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GCSE Chemistry OCR 21st Century (Triple) (9-1) > C3 - Chemicals of the Natural Environment > Flashcards

C3 - Chemicals of the Natural Environment Flashcards

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1
Q

Describe the chemical bonds found in

metals

A
  • Metallic bonding.
  • Many positive metal ions fixed in a giant regular
    structure surrounded by a sea of delocalised
    negative electron.
  • There is strong electrostatic attraction between
    opposite charges.
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2
Q

What are the general properties of

metals?

A
  • High melting points
  • Solid at room temperature
  • Strong and hard
  • Malleable (can be pressed into shape)
  • Ductile (can be drawn into wires)
  • Good electrical and thermal conductors
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3
Q

Why do metals have high melting points?

A

Lots of energy is required to overcome

the many strong metallic bonds.

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4
Q

Why are metals hard?

A

Very strong metallic bonds hold the giant

structure together.

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5
Q

Why are metals malleable and ductile?

A

Metals are made up of uniform layers of
atoms which can easily slide over one
another. So the shape of the metal can
be easily changed.

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6
Q

Why are metals good conductors?

A

The delocalised electrons are free to

move to carry charge.

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7
Q

Write the general equation for the

reaction of metals with water

A

metal + water → metal hydroxide + hydrogen

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8
Q

Write the general equation for the

reaction of metals with dilute acid

A

metal + acid → salt + hydrogen

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9
Q

What is a displacement reaction in terms

of metals?

A

A reaction in which a more reactive metal
displaces (replaces) a less reactive
metal from a compound.

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10
Q

How can the order of the reactivity of
metals be deduced from the results of an

experiment?

A

More reactive metals can displace less
reactive metals from their compounds in a
displacement reaction. A series of
displacement reactions can be carried out to
compare the reactivities of metals.

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11
Q

What is meant by the reactivity of

metals?

A

The tendency of a metal atom to lose

electrons and form its positive ion.

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12
Q

Which metal in the reactivity series

reacts with water most vigorously?

A

Potassium

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13
Q

Using the reactivity series, which

elements don’t react with acids? Why?

A

Copper and silver because
they are below hydrogen in
the reactivity series so are
less reactive than hydrogen.

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14
Q

What is the principle of conservation of

mass?

A

A closed system has a constant mass
during a reaction, no matter is gained or
lost, so the mass of reactants is equal to
the mass of products.

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15
Q

Write a balanced symbol equation for the
displacement reaction between calcium

and copper(II) sulfate

A

Ca(s) + CuSO4(aq)→ CaSO4(aq) +Cu(s)

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16
Q

Write the ionic equation for the reaction

between sodium and iron(II) carbonate

A

2Na(s) + Fe2+(aq) → 2Na+(aq) + Fe(s)

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17
Q

What is an ore?

A

A rock that contains a mineral that can

be extracted.

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18
Q

Which metals can be extracted from their

ores by heating with carbon?

A

Metals which are
below carbon in the
reactivity series,
such as zinc.

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19
Q

Describe how zinc can be extracted from

its ore

A

Heat zinc oxide with carbon to reduce it
and form zinc. Carbon is the reducing
agent and is oxidised. Carbon displaces
zinc from its oxide.

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20
Q

Write a word and symbol equation for the

reduction of zinc oxide with carbon

A

zinc oxide + carbon → zinc + carbon monoxide

ZnO(s) + C(s) → Zn(l) + CO(g)

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21
Q

Why must electrolysis be used to extract

some metals from their ores?

A 
Metals above carbon in
the reactivity series are
more reactive than carbon
so they will not be
displaced from their ores
by carbon.
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22
Q

Why is electrolysis not used to extract

zinc from its ore?

A
  • Zinc is less reactive than carbon so can
    be extracted by heating with carbon.
  • Electrolysis is expensive and requires a
    lot of energy.
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23
Q

How can plants be used as an

alternative metal extraction method?

A

Phytoextraction:

Plants are grown in areas with metals in the soil. The
plants take up metals through their roots and
concentrate them in their shoots and leaves. These
plants are burned and the metals are removed from the
ash.

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24
Q

How can bacteria be used as an

alternative metal extraction method?

A

Bacterial extraction:

Some bacteria absorb metal compounds. These
bacteria produce solutions called leachates
containing the metals. Scrap iron can be used to
remove the metal from the leachate.

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25
Q

What are the limitations of biological

methods of extraction?

A
  • Produces smaller quantities of metals.
  • Slow processes.
  • Require displacement or electrolysis for the final
    step.
  • Bacteria require acidic conditions and may introduce
    toxic substances to the environment.
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26
Q

When do ionic compounds conduct

electricity? Why?

A

When molten or aqueous (dissolved in water)
because the ions are free to move. When solid,
the ions are fixed in the lattice so they can’t
move to carry a charge.

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27
Q

What is an electrolyte?

A

A molten or aqueous ionic compound

that conducts electricity.

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28
Q

What is electrolysis and what can it be

used for?

A

Electrolysis is the decomposition of an
electrolyte using an electric current. It
can be used to extract metals from their

ores.

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29
Q

When using inert electrodes, what

happens at the cathode?

A

Cations (positive ions) move towards the cathode
(negative electrode). Positive metal ions gain electrons
to form metal atoms. If the metal is more reactive than
hydrogen, hydrogen will form at the cathode instead
and the metal will remain in the electrolyte.

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30
Q

When using inert electrodes, what

happens at the anode?

A

Anions (negative ions) move towards the
anode (positive electrode). Negative
non-metal ions lose electrons to form
non-metal atoms.

31
Q

Predict what will form when molten

lead(II) bromide is electrolysed

A

Lead atoms (Pb) at cathode.

Bromine molecules (Br2

) at anode.

32
Q

Write half equations for the reactions that

take place when calcium chloride

undergoes electrolysis

A

Cathode: Ca2+ + 2e- → CaAnode: 2Cl-→ Cl2 + 2e-

33
Q

Describe oxidation and reduction in

terms of electrons

A

Oxidation is loss of electrons.

Reduction is gain of electrons.

34
Q

How can electrolysis be used to extract

aluminium from its ore bauxite?

A
  • Purified to form aluminium oxide.
  • Dissolved in molten cryolite.
  • Insert inert electrodes and connect to power supply.
  • Aluminium ions gain electrons at cathode to produce
    pure aluminium and oxide ions lose electrons to form
    oxygen at anode.
35
Q

Why is aluminium oxide dissolved in

cryolite during electrolysis?

A
  • Cryolite has a lower melting point than
    aluminium oxide.
  • Aluminium oxide is insoluble in water.
  • Reduces energy use and cost.
36
Q

Why must the inert graphite electrodes
be replaced regularly when aluminium is

being extracted from its ore?

A

The oxygen produced at the anode
reacts with carbon in the electrode
forming carbon dioxide meaning carbon
is lost from the anode.

37
Q

When would oxygen not be produced at
the anode during the electrolysis of an
aqueous ionic compound? What would

form instead?

A

When halide ions are present (chloride,
bromide or iodide ions). A halogen would
form (chlorine, bromine or iodine).

38
Q

Write the balanced half equation for the
formation of oxygen from hydroxide ions

at the anode

A

4OH-→ 2H2O +O2+ 4e-

39
Q

Describe how to carry out electrolysis on

an aqueous salt solution

A
  1. Pour the salt solution into a beaker.
  2. Insert 2 graphite electrodes and connect to a power supply.
  3. Fill 2 test tubes with salt solution and place over the
    electrodes to collect any gas produced.
  4. Turn on the power supply, ensuring the electrodes don’t
    touch.
  5. Turn off power and test gases.
40
Q

What is a hydrocarbon?

A

A compound made up of only hydrogen

and carbon atoms.

41
Q

‘Crude oil is the main source of ______’

A

‘Crude oil is the main source of Hydrocarbons’

42
Q

What is crude oil a feedstock for?

A

The petrochemical industry

43
Q

Is crude oil finite or infinite?

A

Finite

44
Q

Why is modern life dependent on

hydrocarbons?

A

Hydrocarbons are a source of fuel which

is relied on heavily for modern life.

45
Q

What is a homologous series?

A

A series of organic molecules with the same general
formula. Successive members in the series differ by
-CH2
.

Molecules in a homologous series have similar chemical
properties because they have the same general formula.

46
Q

What is the general formula for the

alkane homologous series?

A

CnH2n+2

47
Q

What is a fraction of crude oil?

A 
A mixture of similar-sized hydrocarbon
molecules with similar boiling points. These
compounds are generally members of the
alkane homologous series and have the
formula C
n
H2n+2.
48
Q

Why can crude oil be separated by

fractional distillation?

A

Because the different hydrocarbons have
different boiling points so condense at
different temperatures.

49
Q

Describe the fractional distillation of

crude oil

A
  • Crude oil is heated and evaporates.
  • Crude oil vapours enter and rise up a fractionating
    column which is hot at the bottom and cold at the top.
  • Vapours condense when the temperature is below its
    boiling point.
  • Separated liquids leave the column at different heights.
50
Q

Do the longest hydrocarbons leave the
fractionating column at the top or

bottom?

A

Bottom

51
Q

Which forces must be overcome for
alkanes to turn from liquid to gas? What
other bond is found in alkane molecules?

A

Intermolecular forces must be overcome for an alkane to
evaporate.
Covalent bonds are found between carbons and
between carbon and hydrogen. These are not broken
during boiling.

52
Q

Why do different alkanes have different

boiling points?

A
  • Longer hydrocarbons have stronger
    intermolecular forces.
  • More energy is required to overcome the stronger
    forces.
  • Longer hydrocarbons have higher boiling points.
53
Q

What is meant by the term empirical

formula?

A

The simplest whole number ratio of

atoms of each element in a compound.

54
Q

What is the empirical formula of C4H10?

A

C2H5

55
Q

What is a covalent bond?

A

A bond formed from a shared pair of

electrons between atoms.

56
Q

What are the limitations of using dot and
cross diagrams to represent covalent

compounds?

A
  • Don’t show the 3D arrangement of
    atoms in space.
  • Doesn’t show the size of atoms
    relative to one another.
57
Q

What are the limitations of using 3D
diagrams to represent covalent

compounds?

A
  • They are not show to scale.
  • Don’t show how the bond formed.
  • Don’t show the shared pair of
    electrons.
58
Q

Which is stronger: covalent bonds or

intermolecular forces?

A

Covalent bonds

59
Q

Why do alkanes have low melting and

boiling points?

A

During melting and boiling, intermolecular
forces are overcome but covalent bonds
aren’t broken. Intermolecular forces are
relatively weak compared to covalent bonds
so require little energy to overcome.

60
Q

What is cracking?

A

Breaking long chain hydrocarbon

molecules into smaller hydrocarbons.

61
Q

What are the products of cracking?

A

Alkanes and alkenes

Alkenes are a different homologous
series containing a carbon to carbon
double bond.

62
Q

Hexane is cracked to form butane and
ethene. Write a word and symbol

equation for this reaction.

A

hexane → butane + ethene

C6H14 → C4H10 + C2H4

63
Q

Describe what happens during cracking

A

An alkane is heated. The vapours pass
over a catalyst and the covalent bonds
break and reform.

64
Q

Why is cracking important?

A
  • The shorter chained alkanes and alkenes are in
    higher demand than long chained alkanes.
  • Can match the supply of fractions with demand.
    Typically fractional distillation of crude oil produces
    too many long chain hydrocarbons.
  • Alkenes can be produced for use as a feedstock in
    the petrochemical industry.
65
Q

Alkanes are saturated hydrocarbons.

Explain what this means

A

Hydrocarbon - contains only hydrogen and
carbon.

Saturated - carbon atoms are all joined by
single bonds.

66
Q

What is an alkene? Include the general

formula and functional group

A

An unsaturated hydrocarbon.

General formula: C
n
H2n
Functional group: C=C

67
Q

Give examples of molecules that alkenes

react with in an addition reaction

A

React with water when heated with a catalyst to
form alcohols.

React with bromine to form bromoalkanes.

React with other alkenes to form addition
polymers.

68
Q

What are the general formula and

functional group of an alcohol?

A

General formula: Cn
H2n+1OH

Functional group: OH

69
Q

What are the common reactions of

alcohols?

A
  • Complete combustion, producing
    water and carbon dioxide.
  • Oxidation to produce carboxylic acids
    (needs an oxidation agent).
70
Q

What are the general formula and

functional group of a carboxylic acid?

A

General formula: Cn H2n+1COOH

Functional group: COOH

71
Q

What do carboxylic acids react with?

A
  • Metals (forms salt and hydrogen).
  • Bases (forms salt and water).
  • Carbonates (forms salt, water and
    carbon dioxide).
72
Q

Why do members of a homologous

series react similarly?

A

Because they all contain the same

functional groups.

73
Q

Predict the formula of the products when

pentane is completely combusted

A

H2O and CO2

GCSE Chemistry OCR 21st Century (Triple) (9-1) (6 decks)

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