______________________________
CHEMISTRY – HIGHER LEVEL
______________________________DURATION: 3 HOURS
______________________________400 MARKS
______________________________Answer any eight ques ons.
All ques ons carry equal marks (50). ______________________________
The informa on below should be used in your calcula ons.
Rela ve atomic masses (rounded): H = 1, C = 12, O = 16, N = 14, Ba = 137, P = 31, Cl = 35.5, Fe = 56.
*P15*
Section A
1. In an experiment to determine the mass of iron in an iron tablet, four iron tablets of total mass 1.36 g were dissolved and made up to 250 cm3 of solu on in a volumetric fl ask using
dilute sulfuric acid and deionised water. About 10 cm3 of dilute
sulfuric acid was added to 20 cm3 por ons of this iron (II)
solu on and the mixture then trated with a 0.005 M solu on of potassium manganate (VII), KMnO4. The average tra on value was 28.2 cm3 of potassium manganate (VII).
(a) Describe in detail the procedure used for making up the 250 cm3 solu on from the four iron tablets. (15)
(b) Explain why it was important to use dilute sulfuric acid in making up the solu on from the tablets. (5) (c) Before the tra ons were commenced more dilute
sulfuric acid was added to the conical fl ask.
Explain why. (3) (d) How was the end-point detected? (3) (e) Explain why nitric acid could not be used to provide acidic condi ons for this reac on. (3) (f) The tra on reac on is described by the equa on:
MnO4– + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4H 2O
Calculate:
(i) the number of moles in 28.2 cm3 of the potassium manganate (VII) solu on,
(ii) the number of moles of iron (II) solu on required to reduce this quan ty of potassium manganate (VII),
(iii) the concentra on of iron (II) solu on in moles per litre, given that 20 cm3 were
required to reduce 28.2 cm3 of potassium manganate.
(iv) the (a) mass and (b) percentage of iron in each tablet. (21) Bure e Potassium manganate(VII) solu on Solu on containing iron(II) + sulfuric acid Conical fl ask White le 10 20 30 40 50 0
2. A student prepared a sample of soap in the school laboratory. A mixture of 10.08 g of glyceryl tripalmitate (animal fat) and sodium hydroxide were refl uxed using a heater for approximately 20 minutes together with about 30 cm3 of ethanol and some an -bumping
granules.
When cool the apparatus was rearranged for dis lla on and the ethanol was removed. At the end of dis lla on, a small amount of hot water was added to the fl ask and the contents were poured into solu on X where the soap was separated from the mixture. The soap was then isolated and thoroughly washed with ice-cold water.
C15H31COO CH2
C15H31COO CH + 3NaOH 3C15H31COONa + compound Y C15H31COO CH2 Sodium palmitate
Glyceryl tripalmitate
(a) State a reason for refl uxing the reac on mixture. (5) (b) What type of reac on was involved in the prepara on of soap? (3) (c) What was the purpose of having ethanol present in the reac on fl ask? Why was it
necessary to remove the ethanol a er refl uxing? (6) (d) The contents were poured into solu on X. Name solu on X and indicate its func on. (6) (e) A by-product of this reac on is compound Y (see above). Draw the structure or give the
name of compound Y. (6)
(f) Draw a labelled diagram to show how the soap was isolated. (6) (g) Calculate:
(i) how many moles of glyceryl tripalmitate were used in this reac on,
(ii) how many moles of soap were formed if the sodium hydroxide was in excess,
(iii) how many grams of soap were formed if a 70% yield was obtained. (18) Heater Water Condenser
3. A student was provided with standard laboratory apparatus and various reagents and was asked to iden fy six salts. These salts included
NaCl = sodium chloride
Na2HPO4.12H2O = di-sodium hydrogen phosphate dodecahydrate Na2SO4 = sodium sulfate
LiHCO3 = lithium hydrogen carbonate K2SO3 = potassium sulfi te
Cu(NO3)2 = copper (II) nitrate
(a) Describe how the student could have dis nguished between the samples that contained the copper ions and the lithium ions. (11) (b) (i) Which salt could be iden fi ed by adding freshly prepared iron (II) sulfate (Fe2SO4)
and conc. sulfuric acid (H2SO4)? (3)
(ii) Describe how this test was carried out and what observa on indicated a posi ve test
result. (9)
(c) (i) Which of the above salts could be iden fi ed by the addi on of silver nitrate
solu on (AgNO3)? (3)
(ii) What observa on indicates a posi ve test? Write a balanced equa on for
this reac on. (9)
(d) Two of the above salts give a white precipitate when barium chloride (BaCl2) is added.
(i) Iden fy these salts. (6)
(ii) Name the reagent which must be added to dis nguish the salts from each other.
(3) (e) Ammonium molybdate reagent is added to each salt.
(i) Iden fy the salt that gives a posi ve result with this reagent. (3)
Section B
4. Answer eight of the following items (a), (b), (c), etc. (50) (a) Defi ne the relaƟ ve atomic mass of an element.
(b) Write the electronic confi gura on (s.p. etc.) of a copper atom in its ground state. (c) Name the scien st shown in the photograph, who iden fi ed cathode rays
as subatomic par cles.
(d) Dis nguish between sigma (σ) and pi (π) covalent bonding.
(e) What is the oxida on number of sulfur in (i) H2SO4 and (ii) Na2S2O3? (f) How many atoms are present in 560 cm3 of ammonia at s.t.p.?
(g) Following the destruc on caused by ammonium nitrate exploding at Beirut’s port, there are concerns globally about its storage.
Calculate the percentage of nitrogen in ammonium nitrate (NH4NO3). (h) What is meant by heterogeneous catalysis?
(i) What is the purpose of terƟ ary treatment of sewage?
(j) On what principle is the analy cal technique mass spectrometry based?
(k) Give the name and symbol of one metallic element used as a catalyst in the cataly c converter used in a car.
5. (a) Americium–241 is a radioac ve isotope used in domes c smoke detectors. Americium–241 has a half-life of 432 years and decays by emi ng alpha par cles to produce neptunium.
(i) What are alpha par cles? (5)
(ii) Give two proper es of alpha par cles. (6)
(iii) Determine the value of A and the value of Z in the following nuclear equa on for the
alpha decay of an americium–241 nucleus. (6)
95Am ZNp + alpha par cle + energy
(b) Use the electronega vity values provided in the Formulae and Tables booklet on page 81 to predict the bond type in the following compounds.
(i) LiBr (ii) PH3 (iii) H2O (9) (c) Consider the following hydrides from the second and third periods of the periodic table:
BeH2 NH3 H2O MgH2
(i) State the shape of the H2O molecule and explain using electron pair repulsion theory
how this shape arises. (6) (ii) Which two of the hydrides above have the same shape and name this shape. (6) (iii) Select from the list given above the hydride or hydrides in which hydrogen bonding
occurs between the molecules.
(iv) Give one property that is aff ected by the presence of this hydrogen bonding. (6) (d) Dis nguish between intermolecular and intramolecular bonding. (6)
6. (a) Heptene (C7H14), 2-methylbutane and a second alkene (X) were the products of cataly c cracking of a pentadecane (C15H32) molecule.
(i) Draw the structural formula for 2-methylbutane. (ii) Deduce the molecular formula of the third product (X).
(iii) Draw the structural formula of X. (9) (b) State Hess’s law. (5) The heats of forma on of pentadecane, heptene, 2-methylbutane and X are: –354.8, –97.7, –178.4 and 20.0 kJ mol–1 respec vely.
Use the data to calculate the heat change for the cracking reac on:
C15H32(l) heptene (g) + 2-methylbutane (l) + X (g) (15) (c) Other than cataly c cracking name two processes carried out in an oil refi nery to improve the octane number of a fuel. (6)
(d) Ethanol is an example of an oxygenate. Give another example of an oxygenate. Give two reasons why oxygenates are added to petrol. Name an addi ve previously added to petrol and state why its use was discon nued. (15)
7. (a) Draw a clear, labelled diagram of the pH curve you would expect to obtain when 50 cm3 of
a 0.10 M KOH solu on are added gradually to 25 cm3 of a 0.10 M ethanoic acid (CH
3COOH)
solu on. (11)
Name a suitable indicator for a tra on between these two solu ons. (3) Explain your selec on with reference to your pH curve. (3)
(b) A bo le of vinegar is labelled 4.5% (w/v) ethanoic acid. The dissocia on constant, Ka, for ethanoic acid is 1.8 × 10– 5. Calculate the approximate pH of the vinegar solu on. (12)
Find the concentra on of a sulfuric acid (H2SO4) solu on which has the same pH. (6) (c) To determine the biochemical oxygen demand (BOD) of the water in a lake, two samples
were taken and one was tested immediately.
8. Answer the ques ons (a) to (h) with reference to the compounds A, B, C and D.
Alcohol (A) Propanal Carboxylic acid (C) C2H5COOC2H5 (D) Alcohol (B) Propanone
(a) Alcohol A and Alcohol B are structural isomers. Explain the underlined term.
Give the IUPAC name for Alcohol A and Alcohol B. (12) (b) Iden fy another pair of structural isomers from the reac on scheme. (3) (c) Name the homologous series to which D belongs. (5) (d) Classify each of the conversions X, Y and Z as an addiƟ on, subsƟ tuƟ on or oxidaƟ on reac on.
(9) (e) Name the reagents used in the conversion of propanal to carboxylic acid C. (6) (f) Draw the structure of and name the carboxylic acid C. (6) (g) Compound C reacts with the base sodium carbonate (Na2CO3). Write the balanced equa on for this reac on. (6)
(h) Give the IUPAC name of compound D. (3)
9. (a) An acid-base indicator which is itself a weak acid (HIn) dissociates according to the following equilibrium equa on
HIn (red) H+ + In– (yellow)
State and explain the colour changes which occur when (i) an acid and (ii) a base is added. (12) (b) When a yellow solu on of iron (III) chloride (FeCl3) and a colourless solu on of potassium thiocyanate (KCNS) were mixed in a test tube, a red colour appeared and the following equilibrium was established:
FeCl3(aq) + CNS– (aq) Fe(CNS) 2+ (aq) + 3Cl – Yellow Red
State and explain the colour change observed when some brine (NaCl) is added to the
mixture. (6)
The red colour fades when the test tube containing the equilibrium mixture is placed in a beaker of hot water. Is the forward reac on exothermic or endothermic? Jus fy your answer. (6) (c) Consider the following reversible reac on
PCl3 (g) + Cl2(g) PCl5 (g) ∆H = –124 kJ mol-1
(i) Write the equilibrium constant expression Kc for this reac on. (3) (ii) What eff ect if any would:
(1) an increase in the temperature,
(2) an increase in the pressure, have on the number of moles of PCl5 at equilibrium?
Jus fy your answers. (12) (iii) 110 g of phosphorus trichloride was added to 56.8 g of chlorine gas in a sealed 8 litre
fl ask. When equilibrium was reached, it was found that 0.5 moles of phosphorus
X Y Z
10. Answer any two of the parts (a), (b) and (c). (2 x 25) (a) Defi ne reduc on in terms of (i) electron transfer and (ii) change in oxida on number. (6) Use oxida on numbers to iden fy the (i) oxidising agent and (ii) reducing agent in the
following reac on.
SO32– + MnO 4 – + H+ SO 4 2– + Mn2+ + H 2O (12)
Hence or otherwise balance the equa on. (7) (b) The salt barium nitrate (Ba(NO3)2) on hea ng decomposes fully according to the following balanced equa on:
2Ba(NO3)2(s) 2BaO(s) + 4NO2(g) + O2(g)
When 13.05 g of this salt is heated strongly calculate:
(i) how many moles of barium nitrate (Ba(N O3)2) reacted, (6) (ii) the mass of barium oxide (BaO) formed, (6) (iii) calculate the total volume (in litres) of gaseous products, measured at s.t.p. formed in
the reac on, (9)
(iv) the number of oxygen molecules produced. (4) (c) Clove oil is extracted from an emulsion of clove oil and
water by a process called solvent extracƟ on.
(i) State the colour of the emulsion, (3) (ii) name the solvent used. (3) In which layer is the clove oil to be found? (3) Outline the procedure to isolate and dry the clove oil. (12) What safety procedure must be carried out during
the extrac on? (4)
Organic Layer
Aqueous Layer
11. Answer any two of the parts (a), (b) and (c). (2 x 25) (a) Dis nguish between saturated and unsaturated hydrocarbons.
Describe how you would test a given hydrocarbon for unsatura on. (13) Benzene is an aroma c compound and its formula of C6H6 suggests a high degree of
unsatura on. The following structures have been used to describe the structure of benzene.
Fig. 1 Fig. 2 How many pi-electrons are there in the benzene molecule?
Explain why Fig.1 fails to correctly describe the structure of benzene.
Give one piece of experimental evidence in support of your explana on. (12) (b) Defi ne the rate of a chemical reacƟ on. (5)
There is a slow exothermic reac on between hydrogen and nitrogen gases mixed in a 3:1 ra o at room temperature but the reac on speeds up if powdered iron catalyst is added. Suggest the type of catalysis responsible for the increased rate of reac on.
Describe the mechanism by which the powdered iron increases the rate of reac on. (12) Draw a clearly labelled reac on profi le diagram for the reac on with and without the
catalyst. (8)
(c) A sample of water is said to be hard when it is diffi cult for it to form a lather with soap. Dis nguish between the terms permanent hardness and temporary hardness under the following headings:
(i) Name or chemical formula of one compound which causes the hardness.
(ii) One method used in the removal of each. (12) Iden fy the substance used to determine by tra on the total hardness present in a water
sample. (4)
Name the indicator used in this tra on and state the colour change observed at the end
