10) Chemistry of the environment

Define photosynthesis

The reaction between carbon dioxide and water to produce glucose and oxygen in the presence of chlorophyll and using energy from light.

Describe the chemical test for the presence of water using cobalt(II) chloride

Anhydrous cobalt(II) chloride - Blue

CoCl2

Hydrated cobalt(II) chloride - Pink

CoCl2 • 6H2O

Anhydrous cobalt(II) chloride will change from blue to pink in the presence of water.

Describe the chemical test for the presence of water using copper(II) sulfate

Anhydrous copper(II) sulfate - White

CuSO4

Hydrated copper(II) sulfate - Blue

CuSO4 • 5H2O

Anhydrous copper(II) sulfate will change from white to blue in the presence of water.

Describe the test for the purity of water

As mixtures have different substances that have different boiling and melting points, there are no fixed temperatures.

If water melts at 0°C, it is pure. If it melts at a different temperature, it is impure.

If water boils at 100°C, it is pure. If it boils at a different temperature, it is impure.

Why is distilled water used in practical chemistry

Distilled water is water that has been heated to form a vapour, and then condensed back to a liquid, removing any impurities. Distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities, which can interfere with chemical reactions.

Water from natural sources such as lakes, rivers, underground water may contain substances such as:

- Dissolved oxygen

- Metal compounds

- Plastics

- Sewage

- Harmful microbes

- Nitrates from fertilisers

- Phosphates from fertilisers and detergents

How are some of these substances beneficial

- Dissolved oxygen for aquatic life

- Metal compounds provide essential minerals for life

How are some of these substances potentially harmful?

- Some metal compounds are toxic

- Plastics harm aquatic life

- Sewage contains harmful microbes that can cause disease.

- Nitrates and phosphates can lead to deoxygenation of water, which can damage aquatic life

Describe the first stage in process of domestic water treatment

Untreated water contains soluble and insoluble impurities.

1) Sedimentation and filtration to remove solids:

Water is pumped into sedimentation tanks. After a while, mud, sand and particles fall to the bottom of the tank to form a layer of sediment. The water is then filtered through sand and gravel to remove smaller particles.

Describe the second stage in process of domestic water treatment

2) Treatment with carbon:

Water is then treated with carbon to removes tastes and odours.

Describe the third stage in process of domestic water treatment

3) Chlorination:

Water is then treated with chlorine to kill microbes.

What are some substances that are used as fertilisers

Ammonium salts and nitrates (both soluble) are used as fertilisers. Such as:

- Ammonium nitrate NH4NO3

- Ammonium phosphate (NH4)3PO4

- Potassium nitrate

What are NPK fertilisers

NPK fertilisers contain nitrogen, phosphorus and potassium for improved plant growth

What does nitrogen, potassium and phosphorus do in plants

- Nitrogen makes chlorophyll and protein; it promotes healthy leaves.

- Potassium promotes growth and health fruit and flowers.

- Phosphorus promotes health roots.

Describe the composition of clean, dry air

- 78% nitrogen, N2

- 21% oxygen, O2

- 0.04% carbon dioxide, CO2

- 0.9% argon and other noble gases

Name air pollutants and their sources

- Carbon dioxide from the complete combustion of carbon-containing fuels

- Carbon monoxide and particulates of carbon from the incomplete combustion of carbon-containing fuels.

- Methane from the decomposition of vegetation and waste gases from animal digestion.

- Oxides of nitrogen from car engines

- Sulfur dioxide from the combustion of fossil fuels containing sulfur compounds.

Describe the effects of these pollutants

Carbon dioxide: A green house gas. Higher levels of carbon dioxide lead to increased global warming, which leads to climate change.

Carbon monoxide: A toxic gas

Particulates: Increased risk of respiratory problems and cancer.

Methane: A green house gas. Higher levels of methane lead to increase global warming, which leads to climate change.

Oxides of nitrogen: Acid rain (reacts with water to form acid), photochemical smog, and respiratory problems.

Sulfur dioxide: Acid rain.

Describe global warming

Greenhouse gases such as carbon dioxide and methane cause global warming.

The sun emits energy in the form of radiation. Most thermal energy is absorbed and re-emitted from the Earth's surface, and some energy is reflected from the Earth's surface. The energy passes through the atmosphere where some thermal energy is emitted back into space. Greenhouse gases such as carbon dioxide and methane, absorb thermal energy, which is re-emitted in all directions, reducing the thermal energy lost into space, which traps it in the Earth's atmosphere, making it warm. This is the greenhouse effect.

State the effects of global warming

- Climate change due to increase in temperature.

- Glaciers melt, so water levels rise. Low-lying countries get flooded.

- Extinction of species due to habitat destruction.

- Spread of disease caused by warmer climate

What are some strategies to reduce the effects of climate change

- Drastically reducing greenhouse gas production by decreasing fossil fuel usage.

- Reducing livestock farming, which reduces methane emissions.

- Planting more trees, reducing carbon dioxide from the atmosphere.

- Using hydrogen and renewable energy.

What are some strategies to reduce the effects of acid rain

- Reducing sulfur dioxide by using low-sulfur fuels.

- Flue gas desulfurization using calcium oxide; waste gases from coal and passed into a scrubbing chamber, where they are sprayed with a wet slurry of calcium oxide and calcium carbonate. The calcium compounds react with sulfur dioxide to produce calcium sulfate.

- Using catalytic converters in vehicles to remove oxides of nitrogen.

Explain how oxides of nitrogen form in car engines

Oxides of nitrogen are formed when nitrogen (from the air) reacts with oxygen in the high temperature and pressure conditions of combustion engines.

Describe how catalytic converters remove oxides of nitrogen

Catalytic converters contain transition metal catalysts, such as platinum and rhodium.

The metal catalysts are in a honeycomb within the convertor to increase surface area for reaction. These metal catalysts reduce the oxides of nitrogen to form nitrogen and oxygen gas, and oxidise carbon monoxide to carbon dioxide.

What is the word and symbol equation of photosynthesis.

Carbon dioxide + Water → Glucose + Oxygen

6CO2 + 6H2O → C6H12O6 + 6O2