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AQA Chemistry C3 2016 > C3.2 Water > Flashcards

C3.2 Water Flashcards

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1
Q

What does soft water form with soap?

A

A lather.

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2
Q

What does hard water form with soap?

A

Scum- more soap is needed to form a lather.

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3
Q

What kind of detergents do not form scum?

A

Soap-less detergents.

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4
Q

How can the hardness of water be measured?

A

Titration can be performed with soap and water. The harder the water, the more soap is needed.

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5
Q

What is titration?

A

A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution.

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6
Q

What dissolved compounds are usually in hard water?

A

Calcium ions (Ca2+) and Magnesium ions (Mg2+).

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7
Q

Where do the compounds in hard water come from?

A

When water comes into contact with certain rocks, the compounds dissolve in the water.

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8
Q

What are the two types of hard water? What is the difference?

A

Permanent hard water- remains hard when it is boiled and contains dissolved calcium sulphate.

Temporary- contains calcium hydrogencarbonate which is removed when boiled, and thus temporary hard water can be softened through boiling.

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9
Q

What are the main chemicals in soap?

A

Sodium stearate and sodium palmitate.

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10
Q

What precipitate is formed when soap is mixed with hard water?

A

Calcium stearate/calcium palmitate.

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11
Q

Describe the processes involved in the water cycle.

A
  1. Water droplets become to large and heavy and fall as rain or snow.
  2. The water flows into lakes and the earth, and eventually the water returns to the oceans.
  3. Water evaporates from oceans, lakes and rivers to form water vapour.
  4. As air rises it cools, so water vapour in it condenses to form clouds.
    CYCLE!
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12
Q

How is water in the UK treated?

A

Filtration- insoluble substances e.g. twigs, dirt, are removed.

Precipitate- Soluble materials/solids/some metal ions are removed.

Chlorine is added- kills bacteria

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13
Q

What is the word formula for the reaction of hard water and soap?

A

Calcium ions (soluble) + Stearate ions (insoluble) —-> Calcium stearate (insoluble)

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14
Q

What is soft water?

A

Water which does not contain calcium or magnesium ions and does not form scum when soap is added.

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15
Q

What is an advantage of soft water?

A

Less soap is needed to produce a lather.

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16
Q

What is the equation for the formation of temporary hard water? What does temporary hard water exclusively contain?

A

It contains calcium hydrogencarbonate.

H2O(l) + CO2(g) + CaO3(s)—> Ca(HCO3)2(aq)
Rain+ Atmosp.+ Limestone(rocks)–>Tap water

17
Q

What is the formula for temporarily hard water? What are the formulas for what it contains?

A

Ca(HCO3)2(aq)

Ca2+ and HCO3(aq)

18
Q

How can you soften temporarily hard water?

What is the equation for this?

A

Boiling.

Ca(HCO3)2—> CaCo3(s) + CO2(g) + H2O(l)

19
Q

What happens when temporary hard water is boiled?

A

The hydrogencarbonate ions (HCO3-) thermally decompose to produce carbonate ions- which react with the calcium and magnesium ions to form precipitates (insoluble solids- scale).

20
Q

What is the issue with temporarily hard water?

A

When the water is heated it produces scale- this reduces the efficiency of heating systems and kettles as it coats the heating element in kettles and coats the insides of boilers and hot water pipes. More energy needed to heat= higher costs.

21
Q

What problems can temporarily hard water cause in heating systems?

A

The scale produced on heating can block pipes and cause the system to break down- meaning costs to replace or fix it!

22
Q

What are some advantages of hard water?

A
  • Calcium compounds are good for the development and maintenance of bones and teeth
  • Can reduce heart disease
23
Q

How can any hard water be softened?

A

By removing the dissolved calcium and magnesium ions.

24
Q

What are the two methods of softening hard water?

A
  • Sodium Carbonate
  • ->The addition of sodium carbonate (as ‘washing soda’ crystals), which dissolves and then precipitates out the calcium or magnesium ions as their insoluble carbonates(s)
  • ->calcium sulphate + sodium carbonate ==> calcium carbonate + sodium sulphate

-Ion exchange column:
Commercial water softeners often use ion exchange resins.

–> Resin beads have sodium ions attached

–>As the hard water passes through the column, the calcium and magnesium ions swap places with the sodium ions.

–>The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions

(Some ion exchange resins use hydrogen ions instead of sodium ions.)

25
Q

What is distillation?

A

A method of purifying water (sometimes sea water) by evaporating the water leaving impurities and salt behind. This is carried out in a still.

26
Q

What is a solar still?

A

A site of distillation- the sun provides the energy needed for the water to evaporate, leaving impurities behind.

27
Q

What is flash distillation? What are the issues with it?

A

Flash distillation involves heating water under pressure and then allowing it to evaporate quickly. The vapour is then condensed and stored.

Unfortunately, fossil fuels (which are unrenewable resources) are used in this process, and therefore more carbon dioxide is added to the atmosphere. Also, concentrated salty water is formed as a waste product, which can damage the ecology of the sea if it was poured back in.

28
Q

Why is most of the water on earth unfit for drinking?

A

Most of it is seawater, so contains too much sodium!

29
Q

What health concerns have been raised about drinking distilled water?

A

The loss of water when water is distilled can be lead to mineral deficiencies if it is drunk exclusively. Also, CO2 from the air dissolves in the water, making it slightly acidic.

30
Q

Why can too much softened water be bad for your health?

A

It has more sodium ions in it that hard water does, and thus if consumed too much. this can result in heart problems due to excess salt in the body.

31
Q

What are the benefits and drawbacks of adding fluoride to water?

A
  • It is good for dental health.

- It could cause bone weakening and teeth-mottling.

AQA Chemistry C3 2016 (1 decks)

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