Chemistry in society, technology and the environment

Burning petrol, natural gas or coal emits a gas into the atmosphere that enhances the greenhouse effect. Which gas is it? Explain in a simple sentence what the greenhouse effect is.

A domestic boiler burns methane according to the equation $\text{CH}_4 + 2\ \text{O}_2 \rightarrow \text{CO}_2 + 2\ \text{H}_2\text{O}$.

1. a) Which product of this combustion contributes to the greenhouse effect?
2. b) If the boiler is poorly adjusted and burns the gas incompletely, why is it worse for the environment and also for the bill? Give reasons for both answers.

The greenhouse effect is not bad in itself: without it, the average temperature of the Earth would be well below zero. Explain the difference between the natural greenhouse effect and the "enhanced greenhouse effect" mentioned in the news, indicating which human activity is causing it.

A petrol car emits about $120\ \text{g}$ of carbon dioxide for every kilometre travelled, and travels $15\,000\ \text{km}$ per year.

1. a) Calculate how many kilograms of carbon dioxide it emits in a year.
2. b) An electric train emits about $40\ \text{g}$ per passenger-kilometre: calculate the emissions for the same annual journey made by train and compare them.
3. c) Explain how carbon dioxide contributes to climate change and why reducing transport emissions is a priority.

A thermal power station burns coal to generate electricity.

1. a) Name two environmental problems associated with this combustion and explain the reaction or chemical process that causes each one.
2. b) Propose two alternative ways of generating electricity that avoid these problems and justify why.

Over the years, balcony railings end up covered in a reddish-brown layer. What is this process and this brown substance called? What two things does iron need in order to rust?

Name two common ways to protect an iron gate from rusting and explain how each one works.

In an experiment, three iron nails are placed in three tubes: tube 1, containing tap water and open to the air; tube 2, containing dry air inside and tightly stoppered; tube 3, containing boiled water with a layer of oil on top to isolate it from the air. After one week, only the nail in tube 1 has rusted. The figure shows the setup of the three tubes:

Explain what each tube demonstrates about the conditions required for iron to rust.

The frame of many bicycles is painted, that is, covered by a thin layer of paint. The figure shows a cross-section of the frame:

1. a) How does this layer protect the iron from contact with air and moisture?
2. b) If the bicycle gets scratched and iron is exposed, why does rust attack precisely at the scratched area? Relate this to the conditions required for corrosion.

Design an experiment to show that iron needs both water and oxygen to rust.

1. a) Materials you would use.
2. b) Setup of the test tubes: what each one contains and which variables you control.
3. c) What you expect to observe after a few days in each tube.
4. d) Conclusion of the experiment and two ways to protect a bicycle deduced from it.

Ships with steel hulls have zinc blocks bolted to them, which wear away over time and are replaced periodically, as shown in the figure:

1. a) Explain what happens to the zinc while the iron hull remains intact.
2. b) Why does it make sense to "sacrifice" one metal to save the other?
3. c) Compare this method with painting the hull: what do both have in common and how do they differ?

Name two acidic substances you have in your kitchen at home and explain how you know they are acidic (from their taste, smell or use).

Bleach and ammonia used for cleaning are alkaline substances, the opposite of acids. Why must they be handled with care? Name another everyday product that is alkaline.

After a heavy meal, Thiago takes an antacid for heartburn. Knowing that gastric juice in the stomach is acidic:

1. a) How does the antacid work?
2. b) What is the reaction between an acid and a base called?

What is acid rain? Name the gases from combustion in factories and cars that cause it and mention one effect it has on the environment.

When vinegar is mixed with bicarbonate of soda in a glass, vigorous bubbling occurs.

1. a) Which gas is given off in this reaction?
2. b) Name a household application or a science fair activity that makes use of this reaction.
3. c) State what type of substance vinegar is and what type bicarbonate of soda is.

"Normal" rain is already slightly acidic, with a pH of around $5.6$, because carbon dioxide in the air dissolves in the raindrops. Acid rain, on the other hand, can drop to a pH of $4$ or lower. Observe the pH scale in the figure:

1. a) Which pollutants make rain much more acidic than normal?
2. b) Which activities produce these pollutants?

Effervescent antacids contain bicarbonate of soda and a solid acid among their ingredients; when the tablet is dropped into water, both react.

1. a) Why are bubbles produced when the tablet dissolves?
2. b) Relate the relief of heartburn to the reaction that occurs afterwards between the dissolved antacid and the excess stomach acid.

Marble statues and limestone facades ($\text{CaCO}_3$) wear away faster in heavily polluted cities than in the countryside.

1. a) Explain what acid rain does to the calcium carbonate in the stone.
2. b) Reason why wear and tear is much lower in rural areas far from factories.
3. c) Propose two measures to slow down this damage to heritage sites and justify them: one short-term measure targeting the buildings and one long-term measure targeting the source of the problem.

To restore lakes acidified by acid rain, ground limestone is added to them from the air.

1. a) Explain, using what you know about acids and bases, why limestone helps restore the lake.
2. b) What is the type of reaction that takes place called?
3. c) Reason why this emergency solution is no substitute for reducing emissions of sulfur dioxide and nitrogen oxides at source.

What type of energy does a battery store and what type of energy does it transform it into when it lights up a torch? Explain why we say that the chemical reaction occurring inside the battery is a "useful" reaction.

The rechargeable batteries in a games console controller can be used hundreds of times before wearing out.

1. a) What does it mean that the chemical reaction in a rechargeable battery is "reversible"? What does the charger do?
2. b) Why should flat batteries, whether rechargeable or not, not be thrown in the household waste?

In a technology class, a homemade battery is made by inserting a copper electrode and a zinc electrode into a lemon: when a small LED is connected, it lights up faintly. The setup is shown in the figure:

1. a) Where does the energy that lights up the LED come from? What type of reaction supplies it?
2. b) What role does the acidic juice of the lemon play in the setup?
3. c) Predict what would happen if three lemons were connected in series and explain how commercial batteries are similar to these "improved lemons".

Electric car batteries store energy thanks to reversible chemical reactions, just like a giant rechargeable battery.

1. a) Explain the environmental advantage of using such a battery compared to burning petrol in an engine.
2. b) Why is it important that the electricity used to charge the battery comes from renewable sources? What would happen if it were charged by burning coal?
3. c) Batteries contain metals such as lithium or cobalt: reason why battery recycling is an essential part of the solution and not a minor detail.