final paper 1 2011

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A-level Chemistry

Paper 4

Final Mock (2011)

Duration 2 hours

QUESTION MARK OBTAINED

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PROGRESS REPORT

Topic Good PoorBorn-Haber CycleEnthalpy changeElectrochemistrypH calculationTitration curve

Dilution Calculation

Balancing equationRecognizing complex

Splitting pattern of ComplexGroup VII

Techniques for rate Mass spectrometry

Recognizing type of polymerization

Drawing the monomersAS reactions

Reactions of aromatic Reactions of AS organicConcept of delocalization

Isomerism Amino acids

EnzymesKpc

ChromatographyNanotechnology

Oil slicks

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Q.1 Magnesium chloride is the only existing chloride of magnesium. It has ionic bonding with some covalent character. Another chloride of magnesium is hypothetical MgCl3.The theoretical lattice

energy of MgCl3 is -5440 kJ/mole.

(a)Explain, with the aid of a suitable equation containing state symbols, what is meant by the statement the “lattice energy of MgCl3 is -5440 kJ/mole”.

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(b) Use the following data together with the relevant data from the Data Booklet to construct a Born-Haber cycle and calculate the standard enthalpy change of formation of MgCl3.Show all your working.

Lattice energy of MgCl3 = -5440 kJ/mole Enthalpy change of atomization of magnesium(s) = +148 kJ/moleE enthalpy change of atomization of chlorine(g) = +122 kJ/moleIst Ist electron affinity of chlorine = -349 kJ/mole

∆Hf= ----------------------kJ/mole

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(c)When magnesium reacts with chlorine it initially forms MgCl. MgCl then undergoes disproportionation

reaction to produce magnesium and MgCl2.

(i) Write a balanced equation for this reaction.

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(ii) The ∆H for the above reaction is -829 kj/mol. Use this values to calculate the ∆Hf for MgCl2by using the above reaction. You need ∆Hf of MgCl which is -94 kj/mol.

(iii) By comparing your results from (b) and (c)(ii) suggest, with a reason, the non-existence of MgCl3.

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(d)

Chloride Lattice energy/kjmol-1

MgCl2 -2526CaCl2 -2258

By quoting suitable data from the data booklet and by considering the above data would you expect the value for the lattice energy of cobalt(II) chloride to be lower or higher than MgCl2 and CaCl2. Explain your answer.

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[Total 10]

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Q.2 Old mine workings are often the cause of the pollution of mountain streams. One of the main chemical responsible for such pollution is iron pyrites, FeS2, in which iron has an oxidation state of +2. The early miners unwittingly accelerated the chemical processes by grinding up unwanted rock containing some ore and dumping it in waste heaps.

(a) Air and rain combine to oxidize iron pyrites.

Complete the balancing of the equation for this reaction.

…… FeS2(s) + 7O2(g) + 2H2O(l) …… Fe2+(aq) + …… SO42–(aq) + …… H+(aq)

(b) The resulting ions then run off into the local streams where the iron(II) ions are oxidized.

(i) Using the Data Booklet explain why the water in the streams must be acidic for oxygen tooxidize the iron(II) ions.

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(ii) Use the appropriate data from the Data Booklet write an equation for the oxidation of iron(II) ions in the stream water under acidic conditions.

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(c) Iron(III) ions are present in the stream as complex ions.

Complete the following table about these complex ions.

N Name of ligand in complex

Coordination number of complex

N Name of shape of complex

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(d)Explain why the 3d orbitals around a transition metal ion split into two groups when the ion is surrounded by six ligands in an octahedral complex.

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(e) Hexacyanoferrate(III), [Fe(CN)6]3- ,is another complex of iron which is used to test the presence of Fe(III) ions. Draw the splitting pattern of d-orbitals in [Fe(CN)6]3- and the complex mentioned in (c). Properly label each orbital before and after the splitting.

E ___ ___ ___ ___ ___ ___

Complex from (c) [Fe(CN) 6]3-

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[Total 10]

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Q.3 The hydrolysis of ethyl ethanoate is a reversible reaction. The equation for the equilibrium is shown below.

CH3COOC2H5 + H2O CH3COOH + C2H5OH

A student mixed together 8.0 moles of ethyl ethanoate and 5.0 moles of water. He also added a small amount of hydrochloric acid to catalyze the reaction.

The student left the mixture until it had reached equilibrium at constant temperature. He found that 2.0mole of ethanoic acid had formed.

(a)(i)Complete the table below to complete the composition of equilibrium mixture.

Component CH3COOC2H5 H2O CH3COOH C2H5OH

Initial amount/mol 8.0 5.0 0 0

Equilibrium amount/mol2.0

(ii) The mole fraction of ethanoic acid can be found from the composition of the equilibrium mixture.

Explain what is meant by the term mole fraction.

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(iii) Calculate the mole fraction of ethanoic acid in the equilibrium mixture.

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(b) Use your data from (a)(i) to calculate the vale of Kc.

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(c) The student also carried out practical work on acids and alkalis. He measured the pH of aqueous solutions of hydrochloric acid and ethanoic acid. He found that a 0.02 mol/dm3 ethanoic acid has a pH of 3.23.

(i) Calculate the value, including units, of Ka for ethanoic acid.

Answer= --------------------------------------------

(ii) The student found that 0.02 mol/dm3 HCl has a pH of 1.70. He then mixed together 25 cm3 of this solution with 75 cm3 of water.

Determine the pH of the diluted solution.

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pH= ------------------------

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Q.5 Hydrogen iodide gas is mixed with iodine gas.

Two reactions take place forming different compounds of iodine, A and B.

Compounds A and B each contain I and Cl only.

In the first reaction, compound A forms as a reddish-brown liquid.

Compound A contains 78.15%of I by mass.

In the second reaction, compound B forms as yellow crystals.Compound B has a molar mass of 467 g/mol

Deduce possible identities for A and B and write balanced equations for their formation.

A: -----------------------------------------------------------------------------------------------------------------------------------

Equation: -------------------------------------------------------------------------------------------------------------------------

B: -----------------------------------------------------------------------------------------------------------------------------------

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Equation:--------------------------------------------------------------------------------------------------------------------------

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(b) Haloalkanes have been used as aerosoul propellants and refrigerants but are now largely banned due to the damage they cause to ozone layer in stratosphere.

One haloalkane is methylene bromide CH2Br2. A sample of methylene bromide was enriched with deuterium (2H). On analysis it was found that half of the hydrogen content of the sample was deuterium. In the mass spectrum there are peaks with following m/z values. Give the molecular formula of fragment responsible for each m/z value.

m/z Molecular formula

15

173

175

177

(ii) Suggest why it is unlikely to have a m/z value at 179 in the mass spectrum of deuteriated CH2Br2.

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Q.6 Two reaction schemes are given. In both the schemes only the structural formulae of organic compounds have been shown. In your answers show only the structural formulae or skeletal formulae of the organic compounds.

Scheme 1 starts with phenol and scheme 2 starts with S.

NaOH HO Zn dust

I II

B Phenol III

NaOH in ethanol

heat under reflux

V IV

A P S

(a)(i) Give the structural formulae of B.

(ii) Give the reagents and conditions for step III.___________________________________________

and provide the skeletal formula of S in the empty box.

(iii) Give the skeletal formula of P.

(b) (ii) When P is converted to A in reaction step V a gas is also formed. Give the reagents and conditions for step V.

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(iii) State the type of reaction occurring during

Step I _________________________________

Step III ________________________________

Step IV ________________________________

Step V ________________________________

O

OH

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(iv) In a manufacturing process 1000g of benzene were prepared by 1275g of phenol. Calculate the percentage yield of the process. (1 mole of phenol gives 1 mole of benzene)

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Cyclohexenol is a closed-chain organic compound having both the alkene and alcohol functional groups. Some of its reactions are shown below:

MnO 4- + H+/

HO heat under reflux

VI

Cyclohexenol

W T

X

c)(i) Cyclohexenol is heated at 350oC with Al2O3, W and X are obtained which share the same molecular formula. Suggest the skeletal formulae of W and X and draw them in the empty boxes above.

(ii) What type of isomerism exists between W and X?

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(iii) T has the molecular formula C6H8O5 and dissolves in sodium hydroxide. Suggest the structural formula of T and draw it in the empty box above.

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The final structure of benzene has been formulated after long reviews and heated debates among chemists around the world. Modern analytical techniques have facilitated the synthetic organic chemist by fully exposing the structure of benzene. Coupled with analytical techniques the concept of delocalization of -electrons has solved the mystery behind the extraordinary stability of πbenzene molecule.

(d)(i) Without referring to the structure of benzene what do you mean by “delocalization of π electrons”?

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(ii)Now consider the molecules from scheme 1 and 2 together with the following mentioned species to decide which molecule has delocalized π -electrons. Then place a tick in the appropriate column.

Compound Delocalization of π-electrons possible

Delocalization of π electrons

not possible

B

CH3CO2-

S

W

X

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[Total 16]

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SECTION B

Q.7 The most remarkable property of water is that it is a liquid at room temperature found on Earth. Even more interesting is the polar nature of water. The polar nature of water means that most ionic compounds can dissolve in water. But hydrogen bonding also means that polar covalent molecules, sugars and amino acids, for example, are also soluble in water.

(a) What are the two important properties of Hydrogen bonding which make them important for life? Give example in each case.

1_______________________________________________________________________________

Example_________________________________________________________________________

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2_______________________________________________________________________________

Example_________________________________________________________________________

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In common with other catalysts enzymes provide an alternative reaction pathway that has a lower activation energy barrier than the uncatalyzed reaction.

Most inorganic catalysts catalyze a range of reactions involving similar substances. They are able to function over quite a wide range of temperatures and pressures. Although they are able to produce significant effects in speeding up reactions, their effectiveness as catalysts has been minimized by enzymes.

(b) Suggest three ways in which enzymes differ from inorganic catalysts.

1)_______________________________________________________________________________

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2)_______________________________________________________________________________

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(c)Certain metals, particularly certain heavy metals, can have serious health effects even though they may occur only in small amounts in the environment Part of the problem lies in the fact that they can accumulate in the food chain and so build up to toxic levels over a period of time. Lead and mercury are two particular metals for which this has proved a significant problem.

(i) Suggest a source of both mercury and lead in the environment.

Mercury__________________________________________________________________________

Lead____________________________________________________________________________

(ii) Mercury(II)ion disrupts the structure of protein and thereby denature the enzymes. What type of inhibitor is mercury(II)ion and what level of protein structure it disrupts.

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Q.8 A large number of organic compounds are soluble in both water and non-aqueous solvents such as hexane. If such a compound is shaken with a mixture of water and the non-aqueous solvent, it will dissolve in both solvents depending on the solubility in each.

(a)(i) State what is meant by the term partition coefficient.

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(ii) An aqueous solution of a monoprotic organic acid, X, was shaken with hexane until the following equilibrium was established.

X (water) X (hexane)

25.0 cm3 of the hexane layer needed 20.0 cm3 of 0.050 mol dm-3 NaOH(aq) for neutralization.25.0 cm3 of the water layer needed 13.3 cm3 of 0.050 mol ldm-3 NaOH(aq) for neutralization.

Calculate the value of partition coefficient.

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(b)Permethrin pesticides consist of large non-polar groups joined by an ester link. These molecules are much more soluble in fats than they are in water.

In the diagram below, the large non-polar groups are represented by R and R’

O

R-C-O-R’

Kpc is used to measure the relative solubilities of a pesticide in octan-1-ol and water.Octan-1-ol resembles a fat in its solvent abilities.

(i) Suggest why octan-1-ol behaves like a fat in ability to act as a solvent for pesticides.

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(ii) Explain why the most efficient pesticides have high Kpc values.

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(c)Chromatography has evolved as a mandatory discipline at the heart of separation sciences. It normally uses two phases one is mobile phase and the other is stationary phase. Different types of materials are employed for these two phases of chromatography and have found applications in the following chromatographic techniques.

Paper chromatography Thin-layer chromatography Gas-liquid chromatography High-performance liquid chromatography

(PC) (TLC) (GLC) (HPLC)

Different combinations of solid, liquid and gas have been chosen as stationary phase and mobile phase in the table below. If a combination is possible then write the appropriate abbreviation in the column “chromatographic technique”. If no combination is possible then write N. For instance in the first case when both the stationary and the liquid phases are chosen as solids there is no chromatographic technique which uses both stationary phase and the mobile phase as solids so N is written. If possible two abbreviations can be used for one combination.

Stationary phase Mobile phase Chromatographic technique

Solid Solid N

Liquid Gas

Gas Solid

Liquid Liquid

Solid Liquid

Gas Gas

Solid Gas

Liquid Solid

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Gas Liquid

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Q.9 Oil slicks are a major environmental concern when oil is spilled from oil tankers while at sea. Porous materials called sorbents are used which absorb oil.

(a)(i) Unfortunately these materials also soak up water. What does this tell you about the value of Kpc of oil in sorbent and water?

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(ii) What type of intermolecular forces exists between oil and porous material.

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CFCs (CF2Cl2) have been widely used as refrigerators as coolant due to their inertness. They are stable until they are broken down in the upper atmosphere by strong ultraviolet rays which generate chlorine radicals. These radicals then deplete Ozone layer.

CF2Cl2 CF2Cl + .Cl

(b)(i) CH3Br also known to have the ozone depletion effect. Show by giving three equations how this molecule depletes ozone layer in the upper atmosphere.

(ii) Suggest, with a reason, although the mass-scale production of CFCs have been banned following Montreal Protocol in 1986 and later in 1991 the damaging effect of CFCs are still in practice.

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(c) The modern sunscreens contain a variety of compounds that absorb the dangerous UV A and UV B. some sunscreens contain nano-sized particles of titanium dioxide. This substance does not absorb ultraviolet radiation.

(i) Suggest how these nano-particles are able to protect skin from ultraviolet radiation.

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Many people have concerns about problems that the new technologies might cause. This is due to the fact that nanoparticles can have very different properties from their related bulk materials. Many applications only require very small amounts of nanoparticles, so this reduces risks considerably. However some uses involve large quantities, for example sun screens.

(ii)Explain by giving two reasons why the properties of materials can be different at the nanoscale.

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(ii) What risk is associated with these nano-sized particles at large scale?

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[Total 9]

final paper 1 2011

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