SC11

Question 1

SC11c
1) Explain why reactions occurring at the electrodes during electrolysis are redox reactions, and why the redox reactions are needed
2) Describe the meanings of oxidation and reduction in terms of oxygen.
3) Explain which substance has been oxidised and which substance has been reduced in a reaction.

Answer 1

1) As electrolysis involves the simultaneous losing and gaining of electrons, we can say that the reaction is a redox reaction. This loss and gain of electrons by the ions provides the movement of electrons needed for the electrical current to flow.
2) Reduction is the loss of oxygen, and oxidation is the gain of oxygen.
3) The atom that loses electrons becomes oxidised, and the atom that gains electrons becomes reduced.

Question 2

SC11c
1) What type of reaction happens to ores when metals are extracted?
2) Explain how the position of a metal in the reactivity series is related to its resistance to oxidation.

Answer 2

1) All metals are extracted by reduction from their ores.
2) Metals with a lower reactivity than hydrogen are found as the uncombined element, and are resistant to oxidation. Metals with a higher reactivity that carbon are not resistant to oxidation.

Question 3

SC11b
1) Recall the meaning of the term ‘ore’.
2) Recall some metals that are found uncombined in the Earth’s crust.
3) Explain how and why some metals are extracted from their ores by heating with carbon.

Answer 3

1) A metal ore is a rock which contains enough metal to make it economically worthwhile extracting the metal from it.
2) Gold, silver and platinum are found uncombined in the earth’s crust.
3) If a metal is less reactive than carbon, it can be extracted from its oxide by heating with carbon. The carbon displaces the metal from the compound, and removes the oxygen from the oxide. This leaves the metal.

Question 4

SC11b
1) Explain how and why some metals are extracted from their ores by electrolysis.
2) Describe two biological methods of metal extraction.

Answer 4

1) Metals higher than carbon on the reactivity series must be extracted with electrolysis. This involves passing electricity through a molten ionic compound to decompose it into its elements. Often, the metal oxide is mixed with another substance to lower the melting point of the electrolyte or ore. A lot of energy is needed for electrolysis which is expensive. Therefore, electrolysis is only used to extract very reactive metals that cannot be obtained by heating their oxides with carbon.
2) One biological method of metal extraction is phytoextraction.
a. Plants are grown in soil containing metal compounds, which they absorb (via their roots).
b. The plants can neither use nor dispose of the metals, so they accumulate in the leaves.
c. The plants are harvested, dried and burned in a furnace.
d. Metals can be extracted from metal compounds in the ash using electrolysis or displacement reaction.
Bioleaching uses bacteria grown on a low grade ore. The bacteria produce a solution containing copper ions, called a leachate. Copper is extracted from the leachate by displacement using scrap iron, then purified by electrolysis. This method can also be used for metals such as nickel, cobalt and zinc.

Question 5

SC11a
1) State the reactions of common metals with water, steam and acids, and describe what will be seen
2) Describe the reactions of metals with salt solutions.
3) Explain why displacement reactions are redox reactions.

Answer 5

1) Metals that react with cold water form a metal hydroxide solution and hydrogen. The metals that react with steam form hydrogen and a solid metal oxide. Metals that react with dilute acids form hydrogen and salt solution. Bubbles of gas will be seen. The more bubbles formed, the more reactive the metal.
2) Displacement reactions result in a new salt being formed and the weaker metal coming out of solution and being deposited as a metal precipitate.
3) Displacement reactions are redox reactions because one metal loses electrons to form ions while the other metal gains electrons to become neutral. One metal is oxidised, while the other metal is reduced, which is a redox reaction.

Question 6

SC11a
1) Deduce the order of metals in the reactivity series from their reactions with water, acids and salt solutions.
2) Explain the reactivity series in terms of the tendency of different metal atoms to form cations.

Answer 6

1) In general, the more reactive the metal, the more rapid the reaction is with water, acids and salt solutions, and the higher it will be in the reactivity series. A metal below hydrogen in the reactivity series will not react with dilute acids.
2) In most metal reactions the metal atoms lose electrons to form positive ion (cations). The higher the metal is in the reactivity series, the more easily a metal’s atoms lose electrons.

Question 7

SC11a
1) State the reactivity series metals from the most to the least reactive
2) Explain the reactivity series in terms of the different groups

Answer 7

1) The reactivity series typically includes the following elements (from most to least reactive):
- potassium
- sodium
- calcium
- magnesium
- aluminum
- (Carbon)
- zinc
- iron
- tin
- lead
- (Hydrogen)
- copper
- silver
- gold
This is an acronym to remember it: Please stop calling me a careless zebra, instead try learning how copper saves gold.
2) Group 1 contains the most reactive metals, then group 2, then group 3 and finally the transition metals.

Question 8

SC10
Explain why some metals react more violently than others

Answer 8

Some metals lose electrons and form cations more easily than others.

Question 9

SC11b
1) What are the advantages and disadvantages of phytoextraction?
2) What are the advantages and disadvantages of bioleaching?

Answer 9

1) It decontaminates the ground, conserves nickel ores, allows the use of a low grade ore and there is less noise due to mining.
A disadvantage of phytoextraction is that the process is very slow, it is more expensive than mining some ores, and growing pants is dependent on weather conditions.
2) An advantage of bioleaching is that it is less damaging to the environment and landscape than mining, and it does not require high temperatures.
A disadvantage is that bioleaching is very slow, and toxic substances and sulfuric acid is produced by the process, which damages the environment.