5/6 markers Flashcards
This question is about oxides of nitrogen.
An investigation is carried out on the equilibrium system shown below.
2NO2(g) —–> N2O4(g)
∆H = –57.4 kJ mol–1
A sealed flask containing 6.00 moles of NO2(g) is heated to a constant temperature and allowed to reach equilibrium.
The equilibrium mixture contains 5.40 mol of NO2(g), and the total pressure is 5.00 atm.
Determine the value of Kp and give your answer to 3 significant figures.
Include an expression for Kp and the units of Kp in your answer (5)
p(N₂O₄(g))
————– = Kp (Units atm–1)
p(NO₂(g))²
- if answer = 1.17 x 10–2 OR 1.18 x 10–2 award 3 calculation marks
A hydrated nickel(II) complex, A, is heated in a crucible to remove the water of crystallisation. The anhydrous complex B is formed. The results are shown below.
Mass of crucible + hydrated complex A = 59.554 g
Mass of crucible + anhydrous complex B = 58.690 g
Mass of crucible = 51.257 g
The anhydrous complex B is analysed and found to have a molar mass of 309.7 g mol–1 and to contain the following percentage composition by mass:
Ni, 18.95%; C, 23.25%; N, 27.12%; H, 7.75%; Cl, 22.93%.
The anhydrous complex B contains a cation C comprising Ni, C, N and H only.
Cation C is six-coordinate, contains three molecules of the bidentate ligand D, and exists as optical isomers.
Determine the formula of A, B, C and D and show the 3D structures for the optical isomers of C.
Show all your working (6)
https://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Past-Papers/OCR-A/Paper-1/MS/June%202017%20MS.pdf
Healthy human blood needs to be maintained at a pH of 7.40 for the body to function normally
Carbonic acid, H2CO3, is a weak acid which, together with hydrogencarbonate ions, HCO3−, acts as a buffer to maintain the pH of blood.
The pKa value for the dissociation of carbonic acid is 6.38.
Explain, in terms of equilibrium, how the carbonic acid–hydrogencarbonate mixture acts as a buffer in the control of blood pH, and calculate the [HCO3−] : [H2CO3] ratio in healthy blood (6)
Equilibrium and equilibrium shifts
* H2CO3(aq) ⇌ H+ (aq) + HCO3– (aq)
* Addition of H+ causes ⇌ to shift to left
* Addition of OH– causes ⇌ to shift to right
Action of buffer
* Increase in H+ / addition of acid leads to:
H+ (aq) + HCO3– (aq) → H2CO3(aq)
OR
HCO3– reacts with added acid
- Increase in OH– / addition of alkali leads to:
H+ (aq) + OH– (aq) → H2O(l)
OR
H2CO3(aq) + OH– (aq) → HCO3– (aq) + H2O(l)
OR
H2CO3 reacts with added alkali
Calculation of [HCO3–] : [H2CO3] ratio
* Ka = 10–6.38 OR 4.17 × 10–7 (mol dm–3)
* [H+] = 10–7.40 OR 3.98 x 10–8 (mol dm–3)
*[HCO3–]
————–
[H2CO3]
OR
4.17 x 10–7
—————–
3.98 x 10–8
- ratio = 10.47(:1) OR 10.48(:1)
ALLOW 10.5 OR 10(:1) (after working shown)
ALLOW
4.2 x 10–7
4.0 x 10–8
And ratio = 10.5 OR 11 (after working shown)
This question is about copper and copper compounds.
Experiment 1
Hydrochloric acid, HCl (aq), is added to an aqueous solution containing [Cu(H2O)6]2+ complex ions.
A yellow-green solution forms containing complex ion B.
Experiment 2
A piece of copper metal is heated with concentrated sulfuric acid.
A reaction takes place forming a pale blue solution C and 45 cm3 of a gas D, measured at RTP. The mass of gas D is 0.12 g.
Experiment 3
An excess of copper(II) oxide is heated with dilute nitric acid. The resulting mixture is filtered. The filtrate is a blue solution E.
Aqueous potassium iodide, KI(aq), is added to the blue solution E.
A white precipitate F and a brown solution G form.
Determine the formulae of B–G.
Construct equations for the reactions taking place, include any changes in oxidation number,
and show your working where appropriate (6)
Formula
B CuCl4 2–
OR
[CuCl4]2–
C [Cu(H2O)6]2+
OR
CuSO4
D SO2
E Cu(NO3)2
OR
[Cu(H2O)6]2+
F CuI
G Ɪ2
Experiment 1:
Equation
[Cu(H2O)6]2+ + 4Cl– → [CuCl4]2– + 6H2O
[Cu(H2O)6]2+ + 4HCl → [CuCl4]2– + 6H2O + 4H+
Experiment 2:
Evidence
n(D) = 45
——— = 1.875 × 10–3
24000
Molar mass (D) = 0.12
—————— = 64
1.875 × 10–3
Equation
Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
Oxidation numbers: Cu 0 → Cu +2;
S +6 → S +4
Experiment 3:
Equation
CuO + 2HNO3 → Cu(NO3)2 + H2O
2Cu(2+) + 4I – → 2CuI + I 2
OR
2Cu(NO3)2 + 4KI → 2CuI + I 2 +4KNO3
Oxidation numbers: Cu +2 → Cu +1;
I –1 to 0
This question is about the d-block elements in Period 4 of the periodic table (Sc to Zn).
Explain, with examples from Period 4, what is meant by the terms d-block element and transition element.
Explain why some d-block elements are not transition elements.
Use electron configurations to support your explanations (6)
Terms:
d-block element: element with highest energy/valence electron in d-orbital/sub-shell OR d-subshell is being filled
DO NOT ALLOW d block for d-subshells
Transition element:
element forming one or more ions (allow atom and ion - IUPAC definition) with incomplete/partially filled d-subshell/dorbitals
DO NOT ALLOW d shell
d-block element:
ALLOW examples with an ion with an incomplete d-subshell, e.g. Fe2+
- [Ar]4s03d6
ALLOW examples with highest energy electrons in a d-subshell, e.g. Fe - [Ar]4s23d6
Not all d-block are transition elements:
Sc and Zn form ions with complete or empty d-shells ORA
For Sc3+, ALLOW Sc+3 OR Sc forms a 3+ ion
For Zn2+, ALLOW Zn+2 OR Zn forms a 2+ ion
Sc3+ 1s22s22p63s23p6
Sc3+ AND d subshell empty / d orbital(s) empty
Zn2+ 1s22s22p63s23p63d10
Zn2+ AND d subshell full / ALL d orbitals full
Hydrogen is used industrially to manufacture ammonia.
The equilibrium is shown below.
N2(g) + 3H2(g) —-> 2NH3(g)
∆H = –92 kJ mol–1
1.20 mol N2(g) is mixed with 3.60 mol H2(g) in a 8.00 dm3 container.
The mixture is heated to 550 °C with an iron catalyst and allowed to reach equilibrium.
The equilibrium mixture contains 0.160 mol of NH3.
Determine the equilibrium constant and explain why the operational conditions used by industry may be different from those required for a maximum equilibrium yield of ammonia (6)
0.0386 dm6mol-2
Explanation for operational differences.
Temperature
* Low temperature for maximum yield: (∆H –ve \ exothermic)
* High temperature to increase rate
Pressure
* High pressure for maximum yield (fewer (gaseous) moles/molecules of products)
* High pressure expensive to generate
OR
high pressure is a safety hazard
