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MINISTRY OF EDUCATION

FIJI SEVENTH FORM CERTIFICATE EXAMINATION 2013

CHEMISTRY PAPER 2

QUESTION AND ANSWER BOOK

Time Allowed: One Hour

(An extra ten minutes is allowed for reading this paper.)

HAND IN THIS QUESTION AND ANSWER BOOK TO THE SUPERVISOR BEFORE YOU LEAVE THE EXAMINATION ROOM.

INSTRUCTIONS

1. Write your Index Number at the top of this page and inside the back flap of this Question and Answer Book.

2. Write your answer to each question in the space provided in this book.

3. Answer all the questions with a blue or black ballpoint or ink pen. Do not use red ink. Use a pencil only for drawing.

4. If you use extra sheets of paper, be sure to write clearly the question number(s) being answered and to tie each sheet securely in this book in the appropriate places.

5. You may use a calculator, provided it is silent, battery-operated and non-programmable.

6. There are eight questions altogether in this paper. All the questions are compulsory and each one is worth five marks.

7. Spend approximately seven minutes on each question.

8. Before handing in this Question and Answer Book, make sure that your Index Number is at the top of this page, inside the back flap and on any extra sheet(s) of paper you may have used.

Note : A Periodic Table of Elements is provided for your use during this examination. Both the atomic number and the relative atomic mass for each element are given.

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2.

QUESTION 1

(a) During practical classes, it is essential that the students wear safety equipment. Identify any two safety equipment that should be worn during practical classes and explain one use of each equipment.

1. _______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (1 mark) 2. _______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (1 mark) (b) Teachers always emphasise the need to take proper care in carrying out

experiments in the laboratory. Why is it not advisable to directly smell chemicals while conducting experiments?

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark) (c) The choice of apparatus is also very important in practical work.

(i) Which apparatus would be used to prepare a standard solution of 200 mL?

__________________________________________________________ (1 mark)

(ii) Draw the main apparatus that would be used to separate a mixture of methanol and water.

(1 mark)

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QUESTION 2

(a) An experiment was set up to determine the molar mass of a volatile liquid by Dumas method.

The results obtained are as follows:

Mass of the condensed vapour = 0.35 g Volume of the condensed vapour = 116 mL Temperature of the water bath = 80ºC

Atmospheric pressure = 101.3 kPa

(i) Use the data in the results given above to calculate the molar mass of the volatile liquid. [R = 8.314 JK−1 mol−1]

_______________________________________________________________________

_______________________________________________________________________ (2 marks) (ii) In this experiment, the flask containing the volatile liquid was heated in a

boiling water bath. Explain why the liquid was not heated directly.

_______________________________________________________________________

_______________________________________________________________________ (1 mark)

(b) The structures of three hydroxy compounds namely propan-1-ol, 1, 2-propandiol and 1, 2, 3-trihydroxy propane (glycerol) and their boiling points are shown below.

I. propan-1-ol boiling point 97ºC

II. 1 , 2-propandiol boiling point 213ºC

III. 1, 2, 3-trihydroxypropane (glycerol) boiling point 290ºC

H H OH

C

H

C C H H

H H

H OH OH

C

H

C C H H

H H

OH OH OH

C

H

C C H H

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4.

The order of viscosity of the three hydroxy compounds from the most viscous to the least viscous is as follows:

1, 2, 3-trihydroxypropane > 1, 2-propandiol > propan-1-ol.

(i) Why does 1, 2, 3-trihydroxypropane have the highest viscosity?

_______________________________________________________________________

(1 mark) (ii) Devise a simple test to show that 1, 2, 3-trihydroxypropane is the most

viscous.

_______________________________________________________________________

(1 mark)

QUESTION 3

Vanadium, which is a transition metal has variable oxidation states with their corresponding colours.

(a) For the vanadium species, VO2+, state the colour and the oxidation state of vanadium.

Colour: ____________________________________

Oxidation state: ______________________________

(1 mark)

(b) Transition metals are also capable of forming complex ions and salts. In the preparation of tetrammine copper (II) sulphate, Cu(NH3)4SO4.H2O, ethanol is

added during the process. State the reason why it is added.

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark)

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(c) An acid HX is found to be a weak electrolyte. Explain what happens to the degree of dissociation (increases/decreases) of HX in aqueous solution if:

(i) water, H2O is added

_______________________________________________________________________

_______________________________________________________________________ (1 mark) (ii) gaseous HCl is added

_______________________________________________________________________

_______________________________________________________________________ (1 mark) (iii) solid NaX is added

_______________________________________________________________________

_______________________________________________________________________ (1 mark)

QUESTION 4

(a) The alkyl halide, 2-chloro-2-methyl propane is prepared by reacting together methyl-propan-2-ol and concentrated hydrochloric acid.

(i) Write an equation using structural formula for the above preparation.

_______________________________________________________________________

_______________________________________________________________________ (1 mark) (ii) During the preparation, sodium bicarbonate is also added. State the

purpose of its addition and name the gaseous product formed.

Purpose: _______________________________________________________________

_______________________________________________________________________

Gaseous product: ___________________________________________

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6.

(b) Some students made the following models of molecules while studying various types of isomerism.

I. II.

(i) Which one of the models drawn above represents an optical isomer?

________________________________________________________ (1 mark) (ii) Explain the choice of your answer in (i) above.

_______________________________________________________________________

_______________________________________________________________________ (1 mark) (c) To prepare a solution of iodine for the Iodoform test, the following method is

applied.

“To 50 mL of water, add 70 g of iodine and 50 g of potassium iodide (KI). Dilute to 1 litre with alcohol.”

Why was potassium iodide dissolved in water together with the iodine?

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark)

QUESTION 5

(a) The pH of a 0.5 molL−1 solution of lactic acid (2-hydroxypropanoic acid), CH3 CH(OH)COOH is 3.0.

The acid dissociates in water according to the equation:

(i) Write the acid dissociation constant expression, Ka for lactic acid.

_______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ (1 mark) 5 + OH

C COOH

H

CH3 H2O CH3 C COO− + H3O+

OH

H CH3

C

OH COOH Cl

H

C

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(ii) Calculate the value for Ka.

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

(b) In order to measure the solubility product of silver acetate, a student followed the following instructions from the laboratory manual.

1. To each of the seven clean dry graduated test tubes, add varying volumes of 0.2 molL−1 solution of silver nitrate and 0.2 molL−1 solution of sodium acetate.

2. Add distilled water to each of the seven test tubes until the 30 mL mark is reached.

3. Mix the contents of each test tube by swirling and leave them for 30 minutes, scratching the inside of each test tube below the liquid level with a clean glass rod.

(i) Why did the student add distilled water?

_______________________________________________________________________ (1 mark) (ii) Why was the inside of each test tube scratched with the glass rod?

_______________________________________________________________________

_______________________________________________________________________ (1 mark)

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QUESTION 6

In an experiment involving a solution of sodium hydroxide and hydrochloric acid, 40 mL of 0.3 molL−1 solution of sodium hydroxide was rapidly mixed with 40 mL of 0.3 molL−1 hydrochloric acid in a styrofoam cup.

Equation for the reaction:

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

Results of the experiment:

Initial temperature of NaOH(aq) = 28.5ºC

Initial temperature of HCl(aq) = 28.5ºC

Final temperature of the mixture = 33ºC

(a) Explain why a styrofoam cup was used instead of a glass beaker.

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark)

(b) Explain why the two solutions were mixed rapidly.

_____________________________________________________________________________

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(c) Calculate the enthalpy change of this reaction in kJmol−1.

(Assume specific heat capacity of the solution is the same as that of water, that is, 4.2 J/gºC).

_____________________________________________________________________________

_____________________________________________________________________________ (3 marks)

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10.

QUESTION 7

In an experiment to determine the purity of an iron (II) salt, a student recorded the following procedure and results.

Procedure:

1. 0.65 g of iron (II) sulphate crystals was weighed.

2. The salt was dissolved in about 20 mL of sulphuric acid solution in a conical flask.

3. The whole content of the flask was then titrated with a previously standardised solution of potassium permanganate (KMnO4).

Results:

Concentration of KMnO4 = 0.02 molL−1

Volume of KMnO4 required for neutralisation = 42.5 mL

Balanced equation for the reaction:

MnO₄−₍_aq₎ + 5Fe₍2_aq+₎ + 8H+₍_aq₎ Mn2₍_aq+₎ + 5Fe3₍_aq+ ₎ + 4H₂O₍_l₎

(i) Why was the salt dissolved in sulphuric acid solution rather than in water?

_____________________________________________________________________________

(1 mark)

(ii) Calculate the number of moles of permanganate, MnO−4 used in the titration.

_____________________________________________________________________________

(1 mark) (iii) Calculate the mass of Fe2+ present in the sample.

_____________________________________________________________________________

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(iv) Determine the percentage purity of the sample of iron (II) sulphate used.

_____________________________________________________________________________

(1 mark) (v) State the colour change that would be observed during the titration.

_____________________________________________________________________________ (1 mark)

QUESTION 8

A group of Form 7 students set up the following galvanic cell to measure the potential difference between its electrodes. The diagram is partly labelled.

(i) Identify A and B.

A: _______________________________________________

B: _______________________________________________

(1 mark) 5

copper metal

solution of copper nitrate

magnesium metal

solution of magnesium nitrate

A

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12.

(ii) Give one importance of B in a galvanic cell set-up.

_____________________________________________________________________________

(1 mark)

(iii) On the diagram given above, use an arrow to indicate the direction of the flow of

electrons. (1 mark)

(iv) Write the cell notation for this galvanic cell.

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark)

(v) Calculate the potential difference between the electrodes of the cell assuming standard conditions.

Cu2+ / Cu Eº = + 0.34 V Mg2+ / Mg Eº = − 2.36 V

_____________________________________________________________________________

_____________________________________________________________________________ (1 mark)

THE END

__________________________

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INDEX NUMBER

CHEMISTRY PAPER 2 FOR MARKER’S USE

Ques.

No.

Marks

Gained Check

Mark

1

2

3

4

5

6

7

8