H2 Chemistry A Level Exam
With answers
Solubility - answer-The maximum amount of solute that can dissolve in a given amount
of solvent at a given temperature.
I.e. concentration of sth as a solute in a saturated solution
If solubility of PbCl2 is x mol dm-3, concentration of Pb2+ in saturated solution is x,
concentration of Cl- is 2x.
Saturated solution - answer-A solution that contains the maximum amount of solute that
can be dissolved in the given amount of solvent. Dissolution and precipitation occur at
the same rate.
Ksp for sparingly soluble salt MaXb - answer-The equilibrium constant for the
equilibrium established between the undissolved salt and its constituent ions in a
saturated solution. = [Mb+]^a[Xa-]^b
Ionic product - answer-Product of the concentration of the constituent ions in the
solution in that instant raised to the powers of the stoichiometric coefficients.
Common Ion Effect - answer-Reduced solubility of a salt in a solution that already
contains an ion common to that salt.
LSPEC - answer-In aqueous solution, M2+ exists as an octahedral complex
[M(H2O)6}2+. The presence of ligands causes the splitting of the five 3d orbitals into 2
sets of slightly different energy levels since the 3d subshell is partially-filled. Electrons
from lower-energy orbitals can absorb energy corresponding to certain wavelengths
from the visible spectrum of light and get promoted to higher-energy orbitals (d-d
transitions). The colour observed is the complement of the colour absorbed.
Aufbau (building-up) principle - answer-Electrons fill orbitals from the lowest energy
orbital upwards.
Pauli Exclusion Principle - answer-No more than 2 electrons may occupy one orbital;
two electrons in the same orbital must have opposite spins.
Hund's Rule - answer-Orbitals of a subshell (degenerate) must be filled singly with
parallel spins before they can be occupied in pairs (with opposite spins).
,Transition Metals - exceptions to electronic configuration - answer-Crazy Cuckoo
Cr is [Ar]3d5 4s1 and not [Ar] 3d4 4s2
Cu is [Ar]3d10 4s1 and not [Ar] 3d9 4s2
Transition Element (3) - answer-A d-block element which can form one or more stable
ions with a partially-filled d subshell.
Definition of a Complex (3 - CLDC) - answer-contains a central metal atom or ion linked
to one or more surrounding ions or molecules (ligands) by dative covalent bonds.
Ligand (3) - answer-An ion or molecule which contains at least one atom bearing a lone
pair of electrons that can be donated into a low-lying vacant orbital of a central metal
atom/ion forming a co-ordinate bond, resulting in the formation of a complex.
Act as a lewis base, bonding to a lewis acid.
Why do transition metals form (so many) ions with variable oxidation states? - answer-
Because of the close similarity in energy of the 3d and 4s electrons such that both are
available for ionic/covalent bond formation.
Catalyst - answer-A substance that increases the rate of a chemical reaction by
providing an alternate pathway of lower activation energy without itself undergoing any
permanent change.
Haber Process - answer-N2 + 3H2 --> 2NH3, finely divided iron catalyst with aluminium
oxide as promoter, 200 atm, 450ºC
Coordination number - answer-Total number of coordinate bonds of central metal
ion/atom
EDTA - answer-Ethylenediaminetetraacetic acid
Why do transition metals show a high tendency to form complexes? - answer-1. Central
metal ion/atom has high charge density --> high polarising power
2. The central metal ion/atom has low-lying vacant orbitals to accommodate lone pairs
of electrons from ligands.
Stability constant, Kstab - answer-Equilibrium constant for the formation of a complex
(ion).
≠ solubility constant
, Electrolyte - answer-An ionic compound that conducts an electric current in
aqueous/molten state.
Standard electrode potential of a half cell - answer-Electromotive force, measured at
298K, between the half-cell and the Standard Hydrogen Electrode where the
concentration of any reacting species in solution is 1 mol dm-3 and any gaseous
species is at a pressure of 1 bar.
Daniell Cell - answer-Zn2+/Zn half-cell + Cu2+/Cu half-cell (Remember as 'Couzin
Daniell') C for Cu C for Cathode
Standard Cell Potential (E°cell) - answer-Potential difference between 2 half-cells at
standard conditions.
Electrolysis - answer-Passing electricity (from an external source) through an
electrolytic cell to force a non-spontaneous redox reaction to occur.
Formulas to know for electrochemistry - answer-dG (in J mol-1) = -nFe
Q = It = neF (Q is measured in coulombs, = # of electrons x charge carried by an
electron)
Faraday's constant, F = Le = 96500 c mol-1
F = Le = Avogadro's number x charge carried by ONE electron = charge carried by one
mole of electrons
Faraday's first law - answer-The mass of a substance and/or volume of gas liberated
during electrolysis is directly proportional to the amount of electrical charge passed
through the cell.
Buffer solution - answer-A solution that has the ability to resist small changes in pH
upon the addition of small amounts of either acid or base
Henderson-Hasselbalch Equation for a buffer solution consisting of a weak acid and its
conjugate base - answer-pH = pKa + log [A-]/[HA]
Henderson-Hasselbalch Equation for a buffer solution consisting of a weak base and its
conjugate acid - answer-pOH = pKb + log [BH+]/[B]
For a weak acid or weak base, [H+] or [OH-] = - answer-√Ka[HA]initial or
√Kb[B]initial respectively
With answers
Solubility - answer-The maximum amount of solute that can dissolve in a given amount
of solvent at a given temperature.
I.e. concentration of sth as a solute in a saturated solution
If solubility of PbCl2 is x mol dm-3, concentration of Pb2+ in saturated solution is x,
concentration of Cl- is 2x.
Saturated solution - answer-A solution that contains the maximum amount of solute that
can be dissolved in the given amount of solvent. Dissolution and precipitation occur at
the same rate.
Ksp for sparingly soluble salt MaXb - answer-The equilibrium constant for the
equilibrium established between the undissolved salt and its constituent ions in a
saturated solution. = [Mb+]^a[Xa-]^b
Ionic product - answer-Product of the concentration of the constituent ions in the
solution in that instant raised to the powers of the stoichiometric coefficients.
Common Ion Effect - answer-Reduced solubility of a salt in a solution that already
contains an ion common to that salt.
LSPEC - answer-In aqueous solution, M2+ exists as an octahedral complex
[M(H2O)6}2+. The presence of ligands causes the splitting of the five 3d orbitals into 2
sets of slightly different energy levels since the 3d subshell is partially-filled. Electrons
from lower-energy orbitals can absorb energy corresponding to certain wavelengths
from the visible spectrum of light and get promoted to higher-energy orbitals (d-d
transitions). The colour observed is the complement of the colour absorbed.
Aufbau (building-up) principle - answer-Electrons fill orbitals from the lowest energy
orbital upwards.
Pauli Exclusion Principle - answer-No more than 2 electrons may occupy one orbital;
two electrons in the same orbital must have opposite spins.
Hund's Rule - answer-Orbitals of a subshell (degenerate) must be filled singly with
parallel spins before they can be occupied in pairs (with opposite spins).
,Transition Metals - exceptions to electronic configuration - answer-Crazy Cuckoo
Cr is [Ar]3d5 4s1 and not [Ar] 3d4 4s2
Cu is [Ar]3d10 4s1 and not [Ar] 3d9 4s2
Transition Element (3) - answer-A d-block element which can form one or more stable
ions with a partially-filled d subshell.
Definition of a Complex (3 - CLDC) - answer-contains a central metal atom or ion linked
to one or more surrounding ions or molecules (ligands) by dative covalent bonds.
Ligand (3) - answer-An ion or molecule which contains at least one atom bearing a lone
pair of electrons that can be donated into a low-lying vacant orbital of a central metal
atom/ion forming a co-ordinate bond, resulting in the formation of a complex.
Act as a lewis base, bonding to a lewis acid.
Why do transition metals form (so many) ions with variable oxidation states? - answer-
Because of the close similarity in energy of the 3d and 4s electrons such that both are
available for ionic/covalent bond formation.
Catalyst - answer-A substance that increases the rate of a chemical reaction by
providing an alternate pathway of lower activation energy without itself undergoing any
permanent change.
Haber Process - answer-N2 + 3H2 --> 2NH3, finely divided iron catalyst with aluminium
oxide as promoter, 200 atm, 450ºC
Coordination number - answer-Total number of coordinate bonds of central metal
ion/atom
EDTA - answer-Ethylenediaminetetraacetic acid
Why do transition metals show a high tendency to form complexes? - answer-1. Central
metal ion/atom has high charge density --> high polarising power
2. The central metal ion/atom has low-lying vacant orbitals to accommodate lone pairs
of electrons from ligands.
Stability constant, Kstab - answer-Equilibrium constant for the formation of a complex
(ion).
≠ solubility constant
, Electrolyte - answer-An ionic compound that conducts an electric current in
aqueous/molten state.
Standard electrode potential of a half cell - answer-Electromotive force, measured at
298K, between the half-cell and the Standard Hydrogen Electrode where the
concentration of any reacting species in solution is 1 mol dm-3 and any gaseous
species is at a pressure of 1 bar.
Daniell Cell - answer-Zn2+/Zn half-cell + Cu2+/Cu half-cell (Remember as 'Couzin
Daniell') C for Cu C for Cathode
Standard Cell Potential (E°cell) - answer-Potential difference between 2 half-cells at
standard conditions.
Electrolysis - answer-Passing electricity (from an external source) through an
electrolytic cell to force a non-spontaneous redox reaction to occur.
Formulas to know for electrochemistry - answer-dG (in J mol-1) = -nFe
Q = It = neF (Q is measured in coulombs, = # of electrons x charge carried by an
electron)
Faraday's constant, F = Le = 96500 c mol-1
F = Le = Avogadro's number x charge carried by ONE electron = charge carried by one
mole of electrons
Faraday's first law - answer-The mass of a substance and/or volume of gas liberated
during electrolysis is directly proportional to the amount of electrical charge passed
through the cell.
Buffer solution - answer-A solution that has the ability to resist small changes in pH
upon the addition of small amounts of either acid or base
Henderson-Hasselbalch Equation for a buffer solution consisting of a weak acid and its
conjugate base - answer-pH = pKa + log [A-]/[HA]
Henderson-Hasselbalch Equation for a buffer solution consisting of a weak base and its
conjugate acid - answer-pOH = pKb + log [BH+]/[B]
For a weak acid or weak base, [H+] or [OH-] = - answer-√Ka[HA]initial or
√Kb[B]initial respectively
