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Chemisty > C3a > Flashcards

C3a Flashcards

1
Q

Do you get scum with hard or soft water?

A

Hard water

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2
Q

What dissolved ions does hard water contain?

A

Magnesium ions and calcium ions

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3
Q

What happens when hard water is heated?

A

It forms furring or scale (mostly calcium carbonate)

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4
Q

What does hard water do to the inside of pipes, boilers and kettles?

A

Scale likes the inside of pipes reducing the efficiency of heating systems and eventually blocking pipes.

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5
Q

What does scale do to heating elements on a kettle?

A

It acts as a thermal insulator meaning the heating element takes longer to beat up and boil water. Therefore it is less efficient

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6
Q

How does rainwater become hard water?

A

It falls on some types of rocks (limestone, chalk and gypsum) which means magnesium sulfate and and calcium sulfate get dissolved into the water.

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7
Q

Is magnesium sulfate soluble?

A

Yes

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8
Q

Is calcium sulfate soluble?

A

Yes, but only a little bit.

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9
Q

What is good for healthy teeth and bones?

A

Ca2+ ions

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10
Q

What are people who live in hard water areas at less risk of than people who live in soft water areas?

A

Developing heart disease. It could be to do with the minerals in hard water

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11
Q

Two types of hard water

A
  • Temporary hard water

- Permeant hard water

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12
Q

What is temporary hard water caused by?

A

The hydrocarbonate ion HCO3- in Ca(HCO3)2

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13
Q

What is permanent hard water caused by?

A

Dissolved calcium sulfate

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14
Q

How is temporary hardness removed?

A

By boiling

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15
Q

What does boiling temporary hard water do?

A

It causes the calcium hydrocarbonate to dissolve to form calcium carbonate, which is insoluble (this is limescale)

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16
Q

When calcium hydrogencarbonate is heated what does it produce?

A
  • Calcium carbonate
  • Water
  • Carbon dioxide
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17
Q

What happens when Ca(HCO3)2(aq) is heated? What is produced?

A
  • CaCO3(s)
  • H2O(l)
  • CO2(g)
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18
Q

What happens when you boil permanent hard water?

A

Heating a sulfate ion does nothing

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19
Q

How do you soften both types of hard water?

A

You add washing soda (sodium carbonate Na2CO3)

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20
Q

What happens when sodium carbonate is added to hard water?

A

The added carbonate ions react with the Ca2+ and Mg2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The Ca2+ and Mg2+ ions are no longer dissolved so they can’t make it hard

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21
Q

How can both types of hardness be removed?

A

By running the hard water through an ‘ion exchange column’

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22
Q

How do ion exchange columns work?

A

The columns have lots of sodium or hydrogen ions which ‘exchange’ them for calcium or magnesium ions as the water runs through.

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23
Q

Where does most of our drinking water come from?

A

Reservoirs

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24
Q

Microbes in water cause what diseases?

A

Cholera and dysentery

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25
Q

Where does the water in reservoirs come from?

A

Rivers and groundwater

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26
Q

Water treatment process

A
  • Water travels through mesh screen (to remove big stuff e.g. twigs)
  • Chemicals are added to make solids and microbes stick together then fall to the bottom
  • The water is filtered through gravel beds to remove solids
  • the water is chlorinated to remove harmful microbes
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27
Q

What are in water filters that people buy?

A

Carbon to remove chlorine taste and silver to kill bugs

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28
Q

Why is fluorine added to drinking water?

A

It is added in some parts of the country to reduce tooth decay

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29
Q

Why is chlorine added to drinking water?

A

To prevent diseases

30
Q

Disadvantages of adding chlorine to drinking water

A

It can react with other natural substances in water to produce toxic by-products which some people believe could cause cancer

31
Q

What can be caused by high doses of fluoride?

A

Cancer and bone problems

32
Q

Define reversible reactions

A

A reaction where the products of the reaction can themselves react to produce the original reactants

33
Q

What will happen if the reversible reaction happens in a closed system?

A

A state of equilibrium will always be reached

34
Q

What a reaction reaching equilibrium mean?

A

That they reactions are taking place in both directions but the overall effect is zero as they cancel each other out. the reactions happen at the same rate

35
Q

The general formula for an alcohol

A

CnH2n+1OH

36
Q

what is a homologous series?

A

A group of chemicals that react in a similar way because they have the same functional group

37
Q

What is the functional group of alcohols?

A

OH

38
Q

Properties of alcohols

A
  • flammable, burn in air to produce carbon dioxide and water
  • The first three completely dissolve in water to produce neutral solutions
  • They react with sodium to give hydrogen and alkoxides
39
Q

What happens if you raise the temperature in a reversible reaction?

A

The endothermic reaction will increase and increase the yield

40
Q

What happens if you decrease the temperature in a reversible reaction?

A

The exothermic reaction will increase increasing the yield

41
Q

What happens if you raise the pressure in a reversible reaction?

A

The reaction which produces less volume will be encouraged

42
Q

What happens if you decrease the pressure of a reversible reaction?

A

It will encourage the reaction which produces more volume

43
Q

If you add a catalyst to a reversible reaction what will happen to the equilibrium position?

A

It won’t change

44
Q

What does a catalyst do to a reversible reaction?

A

It speeds up both the forward and backward reactions by the same amount

45
Q

How does adding a catalyst change the overall yield in a reversible reaction?

A

The yield is the same however you would reach equilibrium faster

46
Q

In the haber process where is nitrogen obtained from?

A

The air (which is 78% nitrogen and 21% oxygen)

47
Q

Where does the hydrogen come from for the haber process?

A

It comes from natural gas or other sources like crude oil

48
Q

What happens when nitrogen is reacted with hydrogen?

A

It reacts to form ammonia

49
Q

Is the haber process reversible?

A

Yes it is nitrogen and hydrogen react to form ammonia then ammonia breaks down again into nitrogen and hydrogen

50
Q

The industrial conditions of the haber process

  • Pressure
  • Temperature
  • Catalyst
A
  • Pressure - 200 atmospheres
  • Temperature - 450degreesC
  • Catalyst - Iron
51
Q

What is the equation of the haber process?

A

N2(g) + 3H2(g) <=> 2NH3(g)

52
Q

What does increasing the pressure do to the haber process?

A

It favours the forward reaction (as there are 4 molecules of gas on the left and 2 on the right)

53
Q

What is the pressure set for the haber process? Why?

A

-200atm
It is as high as possible to give the highest % yield without being too expensive (to build a plant to withstand really high pressures)

54
Q

What is the forward reaction in the haber process? Exothermic or endothermic?

A

Exothermic

55
Q

What happens if you increase the temperature in the haber process?

A

The equilibrium will move the wrong way. Away from ammonia and towards nitrogen and hydrogen

56
Q

To increase the yield of ammonia would you increase of decrease the temperature?

A

Decrease

57
Q

Lower temperatures mean a lower rate of reaction so what do they do to the haber process?

A

They increase the temperature anyway to get a faster rate of reaction

58
Q

Why do people use a temp of 450degreesC in the haber process?

A

It is a compromise between maximum yield and speed of reaction. It’s better to wait 20 seconds for a 10% yield than 60 seconds for a 20% yield

59
Q

What state is the ammonia field in?

A

A gas but then it is cooled in the condenser, it then liquifies and is removed

60
Q

What happens to the unused hydrogen and nitrogen at the end of the haber process?

A

They are recycled back into the process so nothing is wasted

61
Q

What ratio is the hydrogen to nitrogen in the haber process?

A

3:1

62
Q

What does the iron catalyst do to the haber process?

A

It makes to reaction go faster and it gets to the equilibrium proportions faster. But the catalyst does not affect to position of equilibrium (% yield)

63
Q

What would have to be done if the haber process did not use a catalyst?

A

The temperature would have to be increased to get a quick enough reaction but this would reduce the % yield

64
Q

What is the main alcohol in alcoholic drinks and why?

A

Ethanol - it is not as toxic as methanol (which causes blindness) but it still causes liver and brain damage

65
Q

Why are ethanol, methanol and propanol useful solvents in industry?

A

They can dissolve most compounds that water dissolves, but they also dissolve substances that water can’t dissolve (hydrocarbons, oils and fats)

66
Q

What is the solvent used for perfumes, aftershave lotions? Why?

A

Ethanol - it mixes with both oils (which give the smell) and the water (that makes up the bulk)

67
Q

What is ‘methylated spirit’ (or ‘meths’)?

A

It is ethanol with chemicals (e.g. methanol) added to

68
Q

What are ‘methylated spirits’ used for?

A

They are used to clean paint brushes and as fuel

69
Q

Why is purply-blue dye added to ‘methylated spirit’?

A

To stop people drinking it as it is poisonous

70
Q

Which alcohol is used as a fuel in spirit burners? Why?

A

Ethanol as it burns fairly cleanly and its non smelly

71
Q

Which alcohol is mixed with petrol for fuel for cars and why?

A

Ethanol because it is clean burning, the more ethanol in a petrol/ethanol mix the less pollution is produced

Chemisty (3 decks)

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