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L.34

PRE-LEAVING CERTIFICATE EXAMINATION, 2016

CHEMISTRY – HIGHER LEVEL

TIME : 3 HOURS

400 MARKS

Answer eight questions in all.

These must include at least two questions from Section A.

All questions carry equal marks (50).

The information below should be used in your calculations.

Relative atomic masses (rounded): H = 1, C = 12, O = 16, Na= 23, Cl= 35.5, Ca = 40 Cr = 52, Cu= 63.5

Avogadro constant = 6.0 1023 mol–1

Molar volume at room temperature and pressure = 24.0 litres

The use of the Formulae and Tables booklet approved for use in the State Examinations is permitted. A copy may be obtained from the examination superintendent.

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Section A Answer at least two questions from this section. See page 1 for full instructions. 1. A student compared the total hardness values of a water supply before and after it had been

passed through a laboratory deioniser. The student added a suitable indicator and a small volume of buffer solution to 50.0 cm3 samples of the water in a conical flask and titrated them with edta solution.

The calcium ions and the magnesium ions (represented by M

2+) in the water reacted with

the edta (represented by H2Y2–

) according to the following balanced equation.

M2+

+ H2Y2–

MY2–

+ 2H+

(a) Write the full name of the edta reagent. (5) (b) Name a suitable indicator for this titration. State the colour change observed at the end point of the titration. (9) (c) What is the general purpose of the buffer solution used in this titration? Name a suitable buffer for this titration. What experimental problem would have been encountered if the wrong buffer

was used in this titration? (9) (d) Describe two steps, involving the titration flask and its contents, carried out as

the edta was being added from the burette during the titrations. (6) (e) The student found that 50.0 cm3 samples of the hard water before ion exchange required

an average of 8.30 cm3 of 0.01 M edta solution for complete reaction and that 50.0 cm3 samples of the water after ion exchange required an average of 2.20 cm3 of the same edta solution for complete reaction.

Calculate the total hardness of the water before ion exchange in

(i) moles per litre of calcium and magnesium ions (M2+

),

(ii) grams per litre expressed in terms of CaCO3,

(iii) p.p.m. in terms of CaCO3. Repeat these calculations for the water after ion exchange. (15) (f) Is the water that was passed through the deioniser suitable for use as deionised water in

the laboratory? Justify your answer. (6)

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2. Ethyne gas can be prepared in the school laboratory. (a) Draw a labelled diagram showing the arrangement of apparatus and the reagents

used in the preparation and collection of ethyne gas in the laboratory. (12) (b) Name one impurity which may be present in the sample of ethyne gas obtained. (3) (c) Give two physical properties of ethyne gas. (6) (d) Ethyne is an unsaturated hydrocarbon. Explain the underlined terms. (8) (e) Name the reagent used to show that ethyne gas is unsaturated.

Describe what would be observed when this reagent is applied to a sample of ethyne gas and shaken. (9)

(f) Describe what is observed when a sample of ethyne gas is burned in air.

Write a balanced equation for the complete combustion of ethyne gas. (9) (g) Give a wide-scale use of ethyne gas. (3) 3. A student carried out a number of experiments to investigate redox reactions in group VII

elements. (a) Chlorine water was added to some sodium bromide solution in a test tube.

(i) Describe what the student observed. (3)

(ii) Write the oxidation and reduction equations that take place during this reaction. (6)

(iii) Give a use for this reaction. (3) (b) Chlorine water was added to a solution of sodium sulfite in a test tube.

(i) Give the name or formula of the species that is produced due to oxidation of the sulfite ion. (3)

(ii) Describe briefly how you would test for the presence of this species. (6)

(iii) Write the equation to show the original reaction that takes place. (6) (c) The student added a piece of magnesium ribbon to a solution of copper(II) sulfate.

(i) Write an equation for the reaction which takes place. (5)

(ii) What was observed as the reaction proceeded? (6)

(iii) Show, by means of balanced equations, the oxidation and reduction reactions taking place. (6)

(iv) What conclusion can be drawn from these results about copper and magnesium? (6)

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Section B See page 1 for instructions regarding the number of questions to be answered. 4. Answer eight of the following (a), (b), (c), etc. (50) (a) Name the series of coloured lines in the line emission spectrum of hydrogen

corresponding to transitions of electrons from higher energy levels to the second (n=2) energy level.

(b) What is the oxidation number of (i) manganese in KMnO4, (ii) nitrogen in

3NO ? (c) Explain the effects of an increase in temperature on the rate of a chemical reaction. (d) What is the percentage by mass of chromium in sodium dichromate(VI) (Na2Cr2O7)? (e) State Gay-Lussac’s law of combining volumes. (f) How many electrons are there in 4.6 g of sodium metal (Na)? (g) Name and draw the structure of an aromatic compound of molecular formula C8H10. (h) What mass of copper would be needed to produce 2.56 g of copper(II) oxide (CuO)? (i) Write the electron configuration (s, p, etc.) of the magnesium ion (Mg2+). (j) Name the spectroscopic technique used in environmental analysis to detect

heavy metals such as lead. (k) Answer part A or part B. A Give two structural differences between low-density poly(ethene)

and high-density poly(ethene).

or

B Write an equation for the photodissociation of ozone.

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5. (a) Define first ionisation energy. (5) (b) Using the values given on page 80 of the Formulae and Tables booklet, plot a graph,

on graph paper, of first ionisation energy (y-axis) versus atomic number for the elements neon (Ne) to calcium (Ca) (10 to 20) inclusive. (12)

Account fully for (i) the peaks which occur in the graph between elements 12 and 15,

(ii) the sharp decrease in ionisation energy values between elements 18 and 19. (12) (c) Define relative atomic mass. (5) (d) A sample of the element chlorine is composed of 75% chlorine–35 and

25% chlorine–37. Calculate the relative atomic mass of chlorine from this information. (6)

(e) What contribution did Döbereiner make to

the systematic arrangement of the elements? (6) (f) Give one difference between Mendeleev’s

periodic table and the modern periodic table of the elements. (4)

6. (a) Petrol is obtained from crude oil in an oil refinery. Name the process used to obtain the petrol from the crude oil.

Petrol is obtained from light gasoline and another fraction. Name this fraction. (6)

(b) What is meant by the octane number of a fuel? (5) (c) Give the name and structural formula of the compound found

in petrol which is assigned an octane number of 100.

Give two structural features of hydrocarbons which give them a high octane number. (12)

(d) In an experiment to measure the heat of reaction between hydrochloric acid and sodium

hydroxide, 100 cm3 of 1.0 M HCl was added to 100 cm3 of 1.0 M NaOH solution in a polystyrene foam cup. The resulting increase in temperature was 6.5 °C. The density and the specific heat capacity of the reaction mixture, assumed equal to those of water, are 1.0 g cm–3 and 4.2 kJ kg–1 K–1, respectively.

The equation for the reaction is: HCl + NaOH NaCl + H2O

Calculate the heat of reaction between hydrochloric acid and sodium hydroxide. (15) Why was a polystyrene cup used instead of a glass beaker? (3) State three precautions that should have been taken in order to obtain an accurate

value for the highest temperature reached by the reaction mixture. (9)

Johann Döbereiner Dmitri Mendeleev

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7. Ethanol reacts with ethanoic acid according to the following balanced equation.

C2H5OH + CH3COOH CH3COOC2H5 + H2O

When 3 g of ethanoic acid were reacted with 2.3 g of ethanol and allowed to come to equilibrium at 293 K, it was found that 1.0 g of ethanoic acid remained.

(a) Name the organic product of this reaction and state the homologous series

to which it belongs.

Draw the structural formula of this organic product. (12) (b) Define chemical equilibrium.

Why is a chemical equilibrium described as dynamic? (8)

(c) Write the equilibrium constant expression (Kc) for the above reaction. (6) (d) Calculate the value of the equilibrium constant (Kc) for the reaction. (15) (e) Describe what is observed when a small amount of sodium carbonate is added

to a sample of ethanoic acid. Write a balanced equation for the reaction. (9) 8. (a) Define a (i) conjugate acid-base pair, (ii) weak acid in terms

of Brønsted-Lowry theory. (7) (b) Identify one species acting as a base and its conjugate acid in the following reaction. (6)

23SO + HCN

3HSO + CN– (c) Explain how an acid-base indicator, represented by XOH, and which is itself a weak

base, functions. (12) (d) Define pH. (4) (e) State the colour observed when a few drops of methyl orange solution are added

to (i) 0.1 M solution of HCl, (ii) 0.1 M solution of NaOH. (6) (f) Calculate the pH of a 0.2 M ammonia (NH3) solution given that the dissociation

constant (Kb) for ammonia 1.8 × 10–5.

What is the pH of a sodium hydroxide (NaOH) solution of the same concentration? (15)

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9. Study the reaction scheme below and answer the questions that follow.

(a) Give the IUPAC names for A, B, C and E. (12)

(b) Describe the mechanism of reaction W. (12)

(c) Identify (i) an elimination reaction, (ii) an oxidation reaction in the scheme. (6)

(d) State the reagents used in conversion Y. (6)

(e) What type of reaction is involved in conversion V? Give one use of this reaction in industry. (6)

(f) Name one compound in the scheme that contains at least one planar carbon. (4)

(g) Give one use for the group of compounds to which C belongs. (4) 10. Answer any two of the parts (a), (b) and (c). (2 × 25)

(a) In what type of household product is sodium hypochlorite commonly found? (4)

A solution of sodium hypochlorite (NaClO) is labelled as having a concentration of 5.6% (w/v). Calculate the concentration of this solution in grams per litre. (6)

A 200 cm3 volume of this 5.6% (w/v) solution reacts with excess chloride ions and acid according to the following equation.

OCl– + Cl– + 2H+ Cl2 + H2O

How many atoms of chlorine gas are liberated? (9)

What volume does this quantity of chlorine gas occupy at room temperature and pressure? (6)

(b) Radon–226 decays by alpha particle emission. Carbon–14 decays by beta particle

emission. What is (i) an alpha particle, (ii) a beta particle? (8)

Write a balanced nuclear equation to show (i) the alpha-decay of the Ra22688 nucleus,

(ii) the beta-decay of the C146 nucleus. (12)

What is meant by the half-life of a radioisotope? (5) (c) What is a catalyst? (4)

Name the two theories of catalysis. (6)

Name one element used as a catalyst in a catalytic converter. (3)

Write an equation which describes the reaction that takes place for CO or NO in a catalytic converter. (6)

Explain how leaded petrol affects a catalytic converter. (6)

C2H4A C

C2H5Cl

DC2H5OH

ECH3CHO

V W

ZY

X

BC2H6

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11. Answer any two of the parts (a), (b) and (c). (2 × 25) (a) A student filtered 1500 cm3 of water through a dry filter paper of mass 11.35 g. Upon drying, the mass of the filter paper was found to be 11.47 g. A 500 cm3 sample of the filtered water was then placed in a beaker of mass 131.55 g

and evaporated to dryness. The beaker was then reweighed and found to have a mass of 131.84 g.

Calculate the concentration of

(i) suspended solids in p.p.m.,

(ii) dissolved solids in p.p.m. (12) What term describes the process of

removing suspended solids in the treatment of water for drinking? (3)

Name the substance that is added

to water during this process. (4) Why is it necessary to adjust the pH

of water if it is too acidic? (3) What is used to adjust the pH? (3) (b) Outline the principle on which

all chromatographic separation techniques are based. (6)

Give one application of gas chromatography (GC). (4)

State the fundamental processes

that occur in mass spectrometry. (15)

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(c) Answer part A or part B. A (i) Distinguish between the terms feedstock and co-products. (6) Answer the following questions with respect to one of the following Irish chemical

manufacturing industries:

ammonia manufacture nitric acid manufacture magnesium oxide manufacture Cobh (now closed) Arklow (now closed) Drogheda

(ii) Give a reason for the location of your chosen chemical industry. (4) (iii) What are the raw materials used in the manufacturing process for the chemical

industry you have chosen?

Describe how the raw materials are treated before they become the feedstock for the manufacturing process. (12)

(iv) Name one product of your chosen process which, if discharged, could

cause pollution. (3)

or B In Ireland, the extraction of alumina takes place at the Aughinish Alumina plant,

near Limerick.

(i) Name the main aluminium ore from which alumina is extracted. (4) (ii) Write a balanced equation for the separation of alumina from the other

components of the ore. (6) (iii) How are the other components of the ore removed? (3) The alumina is shipped to a refinery to purify the aluminium by electrolysis. (iv) Name a suitable material for the electrodes. (3) (v) Give a reason for the addition of cryolite (Na3AlF6) to the alumina. (3) (vi) Write balanced equations to describe what happens at the anode and cathode. (6)

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