be made in the lab? (2)

A

1 - Hydrogen Chloride = Conc. sulfurc acid + Sodium Halide

2 - Hydrogen Bromide or Iodie = Conc. Phosphoric acid + Sodium Halide

114
Q

Describe what happens when concentrated acid is added to sodium chloride? (2)

A

1 - You see white fumes of hydrogen chloride as it meets the moist air

2 - Tiny droplets of hydrochloric acid are being made as the gas is very solible in water

115
Q

Desribe what happens when concentrated sulfuric acid is added to Sodium Bromide? (2)

A

1 - First, Sodium Bromide reacts with con. sulfuric acid to produc Hydrogen Bromide

2 - However, the Bromide ions are are strong reducing agents so reduce the sulfuric acid to sulfur dioxide

116
Q

Why is adding concentrated sulfuric acid to Sodium bromide not a good way to make hydorgne bromide gas?

A

1 - The gas made will be a mixture of Hydrogen Bromide and Sulfur dioxide and bromine vapour

2 - Therefore the Hydrogen Bromide won’t be pure

117
Q

Describe what happens when conc. suluric acid is added to Sodium Iodide? (2)

A

1 - Firts, Hydrogen Iodide is produced as white fumes

2 - However, the Iodide ions are very strong reducing agents so reduce the sulfuric acid to mkae hydrogen sulfide gas which smells of rotten eggs

118
Q

Why is adding conc. sulfuric acid to Sodium Iodide not a good way to make Sodium Iodide? (2)

A

1 - The gas will be a mixture of Hydrogen Iodide and Hydorgen Sulfide

2 - Therefore the Hydrogen Iodide won’t be pure

119
Q

Why is phosphoric acid used instead of Sulfuric acid when making Hydrogen Iodie or Bromide? (2)

A

1 - The phosphoric acid won’t be reduced

2 - Therefore pure Hydorgne halide gas is produced

120
Q

What is the trend n thermal stability of the hydrogen halides and why? (3)

A

1 - The thermal stability dcerease down the group - Hydorgen Iodide is broken down into it’s elements at a lower temp than Hydorgen Chlordie

2 - This is because the bond strentgh between the Hydorgen and Halide decreases down the group

3 - So less energy is needed to break the bond

121
Q

What happens to the hydrogen halides when they are heated in a laboratory? (3)

A

1 - Hydrogen Flurodie and Chloride - aren’t broken down

2 - Hydorgen Bromide strongly heated - broken down into hydrogen and brown bromine gas

3 - If a red hot needle plunged into Hydrogen Iodide - Broken down into hydrogen and large amounts purple iodine gas

122
Q

What is the solubility of hydrogen halides?

A

Very soluble

123
Q

Describe what happens when Hydorgne halide is added to water and why (2)

A

1 - They form an acidic solution

2 - This is because there is almost 100% dissociation of the H+ ions from the Hydrogen halide

124
Q

Write an equation for what happens when hydrogen halides are added to water?

A

H2O + HCl –> H3O + (oxonium ion) + Cl-

125
Q

Describe the reaction of Ammonium and Hydrogen Halides?

A

1 - Glas rod dipped into conc. ammonium solution and placed in the hydrogen halide

2 - White cloud of Ammonium Halide produced

126
Q

Desribe how Hydorgen halides react with conc. sulfuric acid and why is this? (4)

A

1 - HF + HCl don’t react

2 - HBr makes sulfur dioxide

3 - HI makes hydrogen sulfide

4 - This is due to the increasing stength of halide ions as reducing agents

127
Q

What is an oxidising agent?

A

Something that removes electrons from something else - and gets reduced itself.

128
Q

What is the tendenecy of halide ions further down the group?

A

They give up there e- to reduce soemthing else

129
Q

Describe what happens to the rate of reaction when you increase the pressure? (2)

A

1 - Increased collision frequencey

2 - Increased rate

130
Q

Describe what happens to rate of reaction when you increase the temperature? (5)

A

1 - Increased kinetic energy of particles

2 - Increased collision freuencey

3 - More particles have the amount or more energy needed to overcome the activation energy

4 - Greater probability of sucessful collision

5 - Increased rate

131
Q

How do you structure an answer on the effect of a pressure increase on yeild? (3)

A

1 - Compare no. moles on reactant and product side

2 - High pressure favours reaction with less moles

3 - either decrease of increase yeild

132
Q

How do you structure an answer on the effect of a higher temperature on yeild? (2)

A

1 - High temp favours the enodthermic reaction

2 - Increaes/decrease yeild

133
Q

Write an equation for hydogn halides recation with ammonia?

A

HX(g) + NH3(g) –> NH4X(s)

134
Q

Write an equation for sodium Chloride reaction with sulfuric acid?

A

NaCl(s) + H2SO4(aq) –> NaHSO4(aq) + HBr(g)

135
Q

Write an equation for sodium Iodie’s reaction with sulfuric acid?

A

1st: NaI(s) + H2SO4(aq) –> HI(g) + NaHSO4(aq
2nd: 8H+(aq) + 8I-(aq) + H2SO4(aq)–> H2S(g) + 4I2(s) + 4H2O(l)

136
Q

Write an eqaution for the reaction between Sodium Bromide and sulfuric acid?

A

1st: NaBr(s) + H2SO4(aq) –> HBr(g) + NaHSO4(aq)
2nd: 2H+(aq) + 2Br-(aq) + H2SO4(aq) –> SO2(g) + Br2(l) + 2H2O(l)

137
Q

What is Hydrogen Chloride dangerous?

A

It is highly toxic

138
Q

What is Le Chatelier’s principle?

A

If a system is at equilibirum and a change is made to the conditions, the system will counteract the change.

139
Q

What is the activation energy?

A

The minimum amount of energy required for a chemical reaction to take place

Chem - A level (units 1 -10) (14 decks)

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