❖ State why two isotopes of have the same chemical properties
same number of electrons same number of outer shell
electrons.
❖ Explain why increasing the temperature increases the rate of
reaction.
particles move faster and have more energy
more collisions per second so greater collision rate. frequency of collision
increase
more of the (colliding) molecules / particles have sufficient energy (activation
energy) to react / more of the collisions have sufficient energy (activation
energy) to react
❖ Explain why decreasing the temperature decrease the rate of reaction.
particles have less energy and move slower.
fewer collisions per second so smaller rate of collision. frequency of
collisions decrease.
fewer portion of particles have sufficient energy to react. fewer portion of
particles have energy greater than equal to activation energy.
Give two properties of aluminium that make it suitable for use in overhead
electricity cables.
ductile / malleable
1
conducts (electricity)
low density
protective oxide layer
What is a saturated solution?
a solution that can dissolve no more solute
at the particular/specific/any given temperature
Why temperature doesn’t increase at boiling or melting?
energy is used to break bonds / overcome attraction
between molecules
Why is cotton wool used in this
experiment?
to allow gas to escape.
to prevent loss of acid.
Why does the graph levels off in
this experiment?
reaction finished
all the reactant is used up.
Describe the structure and bonding of metals
(lattice of) positive ions / cations
(delocalised / sea of) electrons
attraction / attract between positive and negative
Why an atom has overall charge 0?
Same number of protons and electrons
Why an ions has a charge of X+?
X more protons than electrons
Why an ions has a charge of X-?
2
X less protons than electrons
Why using lumps of solids decreases rate of reaction?
(lumps have) smaller surface area OR powder has larger surface area
(lumps have) fewer collisions per unit time / less collision frequency OR
powder has more collisions per unit time / more collision frequency
What is the observation when sodium or any metal react with water?
fizz / bubbles
moves
floats
melts / forms a ball
gets smaller / disappears
Why do gases diffuse?
due to random motion of molecules / particles from the region of higher
concentration to lower concentration.
Which element is found in clean dry air?
Argon
Which compound is found in clean dry air?
Carbon dioxide
Why a solid is added in excess to a acid?
to make sure all the acid reacts
If excess calcium metal is added to dilute hydrochloric acid instead of excess
zinc powder, pure calcium chloride crystals do not form. Explain why
Ca will also react with water
Describe how to check if all the water has been given off from a hydrated salt?
heat again and weigh again and repeat
until mass is constant
Why a reaction is exothermic?
Chemistry past paper Common Questions By Vasumitra Gajbhiye
3
more energy released (in bond formation) than used/taken in (in bond breaking)
Which process is used to separate the products of hydrolysis of long chain
protein.
Chromatography.
Describe how oxides of nitrogen form in a car engine.
nitrogen and oxygen (from the air) react (in the engine)
(due to) high temperatures
Which catalyst is used in catalytic converter?
Platinum / Rohidum
What is catalyst?
(a substance which) increases the rate of a reaction
remains unchanged/ unaffected/ unused or without changing mass
Explain, in terms of particles, why does the rate of reaction decrease as the time
increase?
• concentration of particles decreases
• lower rate of collisions of particles
What are the effects of nitrogen dioxide?
• Respiratory problems
• Acid rain
What is meant by the term redox?
reduction and oxidation occurs simultaneously.
Describe how solid sodium conducts electricity.
electrons move/mobile/flow
4
Explain why sodium chloride conducts electricity when molten.
Ions move/are mobile/flow
What happen to rate of reaction when surface area is increased?
Rate of reaction increase. More collisions per unit time.
When group 1 element react with cold water what is formed?
metal hydroxide
Why a substance is oxidising agent?
It has gain electrons hence reduced.
Why a substance is reducing agent?
It has lost electrons hence oxidised.
What is the colour of bromine?
Orange – Brown liquid
State a pH number that indicates the presence of a strong alkali.
14
State how the energy profile diagram shows this is an exothermic reaction.
energy of products is lower than energy of reactants
5
Describe metallic bonding.
Lattice of (named) metal ions in sea of delocalised electrons
attraction between positive (named metal) ions
and negative electrons
Explain why nitrogen does not conduct electricity.
No mobile electrons OR no ions
Explain, in terms of attractive forces between particles, why nitrogen has a low
melting point.
Weak forces of attraction between molecules
Why ionic compound don’t conduct electricity when solid but conduct when
molten? Explain in terms of structure and bonding.
ions
(ions) are fixed (in a lattice)
ions are mobile
Explain why molten ionic compounds can conduct electricity.
ions can move through the structure
Describe what can be done to any ionic compound to allow it to conduct
electricity.
dissolve it in water
Explain, in terms of attractive forces between particles, why (any covalent
compound) has a low melting point.
forces of attraction between molecules
AND
are weak / need a small amount of energy to break
6
Why ionic compounds have high melting point?
strong forces of attraction (between oppositely charged ions)
Explain why covalent compounds are non-conductors of electricity?
no moving or flowing or mobile charged particles or ions or electrons
Which type of bond is present in carbon dioxide?
Double covalent bond.
What is ionic bond?
oppositely charged ions
(ions) are attracted
Give physical properties of ionic compounds.
physical constants: high boiling point / melting point
conductivity: conduct (electricity) when aqueous or conduct (electricity)
when molten
solubility: soluble in water
Explain, in terms of particles, why brass is harder than pure zinc.
exists as layers
(alloy) contains different sized (copper) atoms
makes it more difficult for layers (of atoms) to slide over each slip/shift other
State the term used to describe the structure of diamond.
Giant covalent
CONTACT PROCESS
What are the steps in contact process
stage 1 Molten sulfur is burned in air to produce sulfur dioxide gas.
stage 2 Sulfur dioxide is reacted with oxygen to form sulfur trioxide.
stage 3 Sulfur trioxide is combined with concentrated sulfuric acid to form
7
oleum, H2S2O7.
stage 4 Oleum is added to water to form sulfuric acid
CRYSTALLISATION
Why is the residue rinsed after filtration?
To make sure all the filtrate goes through. no filtrate left behind in the filter paper.
(This will increase yield). To wash-out / dissolve / remove salt
How to obtain pure crystals from a filtrate?
evaporation
the starting of crystallisation
drying the crystals
Why the mass of crystals obtained was less than theoretical mass?
some salt remains in solution / some salts does not form crystals
OR
some of the crystals decomposed
OR
some crystals lost in transfer
State two observations that would indicate that some salts are in excess in step
1.
no more bubbling / fizzing / effervescence
solid or powder stops dissolving/ solid remains.
What evidence would show that the solution was saturated?
when crystals form on a glass rod withdrawn from solution / on a sample of
solution placed on microscope slide etc.
Why should the aqueous saturated salt not be heated to dryness?
(heating to dryness) would remove water of crystallisation to form anhydrous
powder.
Suggest why more crystals of magnesium sulfate appear on cooling.
8
solubility (of MgSO4 / solid) decreases (as temperature decreases)
ELECTROLYSIS
State what is meant by the term electrolysis
breakdown by (the passage of) electricity
of an ionic compound in molten or aqueous (state)
State and explain what would happen to the mass of the negative electrode
during the electrolysis of concentrated copper(II) chloride.
increases
(solid) copper deposited
What happens to the colour of solution during electrolysis of coloured
compound?
colour fades / becomes pale(r) / becomes colourless / becomes lighter
named anions (ions) removed (from solution)
Give one reason why metal spoons are electroplated with silver.
Improves appearance
prevent / resist corrosion / oxidation
antibacterial
When a gas is formed what is observed?
fizzing/ bubbles/ effervescence
Explain why the ionic compound needs to be aqueous or molten.
So that ions are mobile and can move
Explain why inert electrodes are used.
they do not react
EQUILIBRIUM
9
State features of equilibrium.
reaction is reversible
rate of forward reaction = rate of reverse reaction.
concentrations of reactants and products are constant
Explain, in terms of particles, why a high temperature increases the rate of
reaction.
particles have more energy (E)
rate of collisions increase/ more collisions per unit time(per second)
a higher proportion of particles have energy greater than activation energy
(E > EA)
If forward reaction is exothermic what happens to the amount of product when
temperature is increased?
less amount of product
equilibrium moves left and because forward reaction is exothermic
If a product is removed from the RHS what happens to the mass of
other product?
more product
equilibrium moves right to replace (named product which is removed, e.g.
water)
If the pressure is increased, the yield of ammonia increases. Explain why, in
terms of equilibrium.
equilibrium shifts / moves in forwards direction
fewer molecules / moles (of gas) on RHS
Suggest why the position of equilibrium does not change.
same number of gas moles on both sides of the equilibrium / same number of
gas molecules on both sides of the equilibrium
ETHANOIC ACID MAKING
10
Ethanol will react with hot aqueous potassium manganate(VII) to form ethanoic
acid. State the other condition needed for this reaction to take place.
presence of an acid
ETHANOL MAKING
How ethanol can be made by fermentation.
C6H12O6 → 2CO2 + 2C2 H5 OH
anaerobic respiration
of yeast
at 37°C
using aqueous glucose
What type of reaction is it when ethene is converted to ethanol?
Addition of steam
What are the reagents and conditions required for conversion of ethene to
ethanol?
stem
catalyst
pressure
temperature
What are the two products of fermentation?
Carbon dioxide and ethanol
EXTRACTION
Give two reasons for using coke in the blast furnace.
(coke)
releases heat (when it reacts with oxygen or reacts in air)
OR (acts as a) fuel
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OR increases temperature (in the furnace) / heats (the furnace)
OR source of energy
(coke or carbon monoxide)
reduces iron oxide
OR is a reducing agent
OR converts iron oxide to iron / removes oxygen from iron oxide
(coke)
reacts with oxygen to form carbon monoxide
OR reacts with carbon dioxide to form carbon monoxide
Name two waste gases that leave the blast furnace during extraction of iron.
Nitrogen
Carbon dioxide
Suggest one benefit to the environment of reducing the operating temperature of
electrolysis of aluminium oxide.
less co2 emission
Explain why the anodes need frequent replacement.
anodes or carbon / graphite react with oxygen / O2
(form) carbon dioxide
HARBER PROCESS
State one source of hydrogen for manufacture of ammonia. Methane
Explain why a lower temperature and a higher pressure are not used.
Lower temperature → rate of reaction slower
Higher pressure → expensive/ specialised equipment
12
ORGANIC CHEMISTRY
What is meant by unsaturated?
not all c-c bonds are single. contain at least one c=c bond.
What are the reagents and conditions required for conversion of a alkene
to alkane?
hydrogen
catalyst
high temperature.
State what is meant by the term functional group.
the atoms / group of atoms which give (any molecule its) chemical properties
If the number of carbon in the chain increase what happen to it’s boiling point?
boiling point increase
State are general characteristics of a homologous series.
same or similar chemical properties or reactions
same general formula
consecutive members differ by CH2
13
same functional group
common (allow similar) methods of preparation
physical properties vary in predictable manner / show trends / gradually
change
OR
example of a physical property variation i.e. melting point / boiling point /
volatility
Which process is used to make alkenes?
Cracking
Iron(II) sulfate can be converted to iron(III) sulfate by potassium
manganate(VII) at room temperature. What condition must be used for this
reaction to occur?
presence of acid
What happens to viscosity as we move up the fractionating column.
it decrease
What happens to flammability as we move up the fractionating column.
it increase
What difference in the molecules of gasoline and kerosene causes
differences in viscosity and flammability?
kerosene has molecules with a longer carbon chain
POLYMERS
How many molecules of water is formed when one ester link is formed?
1
14
Describe what is meant by the term addition reaction.
(only) one product is formed.
Give one condition needed when ethanoic acid reacts with the alcohol to make
this ester.
acid conc sulfuric acid / heat (catalyst)
Name a polyester?
Terylene/ PET
PROTECTING IRON
Explain how completely coating an iron object with a layer of zinc prevents
rusting
prevents water or / and oxygen reaching iron
Rusting of iron ships can be prevented by attaching zinc blocks to the hull of the
ship. Explain how this prevents rusting.
zinc more reactive (than iron)
15
zinc corrodes / oxidises / reacts in preference to iron
Explain how the magnesium blocks prevent iron from rusting
magnesium is more reactive than iron / steel ORA (1)
iron is not oxidised
OR
iron does not lose electrons
OR
magnesium loses electrons more easily than or in preference (to iron) ORA
OR
magnesium is oxidised more easily or reacts with oxygen more easily or
corrodes more easily or in preference (to iron)
SALT PREPARATION
What is meant by the term precipitate?
a solid
which forms when two solutions are mixed / reacted / added
What compounds can be used to make metal salts?
Metal oxide, metal carbonate, metal hydroxide
How precipitation is performed practically?
(add) water (to both salts)
dissolve both salts / make solutions
filter (lead(II) iodide)
wash (residue of lead(II) iodide) with water AND dry e.g. with filter paper /
description of washing and drying
How to make salt crystals from metal carbonate and acid?
add metal carbonate to sulfuric acid until
it stops dissolving or no more effervescence
filter excess metal carbonate
16
evaporation of filtrate to form dry crystals
State two observations when metal carbonate reacts with acid?
fizzing / effervescence
solid disappears / dissolves
Name the experimental technique used when salts are made by reacting a dilute
acid with an aqueous alkali.
Titration
TEST
Test for oxygen.
glowing splint
relight
Test for hydrogen.
Burning splint
squeaky pop
Test for sulfur dioxide.
acidified aqueous potassium manganate(VII)
purple to colourless
What is produced when iron(II) sulfate (or any other metal) react with ammonia?
Iron (II) hydroxide is formed (or any other metal hydroxide is formed)
17
TRANSITION & GROUP 1 ELEMENTS
What are the chemical properties of transition metals?
act as catalyst
variable oxidation states
Coloured compounds
What are the physical properties of transition metals?
malleable
good conductors of heat and electricity
high melting point
hard and strong/ tough
high density
What are the difference between physical properties of transition metals and
group 1 elements.
higher melting point
high density
hard
What are the difference between chemical properties of transition metals and
group 1 element.
act as catalyst
have variable oxidation states
form coloured compounds
What are the difference between physical properties of group 1 elements and
transition metals.
low melting point or low boiling point
soft
low density
18
State physical properties of Group I metals which are similar to those of
transition metals.
shiny / lustrous
conduct electricity
conduct heat
❖
❖
❖
❖
POLYESTER
19
❖
EQUAL 6
❖
❖
20
and reactant conc decrease.
Oxidation number
\
21
22
\
23