Water & Water Pollution (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards
Exam code: 0653
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Define anhydrous.
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Cards in this collection (19)
Define anhydrous.
Anhydrous describes a substance that contains no water molecules. Anhydrous salts are used as chemical tests for water because they react with water to form hydrated versions.
What colour change is seen when water is added to anhydrous cobalt(II) chloride?
Anhydrous cobalt(II) chloride changes from blue to pink in the presence of water. This colour change shows that water is present.
True or False?
Anhydrous copper(II) sulfate is blue.
False.
Anhydrous copper(II) sulfate is white. It turns blue when water is added, forming hydrated copper(II) sulfate, CuSO4•5H2O.
Anhydrous cobalt(II) chloride turns from .......... to .......... in the presence of water.
Anhydrous cobalt(II) chloride turns from blue to pink in the presence of water.
How does the boiling point of impure water compare to that of pure water?
Impure water boils at a temperature above 100 °C, because dissolved impurities increase the boiling point. Pure water boils at exactly 100 °C.
Define distilled water.
Distilled water is water that has been boiled to vapour and condensed back to a liquid, removing most dissolved impurities. It is used in practical chemistry to avoid interference from dissolved ions.
True or False?
Impurities in water decrease its boiling point and increase its melting point.
False.
Impurities increase the boiling point and decrease the melting point of water. This is why impure water boils above 100 °C and melts below 0 °C.
Why is distilled water used in practical chemistry rather than tap water?
Distilled water is used because it contains fewer chemical impurities than tap water. Dissolved ions in tap water could interfere with chemical reactions and affect results.
Anhydrous copper(II) sulfate changes from .......... to .......... when water is added.
Anhydrous copper(II) sulfate changes from white to blue when water is added.
Why do pure substances have sharp melting and boiling points, while mixtures do not?
Pure substances contain only one type of particle, so they all change state at the same temperature. Mixtures contain different substances that melt or boil at different temperatures, giving a range rather than a single point.
Define sedimentation in the context of water treatment.
Sedimentation is the process where water is allowed to stand in tanks so that mud, sand, and other solid particles settle to the bottom due to gravity. It is the first stage of water treatment.
Why is chlorine added to water during water treatment?
Chlorine is added to kill microbes (pathogens) such as bacteria that are too small to be removed by filtration. This prevents diseases such as cholera and typhoid.
In water treatment, filtration through .......... is used to remove unpleasant tastes and odours from the water.
In water treatment, filtration through carbon (charcoal) is used to remove unpleasant tastes and odours from the water.
True or False?
Sedimentation and filtration remove soluble impurities from water.
False.
Sedimentation and filtration remove solid (insoluble) impurities such as mud and sand. Soluble impurities require other treatments such as carbon filtration.
What are the three main stages of domestic water treatment, in order?
Sedimentation and filtration to remove solid particles
Filtration through carbon to remove tastes and odours
Chlorination to kill microbes
Define chlorination in water treatment.
Chlorination is the addition of chlorine to treated water to kill microbes (pathogens). It is the final stage of water treatment and prevents diseases caused by bacteria.
Why can't filtration alone make water safe to drink?
Filtration can only remove solid particles, but bacteria and other microorganisms are too small to be trapped by filters. Chlorination is needed to kill these pathogens and make the water safe.
During sedimentation, particles such as mud and sand sink to the bottom of the tank due to ...........
During sedimentation, particles such as mud and sand sink to the bottom of the tank due to gravity.
True or False?
Carbon filtration kills harmful bacteria in water.
False.
Carbon filtration removes unpleasant tastes and odours. It is chlorination that kills harmful bacteria and other microbes.
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