Physical chemistry

June 2022 v1

1) a) The solubility of the Group 2 sulphates decreases down the group. Explain this trend. [3]

[1] Lattice energy and enthalpy change of hydration both become less exothermic

[2] Lattice energy becomes less exothermic by a smaller extent OR enthalpy change of hydration changes by a larger extent

[3] So enthalpy change of solution becomes less exothermic OR more endothermic OR Hsol = Hhyd - Hlatt

June 2022 v1

1) b) Describe what is observed when magnesium and barium are reacted separately with an excess of dilute sulphuric acid [1]

Magnesium: Fizzing

Barium: fizzing AND white precipitate forms

Solubility product equation

C (s) ⇌ aA+ (aq) + bB- (aq)

Ksp = [A+ (aq)]^a [B- (aq)]^b

1) d) ii) Suggest how the lattice energy of BaSO4 differs from the lattice energy of Cs2SO4. Explain your answer. [2]

[1] BaSO4 is more negative as Ba2+ is smaller/has a larger charge

[2] Stronger force of attraction between ions

Equation for Gibbs free energy

ΔG = ΔHr - TΔS

Where ΔS is in kJ

ΔG = -nFEcell

F = 96500C

n = moles of electrons transferred within the reaction

Ideal gas equation

pV = nRT

p = Pressure (Pa)

V = Volume (m3)

R = Gas constant (8.31 J K-1 mol-1)

n = moles of gas

T = Temp (Kelvin)

Percentage yield equation

Percentage yield = actual yield / theoretical yield x 100

Calorimetry equation

Q = mcΔT

Q = energy change

m = mass (g)

c = specific heat capacity (4.18 J/gC° for water)

ΔT = temp change

Entropy change equation

ΔS = Sproducts - Sreactants

Equilibrium constant equation

Kc = [C]^c [D]^d / [A]^a [B]^b

for reaction aA + bB ⇌ cC + dD

(same for partial pressures Kp except replace concentrations with partial pressure of substance)

Partial pressure equation

Partial pressure = mole fraction x total pressure

Partition coefficient equation

Kpc = [A(organic)]/[A(aqueous)]

Stability constant equation

Same as equilibrium constant except conc of water = 1 in all cases

Rate equation

rate = k[A]^x [B]^y [C]^z

x,y,z = orders with respect to A, B and C

k = rate constant

Rate constant equation

k = 0.693 / t1/2

t1/2 = half-life

Acid dissociation constant equation

Ka = [H+][A-]/[HA]

pKa equation

pKa = -log10Ka

Ionic product of water

Kw = [H+][OH-]

Kw = 1x10^-14 at 298K

pH equation

pH = -log10[H+]

Ecell equation

Ecell = Reduction - Oxidation

Faradays constant equation

F = Le

F = 96500 C mol-1

L = Avogadros constant

e = charge of an electron (1.6x10^19)

Nernst equation

𝐸 = 𝐸0 − (0.059/z) log [oxidised species]/[reduced species]

E = electrode potential (V)

𝐸0 = standard electron potential (V)

z = moles of electrons transferred

Mass spectrometry equation

n = 100 x abundance of M+1 ion / 1.1 x abundance of M+ ion

n = number of carbon atoms

June 2022 v1

2) a) Define transition element [1]

[1] An element that forms one or more stable ions with an incomplete d sub-shell

June 2022 v1

2) b) Sketch the shape of a 3dz^2 orbital [1]

Infinity loop on z axis

Donut across y and x

June 2022 v1

2) c) i) Explain what is meant by a heterogenous catalyst [1]

[1] A catalyst that is in a different phase from the reactants

June 2022 v1

2) c) ii) Describe the mode of action of a heterogenous catalyst in a reaction [3]

[1] Adsorption of reactants to the surface of the catalyst

[2] Bonds within the reactants weaken (lowering the activation energy)

[3] Reaction occurs and the products are desorbed

June 2022 v1

2) d) ) Manganese(VII) oxide, Mn2O7, can be made by treatment of KMnO4 with concentrated sulfuric acid (reaction 1).

Mn2O7 readily decomposes at room temperature to form manganese(IV) oxide and a colourless diatomic gas (reaction 2).

Construct equations for both the reactions described. [2]

[1] Reaction 2: 2KMnO4 + H2SO4 → Mn2O7 + H2O + K2SO

[2] Reaction 2: Mn2O7 → 2MnO2 + 1.5O

June 2022 v1

2) e) i) Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H20)6]2+ with NaOH (aq) [2]

[1] [Mn(H2O)6]2+ + 2OH– → Mn(OH)2 + 6H2O

[2] Acid-base

June 2022 v1

2) e) ii) Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H20)6]2+ with concentrated HCl [2]

[1] [Mn(H2O)6]2+ + 4Cl– → [MnCl4]2– + 6H2O

[2] Ligand substitution

What does a more negative cell potential indicate

Stronger reducing agent and more likely to be oxidised

June 2022 v1

3) c) i) Define standard electrode potential [1]

[1] Potential difference when a half-cell is connected to a standard hydrogen electrode under standard conditions

June 2022 v1

3) c) ii) A salt bridge is used in an electrochemical cell. State the function of the salt bridge. Explain your answer. [1]

[1] Ions move to maintain charge balance / to complete the circuit

June 2023 v2

1) a) ii) Describe the variation in the thermal stability of Group 2 carbonates. Explain your answer. [3]

[1] Thermal stability increases down the group

[2] Ionic radius of group 2 ion increases, reducing charge density

[3] So less polarisation/distortion of carbonate ion

June 2023 v2

1) b) i) Define lattice energy [2]

[1] Enthalpy change/energy released when one mole of an ionic solid/compound is formed

[2] From its gaseous ions

June 2023 v2

2) b) ii) [3]

[1] ΔHdecomp becomes more positive down group

[2] Ionic radii of oxide ions are smaller than carbonate ions

[3] So ΔHlatt of oxides becomes less exothermic faster (changes more down grp)

June 2023 v2

2) a) State two properties of a transition element [1]

Two from:

• Have variable oxidation states

• Behave as catalysts

• Form complex ions

• Form coloured ions/compounds

June 2023 v2

2) b) i) Define complex ion [1]

[1] Molecule formed by a central metal ion surrounded by ligands

June 2023 v2

2) c) i) Explain what is meant by a bidentate ligand [2]

[1] Species that donates/uses two lone pairs

[2] To form two dative covalent bonds to a central metal ion

June 2023 v2

3) a) Define enthalpy change of atomisation [2]

[1] Enthalpy change when one mole of gaseous atoms is produced

[2] From its element in its standard state

June 2023 v2

3) f) The standard enthalpy change of solution ΔHsol of AgNO3(s) in water is +22.6kJ mol-1. Suggest how the feasibility of dissolving AgNO3(s) in water changes with temperature. Explain your answer [2]

[1] Feasibility increases as temperature increases

[2] ΔS is positive and -TΔS becomes more negative, so ΔG is negative and becomes more negative

June 2023 v2

4) a) i) Explain what is meant by the overall order of reaction [1]

[1] Sum/total of the powers to which a concentration of a reactant is raised in the rate equation

Nov 2022 v2

2) b) iv) Explain why a reaction can have zero order kinetics when the amount of reactant is large and the amount of catalyst is small [1]

[1] All active sites on the surface of the catalyst are occupied

Nov 2022 v2

3) a) i) Define standard electrode potential. Include details of the standard conditions used. [2]

[1] The voltage produced by a half cell compared with a standard hydrogen electrode

[2] 1 mol dm^-3, 298K, 1 atm

Nov 2022 v2

4) b) i) Define conjugate acid-base pair [1]

[1] Two species that differ by one H+ ion

Nov 2022 v2

5) b) ii) In an isolated Cu2+ ion, the d-orbitals are all degenerate. In a complex ion such as [Cu(H2O)6]2+, the d-orbitals are non degenerate.

Define degenerate and non=degenerate in this context [1]

[1]

Degenerate = of the same energy

Non-degenerate = not of the same energy

Nov 2022 v2

6) b) i) Define stability constant [1]

[1] Equilibrium constant for the formation of a complex ion from its constituent ions

OR

[2] Equilibrium constant for the formation of a complex ion in a solvent

March 2022

1) c) i) Identify a suitable indicator for a reaction producing iodine [1]

[1] Starch

March 2022

1) c) Sketch the shape of a 3dxy orbital

March 2022

3) b) i) TiO2- is a colourless ion. Suggest why [2]

[1] Ti is in a 4+ oxidation state, so no d electrons

[2] So cannot absorb photons

March 2022

3) c) ii) Explain, in terms of d-orbitals, why Ti³+ is able to form complex ions.