2.3 Metals & Their Extraction (WJEC GCSE Chemistry): Flashcards

False.

Metals above carbon in the reactivity series are too reactive to be reduced by carbon. They must be extracted by electrolysis, which is a more expensive process.

Unreactive metals are found as native metals because they do not easily react with other substances. Their chemical stability means they remain as uncombined elements in the Earth's crust.

Metals lower down the reactivity series than carbon can be extracted by heating with carbon in a reduction reaction.

True.

Electrolysis requires a continuous supply of electrical energy to decompose the molten ionic compound, making it significantly more expensive than reduction with carbon.

The position of the metal in the reactivity series determines the extraction method. Metals above carbon require electrolysis; metals below carbon can be reduced using carbon or carbon monoxide.

A reactivity series is an ordered list of metals (and some non-metals) arranged from most reactive to least reactive, based on how readily they lose electrons and react with other substances.

Metal atoms form positive ions by losing electrons when they react with other substances. A more reactive metal loses electrons more easily than a less reactive one.

True.

The tendency to lose electrons is the measure of reactivity. Metals at the top of the series (such as potassium and sodium) lose electrons very readily, making them highly reactive.

In the thermite reaction, aluminium displaces iron from iron(III) oxide because it is more reactive. The iron formed is molten due to the highly exothermic nature of the reaction.

The blue colour of the copper sulfate solution fades as magnesium displaces copper. Colourless magnesium sulfate solution forms and copper metal deposits on the magnesium surface.

False.

Sodium is above zinc in the reactivity series, so zinc is less reactive than sodium. A less reactive metal cannot displace a more reactive metal from its compound.

Carbon and hydrogen are included in the reactivity series because they are useful in extracting metals. Carbon and carbon monoxide can reduce metal oxides of metals that sit below carbon in the series.

In the reaction Zn + CuO → ZnO + Cu, the zinc is the reducing agent because it removes oxygen from the copper oxide.

The dimple tile holds small volumes of metal salt solutions in separate wells so that displacement reactions between different combinations of metals and solutions can be observed at the same time without contamination.

False.

No reaction occurs when a metal is placed in a solution of its own salt. A reaction only takes place when a more reactive metal displaces a less reactive metal from its compound.

In the displacement practical, magnesium is the most reactive metal tested because it displaces all other metals tested from their sulfate solutions.

A separate dropping pipette must be used for each solution to avoid contamination between solutions. Contamination would produce misleading results as foreign metal ions could cause unexpected reactions.

False.

Copper is less reactive than iron, so it cannot displace iron from its sulfate solution. Only a more reactive metal can displace a less reactive one.

From most to least reactive the order is: magnesium, zinc, iron, copper. This order is determined by which metals successfully displace others from their sulfate solutions.

When iron reacts with copper(II) sulfate solution, the products are iron(II) sulfate and copper.

Oxidation is a reaction in which oxygen is added to an element or compound.

Reduction is a reaction in which oxygen is removed from an element or compound.

True.

Oxidation and reduction always occur simultaneously. These are called redox reactions. If one substance gains oxygen, another must lose it in the same reaction.

Carbon is oxidised because it gains oxygen. Zinc oxide is reduced because it loses oxygen. The reaction is a redox reaction as both processes occur simultaneously.

In the blast furnace, iron(III) oxide is reduced by carbon monoxide, which itself is oxidised to carbon dioxide.

False.

It is the iron(III) oxide that is reduced. Reduction involves the removal of oxygen from the compound. The iron(III) oxide loses oxygen to become iron metal.

A redox reaction is a reaction in which oxidation and reduction take place simultaneously. One substance gains oxygen while another loses it.

The three raw materials are:

1. Iron ore (haematite, Fe₂O₃)

2. Coke (carbon)

3. Limestone (calcium carbonate, CaCO₃)

Hot air is also blown in at the bottom.

In Zone 2 of the blast furnace, coke reacts with carbon dioxide to form carbon monoxide. The carbon dioxide is reduced in this reaction.

Limestone (calcium carbonate) is added to neutralise acidic impurities in the ore. It thermally decomposes to form calcium oxide, which then reacts with silicon dioxide impurities to form calcium silicate slag.

True.

In Zone 3, carbon monoxide acts as the reducing agent. The equation is Fe₂O₃ (s) + 3CO (g) → 2Fe (l) + 3CO₂ (g). Molten iron collects at the bottom and is tapped off.

Silicon dioxide reacts with calcium oxide (from decomposed limestone) to form calcium silicate. This melts and collects as molten slag floating on top of the iron, and is tapped off separately.

In Zone 1 of the blast furnace, coke burns in hot air to form carbon dioxide. This reaction is exothermic, which heats the furnace.

False.

The blast furnace runs as a continuous process. New raw materials are added and products are removed all the time, because getting the furnace up to temperature is costly and time-consuming.

Carbon monoxide is oxidised in this reaction. It gains oxygen to form carbon dioxide. The iron(III) oxide is simultaneously reduced as it loses oxygen to form iron.

An electrolyte is a liquid or solution that is able to conduct electricity. Electrolytes are molten ionic compounds or aqueous solutions of ionic compounds.

The ionic compound must be molten or dissolved so that its ions are free to move and carry charge through the electrolyte. In a solid ionic compound the ions are fixed in position and cannot conduct electricity.

False.

Covalent compounds cannot conduct electricity because they have no free ions or charged particles. Only ionic compounds in a molten or dissolved state can undergo electrolysis.

During electrolysis of lead(II) bromide, lead (Pb²⁺) ions migrate to the cathode to form lead metal, while bromide (Br^-) ions migrate to the anode to form bromine gas.

Anions are negatively charged ions. During electrolysis they migrate towards the anode, which is the positive electrode, because opposite charges attract.

True.

The metal is always the positive ion (cation) and migrates to the negative electrode (cathode) where it gains electrons and is deposited as the metal element.

Graphite or platinum are used because they are inert. An inert electrode does not react with the electrolyte or the products of electrolysis, so it does not interfere with the reaction.

At the anode during electrolysis of lead(II) bromide, bromide ions lose electrons to form bromine molecules. This process is called oxidation.

Oxidation is the loss of electrons from a substance during a chemical reaction.

Reduction is the gain of electrons by a substance during a chemical reaction.

False.

Iron is oxidised in this reaction. It loses two electrons to form Fe²⁺. It is the copper ion (Cu²⁺) that is reduced by gaining two electrons to form copper metal.

OIL RIG stands for Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). It is a useful memory aid for recalling the electron-based definitions of oxidation and reduction.

At the cathode during electrolysis, reduction takes place because ions gain electrons. At the anode, oxidation takes place because ions lose electrons.

Aluminium (Al) is oxidised because it gains oxygen to form Al₂O₃.

Simultaneously, iron(III) oxide is reduced because it loses oxygen to form iron. This makes the thermit reaction a redox reaction.

False.

Reduction takes place at the cathode (negative electrode), where positive ions gain electrons. Oxidation takes place at the anode, where negative ions lose electrons. Remember: RED CAT, AN OX.

Aluminium is extracted by electrolysis because it is above carbon in the reactivity series. Carbon cannot reduce aluminium oxide because carbon is less reactive than aluminium.

Aluminium oxide is dissolved in molten cryolite before electrolysis. This lowers the melting point of the mixture and reduces energy costs.

False.

Molten aluminium forms at the cathode (negative electrode), where Al³⁺ ions gain electrons and are reduced. Oxygen gas is produced at the anode.

The graphite anodes need replacing because the oxygen produced at the anode reacts with the carbon in the graphite to form carbon dioxide. This gradually burns away the anode material.

At the cathode in aluminium extraction, Al³⁺ ions gain three electrons to form molten aluminium. This is an example of reduction.

Aluminium is extracted from bauxite. Bauxite contains aluminium oxide (Al₂O₃), which is first purified before being used in electrolysis.

True.

Electrolysis requires a large and continuous supply of electrical energy. This is a significant running cost that makes aluminium extraction considerably more expensive than extraction by reduction with carbon.

Aluminium is used for overhead power cables because it has a low density, is a good conductor of electricity, is strong, and is resistant to corrosion. Its low density makes cables lighter and cheaper to support.

True.

Titanium's high melting point, low density, high strength, and resistance to corrosion make it ideal for use in spacecraft as well as medical implants and sports equipment.

Copper is used in electrical wiring because it is a very good conductor of electricity and is both malleable and ductile.

Steel is used in reinforced concrete because it is hard and strong. Steel rods embedded in concrete increase its overall strength, making it suitable for use in buildings and structures.

False.

Copper is used in pipes primarily because it is malleable, ductile, and resistant to corrosion, not specifically because it is the best conductor of heat. It is a good conductor of heat, but that is not the key reason for use in pipes.

Titanium is used in the medical industry for joint replacements because it is hard, strong, and resistant to corrosion.

Properties that make aluminium suitable for aircraft parts include:

1. Low density (keeping aircraft light)

2. Strength

3. Resistance to corrosion

Transition metals are a block of metallic elements found in the centre of the Periodic Table, known for their high melting points, malleability, high density, and ability to form coloured compounds and more than one type of ion.

Two properties specific to transition metals are:

1. Forming coloured compounds

2. Forming more than one type of ion (e.g. iron forms Fe²⁺ and Fe³⁺)

False.

Transition metals are good conductors of both electricity and heat. This is a typical metallic property shared by all transition metals.

Iron is used as a catalyst in the Haber process, and platinum is used in catalytic converters to reduce harmful exhaust gases.

Compounds containing Fe²⁺ ions are pale green.

True.

Cu²⁺ ions give copper(II) compounds their characteristic blue colour. This is an example of the coloured compounds formed by transition metals.

A catalyst is a substance that speeds up the rate of a chemical reaction without being used up in the process.

Fe³⁺ ions form brown coloured compounds, while Fe²⁺ ions form pale green coloured compounds.

Sodium hydroxide solution, NaOH (aq), is used to identify metal ions by precipitation. A few drops are added and the colour of any precipitate formed is noted.

A precipitate is an insoluble solid that forms when two solutions are mixed together.

Adding NaOH (aq) to a solution containing Cu²⁺ ions produces a blue precipitate of copper(II) hydroxide.

False.

Fe³⁺ ions form an orange/brown precipitate with NaOH solution. It is Fe²⁺ ions that form a pale green precipitate.

The ionic equation for Fe²⁺ reacting with NaOH is: Fe²⁺ (aq) + 2OH^- (aq) → Fe(OH)₂ (s), forming a pale green precipitate.

True.

Cu²⁺ ions react with OH^- ions to form copper(II) hydroxide, Cu(OH)₂, which is a blue precipitate.

Fe³⁺ (aq) + 3 OH^- (aq) → Fe(OH)₃ (s), forming an orange/brown precipitate.

An alloy is a mixture of two or more metals, or a metal with a non-metal such as carbon.

Alloys are harder than pure metals because atoms of different sizes distort the regular arrangement, making it more difficult for layers to slide over each other.

False.

An alloy is a mixture, not a compound. The metals are not chemically combined, so the components are not in fixed ratios and no new chemical bonds are formed.

Brass is an alloy of copper and zinc, used in musical instruments and door knobs because it is much stronger than either pure metal.

Stainless steel is an alloy of iron with chromium, nickel, and carbon. It is used for cutlery because of its hardness and resistance to corrosion.

True.

Aluminium is mixed with copper, manganese, and silicon to produce an alloy that is stronger than pure aluminium but retains a low density, making it ideal for aircraft body production.

Steel is made from iron and carbon. Alloys of iron with chromium or nickel are resistant to corrosion.

Advantages that alloys can have (over the pure metals they contain) include:

1. Stronger

2. Harder

3. More resistant to corrosion or extreme temperatures

Electrolysing water produces hydrogen gas at the cathode and oxygen gas at the anode.

A Hoffman voltameter is a piece of apparatus used to electrolyse water and separately collect the hydrogen and oxygen gases produced at each electrode.

False.

Double the volume of hydrogen is produced compared to oxygen. This reflects the ratio in the equation 2H₂O → 2H₂ + O₂, where 2 moles of hydrogen gas form for every 1 mole of oxygen.

In the electrolysis of water, H⁺ ions are attracted to the cathode and gain electrons to form hydrogen gas.

The half equation at the cathode is: 2H⁺ (aq) + 2e^- (aq) → H₂ (g). Hydrogen ions gain electrons and are reduced to form hydrogen gas.

True.

Hydroxide ions, OH^-, are negatively charged and are therefore attracted to the positive electrode (anode), where they lose electrons and are oxidised to form oxygen gas.

The overall equation for the electrolysis of water is: 2H₂O (l) → 2 H₂ (g) + 1 O₂ (g).

Aqueous solutions always contain H⁺ and OH^- ions because water molecules partially split up: H₂O ⇌ H⁺ (aq) + OH^- (aq), and these ions take part in electrolysis reactions.

Oxidation is the loss of electrons by an atom or ion during a chemical reaction.

True.

When halide ions (Cl^-, Br^-, I^-) are present at the anode along with OH^- ions, the halide ion is preferentially discharged, losing electrons to form the corresponding halogen gas.

When copper(II) chloride solution is electrolysed, chlorine is produced at the anode and copper is produced at the cathode.

Hydrogen gas is produced at the cathode because sodium is above hydrogen in the reactivity series, so H⁺ ions are preferentially discharged rather than Na⁺ ions.

True.

Only metals below hydrogen in the reactivity series are deposited at the cathode. Metals above hydrogen are less easily reduced, so hydrogen gas is produced instead.

During electrolysis of sodium chloride solution, H⁺ ions are discharged at the cathode and Na⁺ and OH^- ions remain in solution to form NaOH.

Gases produced during electrolysis are collected using inverted test tubes filled with water. The gas displaces the water as it is produced at the electrode.

At the cathode, an orange/brown solid (copper) forms on the electrode. At the anode, bubbling is observed as oxygen gas is produced.

An inert electrode is an electrode that does not react with the electrolyte or the products of electrolysis. Graphite is commonly used as an inert electrode.

False.

The mass of the anode decreases because copper atoms are oxidised at the anode and dissolve as Cu²⁺ ions. The cathode increases in mass as Cu²⁺ ions are reduced and deposited.

When copper electrodes are used, the gain in mass of the cathode equals the loss in mass of the anode. This means the Cu²⁺ concentration stays constant.

The half equation at the cathode is: Cu²⁺ (aq) + 2e^- → Cu (s). Copper ions gain electrons and are reduced to form copper metal.

True.

The electrodes must be dry before being weighed. Any liquid remaining on the surface would add to the recorded mass, giving an inaccurate result. Note: do not wipe the electrodes clean, only allow liquid to evaporate.

At the anode during electrolysis of copper sulfate with copper electrodes, copper atoms are oxidised to form Cu²⁺ ions, which go into solution.

Electroplating is a process that uses electrolysis to coat the surface of one metal with a layer of a different metal.

The object to be coated acts as the cathode. Metal ions from the electrolyte are reduced at its surface, depositing a layer of the plating metal onto it.

True.

The anode is always the pure metal you want to coat the object with. Atoms from the anode are oxidised and dissolve into the electrolyte as ions, which then deposit on the cathode.

During electroplating with tin, tin atoms at the anode lose electrons and form Sn²⁺ ions. These ions then gain electrons at the cathode to coat the object.

Electroplating is carried out to:

1. Make metals more resistant to corrosion or damage (e.g. chromium plating)

2. Improve the appearance of an object (e.g. coating jewellery with silver)

Purification of copper by electrolysis is a process where impure copper is used as the anode and pure copper as the cathode in a copper sulfate electrolyte, causing pure copper to dissolve from the anode and deposit on the cathode.

False.

Impurities do not dissolve. They fall to the bottom of the electrolytic cell as anode sludge. This sludge can be valuable as it may contain precious metals such as silver.

The blue colour stays constant because the concentration of Cu²⁺ ions remains unchanged. Cu²⁺ ions leave the anode and enter solution at the same rate as they are removed from solution and deposited at the cathode.

Brine is a concentrated aqueous solution of sodium chloride (salt water).

Electrolysing brine produces chlorine gas at the anode, hydrogen gas at the cathode, and sodium hydroxide solution remaining in the electrolyte.

False.

Sodium is above hydrogen in the reactivity series, so H⁺ ions are preferentially discharged at the cathode. Hydrogen gas is produced, not sodium metal.

Chlorine produced from brine is used to make bleach. Hydrogen produced from brine is used to make margarine.

The half equation at the anode is: 2Cl^- → Cl₂ + 2e^-. Chloride ions lose electrons and are oxidised to form chlorine gas.

True.

Sodium hydroxide is one of the three useful products of the electrolysis of brine, and it is used to make soap and detergents.

In the electrolysis of brine, Na⁺ ions and OH^- ions remain in solution and form sodium hydroxide.

The most important factor is whether the extraction is economically viable. The financial gain from the extracted metal must outweigh the costs of raw materials, energy, and labour.

Sustainability in metal extraction means meeting present needs for metals while conserving resources and minimising environmental impact so that future generations can also meet their needs.

False.

The main reason for coastal locations is to import raw materials. While products may also be exported, the primary driver is access to the raw materials needed for extraction.

Recycling aluminium requires approximately 5 % of the energy needed to extract it from bauxite, making it much more energy efficient.

Three factors to consider are:\n\n1. Transport links (e.g. roads and rail)\n2. Proximity to a workforce without causing noise pollution to built-up areas\n3. Closeness to power stations due to high energy demands

True.

Melting and re-moulding recycled metals requires much less energy than mining and extracting metals from ores. Recycling also reduces landfill waste and the environmental damage caused by mining.

To be sustainable, metal extraction should use renewable energy resources, reduce environmental impact, and recycle materials wherever possible.

Aluminium extraction requires huge amounts of energy for both the electrolysis process and to keep the electrolyte molten. Without a nearby power station, the process would become economically unsustainable.