Tests for water
A sample of water was found in the lab. The boiling point of this sample was found to be 96 0C. What does this say about that sample of water?
It is impure
Name one substance that may be present in water from natural sources.
Dissolved oxygen, metal compounds, plastics, sewage, harmful microbes, nitrates, or phosphates.
What process is used to remove solid particles from water during treatment?
Sedimentation and filtration.
What is the approximate percentage of nitrogen in clean, dry air?
78%
What is the main source of carbon dioxide in the atmosphere?
Complete combustion of carbon-containing fuels.
Name two chemicals that can be used to test for the presence of water.
Anhydrous copper(II) sulfate and anhydrous cobalt(II) chloride.
Why is dissolved oxygen in water important?
It is beneficial for aquatic life, as fish and other organisms need oxygen to survive.
Why is carbon used in the treatment of domestic water?
To remove tastes and odours.
What is the approximate percentage of oxygen in clean, dry air?
21%
What harmful gas is produced by the incomplete combustion of carbon-containing fuels, and why is it dangerous?
Carbon monoxide . it is a toxic gas.
What colour change occurs when water is added to anhydrous cobalt(II) chloride?
It changes from blue to pink.
Give an example of a toxic metal found dissolved in water.
Lead
What is the purpose of chlorination in water treatment?
To kill microbes.
Name two gases, other than nitrogen and oxygen, present in small amounts in clean, dry air.
Noble gases and carbon dioxide (CO₂).
Which air pollutant is produced by car engines and can cause acid rain and respiratory problems?
Oxides of nitrogen.
What colour change occurs when water is added to anhydrous copper(II) sulfate?
It changes from white to blue.
Why can nitrates and phosphates from fertilisers be harmful to aquatic life?
They cause deoxygenation of water, which damages aquatic life.
A sample of water still smells unpleasant after sedimentation and filtration.
Which step of the treatment process has likely been missed?
Use of carbon to remove tastes and odours.
If a sample of air contained 78% nitrogen and 21% oxygen, what percentage is left for other gases?
About 1%.
Name one pollutant formed from fossil fuels that contain sulfur compounds, and state its effect.
Sulfur dioxide. it causes acid rain.
Why is distilled water used in chemistry practicals rather than tap water?
Some substances in water are beneficial, while others are harmful.
State one example of each and describe their effect.
Beneficial: Some metal compounds provide essential minerals for life.
Harmful: Some metal compounds are toxic.
(and similar answers with other compounds)
Explain why all three steps: sedimentation, filtration, use of carbon, and chlorination, are necessary in domestic water treatment.
Sedimentation and filtration remove solid particles
Carbon removes tastes and odours
Chlorination kills harmful microbes
Which gas in clean, dry air helps regulate the Earth’s temperature by trapping heat?
Carbon dioxide (CO₂).
Explain how methane contributes to climate change and give one natural source of it.
Methane traps heat, increasing global warming and causing climate change
it comes from decomposition of vegetation and gases from digestion in animals.