Question
Calcium, magnesium and radium are Group 2 elements. Radium follows the same trends as the other members of Group 2.
(a) Identify the highest energy orbital which contains electrons in a calcium atom. Sketch the shape of this orbital.
identity of highest energy orbital in Ca …………………………shape
(b) (i) Write the equation for the thermal decomposition of calcium nitrate.
(ii) Suggest which of the Group 2 nitrates, calcium, magnesium or radium, requires the highest temperature to decompose. Explain your answer.
(c) Predict what you would observe when aqueous radium chloride is added to aqueous sodium sulfate.
Do not refer to temperature changes in your answer.
(d) (i) \(^{25}_{12}\) Mg is an isotope of magnesium.
Determine the number of protons and neutrons in an atom of \(^{12}_{25}Mg\).
number of protons ………………………………………………………………………………………………..
number of neutrons ………………………………………………………………………………………………
(ii) State the full electronic configuration of an atom of \(^{12}_{25}Mg\).
(e) A sample of magnesium contains three isotopes, \(^{25}\)Mg, \(^{26}\)Mg and X. The percentage abundance of the three isotopes is shown in Table 1.1.
(i) The relative atomic mass, \(A_r\) , is calculated by comparing the average mass of the isotopes of an element to the unified atomic mass unit.
Define the unified atomic mass unit.
(ii) Calculate the mass of X. Use data from Table 1.1 and \(A_r\) (magnesium) = 24.31 in your calculation. Show your working.
mass of X = ………
(iii) State one similarity and one difference in the properties of these isotopes of magnesium.Explain your answer.
(f) Magnesium, Mg, burns in oxygen, \(O_2\).
The activation energy, \(E_a\), for this reaction is +148kJ\(mol^{–1}\).
(i) State one observation when magnesium burns in oxygen.Do not refer to temperature changes in your answer.
(ii) On Fig. 1.1:
● sketch a reaction pathway diagram for the reaction that occurs when Mg burns in \(O_2\)
● label the diagram to show the enthalpy change, ∆H, and the activation energy, \(E_a\), for
the reaction.
(g) Cold water reacts slowly with a piece of Mg to produce bubbles of \(H_2(g)\). Cold water reacts rapidly with burning Mg to produce \(H_2(g)\) in an explosive mixture.
\(Mg + 2H_2O \rightarrow Mg(OH)_2 + H_2\)
Explain why the rate of reaction of cold water with burning magnesium is greater.
Answer/Explanation
Answer:
(a) Identify and draw the shape of highest energy orbital of Ca 4s AND 
(b) (i) \(Ca(NO_3)_2 \rightarrow CaO + 2NO_2 + 1/2O_2\)
(ii) radium (nitrate) as thermal stability increases down group / has the greatest thermal stability
(c) white precipitate / solid (of radium sulfate)
(d) (i) number of protons: 12
number of neutrons: 13
(ii) \(1s^22s^22p^63s^2\)
(e) (i) 1 / 12 (one twelfth) the mass of a carbon-12 / \(^{12}\)C atom
(ii) M1 correct expression relating \(A_r\) to the mass / % abundance of the three isotopes
24.31 = x \times 0.7899 + 24.99 \rightarrow 0.1000 + 25.98 \times 0.1101\)
M2 correct answer to 4 sig figs
atomic mass of X = 23.99
(iii) M1 (magnesium isotopes have) identical chemical properties
AND same electron(ic) arrangement / configuration
M2 different physical properties AND different number of neutrons
(f) (i) white flame / light OR white solid / smoke
(ii) M1 sketch shows exothermic reaction with a ‘hump’ AND labelled reactants \((Mg + O_2)\) and products (MgO)
M2 arrow from reactants / \(Mg + O_2\) to products / MgO shown as ∆H
M3 arrow showing activation energy / \(E_a\) / (+)148
(g) M1 (heat / energy released from burning Mg) provides more particles with energy ⩾ \(E_a\)
M2 frequency of successful / effective collisions is greater
Question
Nitrogen molecules, \(N_2(g)\), contain two atoms attracted to each other by a triple covalent bond.
(a) Describe how the triple covalent bond forms in a \(N_2(g)\) molecule. Refer to orbital overlap and hybridisation in your answer.
(b) Nitrogen oxides, \(NO_2\) and NO, are produced in internal combustion engines. Release of these gases into the atmosphere leads to the formation of photochemical smog.
(i) Outline how nitrogen oxides are involved in the formation of photochemical smog.
(ii) Construct an equation to demonstrate how a catalytic converter reduces the amount of nitrogen oxide gases released into the atmosphere.
(c) \(N_2(g)\) is very unreactive. It is difficult to make ammonia, \(NH_3(g)\), directly from its elements but it can be made from \(NH_4Cl(s)\). Identify a reagent and the conditions required to make \(NH_3(g)\) from \(NH_4Cl(s)\).
(d) \(25cm^3\) of 0.10\(moldm^{–3}\) HCl(aq) is added to a beaker and its pH is recorded. \(50cm^3\) of 0.10\(moldm^{–3}\) \(NH_3(aq)\) is added to the HCl(aq) in 5\(cm^3\) portions.
The pH of the mixture is monitored until all the \(NH_3(aq)\) is added. HCl is a strong Brønsted-Lowry acid.
(i) Describe what is meant by a strong Brønsted-Lowry acid.
(ii) \(NH_3\) is a weak base.
Construct an equation that shows the behaviour of \(NH_3\) as a weak Brønsted-Lowry base when dissolved in water.
(iii) On Fig. 2.1 sketch a graph to show the change in pH which occurs when HCl(aq) is titrated with \(NH_3(aq)\) as described in (d).
Answer/Explanation
Answer:
(a) M1 one sigma / \(\sigma \) bond and two pi / π bonds
M2 sp hybridisation (in each N atom)
M3 sigma / \(\sigma \) forms from direct / head-on / end-on overlap of orbitals
AND pi / \(\pi \) forms sideways / lateral overlap of (p) orbitals
(b) (i) M1 react with (unburnt) hydrocarbons
M2 (form) PAN / peroxyac(et)yl nitrate
(ii) \(2NO + 2CO \rightarrow 2CO_2 + N2\) OR \(NO_2 + 2CO \rightarrow 1⁄2N_2 + 2CO_2\)
(c) any Group 1 hydroxide or \(Ca(OH)_2\) / \(Sr(OH)_2 / Ba(OH)_2\)
(d) (i) M1 proton / \(H^+\) donor
M2 fully dissociates (in aqueous solution / water / solvent)
(ii) \(NH_3 + H_2O ⇌ NH_4^+ + OH^–\)
(iii) M1 correct basic shape extending to ~50\(cm^3\) with vertical portion of curve at 25 \(cm^3\)
M2 initial pH at 0–2 (based on idea that HCl is a strong acid) AND final pH at between 8–12 (based on idea that \(NH_3\) is a
weak alkali)
Question
Liquids that contain molecules of T smell like lemons.
(a) Molecules of T exist as a pair of stereoisomers.
Name the type of stereoisomerism shown by molecules of T. Explain your answer.
(b) Two organic products are produced when a sample of T is heated under reflux with excess acidified concentrated \(KMnO_4\).
Draw the structure of the two organic products, from this reaction, in the boxes.
(c) Fig. 3.2 shows two reactions of T.
(i) Identify a suitable reagent for reaction 1.
(ii) Identify the reagent and conditions needed for reaction 2.
(iii) Suggest which product formed in reaction 2 has a higher yield. Explain your answer.
(d) Separate samples of Q and R are added to separate test-tubes containing acidified \(K_2Cr_2O_7(aq)\) and heated.
(i) Predict the observations for each test-tube. Explain your answer in terms of the functional groups present in Q and R.
(ii) When \(PCl_5(s)\) is added to separate samples of Q and R at room temperature, both react vigorously.
Complete the equation shown in Fig. 3.4 to describe the reaction that occurs when R reacts with \(PCl_5(s)\).
(iii) Suggest why samples of Q and R must be dried before \(PCl_5\) is added. Include a relevant equation to support your answer.
Answer/Explanation
Answer:
(a) M1 optical
M2 one of the C atoms has 4 different groups / atoms attached
(b) 
(c) (i) \(NaBH_4\) / sodium borohydride / \(LiAlH_4\) / lithium tetrahydridoaluminate
(ii) M1 \(H_2O(g)\) / steam
M2 phosphoric acid (catalyst) / \(H_3PO_4\) (catalyst)
(iii) M1 Q AND intermediate / cation is (more) stable
M2 (as the) \(C^+\) has 3 / more alkyl groups attached
M3 (so) greater (positive) inductive effect
(d) (i) M1 Q orange → green
M2 R orange → green
M3 –CHO / aldehyde (in both) (and 2° / secondary alcohol in R) reacts / oxidised
(ii) 
M1 correct formula of organic product
M2 correct inorganic products
(iii) M1 water reacts with / hydrolyses \(PCl_5\)
M2 \(H_2O + PCl_5 \rightarrow POCl_3 + 2HCl\) OR \(4H_2O + PCl5 \rightarrow H_3PO_4 + 5HCl\)
Question
Compound V is a liquid.V contains 77.2% carbon, 11.4% hydrogen and 11.4% oxygen by mass.V has a relative molecular mass of 280.
(a) Calculate the molecular formula of V. Show your working.
molecular formula of V = …………………………
(b) V contains two types of functional group: a carboxylic acid and an alkene.
(i) Describe a chemical test and observation which confirms the presence of a carboxyl functional group.
(ii) A 3.196g sample of \(Br_2\) reacts completely with 2.800g of V.
Calculate how many alkene functional groups are present in one molecule of V. Show your working.
number of alkene functional groups in V = …………………………
(c) W, X and Y have the same molecular formula, \(C_5H_{10}O\).
W, X and Y are added separately to different reagents. Observations for these reactions are described in Table 4.1.
(i) W, X and Y each contain a common functional group.
Name the functional group that is present in all three compounds.
(ii) State the formula of the yellow precipitate produced when X is added to alkaline \(I_2(aq)\).
(iii) W could be one of four structural isomers.
● Draw the skeletal formulae for two possible structural isomers of W.
● Describe the type of structural isomerism shown.
type of structural isomerism
(d) Fig. 5.1 shows the mass spectrum of ketone Z, \(C_5H_{10}O\).
Use the information in Fig. 5.1 to suggest the formulae of the fragments with m/e peaks at 29 and 57. Deduce the identity of Z.
m/e = 29 …………………………………………………………………………………………………………………….
m/e = 57 …………………………………………………………………………………………………………………….
identity of Z ………………………………………………………………………………………………………………..
Answer/Explanation
Answer:
(a) M1 % / Ar for C H O
M2 each % / Ar for C H O divided by the smallest value for % / Ar to give simplest whole number ratio / empirical formula
M3 compare \(M_r\) from M2 ratio with 280 to deduce the actual molecular formula
C H O
77.2 / 12 = 6.433 11.4 / 1 = 11.4 11.4 / 16 = 0.7125
9(.03) 16 1
\(Mr(C_9H_{16}O)\) = 140 so molecular formula of V = \(C_{18}H_{32}O_2\)
(b) (i) M1 (add) group 1 carbonate / group 1 bicarbonate / \(Na_2CO_3\) / \(NaHCO_3\) etc.
M2 effervescence / fizzing / bubbling
(ii) 3.196 g \(Br_2 = 3.196 / 159.8\) (= 0.02 mol \(Br_2\)) AND 2.8(00) / 280 (= 0.01 mol V)
2 alkene / 2 C=C (groups)
(c) (i) carbonyl
(ii) \(CHI_3\)
M3 chain (isomerism)
(d) 