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Chemistry > Topic 5b: Electroysis > Flashcards

Topic 5b: Electroysis Flashcards

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1
Q

What is electrolysis?

A

The process in which energy transferred by direct electrical current decomposes electrolytes.

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2
Q

What is an electrolyte?

A

An ionic compound which is molten or dissolved in water.

(When an ionic compound is melted or dissolved in water its bonds break. This allows the ions to move so the solution can conduct electricity. This is the electrolyte).

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3
Q

What is an electrode?

A

A rod made of a metal or graphite that carry’s the current into or out of the electrolyte.

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4
Q

What do we use electrolysis for today?

A

To break down substances.

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5
Q

What is the difference between cations and anions?

A

Cations are positive ions and are attracted to the negative cathode.

Anions are negative ions and are attracted to the positive anode.

The two ions carry opposite charges.

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6
Q

What happens when you place purple potassium manganate (VII) crystal on a piece of damp filter paper connected to a d.c electricity supply?

A

The purple colour spreads towards the anode.

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7
Q

What happens to electrons at the anode?

A

At the anode negative ions lose electrons (oxidation).

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8
Q

What happens to electrons at the cathode?

A

Positive ions gain electrons (reduction).

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9
Q

What is oxidation and what is reduction?

A

Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons)

OIL RIG

The transfer of electrons changes charged ions into atoms or molecules resulting in chemical changes of the electrodes.

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10
Q

What type of material should the electrodes be made out of and why?

A

Inert materials, usually graphite or platinum.

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11
Q

When a molten salt is electrolysed what happens at the electrodes?

A

When a molten salt is electrolysed ions are discharged as atoms at the electrodes.

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12
Q

Why and how can you predict the electrolysis products of any molten salt?

A

The salt will always decompose into its elements. The metal is produced at the cathode and the non-metal is produced at the anode.

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13
Q

In an aqueous solution of a salt (acting as an electrolyte) what ions are present?

A

Hydroxide ions (OH-), hydrogen ions (H+) and the ions of the dissolved salt.

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14
Q

In the electrolysis if sodium sulphate what subsides form at the cathode and the anode?

A

Cathode: sodium ions and hydrogen ions collect here, where hydrogen gas forms.

Anode: hydroxide ions (OH-) are discharged more readily that sulphate ions (SO42-). So oxygen gas is formed along with water.

Overall hydrogen and oxygen are produced at the electrode.

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15
Q

How can copper be purified during the process of electrolysis using copper electrodes?

A

1) the copper atoms in the anode lose their electrons to become copper ions.
2) these dissolve in the solution and migrate to the cathode, where they are deposited as pure copper.
3) impurities from the anode to not form ions and instead collect below the anode as ‘sludge’.

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16
Q

What is the reactivity series?

A

A lost of metals in the order of their reactivity with the most reactive at the top.

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17
Q

What is the order of the reactivity series?

A 
Potassium
Sodium 
Calcium
Magnesium 
Aluminium 
-Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver 
Gold
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18
Q

How do metals react with water higher up the reactivity series (e.g potassium, sodium)?

A

React with cold water to form hydrogen and a metal hydroxide.

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19
Q

How do metals react with water that are lower down the reactivity series (e.g silver, gold)?

A

Does not react with cold water or steam.

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20
Q

How do metals, in the middle of the reactivity series (e.g magnesium, zinc) react with water?

A

React very slowly if at all with cold water. But react with steam to form hydrogen and a metal oxide.

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21
Q

How do metals react with dilute acid that are lower down the reactivity series (e.g silver, gold)?

A

Do not react.

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22
Q

How do metals, in the middle of the reactivity series (e.g magnesium, zinc) react with dilute acid?

A

React to form hydrogen and a salt solution.

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23
Q

How do metals, at the top of the reactivity series (e.g magnesium, zinc) react with dilute acid?

A

React violently.

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24
Q

What do metals that react with water produce and what do metals that react with steam produce?

A

Metals that react with water produce a metal hydroxide and hydrogen.

Metals that react with steam produce a metal oxide and hydrogen.

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25
Q

What happens to the electrons when metals (in the reactivity series) react with water, steam and dilute acid?

A

The metal atoms lose electrons to form positive ions (cations). The more easily a metal’s atoms lose electrons, the higher the metal is in the reactivity series.

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26
Q

What can the reactivity series be used for?

A

To predict whether a reaction will take place. Each metal will react with compounds below it in the series.

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27
Q

What is a displacement reaction?

A

When a more reactive element displaces a less reactive element from one of its compounds.

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28
Q

What is a redox reaction?

A

This is a reaction in which one substance is oxidised and another is reduced.

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29
Q

What is a half equation?

A

An equation written to describe an oxidation or redox half-reaction.

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30
Q

What are spectator ions?

A

These are ions that died not change during a reaction. They ‘spectate’.

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31
Q

Define the term native state:

A

The native state of an element is is when it is not combined with other elements in compounds. (Uncombined elements).

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32
Q

Give examples of some metals naturally found in their native state:

A

In general inert metals are found in their native state. E.g:

  • gold
  • platinum
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33
Q

What is the process from obtaining a metal that has reacted with other elements to form compounds in rocks?

A

Extraction.

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34
Q

What is an ore?

A

A rock that contains enough of a compound to extract a metal for profit.

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35
Q

How is iron extracted from rocks containing iron oxide?

A

Iron is extracted by heating the iron with carbon. Carbon is more reactive than iron so it displaces it.

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36
Q

Why must some metals be extracted from ores using electrolysis rather than heating or displacing it with a more reactive metal?

A

Metals higher than carbon in the reactivity series must be extracted using a more powerful method called electrolysis.

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37
Q

What does the process of electrolysis involve?

A

This involves passing electricity through a molten ionic compound to decompose it into its elements.

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38
Q

What are the disadvantages of using electrolysis to extract metals?

A

-a lot of energy is needed to keep metal oxides molten for electrolysis, making it extremely expensive.

Therefore it is only used it extract very reactive metals that cannot be obtained by heating their oxides with carbon.

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39
Q

How is copper traditionally extracted?

A

By heating copper sulphide, producing copper and silver dioxide. How we copper ores are running out and so we need to extract copper from ores containing much smaller amounts of copper compounds.

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40
Q

What is bioleaching?

A

This uses bacteria grown on a low grade ore. The bacteria produce a solution containing copper ions, called leachate.

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41
Q

Define the term leachate:

A

A solution produced when water and or another solvents passes through a mixture of substances and dissolves some of them.

42
Q

How is copper extracted from leachate?

A

By displacement using scrap iron, then purified by electrolysis. This metic can also be useful for other metals, such as nickel, cobalt and zinc.

43
Q

Define the term phytoextraction:

A

This involves growing plants that absorb metal compounds. The plants are burnt to form ash, from which the metal is extracted.

44
Q

What are the advantages of both bioleaching and phytoextraction?

A
  • no harmful gases produced (e.g sulphur dioxide).
  • causes less damage to the landscape than mining.
  • conserves supplies or higher grade ores.
45
Q

What are the disadvantages of both bioleaching and phytoextraction?

A

Both methods are very slow.

46
Q

What are the advantages of bioleaching?

A

Does not require high temperatures.

47
Q

What are the advantages of phytoextraction?

A

Can extract metals from contaminated soil.

48
Q

What are the disadvantages of phytoextraction?

A
  • more expensive than mining some ores.

- growing plants is dependant on weather conditions.

49
Q

What are the disadvantages of phytoextraction?

A

Toxic substances and sulphuric acid can be produced by the process and damage the environment.

50
Q

What is the term for when oxygen is removed from a compound.

A

When oxygen is removed form a compound it is said to be reduced.

51
Q

Is metal extraction oxidation or reduction?

A

Reduction.

52
Q

What is oxidation and reduction (in terms of oxygen)?

A

Oxidation is the gain of oxygen by a substance.

Reduction is the loss of oxygen from a substance.

53
Q

Can oxidation occur without reduction or vice versa?

A

Oxidation and reduction always occur together. Reactions in which oxidation and reduction both occur are called redox reactions.

54
Q

When e traction iron from an iron oxide ore how does reduction and oxidation occur?

A

Iron is obtained by removing the oxygen from iron oxide by heating it with carbon. The iron oxide is reduced to iron. Carbon is oxidised to carbon dioxide,

55
Q

What is corrosion?

A

This occurs when a metal reacts with oxygen, making the metal weaker over time. The metal gains oxygen so is oxidised.

56
Q

What does the corrosion of iron require?

A

The corrosion of iron requires water as well as oxygen and is called rusting.

57
Q

What is rusting?

A

The corrosion of iron or steel. Water and oxygen must be present for rusting to occur.

58
Q

How does the reactivity of a metal affect it’s ability to corrode?

A

The more reactive a metal is, the more rapidly it corrodes. Gold does not corrode at all, which is one of the reasons it is used in jewellery.

59
Q

What is a tarnish?

A

A thin layer that forms on a metal due to oxidation. A metal is said to tarnish as this layer forms.

60
Q

Define the term recycling:

A

Converting waste material into new products.

61
Q

What are some of the main advantages of recycling?

A
  • natural reserves of metal ores will last longer.
  • the need to mine ores is reduced. Mining can damage the landscape as well as create noise and dust pollution.
  • less pollution may be produced.
  • many metals need less energy to recycle them than to extract new metal from the ore.
  • less waste metal ends up on the landfill site.
62
Q

What are some of the disadvantages of recycling?

A
  • cost
  • energy used in collecting, transporting and sorting metals into being recycled.
  • sometimes it can be more expensive and require more energy, to recycle than to extract new metals.
63
Q

What is a life cycle assessment (LCA)?

A

An LCA is carried out to work out the environmental impact of a product.

64
Q

Why are LCAs useful?

A

The LCA also helps people to decide whether it is worthwhile to manufacture and recycle a product. LCAs can be used to compare the effect of using different materials for the same product, e.g making a bottle from glass or plastic.

65
Q

What is a reversible reaction?

A

In some chemical reactions the products treat to reform the reactants.

66
Q

Define the term dynamic equilibrium:

A

When the forwards and backwards reaction in a reversible chemical reaction happen at the same rate. The reaction still occurs but the substances remain in balance (equilibrium).

67
Q

Where can a dynamic equilibrium only occur?

A

In a closed system.

68
Q

Why can a dynamic equilibrium not occur in an open system?

A

In an open system gases could escape and so equilibrium would not be achieved.

69
Q

What is the difference between an open and closed system?

A

Open system: a system into or from which substances can entered or leave, such as reactions inside an open test tube.

Closed system: she substances cannot enter or leave an observed environment.

70
Q

What can the equilibrium position be affected by and how can does this change the position?

A

The position can be altered by changes in:

  • temperature
  • pressure
  • concentration

In general, the equilibrium position shifts to reduce the effects of any change to the system.

71
Q

What way does increasing temperature shift the equilibrium position?

A

In the endothermic direction (transferring energy from the surroundings, cooling them down).

72
Q

What way does decreasing temperature shift the equilibrium position?

A

In the exothermic direction (transferring energy to the surroundings, heating them up).

73
Q

What way does increasing gas pressure shift the equilibrium position?

A

In the direction that forms fewer gas molecules (as this reduced pressure).

74
Q

What way does decreasing gas pressure shift the equilibrium position?

A

In the direction that forms more gas molecules (as this increases pressure).

75
Q

What way does increasing concentration shift the equilibrium position?

A

In the direction that uses up the substance that has been added.

76
Q

What way does decreasing a concentration shift the equilibrium position?

A

In the direction that forms more of the substance that has been removed.

77
Q

What are transition metals?

A

These elements are placed in the central block of the periodic table, between groups 2 and 3. They include most the metals used for construction, vehicles, electrical wiring, jewellery and other everyday uses.

78
Q

What are some of the physical properties of transition metals?

A
  • malleable (can be hammered or rolled into shoe without shattering).
  • ductile (can be stretched out to make thin wires).
  • good conductors of electricity.
  • shiny when polished.
79
Q

Compared to metals in group 1 and 2 transition metals have

A
  • high melting points

- high densities.

80
Q

What are some of the chemical properties of transition metals?

A
  • transition metal compounds are usually coloured. (Different transition metal hydroxides are different colours). This is used to identify the transition metal ion in a substance.
  • they show catalytic activity. E.g iron is the catalyst used in the manufacture of ammonia in the Haber process.
81
Q

What is a catalyst?

A

Increases the rate of a reaction without being changed either chemically or in mass.

82
Q

What happens when metals react with oxygen?

A

They react with oxygen in the air, they oxidise to form metal oxides.

83
Q

When do metals oxidise?

A

Metals oxidise when they lose electrons. This happens when metals react with oxygen. It may also happen when metals react with other substances found in air.

84
Q

What is sacrificial protection?

A

This is a method of rust presentation that does not rely on keeping air or water away. Instead a piece of magnesium or zinc is attached to the iron or steel object. Oxygen react with them rather than with the iron or steel object, until this metal corrodes away.

85
Q

How does the reactivity of a metal effect its ability to lose electrons?

A

The more reactive a metal is, the more easily it loses electrons. Zinc and magnesium lose electrons more easily than iron does, so they are more easily oxidised.

86
Q

What is electroplating?

A

This involves coating the surface if one metal with a thin layer of another metal.

87
Q

Why is jewellery electroplated using silver and gold?

A

Silver and gold are very expensive but they can be electroplated onto cheaper ‘base metals’ such as copper or nickel. This produces attractive jewellery that is cheaper than solid silver or gold,

88
Q

What may electroplating be used for apart from making gold or silver plated jewellery?

A

-to improve a metal object’s ability to resist corrosion.
E.g objects such as vehicle and boat parts made from steel may be ‘chrome plated’ using electrolysis. Chromium is a transition metal that resist corrosion. This prevents the object from rusting.

89
Q

To electroplate an object you need:

A
  • an anode (positively charged electrode), made from the plating metal.
  • an cathode (negatively charged electrode), which is the metal object itself.
  • an electrolyte, which is a solution containing ions of the playing metal.
90
Q

What is galvanising?

A

This involves coating iron and steel objects with zinc to prevent them from rusting.

91
Q

How does galvanising prevent iron and steel from rusting?

A

The thin layer of zinc improved corrosion resistance by stopping the water reaching the iron or steel and by acting as a sacrificial metal. This layer of protection can continue even if the zinc layer is damaged.

92
Q

How can galvanised be carried out?

A

Electroplating or by dipping the object in molten zinc.

93
Q

What is an alloy?

A

A mixture of metal elements with one or more other elements, usually metals.

94
Q

How are alloy steels made?

A

Made by deliberately adding other elements to iron.

95
Q

Why is stainless steel different to other alloys of steel and how?

A

Stainless steel can resist rusting, unlike other alloy of steels and iron. Stainless steel contains chromium, which reacts with oxygen in the air. A layer of chromium oxide forms, which is thick enough to stop air and water reaching the metal below but thin enough to be transparent. If the metal is scratched, more chromium reacts to replace the layer.

96
Q

How does carbon content effect the steer the of steel?

A

The greater the carbon content of steel, the stronger and harder it is.

97
Q

Why are alloys used instead of pure metals?

A

alloys are stronger than pure metals.

98
Q

Why are alloys stronger pure metals?

A

In a solid pure metal the atoms are all the same size and arranged regularly in layers. These layers slide past each other when force is applied and is why metals are malleable and ductile.

In an alloy metals the atoms of other metals are different sized. They distort the regular structure making it more difficult for the layers to slide past each other. This is why alloys are often stronger than pure metals.

99
Q

The uses of a metal or alloy depend upon its properties. These properties include:

A
  • chemical properties, e.g resistance to corrosion.

- physical properties, such as density and ability to conduct electricity.

100
Q

Why is aluminium used in over head electrical cables instead of copper?

A

Aluminium resists corrosion, but does not conduct electricity as well as copper. How we it’s cheaper and less dense so used for overhead cables.

101
Q

Why is copper chosen for electrical wiring instead of gold?

A

Gold and copper both resist corrosion. They are both malleable, ductile and very good conductors of electricity. But go
D is thousands of times more expensive so copper is used.

102
Q

What are some of the properties of the alloy magnalium?

A
  • magnalium contains 95% aluminium and 5% magnesium.
  • less dense and almost 4x stronger than aluminium alone.
  • denser than magnesium but 2x as strong and has better resistance to corrosion.
  • used in for aircraft parts and scientific instruments.

Chemistry (14 decks)

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