Chemistry Paper 2

1 Identity card number.................................................Centre number/index number:............................ (Nombor kad pengenalan) (Nombor pusat/angka giliran)

962/2 TRIAL STPM 2009 (PEPERIKSAAN PERCUBAAN STPM 2009)

CHEMISTRY (KIMIA) PAPER 2 (KERTAS 2) Two and a half hours (Dua jam setengah)

Instructions to candidates: DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE TOLD TO DO SO. Answer all questions in section A. Write your answers in the spaces provided. All working should be shown. For numerical answers, units should be quoted wherever they are appropriate. Answer any four questions in section B. Write your answers on the answer sheets provided. Begin each answer on a fresh sheet of paper and arrange your answers in numerical order. Tie your answer sheets to this question paper.

For examiner’s use 1 2 3 4 5 6 7 8 9 10 Total

This question paper consists of 9 printed pages.

2 Section A [ 40 marks ] Answer all questions in this section. 1.(a) The relative atomic mass of an element X is 63.55 (i)

Why is the relative atomic mass of X not a whole number ?

………………………………………………………………………………………………… [1 mark] (ii) X contains two isotopes with nucleon number 63 and 65. Given that the masses of 63 X and 65X are 62.93 and 64.93 respectively.Calculate the relative abundance of the isotopes 63 X and 65X. [3marks]

(iii)

If X exist as a monoatomic element,sketch the mass spectrum of X . [2marks]

(b) (i) Write the fundamental particles for each species in the table below. Species 20

protons

neutrons

electrons

Ne

10

16

O2-

8

[3 marks] (ii)What are the relationship between the two species. ………………………………………………………………………………………………… [ 1 mark]

3 2(a) The mechanism for the ionization of iodide ion by hydrogen peroxide is as shown below : H2O2 +

slow

I¯

fast

H + + IO ¯

fast

HIO + H + + I ¯

H2O + IO ¯ HIO H2 O + I2

(i) Write the overall equation for the reaction above. ............................................................................................................................................................ (ii) What is the rate equation for the oxidation above? ............................................................................................................................................................ (iii) The data obtained from one experiment about the oxidation above is shown below. By assuming that this data is consistent with the mechanism that is suggested, complete the table below. Initial concentration (mol dm-3)

Initial rate (mol dm-3 s-1) H2O2

H+

I¯

1.0 x 10 -4

0.1

0.1

0.1

2.0 x 10 -4

............

0.1

0.1

1.0 x 10 -4

0.1

0.2

............

2.0 x 10 -4

0.2

0.1

0.2

(iv) What is the overall order for the reaction above? ............................................................................................................................................................. [5 marks]

4 (b) The graph below shows the relationship between lg ionization energy and the number of

lg ionization energy

ionizations for all electrons in an atom of X.

(i)

How many protons are there in the nucleus of atom X? .............................................................................................................................................................

ionization number

(ii)

Write the electron configuration for atom X. .............................................................................................................................................................

(iii)

If atom X forms a cation, what is its most probable charge? Give a reason .

............................................................................................................................................................ ........................................................................................................................................................... (iv) Predict the electricity conductivity of element X compared to the other element on its left in the same peiod of the Periodic Table.

............................................................................................................................................................ [5 marks]

5 3.(a) Explain why the reactivity of Group 2 elements in the Periodic Table increases when descending the group from beryllium to barium. ............................................................................................................................................................. ............................................................................................................................................................. ………………………………………………………………………………………………………. [2 marks] (b) i. Write a balanced equation for the reaction of the hydrated beryllium ion , [Be(H 2O)4]2+, in water. ............................................................................................................................................................. ii. What is the property exhibited by the hydrated beryllium ion in the above reaction? ............................................................................................................................................................. [2 marks ] (c) Explain briefly why beryllium forms covalent compounds compared with other elements in the same group. ............................................................................................................................................................. ............................................................................................................................................................. [ 2 marks ] (d) Nitric (V) acid is manufactured from ammonia in the Ostwald process.. i. Name the catalyst used in this reaction. ………………………………………………………………………………………………………. ii. Write equation to show the formation of nitrogen monoxide in the Ostwald process. ……………………………………………………………………………………………………… iii. Predict qualitatively the conditions of temperature and pressure that will give a maximum yield of nitrogen monoxide at equlibrium. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… [4 marks]

6 4.(a) Butanenitrile, CH3CH2CH2CN, is hydrolysed in acidic conditions to yield compound A. When compound A is reacted with phosphorus pentachloride, a compound B is produced. Compound B reacts with ethanol to produce a liquid C which has a sweet smell. i. Determine the structural formulae for compounds A, B, and C. A B C ii. Give the IUPAC name for the compound B. ……………………………………………………………………………………….. iii. Write the chemical equation for the formation of compound C. ………………………………………………………………………………………. [ 5 marks] (b) Glycine (2-aminoethanoic acid) and alanine (2-aminopropanoic acid) are two simple amino acids. i. Draw the structure of the zwiterion of glycine

ii Describe the formation of two possible types of dipeptides from glycine and alanine by giving the equations for the reactions involved. Give the names of the dipeptides formed.

iii. Explain what happens when alanine reacts with hydrochloric acid. Write the equation for the reaction involved. ………………………………………………………………………………….. …………………………………………………………………………… [5 marks]

7

Section B [ 60 marks ] Answer any four questions in this section. 5. (a) Hunds rule and Aufbau principle are two fundamental principles used in electronic configuration of elements. (i)Hunds Rule states that in a set of degenerate orbitals, the orbitals are each filled with one electron with parallel spins before pairing occurs. State the meaning of degenerate orbitals and give example of a set of degenerate orbitals. (ii)Using Aufbau’s principle, explain how the valence electron configuration for nitrogen is written. [ 6 marks ] (b) Give the electronic configuration of iron in the oxidation state of +2 and +3. Hence explain why iron(III)compounds are more stable than iron (II) compounds. [ 4 marks ] (c ) Explain the overlapping of orbitals in ammonia molecule. [ 5 marks ] 6. (a) What do you understand by dynamic equilibrium? [ 2 marks ] (b) In an experiment, 0.100 moles of dinitrogen tetraoxide is allowed to dissociate to nitrogen dioxide in a 1.00 dm3 container at 383 K. The graph of concentrations of both gases against time is shown below.

(i) Calculate the equilibrium constant, Kc for the above reaction at 383 K. (ii) Calculate the pressure in the container after the system had achieved equilibrium at 383 K. [ 8 marks ]

8

(c) The graph below shows the percentage of ammonia gas in an equilibrium mixture for the system N2(g) + 3H2(g) 2NH3(g) at various temperatures and pressures. 100 -

473 K

% ammonia in 80 equilibrium mixture 60 -

673 K

773 K

40 20 0

0

2.0

4.0

6.0

8.0

10.0

12.0 Pressure, p x 104 kPa

Explain the conclusions that can be obtained from the graph above.

[5 marks]

7. (a) The ore of aluminium is bauxite. (i) Briefly describe the extraction of aluminium from pure bauxite. (ii) Explain the use of aluminium in aircraft construction.

[ 7 marks]

(b) Aluminium, silicon,phosphorus and sulphur are Third Period elements in the Periodic Table. The melting points of the elements are given in the following table. Element Aluminium Silicon Phosphorus Sulphur

Melting points/0C 660 1410 44 119

Explain the melting points of the elements in terms of structure and bonding. [8 marks] 8. (a) Explain why chlorine is used in the large scale preparation of bromine from sea water which contains bromide ions. [4 marks] (b) Explain why iodine is more soluble in potassium iodide solution than in water.Write balanced equations for the reactions that occur. [4 marks] © How,and under what conditions,does sodium chloride react with concentrated sulphuric acid ? Write balanced equations for the reactions that occur. [4 marks] (d) Explain what happens when solid potassium iodide is heated with concentrated sulphuric acid. [3 marks]

9

9.( a ) Three compounds W, X and Y have the following structures shown below: W ―NH2 (i)

X

Y

CH3 CH2NH2

NH3

Arrange W, X and Y in ascending order of their basicity. Explain your answer.

[ 5 marks ]

( ii ) W has a pKb value of 9.39. Predict the pKb value of the compound Z shown below. Compound Z :

―NH2 Cl

Explain your answer. (b)

[ 4 marks ]

Nitration of benzene is an electrophilic substitution reaction. Write the reaction mechanism of the nitration of benzene. In your answer, state the reagents and conditions of the reaction. [6 marks ]

10. ( a ) A synthetic polymer R is synthesised from monomers P and Q shown below. P:

HOCH2CH2OH

and

Q

: HO2C–

–CO2H

( i ) Name this synthetic polymer R and draw two repeating units of this polymer. ( ii ) State the type of polymerisation that takes place during the formation of R and give one use of R in our daily life. [5 marks] ( b ) The molecular formulae and some properties of two compounds K and L are given below. For each compound, identify a functional group which must be present and give the structural formulae of two possible isomers. ( i ) K , C3H8O, gives white fumes of hydrogen chloride with phosphorus pentachloride. ( ii ) L , C3H6O , gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent. For each pair of isomers K and L, give one chemical test that would enable you to distinguish between them, stating clearly how each isomer would behave. [10 marks] END OF QUESTION PAPER

10 No. 7 (a) (i) Aluminium metal is extracted by electrolysis The electrolyte is molten bauxite in sodium hexafluoroaluminate. The electroyte has aluminium ion and oxide ions. Anode : 2O2- --- > O2 + 4e Cathode : Al3+ + 3e --- > Al [5] (ii) (Any 2 points) light Resistant to corrosion Strong alloy [2] `(b)

No 8.

aluminium : A giant metallic structure, strong metallic bonf. Silicon : giant 3 D covalent structure. Strong covalent bond between silicon atomes. higher melting point Phosphorus and sulphur - Both are simple molecules. Weak van der waals between molecules Sulphur has a stronger intermolecular forces – S8 larger than P4 [8]

(a) chlorine – strong oxidation agent Bromide is oxidized to bromine E° of chlorine is more positive than that of bromine. Cl2 + 2Br- ---- > 2Cl- + Br2 [4] (b) iodine forms triodes complex in KI. I2 + I- ---- > I3Iodine does not form any complex ions in water. I2 + 2H2O --- > I- + HIO + H3O+ [4]

(b) HCl is released in cold acid NaCl + H2SO4  NaHSO4 + HCl If heated more HCl released. NaHSO4 + NaCl - Na2SO4 + HCl [4] (d) Iodide is oxidized to iodine Purple Iodine is released Pungent smell of H2S is detected

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