OCR AS Level Chemistry B
(Salters) Paper 2 Mark Scheme:
June 2025 | Latest 2025/2026
Edition for First-Time Exam
Success
,State Hess's Law - correct answers--The total enthalpy change of a reaction is
independent of the route taken.
What is meant by standard conditions? - correct answers--.Temp - 25 dc, 298K
.Pressure - 100kPa
.Conc - 1 mol / dm-3
.Standard state
What is meant by standard enthalpy change of neutralisation? - correct answers--The
enthalpy change when one mole of water is formed in a neutralisation reaction under
standard conditions (-57kj/mol for any strong acid + alkali)
Shape of a molecule with 4 bonding pairs of electrons and explain? - correct answers--
Tetrahedral, 109.5
Electrons arranged to minimise repulsion
Shape of a molecule with 2 bonding electron pairs? - correct answers--Linear , 180
Electrons arranged to minimise repulsion
Shape of molecule with 3 bonding electron pairs? - correct answers--Trigonal Planar,
120
Ideal gas equation? - correct answers--pv = nRt
(penis vagina = naughty rectum tickle)
What is a sub-shell? - correct answers--A group of orbitals of the same type within a
shell e.g the 2p subshell contains 3 p orbitals in the second shell
What is an atomic orbital? - correct answers--A region around the nucleus that can hold
up to 2 electrons with opposite spins
What is the empirical formula? - correct answers--The simplest whole number ratio of
atoms of each element in a compound
What is an aromatic compound? - correct answers--A compound that contains at least
one benzene ring
What is an aliphatic compound? - correct answers--An organic compound that does not
contain a benzene ring
What is an arene? - correct answers--An aromatic hydrocarbon.
,What is a structural isomer? - correct answers--Compounds with the same molecular
formula but different structural formula (may have alkyl group)
What is a benzene ring? - correct answers--Simplest aromatic hydrocarbon C6H6
General formula for cycloalkanes? - correct answers--CnH2n
Why don't alkanes mix with water? - correct answers--Alkanes contain non-polar
molecules but water contains polar molecules that attract each other and stop the
alkane from mixing
What is a heterogeneous catalyst? - correct answers--A catalyst in a different physical
state to the reactants
How do heterogeneous catalysts work? - correct answers--1)Reactant molecules bond
with catalyst surface = adsorption
2)Reactant bonds are broken, forming radicals (atoms with unpaired electrons)
3)Radicals get together to make new molecules
4)New molecules detach from catalyst - desorption and diffuses away
Why may a catalyst become poisoned? - correct answers--The poison molecule (eg
CO) bonds to the catalyst more strongly than the reactant so the catalyst is blocked to
the reaction
What letter is used to represent atomic number? - correct answers--Z
What state of matter do enthalpy values apply to? - correct answers--Gaseous
Why might a calculated bond enthalpy be different from the standard value? - correct
answers--1)The value in data sheets is the average bond enthalpy from several
compounds
2)Reactants may not be in a gaseous state (e.g water and alcohols)
What are sterioisomers? - correct answers--Molecules with the same structural formula
but a different spatial arrangement of atoms
What is the difference between E/Z isomers? - correct answers--E (trans) isomers have
the H group on opposite sides but Z (cis) isomers have the H group on zee zame zide
Why can't alkanes be E/Z isomers? - correct answers--E/Z isomerism occurs because
atoms cannot rotate about the C=C double bond but atoms can rotate about single
bonds like in alkanes
How does a mass spectrometer work? - correct answers--1) Atoms are ionised to
become cations
, 2) Cations are accelerated down a chamber
3) Ions are separated according to mass/charge ratio
4) Mass an abundance of each ion is detected
What are absorption spectra? - correct answers--Black lines on a coloured background
that represent certain frequencies of light being absorbed by electrons when they
absorb energy to move up energy levels. Energy transitions are unique to each element
What are emission spectra? - correct answers--Coloured lines on a black background
that represent frequencies of light being emitted by electrons as they move down
energy levels closer to the nucleus
Equation for energy of a photon? - correct answers--Energy photon = frequency x
Plank's Constant (6.626 x 10⁻³⁴ j/s)
E = hv
Flame colour lithium ion? - correct answers--Bright red
Flames colour calcium ion? - correct answers--Brick red
Explain the boiling point trend within hydrocarbons - correct answers--Boiling point
increases with chain length due to larger intermolecular forces
What is a free radical? - correct answers--A species with an unpaired electron
Why do the lines on absorption spectra get closer together towards the higher
frequency end? - correct answers--Energy levels get closer together with increasing
energy
How many orbitals are in the p sublevel? - correct answers--3 orbitals, 6 electrons
How many orbitals does d have? - correct answers--5 orbitals, 10 electrons
How many orbitals are in f sublevel? - correct answers--7 orbitals, 14 electrons
What is a dative covalent bond? - correct answers--A covalent bond in which a shared
pair of electrons is supplied by one of the bonding atoms only.
Properties of simple covalent molecules - correct answers--- Low melting and boiling
points (weak intermoleculer forces)
- Do not conduct electricity (no charged particles)
- Most do not dissolve in water
What does a dashed wedge represent? - correct answers--Going into the page
Equation for enthalpy change? - correct answers--q=mcΔT
(Salters) Paper 2 Mark Scheme:
June 2025 | Latest 2025/2026
Edition for First-Time Exam
Success
,State Hess's Law - correct answers--The total enthalpy change of a reaction is
independent of the route taken.
What is meant by standard conditions? - correct answers--.Temp - 25 dc, 298K
.Pressure - 100kPa
.Conc - 1 mol / dm-3
.Standard state
What is meant by standard enthalpy change of neutralisation? - correct answers--The
enthalpy change when one mole of water is formed in a neutralisation reaction under
standard conditions (-57kj/mol for any strong acid + alkali)
Shape of a molecule with 4 bonding pairs of electrons and explain? - correct answers--
Tetrahedral, 109.5
Electrons arranged to minimise repulsion
Shape of a molecule with 2 bonding electron pairs? - correct answers--Linear , 180
Electrons arranged to minimise repulsion
Shape of molecule with 3 bonding electron pairs? - correct answers--Trigonal Planar,
120
Ideal gas equation? - correct answers--pv = nRt
(penis vagina = naughty rectum tickle)
What is a sub-shell? - correct answers--A group of orbitals of the same type within a
shell e.g the 2p subshell contains 3 p orbitals in the second shell
What is an atomic orbital? - correct answers--A region around the nucleus that can hold
up to 2 electrons with opposite spins
What is the empirical formula? - correct answers--The simplest whole number ratio of
atoms of each element in a compound
What is an aromatic compound? - correct answers--A compound that contains at least
one benzene ring
What is an aliphatic compound? - correct answers--An organic compound that does not
contain a benzene ring
What is an arene? - correct answers--An aromatic hydrocarbon.
,What is a structural isomer? - correct answers--Compounds with the same molecular
formula but different structural formula (may have alkyl group)
What is a benzene ring? - correct answers--Simplest aromatic hydrocarbon C6H6
General formula for cycloalkanes? - correct answers--CnH2n
Why don't alkanes mix with water? - correct answers--Alkanes contain non-polar
molecules but water contains polar molecules that attract each other and stop the
alkane from mixing
What is a heterogeneous catalyst? - correct answers--A catalyst in a different physical
state to the reactants
How do heterogeneous catalysts work? - correct answers--1)Reactant molecules bond
with catalyst surface = adsorption
2)Reactant bonds are broken, forming radicals (atoms with unpaired electrons)
3)Radicals get together to make new molecules
4)New molecules detach from catalyst - desorption and diffuses away
Why may a catalyst become poisoned? - correct answers--The poison molecule (eg
CO) bonds to the catalyst more strongly than the reactant so the catalyst is blocked to
the reaction
What letter is used to represent atomic number? - correct answers--Z
What state of matter do enthalpy values apply to? - correct answers--Gaseous
Why might a calculated bond enthalpy be different from the standard value? - correct
answers--1)The value in data sheets is the average bond enthalpy from several
compounds
2)Reactants may not be in a gaseous state (e.g water and alcohols)
What are sterioisomers? - correct answers--Molecules with the same structural formula
but a different spatial arrangement of atoms
What is the difference between E/Z isomers? - correct answers--E (trans) isomers have
the H group on opposite sides but Z (cis) isomers have the H group on zee zame zide
Why can't alkanes be E/Z isomers? - correct answers--E/Z isomerism occurs because
atoms cannot rotate about the C=C double bond but atoms can rotate about single
bonds like in alkanes
How does a mass spectrometer work? - correct answers--1) Atoms are ionised to
become cations
, 2) Cations are accelerated down a chamber
3) Ions are separated according to mass/charge ratio
4) Mass an abundance of each ion is detected
What are absorption spectra? - correct answers--Black lines on a coloured background
that represent certain frequencies of light being absorbed by electrons when they
absorb energy to move up energy levels. Energy transitions are unique to each element
What are emission spectra? - correct answers--Coloured lines on a black background
that represent frequencies of light being emitted by electrons as they move down
energy levels closer to the nucleus
Equation for energy of a photon? - correct answers--Energy photon = frequency x
Plank's Constant (6.626 x 10⁻³⁴ j/s)
E = hv
Flame colour lithium ion? - correct answers--Bright red
Flames colour calcium ion? - correct answers--Brick red
Explain the boiling point trend within hydrocarbons - correct answers--Boiling point
increases with chain length due to larger intermolecular forces
What is a free radical? - correct answers--A species with an unpaired electron
Why do the lines on absorption spectra get closer together towards the higher
frequency end? - correct answers--Energy levels get closer together with increasing
energy
How many orbitals are in the p sublevel? - correct answers--3 orbitals, 6 electrons
How many orbitals does d have? - correct answers--5 orbitals, 10 electrons
How many orbitals are in f sublevel? - correct answers--7 orbitals, 14 electrons
What is a dative covalent bond? - correct answers--A covalent bond in which a shared
pair of electrons is supplied by one of the bonding atoms only.
Properties of simple covalent molecules - correct answers--- Low melting and boiling
points (weak intermoleculer forces)
- Do not conduct electricity (no charged particles)
- Most do not dissolve in water
What does a dashed wedge represent? - correct answers--Going into the page
Equation for enthalpy change? - correct answers--q=mcΔT
