Water Unit 2 Topic 2 Flashcards

1
Q

How much of the earth is covered in water?

A

70%

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2
Q

2 chemical tests for water?

A

Anhydrous copper sulfate - white to blue

Anhydrous cobalt chloride - blue to pink

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3
Q

2 physical tests for water?

A

Melts at 0c

Boils at 100c

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4
Q

What is hard water?

A

Water that doesn’t lather easily with soap

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5
Q

What ions cause hard water?

A

Magnesium and Calcium cations

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6
Q

How is scum formed from hard water & soap?

A

Calcium ions (water) + stearate (soap) ions to form insoluble calcium stearate (scum)

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7
Q

Does hard water affect detergents?

Example of a detergent?

A

No

Cilit bang

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8
Q

Word equation for the formation of scum

Ionic equation for the formation of scum

A

Sodium Stearate + hard water -> Calcium Stearate

2C17H35COONa (aq) + Ca 2+ (aq) -> (C17H35COO)2Ca (s) + Na +

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9
Q

Describe how you would identify whether a sample of water was hard or soft/

A

10cm3 waer sample. Add 1cm3 soap solution & shake 30 secs. Continue to add soap until permanent lather formed. Record volume of soap needed. More soap = harder water

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10
Q

What is a permanent lather?

A

Lather lasting more than 30 seconds

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11
Q

How is temporary hard water formed?

A

Calcium/magnesium hydrogencarbonate in it are caused by limestone reacting with carbonic acid in rainwater.`

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12
Q

What is permanent hard water?

A

Hard water that can’t be softened by boiling.

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13
Q

Equation for formation of temporary hard water?

A

Carbonic acid + Calcium Carbonate -> Calcium Hydrogencarbonate
H2CO3 (aq) + CaCO3 (s) -> Ca(HCO3)2 (aq)

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14
Q

How is permanent hard water formed?

A

Rain water passes over rocks containing calcium compounds (calcium sulphate) which dissolves into water

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15
Q

4 features of hard water areas?

A

Pot holes
Caverns
Stalagmites (up) & stalactites (down)

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16
Q

Word equation for heating temporary hard water?

A

Calcium hydrogencarbonate -> CO2 + H20 + Calcium carbonate

17
Q

Symbol equation for heating temporary hard water?

A

Ca(HCO3)2 (aq) -> Co2 (g) + H20 (l) + CaCO3 (s)

18
Q

2 methods to remove permanent hardness?

A

Washing soda & ion exchange column

19
Q

Explain how washing soda removes permanent hardness?

A

Sodium carbonate = washing soda Na2CO3
Sodium carbonate added to water, calcium ions combine with carbonate ions and precipitate out as insoluble calcium carbonate

20
Q

Word & symbol equation for washing soda + hard water?

A

Calcium Chloride + Sodium carbonate -> Calcium Carbonate + Sodium Chloride
CaCl2 (aq) + Na2CO3 (aq) -> CaCO3 (s) + 2NaCl (aq)

21
Q

Explain how an ion exchange column works?

A

Glass tube filled with resin with sodium ions attached.
Hard water contains calcium ions.
Calcium ions removed & replaced with sodium ions as water flows through. Water is softened.

22
Q

What is a precipitation reaction?

A

Ions in 2 solutions react to make an insoluble substance

23
Q

How is an ion exchange column regenerated/

A

Pour sodium chloride (salt) solution through. Replaces calcium ions for sodium ions.

24
Q

Advantages of hard water (4)

A

Tastes better
Provides calcium ions for bones & teeth
Better for tanning leather
Better for brewing beer

25
Q

Disadvantages of hard water (4)

A

Fur & scale in kettles & pipes
Wastes soap, expensive
Dishwasher soap to remove limescale expensive
Produces scum

26
Q

What is a dessicant?

A

A substance which absorbs moisture

27
Q

What is a deliquescent?

A

A substance that absorbs so much moisture from air that it dissolves in it, forming a solution

28
Q

Example of dessicant & use?

A

Silica gel

Leather & electrical goods

29
Q

Medical use of barium sulphate?

A

To examine digestive tract in x-rays. Doesn’t allow ray through. Barium toxic but sulfate insoluble & safe. Passes through body without being digested (low solubility)

30
Q

Fluoridation of drinking water?

A

Too much = fluorosis (mottled tooth enamel)

Helps bone & teeth strength