Edexcel GCSE 9-1 Chemistry: SC10/11/12/13 - Extracting metals and equilibria

Paper 1 Specification: https://qualifications.pearson.com/content/dam/pdf/GCSE/Science/2016/Specification/GCSE_Chemistry_Spec.pdf

4.1 Deduce the relative reactivity of some metals, by their reactions with water, acids and salt solutions

Most reactive - react with water
(metal + water = metal hydroxide + hydrogen)
Reactive - react with acid
(metal + acid = salt + hydrogen)
Least reactive - react with oxygen
(metal + oxygen = metal oxide)

4.2 Explain displacement reactions as redox reactions, in terms of gain or loss of electrons

In displacement reactions, both oxidation and reduction takes place.

- Most reactive metal is oxidised. (loses electrons)
- Least reactive metal is reduced. (gain electrons)

The Reactivity Series

potassium
sodium
calcium
magnesium
aluminium
(carbon)
zinc
iron
(hydrogen)
copper
silver
gold

More reactive a metal, the more easily it loses its electrons to form cations.

Recall that:

• Most metals are extracted from ores found in the Earth's crust

• Unreactive metals are found in the Earth's crust as the
  uncombined elements

Oxidation

Gain of oxygen

Reduction

Loss of oxygen

Recall that the extraction of metals involves…

Extraction of metals involves reduction of ores.
(Loss of oxygen)

Ore

metal oxide

4.7 Explain why the method used to extract a metal from its ore is related to its position in the reactivity series and the cost of the extraction process, illustrated by
a heating with carbon (including iron)

Ores are reduced using carbon to extract metals.

e.g iron oxide + carbon = iron + carbon dioxide

- Cheaper than electrolysis
(zinc - copper)

4.7 Explain why the method used to extract a metal from its ore is related to its position in the reactivity series and the cost of the extraction process, illustrated by
b electrolysis (including aluminium)

Ores are reduced using electrolysis to extract metals.

e.g aluminium oxide = aluminium + oxygen

- Requires large amounts of energy so very expensive
(aluminium - potassium)

4.8 Evaluate alternative biological methods of metal
extraction (bioleaching)

- Uses bacteria to separate metals from ores

- The solution produced by the process contains metal ions which can be extracted by heating with carbon or electrolysis.

4.8 Evaluate alternative biological methods of metal
extraction (phytoextraction)

- Growing plants in soil containing metal compounds
- Metals build-up in leaves
- Plants are harvested, dried and burned.
- The ash contains metal compounds which can be extracted by heating with carbon or electrolysis.

4.9 Explain how a metal's relative resistance to oxidation is related to its position in the reactivity series

The higher on the reactivity series, the least resistant to oxidation (the gain of electrons)

4.10 Evaluate the advantages of recycling metals, including economic implications and how recycling can preserve both the environment and the supply of valuable raw materials

• requires less energy compared to electrolysis

• more sustainable as not using up finite resources

• cheaper

• creates lots of jobs

• recycling materials cuts down on the amount of rubbish that gets sent to landfill

4.11 Describe that a life-cycle assessment for a product involves consideration of the effect on the environment of obtaining the raw materials, manufacturing the product, using the product and disposing of the product when it is no longer useful

a life-cycle assessment for a product involves consideration of the effect on the environment of obtaining the raw materials, manufacturing the product, using the product and disposing of the product when it is no longer useful

4.13 Recall that chemical reactions are reversible, the use of the symbol ⇌ in equations and that the direction of some reversible reactions can be altered by changing the reaction conditions

• chemical reactions are reversible, the use of the symbol ⇌ in equations and that the direction of some reversible reactions can be altered by changing the reaction condition

• If the equilibrium is position on one side, it will be more favourable for the other side.

4.14 Explain what is meant by dynamic equilibrium

• Dynamic equilibrium is when the rate of the forward reaction is at the same rate as the backwards reactions

• AND the concentrations of reactants and products have reached a balance.

4.15 Describe the formation of ammonia as a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas) and that it can reach a dynamic equilibrium

• a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas) = ammonia

• reversible

• can reach a dynamic equilibrium

4.16 Recall the conditions for the Haber process as:

a) temperature 450 °C

b) pressure 200 atmospheres

c) iron catalyst

Conditions for Haber Process:

• 450°C

• 200 atm

• iron catalyst

4.17 Predict how the position of a dynamic equilibrium is affected by changes in:

a) temperature

Temperature

+: equilibrium moves in endothermic direction
• absorbs extra heat

-: equilibrium moves in exothermic direction
• produces more heat

4.17 Predict how the position of a dynamic equilibrium is affected by changes in:

b) pressure

Pressure

+: equilibrium moves to side with fewer moles
• reducing pressure

-: equilibrium moves to side with more moles
• increasing pressure

4.17 Predict how the position of a dynamic equilibrium is affected by changes in:

c) concentration

Concentration

+: equilibrium moves to right side to use up reactants
• producing more products

-: equilibrium moves to left side to conserve reactants
• producing less products

C3.22 Recall that electrolytes are ionic compounds in the molten state or dissolved in water.

electrolytes are ionic compounds in the molten state or dissolved in water.

C3.23 Describe electrolysis as a process in which electrical energy, from a direct current supply, decomposes electrolytes.

The decomposition (breaking down) of electrolytes using a direct current into the elements they're made from

C3.24 Explain the movement of ions during electrolysis, in which:
a) positively charged cations migrate to the negatively charged cathode

Cations are positive ions and are attracted to the negatively charged cathode - gain electrons (reduction)

C3.24 Explain the movement of ions during electrolysis, in which:
b) negatively charged anions migrate to the positively charged anode.

Anions are negative ions and are attracted to the positively charged anode - lose electrons (oxidation)

C3.27 H Write half equations for reactions occurring at the anode and cathode in electrolysis.

e.g.
Cathode reaction;
Zn2+ + 2e --> Zn reduction
Anode reaction;
2Cl- --> Cl2 + 2e oxidation

C3.28 H Explain oxidation and reduction in terms of loss or gain of electrons

OIL RIG
Oxidation Is Loss of electrons
Reduction Is Gain of electrons

C3.29 H Recall that reduction occurs at the cathode and that oxidation occurs at the anode in electrolysis reactions

Reduction takes place at the cathode. Oxidation takes place in the anode

C3.31 Investigate the electrolysis of copper sulphate solution with inert electrodes and copper electrodes.

During electrolysis, the copper atoms in the anode lose two electrons each to become copper ions. These ions dissolve into the solution and migrate to the cathode where they deposit a pure copper. So the impure copper anode loses mass and the pure copper cathode gains mass. Impurities from the anode do not form ions and collect below the anode as a 'sludge'. The anode sludge is collected because it may contain valuable metal elements.

Currents effect on mass lost or gained at electrodes.

The higher the current, the more mass lost at anode and the more mass gained at cathode.

Half equations of the electrolysis of copper sulphate solution

At the anode:
Cu --> Cu^2+ + 2e- (oxidation)
At the cathode:
Cu^2+ + 2e --> Cu (reduction

C3.25 Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
a) copper chloride solution CuCl2 (aq)

reaction at cathode;
Cu^2+ (aq) + 2e- --> Cu (s) the element (reduction)
Reaction at anode:
Cl^2- (aq) --> Cl2 (g) + 2e- the element (oxidation)
Copper chloride decomposes but water does not change.

C3.25 Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
b) sodium chloride solution NaCL (aq)

Reaction at cathode:
2H+ (aq) + 2e- --> H2 (g) - reduction
Na+ (aq) and H+ (aq) ions are attracted to the cathode. Hydrogen ions are discharged more easily than sodium ions so hydrogen is formed.
Reaction at anode:
2Cl- (aq) --> Cl2 (g) + 2e-
The sodium chloride decomposes to form hydrogen and chlorine. Sodium and hydroxide ions remain in solution.

C3.25 Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
c) sodium sulfate solution Na2SO4

Cathode:
2H+ (aq) + 2e- --> H2 (reduction)
Anode:
4OH- (aq) --> O2 (g) + 2H2O (l) + 4e-

C3.25 Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
d) water acidified with sulfuric acid

At the cathode:
2H+ +2e- → H2
At the anode:
4OH- - 4e- → 2H2O + O2

C3.25 Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
e) molten lead bromide (demonstration).

Anode:
2Br- --> Br2 + 2e-
Cathode:
Pb^2+ +2e- --> Pb

Half equations

Half equations describe the 'reaction' at each electrode. They show how many electrons exchanged between electrode and ion

C3.26 Predict the products of electrolysis of other binary, ionic compounds in the molten state.

Zinc chloride (and lead bromide) is a binary ionic compound - consist of two elements only.
In the molten state, the metal cation will go to the cathode and produce the metal element. At the anode, the non-metal anion will go to the anode and produce non-metal element.
e.g.
Zinc chloride will produce zinc and chlorine

C3.30 Explain the formation of the products in the electrolysis of copper sulphate solution, using copper electrodes, and how this electrolysis can be used to purify copper.

The copper atoms in the anode lose electrons to become copper ions. These dissolve into the solution and migrate to the cathode, where they are deposited as pure copper. Impurities from the anode do not form ions and collect below to anode as a sludge.

C1.52 H Explain why, in a reaction, the mass of product formed is controlled by the mass of the reactant which is not in excess.

The amount of product formed is determined by the mount of reactant that is not in excess and so is used up completely in the reaction - limiting reactant.

C1.53 H Deduce the stoichiometry of a reaction from the masses of the reactants and products.

1 calculate number of moles (mass/Mr or Ar)
2 divide by smaller
3 simplest whole number ratio

5.1C Recall that most metals are transition metals and that their typical properties include:

a high melting point

b high density

c the formation of coloured compounds

d catalytic activity of the metals and their compounds as exemplified by iron

• high mpt + bpt

• high density'

• forms coloured compounds

• can be used as catalysts i.e. iron

5.2C Recall that the oxidation of metals results in corrosion

oxidation of metals results in corrosion

5.3C Explain how rusting of iron can be prevented by:

a) exclusion of oxygen

Rusting of iron can be prevented if air is kept away. This can be done by storing the metal in an unreactive atmosphere of nitrogen/argon.

5.3C Explain how rusting of iron can be prevented by:

b) exclusion of water

Rusting of water can be prevented if water is kept away by using a desiccant powder that absorbs water i.e. silica gel

5.3C Explain how rusting of iron can be prevented by:

c) sacrificial protection

• magnesium or zinc is attached to the iron or steel object.

• magnesium and zinc oxidise more easily than iron

• oxygen will react with them instead of the iron or steel

5.4C Explain how electroplating can be used to improve the appearance and/or the resistance to corrosion of metal objects

• Attractive transition metals such as gold and silver can be electroplated onto cheaper base metals such as copper or nickel

• A transition metals such as chromium can be electroplated onto the object that you don't want to corrode. The air and water will react with chromium so it won't affect the metal below.

5.5C Explain, using models, why converting pure metals into alloys often increases the strength of the product

In a pure metal, the atoms are arranged regularly in layers and these layers can easily slide past each other. Whereas in an alloy the atoms are in an irregular structure due to the different sizes. This will make it harder for layers to slide past each other which makes them stronger than pure metals.

5.6C Explain why iron is alloyed with other metals to produce alloy steels

Iron is a pure metal and by alloying iron, it will be more stronger which is useful for car parts which need to be strong.

5.7C Explain how the uses of metals are related to their properties (and vice versa), including aluminium

Al:

• able to resist corrosion but can not conduct electricity as well as copper

• aluminium is stronger, cheaper and less dense than copper so it is used for overhead electrical cables

5.7C Explain how the uses of metals are related to their properties (and vice versa), including copper

Cu:

• resistant to corrosion

• better conductor of electricity than brass

5.7C Explain how the uses of metals are related to their properties (and vice versa), including magnalium (an alloy)

magnalium:

• made up of 90% aluminium and 5% magnesium

• used to manufacture strong but lightweight metal parts

• less dense than aluminium but is 4 times stronger than aluminium itself

• twice as strong as magnesium and has better resistance to corrosion