C3 - Chemicals of the Natural Environment Flashcards
Describe the chemical bonds found in
metals
- 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.
What are the general properties of
metals?
- 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
Why do metals have high melting points?
Lots of energy is required to overcome
the many strong metallic bonds.
Why are metals hard?
Very strong metallic bonds hold the giant
structure together.
Why are metals malleable and ductile?
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.
Why are metals good conductors?
The delocalised electrons are free to
move to carry charge.
Write the general equation for the
reaction of metals with water
metal + water → metal hydroxide + hydrogen
Write the general equation for the
reaction of metals with dilute acid
metal + acid → salt + hydrogen
What is a displacement reaction in terms
of metals?
A reaction in which a more reactive metal
displaces (replaces) a less reactive
metal from a compound.
How can the order of the reactivity of
metals be deduced from the results of an
experiment?
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.
What is meant by the reactivity of
metals?
The tendency of a metal atom to lose
electrons and form its positive ion.
Which metal in the reactivity series
reacts with water most vigorously?
Potassium
Using the reactivity series, which
elements don’t react with acids? Why?
Copper and silver because
they are below hydrogen in
the reactivity series so are
less reactive than hydrogen.
What is the principle of conservation of
mass?
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.
Write a balanced symbol equation for the
displacement reaction between calcium
and copper(II) sulfate
Ca(s) + CuSO4(aq)→ CaSO4(aq) +Cu(s)
Write the ionic equation for the reaction
between sodium and iron(II) carbonate
2Na(s) + Fe2+(aq) → 2Na+(aq) + Fe(s)
What is an ore?
A rock that contains a mineral that can
be extracted.
Which metals can be extracted from their
ores by heating with carbon?
Metals which are
below carbon in the
reactivity series,
such as zinc.
Describe how zinc can be extracted from
its ore
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.
Write a word and symbol equation for the
reduction of zinc oxide with carbon
zinc oxide + carbon → zinc + carbon monoxide
ZnO(s) + C(s) → Zn(l) + CO(g)
Why must electrolysis be used to extract
some metals from their ores?
Metals above carbon in the reactivity series are more reactive than carbon so they will not be displaced from their ores by carbon.
Why is electrolysis not used to extract
zinc from its ore?
- Zinc is less reactive than carbon so can
be extracted by heating with carbon. - Electrolysis is expensive and requires a
lot of energy.
How can plants be used as an
alternative metal extraction method?
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.
How can bacteria be used as an
alternative metal extraction method?
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.
What are the limitations of biological
methods of extraction?
- 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.
When do ionic compounds conduct
electricity? Why?
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.
What is an electrolyte?
A molten or aqueous ionic compound
that conducts electricity.
What is electrolysis and what can it be
used for?
Electrolysis is the decomposition of an
electrolyte using an electric current. It
can be used to extract metals from their
ores.
When using inert electrodes, what
happens at the cathode?
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.
When using inert electrodes, what
happens at the anode?
Anions (negative ions) move towards the
anode (positive electrode). Negative
non-metal ions lose electrons to form
non-metal atoms.
Predict what will form when molten
lead(II) bromide is electrolysed
Lead atoms (Pb) at cathode.
Bromine molecules (Br2
) at anode.
Write half equations for the reactions that
take place when calcium chloride
undergoes electrolysis
Cathode: Ca2+ + 2e- → CaAnode: 2Cl-→ Cl2 + 2e-
Describe oxidation and reduction in
terms of electrons
Oxidation is loss of electrons.
Reduction is gain of electrons.
How can electrolysis be used to extract
aluminium from its ore bauxite?
- 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.
Why is aluminium oxide dissolved in
cryolite during electrolysis?
- Cryolite has a lower melting point than
aluminium oxide. - Aluminium oxide is insoluble in water.
- Reduces energy use and cost.
Why must the inert graphite electrodes
be replaced regularly when aluminium is
being extracted from its ore?
The oxygen produced at the anode
reacts with carbon in the electrode
forming carbon dioxide meaning carbon
is lost from the anode.
When would oxygen not be produced at
the anode during the electrolysis of an
aqueous ionic compound? What would
form instead?
When halide ions are present (chloride,
bromide or iodide ions). A halogen would
form (chlorine, bromine or iodine).
Write the balanced half equation for the
formation of oxygen from hydroxide ions
at the anode
4OH-→ 2H2O +O2+ 4e-
Describe how to carry out electrolysis on
an aqueous salt solution
- Pour the salt solution into a beaker.
- Insert 2 graphite electrodes and connect to a power supply.
- Fill 2 test tubes with salt solution and place over the
electrodes to collect any gas produced. - Turn on the power supply, ensuring the electrodes don’t
touch. - Turn off power and test gases.
What is a hydrocarbon?
A compound made up of only hydrogen
and carbon atoms.
‘Crude oil is the main source of ______’
‘Crude oil is the main source of Hydrocarbons’
What is crude oil a feedstock for?
The petrochemical industry
Is crude oil finite or infinite?
Finite
Why is modern life dependent on
hydrocarbons?
Hydrocarbons are a source of fuel which
is relied on heavily for modern life.
What is a homologous series?
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.
What is the general formula for the
alkane homologous series?
CnH2n+2
What is a fraction of crude oil?
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.
Why can crude oil be separated by
fractional distillation?
Because the different hydrocarbons have
different boiling points so condense at
different temperatures.
Describe the fractional distillation of
crude oil
- 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.
Do the longest hydrocarbons leave the
fractionating column at the top or
bottom?
Bottom
Which forces must be overcome for
alkanes to turn from liquid to gas? What
other bond is found in alkane molecules?
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.
Why do different alkanes have different
boiling points?
- Longer hydrocarbons have stronger
intermolecular forces. - More energy is required to overcome the stronger
forces. - Longer hydrocarbons have higher boiling points.
What is meant by the term empirical
formula?
The simplest whole number ratio of
atoms of each element in a compound.
What is the empirical formula of C4H10?
C2H5
What is a covalent bond?
A bond formed from a shared pair of
electrons between atoms.
What are the limitations of using dot and
cross diagrams to represent covalent
compounds?
- Don’t show the 3D arrangement of
atoms in space. - Doesn’t show the size of atoms
relative to one another.
What are the limitations of using 3D
diagrams to represent covalent
compounds?
- They are not show to scale.
- Don’t show how the bond formed.
- Don’t show the shared pair of
electrons.
Which is stronger: covalent bonds or
intermolecular forces?
Covalent bonds
Why do alkanes have low melting and
boiling points?
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.
What is cracking?
Breaking long chain hydrocarbon
molecules into smaller hydrocarbons.
What are the products of cracking?
Alkanes and alkenes
Alkenes are a different homologous
series containing a carbon to carbon
double bond.
Hexane is cracked to form butane and
ethene. Write a word and symbol
equation for this reaction.
hexane → butane + ethene
C6H14 → C4H10 + C2H4
Describe what happens during cracking
An alkane is heated. The vapours pass
over a catalyst and the covalent bonds
break and reform.
Why is cracking important?
- 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.
Alkanes are saturated hydrocarbons.
Explain what this means
Hydrocarbon - contains only hydrogen and
carbon.
Saturated - carbon atoms are all joined by
single bonds.
What is an alkene? Include the general
formula and functional group
An unsaturated hydrocarbon.
General formula: C
n
H2n
Functional group: C=C
Give examples of molecules that alkenes
react with in an addition reaction
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.
What are the general formula and
functional group of an alcohol?
General formula: Cn
H2n+1OH
Functional group: OH
What are the common reactions of
alcohols?
- Complete combustion, producing
water and carbon dioxide. - Oxidation to produce carboxylic acids
(needs an oxidation agent).
What are the general formula and
functional group of a carboxylic acid?
General formula: Cn H2n+1COOH
Functional group: COOH
What do carboxylic acids react with?
- Metals (forms salt and hydrogen).
- Bases (forms salt and water).
- Carbonates (forms salt, water and
carbon dioxide).
Why do members of a homologous
series react similarly?
Because they all contain the same
functional groups.
Predict the formula of the products when
pentane is completely combusted
H2O and CO2
