unit 10 - chemistry of the environment

What are two common chemical tests for water?

Anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate.

What is the color change when anhydrous copper(II) sulfate reacts with water?

White to blue.

What is the chemical equation for the reaction of anhydrous copper(II) sulfate with water?

CuSO₄ (s) + 5H₂O (l) ⇌ CuSO₄•5H₂O (s)

How can boiling and melting points be used to determine water purity?

Pure water boils at 100°C and melts at 0°C. Impurities cause higher boiling points and lower melting points.

How does impure water affect boiling and melting points?

It increases the boiling point above 100°C and decreases the melting point below 0°C.

What is distilled water, and why is it used in chemistry?

Distilled water is purified by vaporization and condensation, removing most impurities. It is used in chemistry to prevent interference in reactions.

What is the color change when anhydrous cobalt(II) chloride reacts with water?

Blue to pink.

What is the chemical equation for the reaction of anhydrous cobalt(II) chloride with water?

CoCl₂ (s) + 6H₂O (l) ⇌ CoCl₂•6H₂O (s)

Why is tap water not typically used in chemical experiments?

It contains impurities that could interfere with reactions

What are three main uses of water in everyday life?

Domestic, agricultural, and industrial uses.

Give examples of domestic uses of water.

Drinking, cooking, gardening, and general sanitation.

How is water used in agriculture?

As a drink for animals and for watering crops.

How is water used in industry?

As a solvent, coolant, and for generating steam to produce electricity.

What are natural sources of water?

Lakes, rivers, and underground water sources (groundwater).

What is an aquifer?

A rock that stores water.

Name some substances that may be found in water from natural sources.

Dissolved oxygen, metal ions (Ca²⁺, K⁺, Na⁺, Mg²⁺), plastics, sewage, harmful microbes, nitrates, and phosphates.

How do harmful substances enter water sources?

Rain washes them into lakes, rivers, or groundwater.

What are common sources of nitrates in water?

Fertilisers.

What are common sources of phosphates in water?

Fertilisers and detergents.

What are the two types of impurities in untreated water?

Soluble and insoluble impurities.

Give examples of insoluble impurities in water.

Soil, plant pieces, and other organic matter.

Give examples of soluble impurities in water.

Dissolved calcium, metallic compounds, and inorganic pollutants.

What is the first step of water treatment?

Sedimentation and filtration.

How does sedimentation work?

Water is left to stand in tanks so that mud, sand, and particles settle at the bottom.

What is the purpose of filtering water through sand and gravel?

To remove smaller particles after sedimentation.

What is the second step of water treatment?

Filtration or treatment with carbon (charcoal).

Why is carbon used in water treatment?

It removes unpleasant tastes and odours.

What is the final step of water treatment?

Chlorination.

Why is chlorine added to water?

To kill bacteria and microorganisms that are too small to be filtered out.

Name two bacterial diseases that can result from consuming untreated water.

Cholera and typhoid.

What are NPK fertilisers?

Fertilisers that contain nitrogen, potassium, and phosphorus to promote plant growth.

What is the role of nitrogen in fertilisers?

It helps in making chlorophyll and proteins, promoting healthy leaves.

What is the role of potassium in fertilisers?

It promotes growth and healthy fruit and flowers.

What is the role of phosphorus in fertilisers?

It promotes healthy roots.

What are the sources of soluble nitrogen in fertilisers?

Ammonium ions (NH₄⁺) and nitrate ions (NO₃⁻).

What is the source of soluble phosphorus in fertilisers?

Phosphate ions (PO₄³⁻).

How do potassium compounds contribute to fertilisers?

They dissolve in water to produce potassium ions (K⁺).

Name three common fertiliser compounds.

Ammonium nitrate (NH₄NO₃), ammonium phosphate ((NH₄)₃PO₄), and potassium nitrate (KNO₃).

Why do different fertilisers have different effects?

They contain different proportions of nitrogen, potassium, and phosphorus.

The composition of air has remained unchanged for how long?

200 million years.

What fraction of the air is nitrogen?

About four-fifths

What fraction of the air is oxygen?

About one-fifth

What other gases are present in the air?

Carbon dioxide, water vapour, and trace amounts of noble gases

What are air pollutants?

Gases present in the atmosphere due to human activities.

What are the sources of carbon dioxide?

Complete combustion of carbon

Give an example of the complete combustion of methane.

CH₄ + 2O₂ → CO₂ + 2H₂O.

What are the adverse effects of carbon dioxide?

Increases global warming, leading to climate change.

What are the sources of carbon monoxide?

Incomplete combustion of carbon

Give an example of the incomplete combustion of octane.

C₈H₁₈ + 9O₂ → 5CO + 2CO₂ + 9H₂O.

Why is carbon monoxide dangerous?

It is toxic and binds with haemoglobin, preventing oxygen transport in the blood.

What are the sources of particulates?

Incomplete combustion of carbon

Give an example of incomplete combustion producing particulates.

CH₄ + O₂ → C + 2H₂O.

What are the adverse effects of particulates?

Causes respiratory problems and cancer.

What are the sources of methane?

Digestive gases from animals, decomposition of vegetation, bacterial action in swamps, rice fields, and landfill sites.

What are the adverse effects of methane?

Increases global warming, leading to climate change.

What are the sources of oxides of nitrogen?

High-temperature reactions between nitrogen and oxygen in car engines, furnaces, and lightning; bacterial action in soil.

What are the adverse effects of oxides of nitrogen?

Produces photochemical smog, acid rain, damages buildings and aquatic life, pollutes crops and water, and causes respiratory problems.

What are the sources of sulfur dioxide?

Combustion of fossil fuels containing sulfur compounds (e.g. in power stations).

Give the reaction of sulfur combustion.

S + O₂ → SO₂.

What are the adverse effects of sulfur dioxide?

Forms acid rain, leading to corrosion of metal structures, damage to aquatic life, and respiratory problems.

What energy does the Sun emit?

Radiation.

How does thermal energy interact with the Earth's surface?

Some energy is reflected, while most is absorbed and re

What happens to thermal energy as it passes through the atmosphere?

Some passes straight through and is emitted into space, while some is absorbed by greenhouse gases.

What role do greenhouse gases play in the atmosphere?

They absorb thermal energy and re

What is the greenhouse effect?

The trapping of thermal energy within the Earth’s atmosphere by greenhouse gases, keeping the Earth warm.

What happens when the concentration of greenhouse gases increases?

More thermal energy is trapped, causing the Earth’s average temperature to rise (global warming).

What is the process called when more greenhouse gases cause global warming?

The enhanced greenhouse effect.

What happens as the Earth's temperature increases due to climate change?

Water levels rise as glaciers melt, causing flooding in low

How does global warming affect species?

It leads to the extinction of species due to habitat destruction and migration to more habitable areas.

What diseases are spread due to a warmer climate?

Diseases caused by warmer temperatures, including those related to water and vector

What is a major consequence of global warming for animals?

Loss of habitat, especially for those living on glaciers or in low

How can we reduce carbon dioxide emissions?

By using hydrogen and renewable energy, using fuel

How can methane emissions be reduced?

By reducing livestock farming, as methane is produced during animal digestion.

How can acid rain be reduced?

By decreasing oxides of nitrogen and sulfur dioxide production, using catalytic converters in cars, and using fuels with low sulfur content.

What is flue gas desulfurization?

It is the process where waste gases from power stations are treated with a calcium slurry to remove sulfur dioxide and produce calcium sulfate.

How are oxides of nitrogen formed in car engines?

They are formed when nitrogen and oxygen react in high

What is the function of catalytic converters?

They reduce harmful gases from car exhaust, including carbon monoxide and oxides of nitrogen, through redox reactions.

What is the main reaction that occurs in a catalytic converter?

2NO + 2CO → N2 + 2CO2.

What type of reaction is photosynthesis?

Photosynthesis is an endothermic reaction, meaning energy is taken in from the environment.

What are the reactants of photosynthesis?

Carbon dioxide and water.

What products are formed in photosynthesis?

Glucose and oxygen.

What is required for photosynthesis to occur?

Chlorophyll (in chloroplasts) and energy from light.

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen.

What is the balanced symbol equation for photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2.