Extracting metals

To choose correctly, we must separate different categories of impacts. In IB science, a social impact is about what happens to people—their health, living conditions, jobs, traditions, or communities.

That differs from environmental impacts (effects on air, water, land, and ecosystems) and economic impacts (effects on costs, profits, and trade).

Now check which choices describe changes to Earth’s physical systems rather than to human society.

Option A is about changing the atmosphere by adding $C{O}_2$. Option D is about polluting water with $heavymetals$. Both describe environmental impacts, not social ones.

Option B refers to habitats being destroyed and biodiversity dropping. That is a serious outcome, but it is still an ecological/environmental impact because it focuses on plants, animals, and ecosystems rather than on people directly.

Option C is about communities being forced to relocate. Because it involves human populations losing homes, land, and cultural connections, it matches the definition of a social impact.

To get this right, we need to tell apart social effects from environmental ones. A social impact is something that changes how people live—such as their housing, work, community relationships, culture, and ability to meet daily needs.

We can test each option by asking: is it mainly about nature, or mainly about human society?

Option A describes $C{O}_2$ coming from mining vehicles and machines. This changes the atmosphere and links to the greenhouse effect. Since it mainly concerns climate and natural systems, it is an environmental (atmospheric) impact, not a social one.

Option B is about losing habitats and reducing biodiversity. That is about the condition of ecosystems and non-human organisms, so it is an environmental (ecological) impact.

Option D focuses on heavy metals contaminating groundwater. This is pollution that damages a natural resource. Even though people could be harmed later if they use the water, the impact described is classified directly as an environmental (hydrological) impact.

After removing the environmental choices, Option C remains. Forcing communities to leave their land disrupts culture, income sources, and social networks. Because it directly impacts people, it is the correct social impact.

To explain the energy gap, we need to set the two processes side by side: Primary Extraction means producing aluminium from its ore, while Recycling means reheating aluminium that has already been made and using it again.

In primary extraction, aluminium is found as aluminium oxide ($A{l}_2{O}_3$). This substance contains strong ionic bonding because the ions $A{l}^{3+}$ and $O^{2-}$ have high charges and attract each other strongly. Separating these ions and turning $A{l}^{3+}$ into aluminium metal requires electrolysis, which needs a very large input of electrical energy to overcome those strong chemical bonds.

Recycling is mainly a physical change. The aluminium in a used can or foil is already metallic aluminium, so the key step is supplying heat so it can melt and be reshaped. Melting only means weakening the metallic lattice forces enough for the metal to flow, which takes much less energy than breaking the strong ionic bonds in an oxide.

The remaining options can be rejected using basic chemical reasoning:

• A is incorrect: aluminium is too reactive to be produced by carbon reduction.
• B is incorrect: there is no catalyst that makes aluminium come out of its oxide at room temperature.
• C is incorrect: recycled aluminium is already a metal, not a collection of ions in an ionic compound.

The reason recycling saves about 95% of the energy is that melting aluminium is a physical process, while extracting aluminium from $A{l}_2{O}_3$ is a chemical process that requires electrolysis to break very strong bonds.

To see why recycling is cheaper in energy, start with how aluminium is made from scratch. Aluminium comes from the ore bauxite. Because aluminium is very reactive, it is found combined with oxygen as aluminium oxide ($A{l}_2{O}_3$), where the ionic attraction is extremely strong.

To separate it, industry uses electrolysis, which demands a lot of energy. The oxide must be molten (very high melting point) and then a large electric current is used to convert $A{l}^{3+}$ ions into aluminium metal ($Al$).

Now consider Option A. The reactivity series places aluminium above carbon, meaning carbon cannot remove oxygen from aluminium compounds effectively.

If carbon reduction worked for aluminium, it would be used for the main extraction method (as it is for iron), but it does not. Also, recycling is not about reducing an oxide—it's about reprocessing aluminium that is already metal.

Option B claims recycling uses catalysts to get aluminium from its oxide at room temperature. This does not match the chemistry:

1. Recycling is about melting metal that already exists, not separating aluminium from an oxide.
2. Aluminium oxide does not have an industrial room-temperature catalyst route for producing aluminium; it still requires a high-energy electrolytic method.

Option C says recycled aluminium is already ionic. But objects like cans and foil are metallic aluminium ($Al(s)$), not $A{l}^{3+}$ ions.

If the aluminium were present as ions (as in a salt), electrons would still need to be supplied to form the metal, which would make the energy demand much closer to primary extraction. Because it is already metallic, that electron transfer step is not needed.

After removing the incorrect statements, Option D matches the real reason.

Recycling is a physical process: solid aluminium is heated until it melts and can be remoulded. Primary extraction is a chemical process: electricity is used to break the very strong bonding in $A{l}_2{O}_3$.

So the energy for melting (a change of state) is only a small fraction of the energy needed to break bonds and reduce ions during electrolysis.

We are told the new metal is more reactive than carbon but not as reactive as potassium.

In extraction questions, the key decision is whether the metal is above or below carbon in the reactivity series, because that determines whether carbon-based reduction can work. This links directly to the Reactivity series and Extraction ideas in the course.

A common extraction rule is: if a metal is more reactive than carbon, carbon cannot remove oxygen from its oxide effectively.

So any method that depends on blast-furnace style reduction (using carbon monoxide) will not succeed for this metal, so that option is eliminated.

Now consider the other choices:

• Hydrogen gas (Option A): Hydrogen is less able to reduce metal oxides than carbon in this context. If carbon cannot reduce the oxide, hydrogen will not manage it either.
• Physical separation (Option B): Techniques like panning only work when metals are found as native elements (very unreactive metals such as gold). A metal that is more reactive than carbon will be found as a compound in ores, not as pure metal.

Because the metal is above carbon in the reactivity series, its compounds are too stable for chemical reduction using carbon or hydrogen.

To separate the metal from its ions, we must supply energy using electricity, so electrolysis of a molten compound is the correct method.

This is the same general approach used to obtain reactive metals such as aluminum and magnesium.

Start by locating the metal in the reactivity series. The prompt tells us it is:

• More reactive than carbon
• Less reactive than potassium

Metals in this section (like magnesium or aluminum) usually form very stable compounds since they react strongly with oxygen and other non-metals. We can now apply Elimination of Extraction Techniques to decide the best method.

Methods such as panning only succeed for native metals, meaning metals found naturally as pure elements (very unreactive ones like gold or silver).

Since this metal is quite reactive, it will be present in ores as compounds, not as the pure element, so this option is eliminated.

Extraction by reduction with carbon monoxide or hydrogen gas only works when the reducing agent (C, CO, or $H_2$) can take oxygen away from the metal compound.

But because the metal is more reactive than carbon, carbon (and CO) cannot effectively strip oxygen from its oxide. Hydrogen is also not strong enough to reduce oxides of metals in this reactivity range.

After excluding physical separation and chemical reduction, the only method left is electrolysis.

For metals above carbon, electricity is needed to break the strong bonds in the molten ionic compound and release the metal. This is why electrolysis is the only economically and chemically sensible option for extracting very reactive metals.

To choose an extraction method, begin with the Reactivity Series, which orders metals from very reactive to not very reactive. Carbon is commonly shown on the same list because it is an inexpensive substance that can remove oxygen from some metal oxides.

The metal is stated to be below carbon. That tells us the metal is less reactive than carbon. Since carbon reacts with oxygen more strongly than the metal does, carbon can take the oxygen away from the metal oxide during a redox reaction, leaving the metal behind.

Getting a metal from an ore usually requires a chemical reaction because the metal is bonded to oxygen (or another non-metal).

• Fractional distillation is used to separate liquids in a mixture by different boiling points (for example, crude oil fractions).
• Physical filtration can remove bits of unwanted rock (gangue), but it does not break the chemical bonds in a metal oxide, so it cannot produce the metal.

Electrolysis is typically chosen for metals that are more reactive than carbon, because carbon cannot reduce their compounds. It also uses a lot of energy and is costly. Since the metal here is below carbon, electrolysis is not the usual choice.

For metals below carbon, extraction is commonly done by reduction. In a blast furnace or similar setup, carbon (or carbon monoxide) reacts with the metal oxide, removing oxygen. Carbon is oxidized, and the metal ions gain electrons (are reduced) to form the metal.

$\text{Metal Oxide}+\text{Carbon}\to \text{Metal}+\text{Carbon Dioxide}$

A metal’s extraction route depends on where it sits in the reactivity series. Carbon is used as a key comparison. If a metal is below carbon, then carbon is more reactive and can push the metal out of its compounds by removing oxygen.

Fractional distillation separates liquid mixtures based on boiling points (such as separating crude oil). Most metal oxides are ionic solids with very high melting and boiling points, so distillation is not a realistic way to obtain the metal from its oxide.

Electrolysis is effective but expensive, so it is mainly used for metals above carbon in the reactivity series (like aluminum or sodium). Those metals form compounds that carbon cannot reduce. Because this metal is below carbon, a cheaper chemical method is normally used instead.

Filtration can help separate solid waste (gangue) from useful ore, but it only separates physical mixtures. It cannot break the metal–oxygen bonds in a metal oxide, so it cannot produce the pure metal.

Since the metal is less reactive than carbon, carbon (or carbon monoxide) can act as a reducing agent and remove oxygen from the metal oxide, producing the metal in a redox reaction:

$\text{Metal Oxide}+\text{Carbon}\to \text{Metal}+\text{Carbon Dioxide}$

This is the common, cost-effective approach for metals such as iron, zinc, and lead.

Making aluminium from its main ore, bauxite, takes a huge amount of energy. The process requires electrolysis of molten aluminium oxide (alumina) at very high temperatures, using lots of electrical energy to separate aluminium from oxygen because the bonds are very strong.

When aluminium is recycled, the metal already exists as aluminium, so it can be reused by melting and reshaping it. Since there is no need to carry out electrolysis to break compounds apart, the energy demand is much lower. Aluminium melts at about $660^{\circ }\text{C}$, which is far less energy-intensive than extracting it from ore.

A key statistic taught in Extraction and sustainability is that recycling aluminium needs only 5% of the energy required for extracting the same mass of aluminium from bauxite. In other words, recycling avoids about 95% of the energy use.

Now compare each option with the known curriculum figure:

• 95% describes energy that would be nearly the same as extraction; it’s closer to the energy saved idea, not the energy needed.
• 25% and 50% are still far too large because recycling is much more energy-efficient than that.

Because aluminium recycling takes only about 5% of the energy of producing aluminium from bauxite, it is a classic example of a highly sustainable recycling process.

The prompt says recycling aluminium is highly sustainable. In chemistry and industry, that usually means the process uses much less energy and causes less environmental harm. So the recycling energy should be only a small fraction of the energy needed to extract aluminium from ore.

To match “highly sustainable,” we should look for the smallest energy requirement in the list.

Consider the options:

• $95\%$ would mean recycling uses almost the same energy as extraction.
• $50\%$ and $25\%$ are reductions, but they don’t reflect the exceptionally large energy saving aluminium recycling is known for.

If recycling really needed $95\%$, $50\%$, or even $25\%$ of the original extraction energy, it wouldn’t be considered such an outstanding sustainability example. So those options should be rejected.

The smallest option is $5\%$. That corresponds to saving roughly $95\%$ of the energy compared with the Hall-Héroult (electrolytic) extraction from bauxite, so $5\%$ is the correct choice.