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Chemistry Edexcel > Topic 5 - Separate Chemistry > Flashcards

Topic 5 - Separate Chemistry Flashcards

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1
Q

What are the typical properties of transition metals?

A
  • High melting point.
  • High density.
  • Form coloured compounds.
  • Transition metals and their compounds can be used as catalysts
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2
Q

Which transition metal is used as a catalyst in the Haber process?

A

Iron

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3
Q

What causes metals to corrode

A

Oxygen reacts with the metal to form a metal oxide

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4
Q

Why is corrosion of a metal a redox reaction?

A

The metals loses electrons so is oxidised.
Oxygen gains electrons so is reduced.

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5
Q

What is rusting?

A

Rusting is the name specifically given to the corrosion of iron when it reacts to oxygen and water in the air.

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6
Q

What two substances need to be excluded to prevent rusting?

A

Oxygen (O2)
Water (H2O)

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7
Q

How can oxygen and water be excluded to prevent
iron rusting?

A

Paint the metal.
Coat the metal in oil/grease.
Cover the metal in plastic.
Keep the metal in a vacuum container.

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8
Q

What is sacrificial protection? How does it prevent
corrosion?

A

Sacrificial protection is when the metal being
protected from rusting is galvanized with a
more reactive metal.
The outer metal will corrode first and will
prevent the corrosion of the inner metal.

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9
Q

Which metal is used to in the sacrificial protection of
iron?

A

Zinc

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10
Q

What is electroplating?

A

A process in which a metal is coated with
a layer of another metal.

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11
Q

What are two reasons for using electroplating?

A
  • To make a metal more resistant to
    corrosion.
  • To improve the appearance of a metal
    (e.g. silver plated cutlery).
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12
Q

Explain how the process of electroplating works

A

Similar setup to electrolysis:
The metal being coated is the cathode. The
metal that will form the exterior layer is the
anode. The electrolyte solution must contain ions
of the metal which will form the outer coating. A
power supply is connected to both electrodes.

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13
Q

Why are pure metals generally very malleable?

A

The atoms lie in uniform rows which are
able to slide over one another.

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14
Q

What is an alloy?

A

An alloy is a mixture of two or more
metals or a metal and another element.

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15
Q

A pure metal can be converted into an alloy. How
does this increase the strength of the product?

A

Alloys contain several metals which will have
different sized atoms. This distorts the regular
arrangement of the atoms so the layers are
unable to slide over one another very easily.

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16
Q

Why is iron alloyed with other metals to produce
alloy steels?

A

Iron is relatively brittle so it is combined with other elements
such as carbon produces a material with more desirable
qualities.
● Low carbon steel: Malleable so used for sheeting.
● High carbon steel: Hard so used for cutting tools.
● Stainless steel: Corrosion resistant so used for cutlery.

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17
Q

What property of copper makes it suitable to be used
in electrical cables?

A

Very good electrical conductor.

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18
Q

What property of aluminium makes it suitable for use
in aircrafts?

A

Low density

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19
Q

What is a key property of gold that makes it suitable
for use in jewellery?

A

Very unreactive so resist to corrosion.
Jewellery appearance will not be
affected over time.

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20
Q

What is magnalium? What is it used for?

A

Magnalium is an alloy of magnesium and
aluminium.
It is lighter and stronger than aluminium and
more resistant to corrosion. It is used for car and
aircrafts.

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21
Q

What is brass? What is it used for?

A

Brass is an alloy of copper and zinc.
Brass is hard and resistant to corrosion.
It is used for decorative hardware such
as plumbing fittings.

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22
Q

How do you calculate the concentration of a solution
in mol dm-3?

A

Concentration (mol dm-3) = moles ÷ volume (dm3)

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23
Q

How can you convert concentration in g dm-3 to mol
dm-3?

A

Concentration(mol dm-3) = concentration(g dm-3) ÷Mr

Mr - molecular mass

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24
Q

Describe how to carry out an acid-alkali titration to
find the concentration of alkali

A
  1. Rinse the pipette with the solution of unknown concentration (alkali). Use
    this pipette to add a known volume of alkali to a conical flask.
  2. Add a few drops of indicator.
  3. Rinse and fill the burette with acid.
  4. Gradually add the acid to the conical flask.
  5. Record the volume in the burette when the indicator changes colour.
  6. Repeat the experiment until you have concordant results.
  7. Use results to calculate a mean titre and the concentration of alkali.
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25
Q

If you know the volume of acid required to neutralise an
alkali, how could you calculate the concentration of the acid,
given the alkali concentration and volume?

A
  • Calculate the number of moles of the alkali using the known volume
    and concentration (moles = concentration x volume).
  • Use the chemical equation to work out the ratio of acid and alkali
    that react and hence work out how many mole of acid have reacted.
  • Divide the moles of acid by the volume used in neutralisation to find
    concentration.
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26
Q

What is meant by the term theoretical yield?

A

The amount of product that would be
collected under perfect reaction
conditions.

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27
Q

How do you calculate percentage yield?

A

Percentage yield =
(Actual yield ÷ Theoretical yield) x 100

28
Q

What is the percentage yield of NH3 if 40.5 g of NH3
is produced from 20.0 mol H2 and excess N2?

A
  1. Equation: N2 + 3H2 → 2NH3
  2. Moles of ammonia = 20/1.5 = 13.3 moles
  3. Mass of ammonia = 13.3 x (14+1+1+1) = 227 g
  4. Percentage yield = (40.5/227) x 100 = 17.8%
29
Q

Why could the actual yield of product be less than
expected?

A
  • Incomplete reaction.
  • Competing, unwanted side reactions.
  • Practical losses, for example some solid
    may get lost when being transferred
    between beakers.
30
Q

What is the atom economy of a reaction?

A

Atom economy is a measure of the
efficiency of the reaction. It looks at the
amount of reactants that get turned into
useful products.

31
Q

How can atom economy be calculated?

A

Atom economy =
(Mr of desired product ÷ Mr of reactants) x 100

Mr - molecular mass

32
Q

Fill in the gap: ‘The _____ the atom economy, the
more sustainable and efficient the process’

A

Higher

33
Q

Why might one reaction pathway be chosen over
another?

A

Higher atom economy.
Higher yield.
Faster rate.
Equilibrium position favours products more.
By-products are more useful / less harmful.

34
Q

What does Avogadro’s Law state about gas
volumes?

A

At the same temperature and pressure,
equal amounts of gas will occupy the
same volume.

35
Q

What is the molar volume of a gas?

A

The volume occupied by one mole of
molecules of any gas at room
temperature and pressure.

36
Q

What is RTP?

A

Room temperature and pressure:
- 20 degrees C
- 1 atmosphere

37
Q

How can the molar volume of a gas be calculated?
What are the units?

A

Molar volume = volume (dm3) ÷ moles of gas
Units: dm3 mol-1

38
Q

What is the Haber process?

A

A reversible reaction that forms ammonia
from nitrogen and hydrogen.

39
Q

Describe the steps that are carried out during the
Haber process

A
  1. Reactants are obtained (hydrogen from natural gas, nitrogen from air).
  2. The gases are compressed to 200 atm and heated to 450oC before
    being pumped into a tank containing layers of catalytic iron beads.
  3. Ammonia forms.
  4. Ammonia and unreacted hydrogen and nitrogen pass into a cooling
    tank where the ammonia is collected as a liquid.
  5. The unreacted hydrogen and nitrogen are recycled back into the tank.
40
Q

What is meant by the term dynamic equilibrium?

A

The rate of the forward reaction equals the
rate of the backwards reaction. The
concentration of reactants and products are
constant.

41
Q

What is the chemical equation for the formation of
ammonia from hydrogen and nitrogen?

A

N2 + 3H2 ⇌ 2NH3

42
Q

What are the ideal conditions for the Haber process?

A
  • 450 C temperature
  • 200 atm pressure
  • Iron catalyst
43
Q

How is the rate of attainment of equilibrium affected
by temperature?

A

A higher temperature means equilibrium is
reached quicker. This is because the reacting
particles have more kinetic energy so there
are more frequent successful collisions.

44
Q

How is the rate of attainment of equilibrium affected
by a catalyst?

A

Equilibrium is reached faster when a
catalyst is used because the catalyst
provides an alternative reaction pathway
with a lower activation energy.

45
Q

How is the rate of attainment of equilibrium affected
by pressure?

A

Equilibrium is reached faster with a higher
pressure. This is because there are more particles
in the same volume (or the same number of
particles in a smaller volume) so more collisions
between reacting particles.

46
Q

How is the rate of attainment of equilibrium affected
by concentration?

A

Equilibrium is reached faster at a higher
concentration. This is because there are
more particles in the same volume so more
collisions between the reacting particles.

47
Q

Why are the conditions used in the Haber process a
compromise?

A
  • A high temperature increases the rate of reaction however, it will
    favour the reverse reaction, decreasing the yield. A compromise of
    450 degrees C is used to obtain a sufficient rate and yield.
  • A high pressure speeds up the rate and favours the forward
    reaction (increasing the yield). High pressures can be dangerous
    and require expensive machinery so a compromise of 200 atm is
    used.
48
Q

Why is a catalyst used in the Haber process?

A

To increase the rate of reaction so more
product is produced within the same
time frame.

49
Q

What factors should be considered before deciding
the conditions for an industrial reaction?

A
  • Availability and cost of raw materials.
  • Energy requirements.
  • Optimum temperature and pressure for high
    yield and fast rate of reaction.
  • Need for a catalyst.
50
Q

What is the purpose of fertilisers?

A

To promote plant growth.

51
Q

What chemical compounds might fertilisers contain?

A

Nitrogen, phosphorus and potassium
compounds.

52
Q

What compounds are found in NPK fertilisers?

A

A combination of all three fertiliser
compounds: nitrogen, phosphorus and
potassium compounds.

53
Q

Which parts of plant growth do the compounds
nitrogen, potassium and phosphorus help with?

A

Nitrogen: Healthy leaves.
Phosphorus: Healthy roots.
Potassium: Growth and healthy fruit /
flowers.

54
Q

Which ammonium salt is most commonly used in
fertilisers?

A

Ammonium nitrate

55
Q

How is the salt ammonium nitrate formed? Write a
chemical equation for the reaction taking place

A

React ammonia with nitric acid
NH3 + HNO3 → NH4NO3

56
Q

What is the chemical equation for the formation of
ammonium sulfate from ammonia and sulfuric acid?

A

2NH3 + H2SO4 → (NH4)2SO4

57
Q

How can ammonium sulfate be prepared in a
laboratory?

A

Titration between ammonia and sulfuric acid:
- Exact volume of NH3 added to a conical flask using a pipette.
- Add a few drops of indicator.
- Add H2SO4 from the burette drop by drop. Stop when the indicator changes
colour.
- Repeat, adding the exact volumes of reactants without the indicator (as it is
an impurity).
- Remove the water by evaporation and crystallisation, leaving pure crystals.

58
Q

How can ammonium sulfate be produced on an
industrial scale?

A

Raw materials obtained from the Haber process
(ammonia) and the contact process (sulfuric acid). A
large reactor chamber is filled with ammonia gas.
Sulfuric acid is sprayed into the chamber from
above. Ammonium sulfate crystals are produced.

59
Q

Compare the laboratory method of producing
ammonium sulfate with the industrial process

A

Laboratory method:
Faster rate of reaction.
Small reactant quantities can easily be
bought.
Room temperature and pressure
Simple equipment required.
Very small yield.

Industrial process:
Very expensive and complex.
Continuous process so continuous yield.
Large volumes of product.
Slow rate of reaction.
High energy requirement.
Other industrial processes required to
obtain the reactants.

60
Q

Describe how to set up a chemical cell. How is a
voltage produced from a chemical cell?

A

Two metals of different reactivities are placed in an electrolyte.
The more reactive metal releases electrons, becoming positively
charged. The electrons flow to the other electrode which
becomes negatively charged. The difference in the ability of
each electrode to release electrons causes a voltage to be
produced.

61
Q

When will a chemical cell stop producing a voltage?

A

When one of the reactants has been
used up.

62
Q

What is a fuel cell?

A

A cell that continually produces a voltage
as long as it is supplied with oxygen and
a fuel (like hydrogen).

63
Q

What is the only product of a hydrogen-oxygen fuel
cell?

A

Water

64
Q

How does a hydrogen-oxygen fuel cell work?

A

Hydrogen and oxygen are pumped through
porous electrodes. The electrolyte is often
an acid such as phosphoric acid.
Hydrogen and oxygen react, producing
electricity and water.

65
Q

Write an equation for the overall reaction that takes
place in a hydrogen-oxygen fuel cell

A

2H2 + O2 → 2H2O

66
Q

What are the advantages of using fuel cells?

A
  • No pollution produced.
  • Produce more energy than an alternative
    fuel like petrol.
  • Continuous process as long as fuel is
    supplied.
67
Q

What are the disadvantages of using fuel cells?

A
  • Materials used to make them are expensive.
  • High pressure tanks required to store oxygen
    and fuels like hydrogen.
  • Hydrogen is expensive and hard to store.
  • Efficiency is affected by temperature.

Chemistry Edexcel (1 decks)

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