Chemestry K2

8/11/2019 Chemestry K2

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Instructions to candidates :

This paper consists of 10 printed pages

Section A[ 40 marks ]

Answer all the questions in this section.

This question paper consists of 8 printed pages.

For Examiners Use

Section A

1

2

3

4

Section B

Total

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Chemistry

Gerak Gempur ( 2012 )

Chemistry Paper 2

( Structure & Essay )

DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE

TOLD TO DO SO.

Answer all the questions in Section A. Write your answers in

the spaces provided.

Answer any four questions from Section B. Write your

answers on papers provided. Begin each answer on a fresh

sheet of paper, and arrange your answers in numerical order.

Tie your answer sheets to this booklet.

All working must be shown. Numerical answers should begiven to an appropriate number of significant figures ; units

should be quoted wherever they are appropriate.

A Data Booklet is provided.

STPMName: ______________________________

Class: ______________________________


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Section A [ 40 marks ]

Answer ALL questions in this section.

1. Biodiesel makes use of plants ability to fix atmospheric carbon by photosynthesis. Many companies and

individuals are now using biodiesel as a fuel in order to reduce their carbon footprint. Biodiesel can be

synthesized from vegetable oil according to the following reaction.

(a) Identify the organic functional group present in both vegetable oil and biodiesel.

[1]

(b) For part of her extended essay investigation into the efficiency of the process, a student reacted a pure

sample of a vegetable oil (where R = C17H33) with methanol.

The raw data recorded for the reaction is below.

The relative molecular mass of the oil used by the student is 885.6. Calculate the amount (in moles) of

the oil and the methanol used, and hence the amount (in moles) of excess methanol.

[2]

(c) The reversible arrows in the equation indicate that the production of biodiesel is an equilibrium process.

(i) State what is meant by the term dynamic equilibrium. [1]

..

..

(ii) Using the abbreviations [vegetable oil], [methanol], [glycerol] and [biodiesel], deduce the equilibrium

constant expression (Kc) for this reaction. [1]

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Mass of oil = 1013.0 g

Mass of methanol = 200.0 g

Mass of sodium hydroxide = 3.500 gMass of biodiesel produced = 811.0 g


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(iii) Suggest a reason why excess methanol is used in this process. [1]

......

(iv) State and explain the effect that the addition of the sodium hydroxide catalyst will have on the position

of equilibrium. [2]

..

..

(d) Calculate the percentage yield of biodiesel obtained in this process. [2]

2 (a) State the meaning of the termfirst ionisation energy of an atom. [1]

.

(b) Explain the trend in variation of the first ionisation energies of the Period 3 elements Na to Ar. [2]

.....

.

(c) Compare the first ionisation of phosphorus and sulphur . Explain your answer. [3]

(d) (i) Draw the shape of a BF3molecule and the shape of a H2S molecule. In each case show any lone pairs

of electrons. [2]

BF3 H2S

(ii) Hydrogen sulphide, H2S, reacts with boron trifluoride, BF3, to form compound A.

Explain the formation of compound A with the help of its Lewis structure to indicate the type of

bonding involved . [2]

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3. Nitrogen(II) oxide reacts with hydrogen as shown by the following equation.

2NO(g) + 2H2(g) N2(g) + 2H2O(g)

The table below shows how the rate of reaction varies as the reactant concentrations vary.

(a) Determine the order of reaction with respect to (i) NO (ii) H2 [2]

(b) Write the rate law for the above reaction. [1]

......

(c) Calculate the value for the rate constant, including its units. [2]

(d) A suggested mechanism for this reaction is as follows.

H2 + NO X fast

X + NO Y + H2O slow

Y + H2 N2 + H2O fast

State and explain whether this mechanism agrees with the experimental rate expression in (b). [3]

e) Deduce the initial rate of formation of H2O(g) as compared to that of N2(g) for experiment 1. Explain

your answer. [2]

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4. (a) 2butene is a straight-chain alkene with formula C4H8. The molecule contains both and bonds.

H H H H

H C C = C C H

H H

(i) Name the type of hybridisation shown by the C2carbon atom . [1]

.

(ii) Explain the formation of the bond in terms of overlapping of orbitals. [1]

..

(b) 2butene shows structural isomerism and also stereoisomerism.

(i) Draw and name one otherstructural isomer of 2butene . [1]

(ii) Draw and name 2 stereoisomers of 2butene . [2]

(c) Identify the structural formula of an isomer of 2butene which does not decolourise bromine water.

[1]

(d) The polymerisation of alkenes is one of the most significant reactions of the twentieth century.

(i) Give two reasons why the polymers of alkenes are of economic importance. [2]

..

..

(ii) Deduce the structure of the polymer for 2butene showing 3 repeating units . [1]

(iii) Explain why monomers are often gases or volatile liquids but polymers are solids. [1]

..

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Section B [ 60 marks ]

Answer any FOUR questions in this section.

5. (a) X, Y and Z represent elements of proton number 9 , 19 and 34 .

Predict the type of bonding and draw dot cross diagrams for the compounds formed

( showing only the electrons in the outermost shell for each atom ) between

(i) X and Y (ii) X and Z [6]

(b) Predict, giving reasons, the relative (i) volatility (ii) electrical conductivity

of the compound formed between X and Y compared with that formed between X and Z.

[4]

(c) (i) Define the term activation energy.

(ii) The endothermic reaction between substances P and Q can be represented by the following

equation.

P(g) + Q(g) R(g) + S(g)

Draw the energy profile for this reaction.

Indicate and label clearly the activation energy and the enthalpy change for the reaction.

(iii) Explain how a catalyst affects the rate of a chemical reaction. [5]

6. The table shows the variation of pV against p for 65.0 g of a gas M at 298 K.

p ( x 103) kPa 0.20 0.40 0.60 0.80 1.00

pV kPa m3 6.82 6.81 6.80 6.79 6.78

(a) (i) Plot a graph of pV against p.

(ii) Add to your graph the line expected if gas M is an ideal gas.

(iii) Comment on the shape of your graph.

(iv) Use the data in the graph to calculate the relative molecular mass of M . [8]

(b) Sketch the phase diagram of carbon dioxide.

Label the areas and explain why solid carbon dioxide can sublime under room conditions. [4]

(c) (i) Write an expression for Kw, the ionic product of water.

(ii) Use the expression above, to determine the pH value for 0.200 moldm3NaOH (aq ) . [3]

7. (a) Describe the reactions, if any , that will occur when separate samples of sodium and phosphorus are

(i) added to water

(ii) burned in excess oxygen and then water is added to the resulting oxide.

Write equations wherever appropriate and suggest pH of any aqueous solution formed. [8]

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(b) (i) Aluminium is extracted by the electrolysis of its mineral bauxite.

Identify some important aspects of this process, including equations for the reactions at the

electrodes.

(ii) When heated both aluminium fluoride and aluminium chloride sublime at 1270 oC and

178 oC respectively . Explain differences in these values based on the bonding in both compounds.

[7]

8. Hydrogen cyanide, HCN, is a highly toxic substance. 50.0 mg of it will cause death in a few seconds.

(a)

Calculate the lethal dose (50.0 mg) of hydrogen cyanide in moles. [2]

(b)Hydrogen cyanide is manufactured by passing a mixture of ammonia and methane over a platinum

catalyst. The reaction is endothermic.

NH3(g) + CH4(g) HCN(g) + 3H2(g)

(i) Suggest why the reaction is carried out at 1000 C.

(ii) Explain if a high pressure should be used in the manufacture of hydrogen cyanide. [4]

(c) If ammonia (0.200 mol) and methane (0.200 mol) are placed in a 1.00 dm3container and heated

to 500C, it is found that 0.100 mol of hydrogen cyanide and 0.300 mol of hydrogen are produced at

1.00 atmosphere pressure. Calculate the equilibrium constant, Kc for the reaction under these

conditions and state its units. [3]

(d)Hydrogen cyanide dissolves in water to form a weakly acidic solution. It has a dissociation constant of

4.90 1010at 25 C. Alkalis react with hydrogen cyanide to form salts known as cyanides.

(i) Explain why an aqueous solution of sodium cyanide is alkaline.(ii) Using equations, explain how a mixture of sodium cyanide and hydrogen cyanide is able to act as a

buffer.

(iii) Calculate the pH of the buffer solution formed when 200 cm3of a 0.500 mol dm3solution of

hydrogen cyanide is added to 200 cm3of a 1.00 mol dm3solution of sodium cyanide. [6]

9. Carefully study the steps involved in the conversion of the starting reagent to the final product.

(a) With the help of equations, describe the mechanism for step 1. [4]

(b) (i) Suggest why SnCl2is used as the reducing agent for step 3 instead of lithium

tetrahydridoaluminate(III), LiAlH4.

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CH3 CH3 COOH COOH COOCH2CH3

conc. HNO3 KMnO4 / H

+

SnCl2

conc. H2SO4

Step 1 Step 2 Step 3 Step 4

NO2 NO2 NH2 NH2


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(ii) SnCl2is formed by the following reaction.

100oC

SnCl4 SnCl2 + Cl2

Show the oxidation state of each element in the equation and name the type of reaction that

has taken place in the above reaction.

(iii) Despite the metallic nature of tin, SnCl4has a molecular structure.

Draw the molecular structure of SnCl4.

What will be observed when a little water is added to SnCl4? Give reasons for your answer. [6]

(c) Describe a chemical test to confirm that step 3 has produced the amino group. [3]

(d) (i) Give the reagents and conditions for step 4.

(ii) Write a balanced equation for step 4 . [2]

10. (a) Draw all structural formulae for all the monobrominated product formed when 2methylpropane istreated with bromine gas in the presence of sunlight.

Predict the major product. [3]

(b) Compound X, C7H14is optically active. On catalytic reduction of X over nickel, 1 mole of hydrogen

gas is absorbed giving 1 mole of compound Y, C7H16. Reaction of X with hot acidified potassium

manganate(VII) produces ethanoic acid and compound Z , C5H10O2 which is a carboxylic acid and is

also optically active.

(i) Draw the structures of X, Y and Z . Explain your answers.

(ii) Identify a chemical test to distinguish X from Y . [9]

(c) Give structures of the organic products, A, B and C formed in the following reaction scheme.

Compound Z

LiAlH4, dry ether

H3O+ SOCl2 Mg

A B C [3]

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Chemestry K2