1.structures and bonding 2.structures and properties 3.how … · 2016-11-17 · chapter...
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C2 exam questions
1. Structures and bonding2. Structures and properties3. How much?4. Rates and energy5. Salts and electrolysis
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Chapter 1- structures and bonding
1. What is a compound?2. How can you observe if a chemical reaction has occurred or not?3. What part of an atom is involved in bonding?4. How many electrons can the first energy level/shell hold?5. How many electrons can the second energy level/shell hold?6. If an atom gains electrons, what does it become?7. If an atom loses electrons, what does it become?8. What is the overall charge of an ionic compound?9. How are the atoms in a metal held together?10. What is metallic bonding?11. Describe ionic bonding.12. The atoms in group 1 form +1/+ ions. What to the atoms in group 2, 6
and 7 form?13. Metals for m___________ ions and non-metals form __________
ions14. What is covalent bonding- describe it in detail.
1. Two or more elements chemically bonded together2. bubbles/fizzing, colour change, temperature change or a precipitate (solid) is formed3. electrons
4. Two 5. Eight
6. A negative ion.An ion is a CHARGED ATOM BECAUSE IT HAS EITHER LOST OR GAINED ELECTRONS7. A positive ion8. It is zero!9. The metallic bond is the force of attraction
between these free electrons and metal ions.10. The metal atom loses its outer shell electrons to become a positive ion. The force of attraction between the electrons (neg) and the positive ions.
11. Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions (because the donate their electron to the non-metal atom); non-metals form negative ions (because they gain an electron from the metal atom). So now both the metal atom and the non-metal atom are ions as they have less/more electrons than they normally do. Ionic bonds are the electrostatic forces of attraction between oppositely charged ions.
12. Group 2 = + 2 ionsGroup 6 = -2 ions (it is easier to gain two than lose 6)Group 7= -1 ions (gain one more to get a full outer shellGroup 8= do not form ions as they have a full outer shell
13. Metals form positive ions (lost electrons) and non-metals form negative ions (gain electrons)14. Shared pair of electrons (in the exam you must say all of this statement to gain two marks).
It occurs between two non-metals to form a covalent molecule. It is their outer electrons that are shared.
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proton + (1)
neutron 1
electron - (1)
2.8.3
24
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electron -(1)
1 0
proton +(1)
protons
electrons
protons
neutrons
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4
9
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sodium........ positive or +
chloride... negative or –
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positive
any reference to loss of electrons
for 1 mark
reference to charge being +2 (in (a)) or to loss of 2
electrons (in (b))
for 1 mark
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covalent bonds
any reference to shared electrons
gains 1 mark
but idea that bond is shared pair of
electrons
gains 2 marks
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element
compound
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an / one electron from the sodium atom
is lost / transferred to form a sodium ion
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because oppositely charged ions attract each
other
or
because chloride ions are negative and sodium
ions are positive
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13
14
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4
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nucleus
it has 2 more neutrons or converse
or
O-16 has 8 neutrons (1 mark)
O-18 has 10 neutrons (1 mark)
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because ammonia is made of small molecules
/ simple
molecules / simple molecular structures
1
and so there are weak forces between the
molecules
1
or
and so the intermolecular forces are weak
incomplete answers that link only size of
molecule or strength of intermolecular forces
with boiling point only gain 1 mark
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can be from diagram chlorine (2.8).7.
accept chlorine needs one more electron
1
can be from diagram shares a pair of electrons
1
shared pair of electrons is a covalent bond
do not accept ionic bond
1
can be from diagram and appropriately annotated sodium (2.8). 1.
and chlorine (2.8).7
1
sodium loses one electron and chlorine gains one electron
1
Na+ and Cl– formed
1
bond formed between oppositely charged ions or ionic bond
is formed
do not accept covalent bond
1
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same element
different number of neutrons
same number of protons and electrons
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4 mark question
• the layers / atoms can slide over each
other
• because there are only weak /
intermolecular forces (of
attraction) / bonds between layers
• graphite conducts electricity because the
electrons are
delocalised or electrons free
• this is because each carbon / atom is
joined / bonded to
three other carbon / atoms or each carbon
forms 3 bonds /
one electron on each carbon is not used for
bonding
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in pure copper the atoms are arranged in layers
accept a correct diagram
1
therefore copper is soft because copper atoms can slide over each
other
1
in bronze the tin atoms disrupt / distort the structure
accept a correct diagram
1
therefore bronze is harder than copper because the metal atoms
cannot slide over each other
1
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Carbon dioxide
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4
A
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because nano-sized particles are smaller than
normal sized particles
may cause harm when they are inside the
body
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the sodium atom loses / transfers an / one
electron
1
the chlorine atom gain(s) this / an / one
electron
1
involves electrons in the outer energy levels /
shells of
both the sodium atom and the chlorine atom
1
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sodium chloride has a giant structure / lattice
of oppositely
charged ions / positive and negative ions
1
the electrostatic forces of attraction / bonds
between ions
are strong
1
therefore sodium chloride has a high melting
point because a
large amount of energy is needed to make the
ions mobile
1
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increase (owtte) or gets hotter
ignore gives out heat / takes in heat
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CH4
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4 mark question
any four points from:
• high melting point owtte
ignore boiling point
• many or all atoms joined together
• each silicon (atom) joined to four oxygen (atoms) or
each oxygen joined to two silicon
• covalent (bonds)
• many bonds would need to be broken
• strong bonds
allow hard to break bonds
• lot of energy / heat needed to break bonds
allow high temperature needed to break bonds
• giant / macromolecular / lattice / diamond structure
• unreactive
allow doesn’t react with materials within furnace = 1 mark
• rigid / hard structure
• no free electrons
• poor conductor of heat
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2.8.3 on diagram as Xs / dots
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any two from:
• electrons in highest energy level or
electrons in outer shell
• electrons are delocalised or sea of
electrons
• electrons are free or electrons move
around / flow
• electrons carry charge / current
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H2 + Cl2 → 2HCl
MgCl2
because magnesium chloride is made of ions
or is ionic
accept there are strong forces of attraction
between the ions / particles in MgCl2 or strong
electrostatic attractions
accept more energy to separate particles in
MgCl2
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answers apply to:
accept diagrams and/or descriptions
carbon dioxide CO2
ammonia NH3
methane CH4
water H2O
*outer electronic structure of one atom correct or needs
correct number of electrons to complete outer shell
1
*outer electronic structure of other atom correct or needs
correct number of electrons to complete outer shell
1
*one shared pair of electrons (as one covalent bond)
use of ions or reference to ionic bonding negates this mark
1
*outer electronic structure of compound correct or each atom now
has a full outer shell/noble gas electron structure
1
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5 mark question
calcium atom loses two electrons
accept diagrams with correct labelling
1
(each) fluorine atom gains one electron
accept two electrons transfer from a calcium atom to the
two fluorine atoms for these first two marks
1
forming full (outer) shells of electrons
accept forming full (outer) energy levels or noble gas
electronic structures
1
giving the ions Ca2+ and F-
1
attraction between ions of opposite charges
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any (must be named)
F2
–/F–
covalent
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electrons
covalent
made of small molecules:
usually gas or liquid ) dependent on
have low melting points ) having first
have low boiling points ) point above
forces between molecules are weak
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C16 H34
electron
gains 1 mark
but shared electrons
gains 2 marks
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Group 2 / Alkaline Earth Metals
MgCl2/Mg2+ (Cl–)2
(or equation with correct answer)
for 1 mark
ionic / electrovalent
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covalent/description of covalent
forces/bonds between the molecules/particles
(not atoms) are weak
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some electrons from outer shells
(some electrons) free to move/mobile
through whole structure/between atoms/sea
of electrons
hold atoms together
for 1 mark each
or positive ions in a sea of electrons (owtte)
2 marks
atoms in regular structure/layers
giant structure
close packed
credit diagrams – look for labels
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electrons,
free to move
layers/atoms can slide over each other
free electrons hold atoms strongly
together/strong forces of attraction/bonds
(between atoms)/tight packing of atoms
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made of layers
of carbon atoms
weak forces of attraction between layers
(owtte) / weak
vertical bonds i.e.
candidate refers to the diagram
layers can slide over each other
layers peel off
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because there are electrons
which are free (to move)
reason for free electrons / each carbon atom
has 3 covalent bonds
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8 electrons in outer shell
accept anywhere in outer shell
accept dots or crosses
1
negative sign outside bracket
1
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(metal) atom / ion
electron
free electrons or electrons move
1
(allow metal) atoms / ions to slide over each
other
OR
bonding non - directional for 2 marks
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any two from
• large numbers of covalent bonds
allow giant lattice / structure
• between atoms
do not accept between molecules
• (covalent) bonds strong
accept need much energy to break
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lithium + water � hydrogen + lithium hydroxide
any three from:
one / the carbon (atom)
reject molecules once
four hydrogen (atoms)
shape / properties neutral
CH4
hydrocarbon
saturated / single bond
covalent bond / shared electrons
alkane
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1
weak forces
accept weak bonds
1
between molecules / intermolecular
reject intramolecular
1
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Chapter 2- structures and properties
1. Describe how ionic compounds form giant ionic lattices.2. Why do ionic substances conduct electricity when moltenor in
solution but not when solid?3. What are the two types of covalent structures?4. Describe simple covalent molecules 5. Describe giant covalent structures6. Describe giant metallic structures7. What is a polymer?8. How are polymers formed?9. What is the difference between thermosoftening and
thermosetting polymers?10. What is nanoscience?11. What is a nanoparticle?12. What are the advantages and disadvantages of nanoscience?
1. bonding: between a metal and a non-metal which lose and gain electrons respectively to form an ionic compound. Held together by strong electrostatic forces of attraction between positive ions and negative ions. Structure: forms a regular structure known as a giant ionic lattice.
2. Because it is only when they are molten or in solution do they have free electrons, therefore can carry charge and conduct electricity4. Covalent bonding: shared pair of electrons Simple covalent structure properties:a) DON’T CONDUCT ELECTRICITY: no free electrons and no
ions so they don't conduct electricity.b) LOW MELTING AND BOILING POINTS: This is because the
weak intermolecular forces break down easily.
Hydrogen, ammonia, methane and water are also simple molecules with
covalent bonds. All have very strong bonds between the atoms, but much
weaker forces holding the molecules together. When one of these
substances melts or boils, it is these weak 'intermolecular forces' that break,
not the strong covalent bonds. Simple molecular substances are gases,
liquids or solids with low melting and boiling points.
3. Simple molecules and giant covalent structures.Simple molecules consist of a small number of atoms joined by covalent bonds. For example, water and carbon dioxide exist as simple molecules The covalent bonds joining the atoms together in a simple molecule are strong. However, the intermolecular forces between simple molecules are weak.
5. Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds. The atoms are usually arranged into giant regular lattices - extremely strong structures because of the many bonds involved. The graphic shows the molecular structure of diamond and graphite: two allotropes of carbon, and of silica (silicon dioxide).PROPERTIES: a) Very high melting and boiling points: because a lot of strong
covalent bondsb) ONLY SOME CONDUCT ELECTRICITY- e.g. graphite- because
it has free electrons.Examples: diamond, graphite, silicon dioxide, Buckminsterfullerene
6. Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile.
7. Many monomers bonded together8. Polymers have properties which depend on the chemicals they are made from, and the conditions in which they are made. For example, poly(ethene) can be low-density or high-density depending upon the catalyst and reaction condition used to make it
9. Thermosoftening polymers soften when heated and can be shaped when hot. The shape will harden when it is cooled, but can be reshaped when heated up again. Poly(ethene) is a thermosoftening polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material. Thermosetting polymers have different properties to thermosoftening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.
10. A nanometre, 1 nm, is one billionth of a metre (or a millionth of a millimetre). Nanoparticles range in size from about 100 nm down to about 1 nm. They are typically the size of small molecules, and far too small to see with a microscope.Properties and uses of nanoparticlesNanoparticles have a very large surface area compared with their volume, so they are often able to react very quickly. This makes them useful as catalysts to speed up reactions. They can, for example, be used in self-cleaning ovens and windows.Nanoparticles also have different properties to the same substance in normal-sized pieces. For example, titanium dioxide is a white solid used in house paint and certain sweet-coated chocolates. Titanium dioxide nanoparticles are so small that they do not reflect visible light, so cannot be seen. They are used in sun screens to block harmful ultraviolet light without appearing white on the skin.
11. Very tiny particles/nanoparticles range in size from about 100 nm down to about 1 nm.12. Nanoparticles are used in products that are currently available.sports equipment: nanoparticles are added to materials to make them stronger whilst often being lighter. They have been used in tennis rackets, golf clubs and shoesclothing: silver nanoparticles have been added to socks. This stops them from absorbing the smell of sweaty feet as the nanoparticles have antibacterial propertieshealthcare: nanoparticles are used in sunscreens. They offer protection and can be rubbed in so there are no white marks.Harmful effectsThere are some concerns that nanoparticles may be toxic to people. They may be able to enter the brain from the bloodstream and cause harm. Some people think more tests should take place before nanoparticles of a material are used on a wider scale.
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layers / lattice / giant structure / regular
pattern of atoms (diagram)
allow layers / lattice / giant structure / regular
pattern of ions
do not accept particles
1
outer (shell) electrons
accept valence electrons
1
(free to) move (through whole structure)
accept delocalised / mobile / free
1
3 mark question
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covalent
four
hard
three
soft
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electron
any three from
• (is a) giant structure/lattice structure
• crystalline / hard
accept just 'crystals(s)’
• high melting point / solid
• high boiling point
• conductor (of electricity) when dissolved
in water
or conductor (of electricity) when ions are free
to move
• conductor (of electricity) when molten
• soluble in water
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4 mark question
heat
1
then mould / extrude into a new shape /
object
1
plastic made of polymer chains that can move
(when heated)
1
because plastic / polymer has weak
intermolecular forces
1
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hard
carbon dioxide
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because nano-sized particles are smaller than
normal-sized particles
1
may cause harm when they are inside the
body
any two from:
• (new) computers
• (new) catalysts
• (new) coatings
• highly selective sensors
• stronger / lighter
construction materials
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small or few atoms thick or size in the range 1–
100 nanometres
sensible idea of passing through smaller gaps owtte
eg can pass through skin / pores / cells or more easily absorbed
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there are delocalised electrons / free electrons
/ electrons
which move within the aluminium / metallic
structure
1
therefore these electrons are able to carry the
current / charge
1
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any two from:
• good at absorbing UV light / radiation
• spread more easily
• cover better
• save money / use less
• transparent
• less chance of getting skin cancer or
stops skin cancer
toxic to (cells / specific cells)
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1-100 nm in size
or
a few (hundred) atoms in size
accept very / really small / tiny
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C3H8
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reduce wear of metal ie don’t get damaged
or other sensible answer
or
stop / reduce friction
accept stop metal heating up
accept move more smoothly
ignore make it slippery / rub more smoothly
or
prevent seizing
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layers (of atoms)
1
can slide / slip over each other
allow slip off
or
weak forces of attraction / weak bonds (between layers)
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intermolecular forces / bonds
1
are weak
(covalent) bonds are weak = 0
or
forces between molecules or bonds
between molecules (1)
(attractive) forces are weak = 1
are weak (1)
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to check the safety of the perfume (owtte)
accept references to possible harmful /
dangerous effects of perfume or possible
reactions on skin
eg to show it does not damage skin / cause
cancer etc.
allow to see what it smells like on the skin
allow so the company do not have to test on
animals
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fertilisers
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nitrogen
accept N or N2
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Chapter 3- How much?1. What is the mass of a proton, neutron and electron?
2. What is the charge of a proton, neutron and electron?
3. What is the mass number and atomic number of Na?
4. What is the difference between relative atomic mass (Ar) and relative formula mass (Mr)
5. What is the percentage of magnesium in magnesium oxide. The Ar of Magnesium is 24 and the Ar of O is 16.
6. What is the difference between empirical formula and molecular formula of a compound?
7. What is a mole?
8. How can you calculate moles?
9. What is a reversible reaction? Give an example.
10. What are food additives and how can we identify them?
11. Describe methods of instrumental analysis to detect substances in a sample mixture
1. proton= 1, neutron= 1, electron= 1/1849 (0.0005)2. proton= +, neutron= 0, electron= -!
3. Na- mass number= 23, atomic/proton number= 11 4. Relative atomic mass is of the element (Ar) e.g. Na, the Ar= 23, Cl, the Ar= 35.5. Relative formula mass (Mr) of NaCl is (23+ 35.5= 58.5)
5.
Mr of MgO= (24+16)= 40Ar of Mg is 24.Percentage of magnesium in magnesium oxide= 24/40= 60%
6. Empirical formula is the simplest form of the molecular formula. For example,
Molecular formula: C6H12
Empirical formula: CH2 (divided by 6)
7. One mole is a substance contains 6.02 x 1023
This number is known as the Avogadro constant.9. In a reversible reaction, the products can react to produce the original reactants again.For example,
ammonium chloride ammonia + hydrogen chloride
The equation shows that ammonium chloride (a white solid) can break down to form ammonia and hydrogen chloride. It also shows that ammonia and hydrogen chloride (colourless gases) can react to form ammonium chloride again.
10. A food additive is a substance added to food to make it look or taste better. The food additives that are legal to use in Europe are given E numbers. Paper chromatography can be used to detect substances in food. It works because some compounds dissolve better than others in particular solvents and so they travel up the paper differently and can therefore be compared. Instrumental analysis is faster and more accurate than paper chromatography.
11. Instrumental analysis- Many substances are made up of a mixture of compounds.- So scientists have thought of a way called gas-chromatography and
mass spectrometry to separate the substances.- First they use gas chromatography to separate substances (like paper
chromatography but the substances need to be vaporised (turned into gas)
- Then pass the separated substances through a mass spectrometer so the elements and compounds can be identified. The pattern of peaks it produces will help you identify what the element or compound is.
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157
correct answer with or without working
(2 × 19 + 119) for 1 mark only
allow (119 + 19 =) 138 for 1 mark only
ignore units
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160 ignore units
(2 × 56) + (3 × 16) for 1 mark
70
700
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measure volume / mass of gas produced (1)
in a certain time period
or measure decrease in mass of flask and
contents at regular time intervals (1)
or time taken for the mass to decrease by
certain amount (1)
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349
RFM
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160
112
70
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neutralisation/acid base reaction
17 (tonnes)
give 80 (tonnes) (even if only in working)
for 1 mark each
320 (tonnes) or alternative method)
3 marks for correct answer
(if 17 and 80 not given allow 1 mark for correct
answer using their figures)
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correct named instrumental method
eg
atomic absorption spectroscopy / spectrometry
accept atomic / absorption spectroscopy
accept aas
or
mass spectrometry / spectroscopy
accept mass spec
or
infrared (spectrometry) / IR
or
ultraviolet / spectroscopy / UV
or
nuclear magnetic spectroscopy / nmr
or
gas-liquid chromatography / GLC
any one from:
• fast / quick or comment about speed
ignore lost
ignore human error
• small amount
accept operators do not need chemical skills
• sensitive / accurate / precise
ignore safe / easier to use
• ease of automation
• reliable / efficient
• can be left to run / continuous analysis
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144
accept TiCl4 = 190 for 1 mark
accept another correct step in calculation
eg 570/190 = 3 for 1 mark
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1000 × 1000 / 0.065
gains 1 mark
but
15384615g (accept answer rounded to
minimum of 2 sig. figures)
(accept answer with no units or correct units
but incorrect unit loses one mark)
(answer correctly worked out in kg is
acceptable)
gains 2 marks
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Empirical formula
4 mark question
C H O
0.60 0.15 0.40
12 1 16
= 0.05 = 0.15 = 0.025
2 6 1
C2H6O
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Chapter 4- Rates of reaction1. What do we mean by the rate of a chemical reaction?2. How can we measure the rate of a chemical reaction in the lab?3. What affects the rate of chemical reaction?4. What is the collision theory?5. How does surface area affect the rate of a chemical reaction?6. How does temperature affect the rate of a chemical reaction?7. How does a catalyst affect the rate of a chemical reaction?8. How does concentration affect the rate of a chemical reaction?9. What is the difference between an exothermic and endothermic
reaction?10. What happens in the energy transfers in a reversible reaction?11. How can we use the energy from exothermic reactions?12. How can we use the cooling effect of endothermic reactions?13. What are the advantages and disadvantages of each type of hand
warmer.
1. The phrase ‘rate of reaction’ means ‘how fast is the reaction’ or 'the speed of the reaction'.
2. It can be measured as the 'rate of formation of product' (e.g. collecting gaseous product in a syringe) or the 'rate of removal of reactant'. The speeds of reactions are very varied.
3. - Temperature- Surface area- Pressure - Concentration - Use of a catalyst
4. For a chemical reaction to occur, the reactant particles must collide. But collisions with too little energy do not produce a reaction.The particles must have enough energy for the collision to be successful in producing a reaction.The rate of reaction depends on the rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction.
5. Surface area:If a solid reactant is broken into small pieces or ground into a powder: - its surface area increases- more particles are exposed to the other reactant- there are more collisions- the rate of reaction increases
6. temperature:If the temperature is increased: - the reactant particles move more quickly- they have more kinetic energy- the particles collide more often, and more of the collisions result in a reaction- the rate of reaction increases
7. catalyst:A catalyst is a substance that can increase the rate of a reaction. The catalyst itself remains unchanged at the end of the reaction it catalyses. A catalyst speed up the rate of a chemical reaction by lowering the activation energy (the minimum amount of energy needed to start a chemical reaction).
8. concentration:If the concentration of a dissolved reactant is increased, or the pressure of a reacting gas is increased: the reactant particles become more crowdedthere is a greater chance of the particles collidingthe rate of reaction increases
9.Exothermic reactionsThese are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are:burningneutralisation reactions between acids and alkalisthe reaction between water and calcium oxideEndothermic reactionsThese are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are:electrolysisthe reaction between ethanoic acid and sodium carbonatethe thermal decomposition of calcium carbonate in a blast furnace
10. Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.The decomposition of ammonium chloride is a reversible reaction:ammonium chloride ammonia + hydrogen chlorideAmmonium chloride decomposes when it is heated, so the forward reaction is endothermic - energy must be transferred from the surroundings for it to happen. The backward reaction is exothermic -energy is transferred to the surroundings when it happens.
11. Exothermic reactions can be used for everyday purposes. For example, hand warmers and self-heating cans for drinks (such as coffee) use exothermic reactions.
12. Endothermic reactions can be used for everyday purposes. For example, certain sports injury cold packs use endothermic reactions.13. The disposable hand warmer lasts longer when activated than the
reusable warmer. However, it can only be used once. The opposite applies to the re-usable hand warmers.
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because this is an endothermic reaction
1
that takes in energy from the surroundings as
the ammonium
nitrate dissolves
1
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any two from:
• A has four colours(*)
• B has three colours(*)
(*) if first two bullets not stated
accept A has more colours (than B) or B has less colours (than
A) for 1 mark only
• A / B have two colours the same
• B has one different colour
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drinks / colours B and C are safe
1
drinks / colours A and D are not safe
1
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use of solvent / solution / water / any named solvent
1
separates / carries colour(s) / dye(s)
allow any idea of movement
eg runs / moves
1
match against Rf value / known chromatogram / similar pattern
or comparison to permitted additive / colour
removal of coloured additive from salmon does not gain any marks
ignore reasons for separation
maximum 2 if technique clearly doesn’t work
1
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any three from:
accept colour 3 is a mixture of colours 1 and 2 for 3 marks
• colour 1 is made up of only one colour / dye
• colour 2 is made up of only one colour / dye
• colour 3 is made up of two colours / dyes
or
more colours (than colours 1 and 2)
• colours 1, 2 and 3 are all different
• colour 1 is less dark than colour 2
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gives out
heat
chromium and aluminium oxide
chromium oxide
oxygen removed/gains electrons
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Chapter 5- salts and electrolysis
1. What is the difference between an acid and an alkali?2. What is the difference between an alkali and a base?3. Give examples of acidic products.4. Give examples of alkali products.5. Give an example of a substance that is neutral.6. What is a state symbol?7. How can we test the pH of a substance?8. What ions do all acids form when we add them to water?9. What ions do all alkalis form when we add them to water?10. Metal + acid � ______ + ________11. Acid + base/alkali � ___________ + _________12. What is electrolysis?13. How is aluminium obtained from aluminium oxide? Why is
cryolite used in the process?14. What is produced in the electrolysis of brine?15. Why do we electroplate objects?
1. Acids have a pH below 7 and alkalis have a pH above 72. Alkalis and bases both neutralise acids. If a base does dissolve in water, we call it an alkali.
3. Vinegar (ethanoic acid)Fizzy drinks (carbonic acids)Tea (tannic acid)In the lab: sulphuric acid and hydrochloric acid
4. Drain cleanerBleach Sea water
5. Water
Symbol Meaning
(s) solid
(l) liquid
(g) gas
(aq) aqueous (dissolved in water)
7.Litmus paper:red litmus: stays red if acid, stays red is neutral, turns blue if alkali.Blue litmus: stays blue if alkali, stays blue if neutral, turns red is acidic
Universal indicator
pH meter (most accurate)
8. H + ions9. OH- ions
10. MASH
METAL+ ACID� SALT + HYDROGEN
11. ACID + BASE � SALT + WATER
12. Splitting of a compound using electricity13. By electrolysis:• aluminium oxide (bauxite) is melted / made liquid• aluminium ions are attracted to the negative electrode• at the negative electrode aluminium is formed oraluminium ions gain electrons• oxide ions are attracted to the positive electrode• oxygen is formed at the positive electrode or oxideions lose electrons
• the oxygen reacts with carbon to make carbon dioxide orcarbon dioxide formed at positive electrode.
Aluminium oxide has a very high melting point (over 2,000°C), so it would be expensive to melt it. Instead, it is dissolved in molten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
14.Brine is a solution of sodium chloride (NaCl) and water (H2O). The process of electrolysis involves using an electric current to bring about a chemical change and make new chemicals. The electrolysisof brine is a large-scale process used to manufacture chlorinefrom salt. Two other useful chemicals are obtained during the process, sodium hydroxide (NaOH) and hydrogen (H2).It is important that the chlorine and sodium hydroxide produced in the process are separated they react when they come into contact with each other. Chorine: disinfectant (swimming pools)Sodium hydroxide: manufacture of paperHydrogen: manufacture of hydrochloric acid and potential as a pollution-free fuel
15.Electrolysis is used to electroplate objects. This is useful for coating a cheaper metal with a more expensive one, such as copper or silver.How it worksThe negative electrode should be the object that is to be electroplatedThe positive electrode should be the metal that you want to coat the object withThe electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfateHere are two examples.Electroplating with silverThe object to be plated, such as a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.
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hydroxide
nitric
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Mg MgSO4 H2
to remove the (excess) magnesium
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breakdown / decomposition / splits into elements (1)
using electricity (1)
lead bromide melted / free ions
(+) bromine
(–) lead
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substance brokendown / separates / splits into elements
by electric current / electricity
ions free to move e.g. when molten / in solution
allow 1 mark for “a substance that conducts electricity”
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hydrogen (ion)
H+
neutralisation
NaOH HCl NaCl H2O
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Nitric acid
Potassium hydroxide water
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6 mark question
examples of the chemistry points made in the response
• aluminium oxide is melted / made liquid
• aluminium ions are attracted to the negative
electrode
• at the negative electrode aluminium is formed or
aluminium ions gain electrons
• oxide ions are attracted to the positive electrode
• oxygen is formed at the positive electrode or oxide
ions lose electrons
• the oxygen reacts with carbon to make carbon
dioxide or
carbon dioxide formed at positive electrode.
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6 mark question
examples of the chemistry points made in the
response
• aluminium oxide is melted / made liquid
• aluminium ions are attracted to the
negative electrode
• at the negative electrode aluminium is
formed or
aluminium ions gain electrons
• oxide ions are attracted to the positive
electrode
• oxygen is formed at the positive
electrode or oxide
ions lose electrons
• the oxygen reacts with carbon to make
carbon dioxide or
carbon dioxide formed at positive electrode.
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H2SO4 or red (acidic) pH < 7
accept names of compounds
accept correct use of acidic
1
NaOH or purple (alkaline) pH > 7
alkaline and neutral without any mention of
pH for 1 mark only
1
NaCl or green (neutral) pH 7
ignore high or low pH
1
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nitric (acid)
accept HN03
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sodium hydroxide / caustic soda / NAOH
negative ions move to the positive electrode etc.
/because it is negative
/opposite charges attract
loss of electrons
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chloride ions lose electrons to form chlorine
Cl– – e– → Cl
1
hydrogen ions gain electrons to form hydrogen
H+ + e– → H
1
sodium hydroxide remains in solution
Na + and OH– remain in solution to form sodium hydroxide
1
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bulb lights up
bubbles / fizz / gas or chlorine given off
in solid, ions
1
are not free to move / (charged) particles
cannot move or converse
atoms / electrons cannot move worth 0 marks
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breakdown / decomposition / splitting up (1)
not separation
by using electricity (1)
gas A = chlorine / oxygen
1
deposit B = copper
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any one from:
• manufacturer of chlorine / sodium
hydroxide / hydrogen / sodium
• electroplating of steel / reference to
plating
not galvanising
• extraction of aluminium / metal
reactivity series specified
• purification of copper
not making copper
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H+(aq) + OH– (aq) → H2O(l) or
H3O+(aq) + OH–(aq) → H2O(l)
nitric acid and ammonia (solution)