Chemistry unit 2 (water)

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What are the physical properties of water?
It is a colourless liquid at room temperature and pressure, it's melting point is 0 and its boiling point is 100
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Chemical tests for water
Anhydrous copper (II) sulfate - white solid to blue, anhydrous cobalt (II) chloride - pale blue to pink
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What causes hardness in water?
Hard water does not easily form a lather in soap. It is caused by dissolved ca2+ ions and/or mg2+ ions
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What is scum?
Hard water reacts with soap (sodium stearate) to form an insoluble scum: calcium/magnesium stearate
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Types of hardness
Temporary hardness is caused by calcium hydrogen carbonate and can be removed by boiling. Permanent hardness is caused by dissolved CaSO4, MgSO4, CaCl or MgCl
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How does temporary hardness arise in water?
Limestone reacts with rainwater containing carbon dioxide to form calcium hydrogen carbonate
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Removing temporary hardness...
Boiling removes temporary hardness. Dissolved calcium ions in the hard water are removed as insoluble calcium carbonate
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Removing permanent hardness (1)...
Ion exchange - dissolved calcium/magnesium ions are removed and replaced by sodium ions from the ion exchange resin
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Removing permanent hardness (2)...
Washing soda/hydrated sodium carbonate - dissolved calcium/magnesium ions are removed in a reaction with carbonate ions to form insoluble calcium carbonate
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Advantages of hard water...
Hard water tastes better, is better for brewing beer, is cheaper and provides calcium
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Disadvantages of hard water...
Hardwater produces a scum which wastes soap, produces limes cake which clogs pipes and kettles
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Reaction of substances with moist air
Anhydrous calcium chloride - white solid absorbs moisture until a colourless solution is formed. Silica gel - self indicating changes from blue to white as it absorbs moisture
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What is a desiccant?
A chemical that is hygroscopic ie absorbs moisture from the air
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What is a deliquescent?
A substance that absorbs moisture from the air until eventually it dissolves forming a solution
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In some areas fluoride ions are added to water as it helps tooth decay, why are some against this?
It is considered mass medication and the consumer has no choice. Fluoridation has been linked to various diseases.
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Medical use of barium sulfate...
Barium sulfate does not allow X-Ray's to pass through it and is used to X-ray patients with stomach and bowel problems. It is not toxic to the human body as it has a very low solubility
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Other cards in this set

Card 2

Front

Chemical tests for water

Back

Anhydrous copper (II) sulfate - white solid to blue, anhydrous cobalt (II) chloride - pale blue to pink

Card 3

Front

What causes hardness in water?

Back

Preview of the front of card 3

Card 4

Front

What is scum?

Back

Preview of the front of card 4

Card 5

Front

Types of hardness

Back

Preview of the front of card 5
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