IGCSE Chemistry - Topic 8 (Chemistry of the Environment)

Anhydrous cobalt(II) chloride becomes what colour when water is added?

Blue to Pink

Anhydrous copper(II) sulfate becomes what colour when water is added?

White to Blue

How can you use melting and boiling points to determine purity of water?

Pure substances have sharp melting and boiling points, whilst impure mixtures will have different ones as they are made up of more than one element. This means that melting and boiling point data can be used whether water is pure.

What process is used to make distilled water?

Distillation

Why do we distill water in chemistry?

Because it contains fewer chemical impurities

Water from natural sources could contain these substances:

* Dissolved oxygen
* Metal compounds
* Plastics
* Sewage
* Harmful microbes
* Nitrates from fertiliser
* Phosphates from fertilisters and detergents

These substances in natural water are beneficial:

* Dissolved oxygen - essential for aquatic life
* Metal compounds - some provide essential **minerals** for life, like Ca and Mg

Why are these substances in natural water harmful:


1. Metal compounds
2. Some plastics
3. Sewage
4. Nitrates and phosphates

1. some are **toxic** to life, like aluminium and lead
2. **harm** aquatic life
3. contain harmful **microbes** which can cause **disease**
4. lead to **excess** growth of aquatic plant life, leading to **deoxygenating** of water, damaging aquatic life

**Water Treatment Stage 1**

Sedimentation and filtration

What happens in sedimentation and filtration?

Water is pumped into sedimentation tanks, where water is allowed to **stand** for a few hours. Mud, sand, and other particles found in the water fall to the bottom due to gravity, forming a layer of sediment.

Filtration is the process where water is passed through **layers** of **sand** and **gravel** **filters** that **trap** solid particles still in the water 

**Water Treatment Stage 2**

Passing through carbon

Why is water passed through carbon (charcoal)?

To remove **tastes** and **odours**

**Water Treatment Stage 3**

Chlorination

Why is water chlorinated?

Chlorine is added to the treated water to kill **harmful** microbes, which are too **small** to be caught by the filters, like **cholera**

What do **NPK** fertilisers contain?

Nitrogen, phosphorous and potassium

What are the **sources** of:


1. Nitrogen
2. Phosphorous
3. Potassium

1. Ammonium ions, NH4+ and nitrate ions, NO3-, are sources of soluble nitrogen
2. Phosphate ions, PO43- are a source of soluble phosphorus
3. Most common potassium compounds dissolve in water to produce potassium ions, K+

What compounds are commonly used for fertilisers?

Ammonium salts and nitrates

Why do plants need NPK?

* Nitrogen makes **chlorophyll**, protein and promotes healthy **leaves** 
* Potassium promotes **growth** and healthy **fruit** and **flowers**
* Phosphorus promotes healthy **roots**

What is the composition of clean, dry air?

78% nitrogen

21% oxygen

Remainder is a mixture of noble gases (0.9% Ar) and carbon dioxide (0.04%)

What are the sources and adverse effects of **carbon dioxide**?

Complete combustion of fossil fuels. Increased global warming

What are the sources and adverse effects of **carbon monoxide?**

Incomplete combustion of fossil fuels, toxic gas 

What are the sources and adverse effects of **particulates?**

Incomplete combustion of fossil fuels can also produce particulates of carbon (soot), e.g the incomplete combustion of methane can produce CO and C. Increased risk of respiratory problems and cancer

What are the sources and adverse effects of **methane?**

Decomposition of vegetation and waste gases from digestion in animals, increased global warming

What are the sources and adverse effects of **oxides of nitrogen?**

Reaction of nitrogen with oxygen in high heat, like in car engines. Acid rain, photochemical smog and respiratory problems 

What are the sources and adverse effects of **sulfur dioxide?**

Combustion of fossil fuels containing sulfur compounds, acid rain

How do greenhouse gases cause global warming?

The Sun's radiation enters Earth's atmosphere and some thermal energy is reflected from the surface. Most thermal energy is absorbed and re-emitted by the surface. As the energy passes through the atmosphere, some escapes into space while some is absorbed by greenhouse gases like carbon dioxide and methane. These gases re-emit the energy in all directions, reducing the amount lost to space and keeping the Earth warm.

Explain the strategies used to reduce the effects of climate change. 

* Planting trees
* Reduction in livestock farming
* Decreasing use of fossil fuels
* Increasing use of hydrogen and renewable energy, e.g. wind, solar

Explain the strategies used to reduce the effects of acid rain. 

* Use of **catalytic converters** in vehicles
* **Reducing** emissions of sulfur dioxide by using low-sulfur fuels
* **Flue gas desulfurisation** - reacting SO2 emmisions from fossil fuels with calcium oxide, removing it from the flue gas

How are the oxides of nitrogen formed in car exhausts? 

When nitrogen gas and oxygen react, under high temperature and pressure found in internal combustion engines 

What do catalytic converters do?

Catalytic converters contain transition metal catalysts, normally rhodium, palladium or platinum. They are in a **honeycomb** structure. On the surface of the metals, redox reactions occur that convert more dangerous gases to harmless gases

What is the chemical equation for the catalytic conversion of CO?

**2**CO + O2 → **2**CO2 

What is the chemical equation for the catalytic conversion of nitrogen (di)oxides?

* **2**NO → N2 + O2
* **2**NO2 → N2 + **2**O2

What is photosynthesis?

Photosynthesis is the reaction between **carbon** **dioxide** and **water** to produce **glucose** and **oxygen** in the presence of **chlorophyll** and using energy from **light**

What is the chemical equation for photosynthesis?

**6**CO2 + **6**H2O → C6H12O6 + **6**O2