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X Chemistry. > C3 Hard And Soft Water. > Flashcards

C3 Hard And Soft Water. Flashcards

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0
Q

What are the salts that hard water can contain?

A

Magnesium 2+ and calcium 2+ ions which are also salts.

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1
Q

What is the difference between hard and soft water?

A

Soft water will form a thick lather when soap is added.

Hard water will produce lots of scum when soap is added so more soap must be used to get a lather.

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2
Q

How can water become hard?

A

Water can have carbon dioxide dissolved in it. This water will fall as acid rain and flow over rocks which will cause it to become hard.

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3
Q

Which two types of rock can acid rain pour over to produce hard water.

A

Gypsum (calcium sulphate) CaSO4

Limestone(calcium carbonate) CaCO3

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4
Q

Give an equation on the formation of Ca 2+ ions from when acid rain produces hard water

A

CaCO3+H2O+CO2=Ca2+ and 2HCO3-

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5
Q

Give the equation for when temporary hard water is boiled.

A

Ca(HCO3)2=CaCO3+H2O+CO2

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6
Q

How does hard water form scum?

A

Sodium sterate(soap) +Ca2+ ions = calcium sterate precipitate (scum)+ Na+ions

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7
Q

Name the advantages of hard water.

A

Some evidence for it stopping heart disease.

Better for your teeth and bones.

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8
Q

Disadvantages of hard water.

A

Wastes soap, which is expensive.
Wasted energy, which is expensive.
Produces scum and limescale.

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9
Q

Name the steps water has to go through when it is made safe to drink.

A

It goes through a mesh screen which catches large objects.
Settlement like sand and soil sink to the bottom.
Aluminium sulphate and lime are added causing particles of dirt to stick together and they sink to the bottom.
The water goes through a filter of sand. Remaining grit and mud is removed and the water is clear.
Small amounts of chlorine are added. This kills bacteria.

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10
Q

In a water filter jug, what will you find that cleans the water?

A

Activated carbon, an ion exchange resin and silver.

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11
Q

What does activated carbon in a water filter jug do?

A

Reduce the levels of chlorine, as well as pesticides and other organic impureities.

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12
Q

What does The ion-exchange resin do in a water filter jug?

A

It removes calcium,magnesium,lead,copper,and aluminium ions.

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13
Q

What does the silver in a water filter jug do?

A

It discourages the growth of bacteria in the filter.

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14
Q

It water that is fit to drink “pure”?

A

No as it will contain substances dissoved in it.

Pure water will only have hydrogen and oxygen.

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15
Q

What are the advantages of adding fluoride to water?

A

It reduces cavities by 30%
There is no proof that there is anything harmful.
Protects us from bacteria that causes tooth decay and heart disease.

16
Q

What are the disadvantages of adding fluoride to water?

A

It can cause fluorosis which damages teeth and bones.
It could cause certain types of cancer.
It isn’t right to chose what people should have in their water.

17
Q

What does permeant hard water contain?

A

Calcium sulphates (CaSO4) or magnesium sulphates (MgSO4)

18
Q

What happens to the Ca2+ and Mg2+ ions when they are heated?

A

They react with the carbonates ions forming calcium or magnesium carbonate.
Ca2+ and Co3 (-2) forms CaCO3

19
Q

What can be added to permeant hard water to make it soft?

A

Sodium carbonate (Na2CO3)

20
Q

When washing soda is added to hard water, what happens?

A

The calcium or magnesium ions precipitate out forming insoluble carbonates.
Na(2)CO(3)+Ca(2+)=CaCO(3)+2Na(+)

21
Q

How does an ion exchange column soften water?

A

The resin has many Na+ ions.

These are exchanged for the Ca2+ or Mg2+ ions.

22
Q

What must you never talk about with ion exchange columns or adding washing soda? What should you talk about?

A

Don’t mention reactivity or displacement.

Only mention ions being replaced or exchanged.

23
Q

What ions must water contain?

A

Ca 2+

Mg 2+

24
Q

What does permeant hard water contain?

A

Sulphates SO”4”

25
Q

What does temporary hard water contain?

A

Hydrogen carbonates HCO”3”

26
Q

What are the advantages of adding chlorine to water?

A

Kills bacteria.

27
Q

What are the disadvantages of adding chlorine to water?

A

Toxic in large amounts.

X Chemistry. (12 decks)

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