CHEMISTRY STPM Trial First Term 2013

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SUMMATIVE ASSESSMENT FIRST TERM STPM 2013

CHEMISTRY 962/1 One hour and a half hours

2 Section A [15 marks] Answer all questions in this section. 12

1

6

14

C and

6

C atoms are isotopes of carbon. Which of the following is the same

for the isotopes? A B C D 2

Stability Nuclear charge Nucleon number Relative isotopic mass

Relative intensity

0

20

40

60

80

100 120 140 160

m/e

Which of the following unknown organic compound will release a spectrum as the one shown above? A B C D 3

C4H8 C8H16 C10H20 C10H22

Vanadium has the electronic configuration of 1s22s22p63s23p63d34s2. Which ion does not exist? A

VO42-

B VO3-

C

VO2+

D VO2+

3 4

The energy-level diagram for a hydrogen atom shows several electronic transitions with frequencies f1, f2, f3, f4 and f5.

Energy n=∞ n=4 n=3 f4

f1

f2

n=2

f5

n=1 f3

Which of the following statements is / are true of the above diagram? I II III IV A B C D 5

I and II I and IV II and III III and IV

Based on the band theory, the conductivity of metal is due to delocalized electrons in the conduction band. How many electrons are found in the conduction band of a 10.0 g magnesium metal strip? [Relative atomic mass of Mg is 24.0; Avogadro constant is 6.02 x 1023 mol-1] A

6

f1 represents the convergence limit of the Lyman series. f1, f2 and f3 represent lines in the Lyman series. f4 and f5 are used to calculate the difference between the energy levels of n = 3 and n = 4. The electronic transition of f3 gives a line spectrum that corresponds to the region of visible light.

2.51 x 1023

B

5.02 x 1023

C 2.51 x 1024

Which of the following has van der Waals forces? A B C D

Sulphur. Diamond. Sodium chloride. Magnesium oxide.

D

3.01 x 1024

4 7

Which species is drawn with the correct shape? O [ I — I — I ]-

A

2-

O

B

S O

O H

B C

D F

F

P

F H

H

8

The diagram above shows the body-centred cubic structure of a unit cell. How many atoms are there in the unit cell above? A 9

1

B 2

C 3

D 4

The Boltzmann distribution curves at temperature T1 and T2 are shown below.

Fraction of molecules T2 T1 Energy

Ea At temperature T1, I II III IV

the activation energy is lower. more molecules have lower energy. the total number of molecules remain constant. the maximum point of the curve is displaced to the right.

A

I and II

B

I and IV

C

II and III

D

III and IV

5 10

A phase diagram of water is shown below. C

B

Pressure / Pa

611

O A

Temperature / K

273.16 What can you deduced from the phase diagram? A B C D 11

An increase in pressure will decrease the freezing point of water. An increase in pressure will decrease the boiling point of water. Ice sublimes at a pressure higher than 611 Pa. Water exists as liquid at a pressure of 611 Pa and temperature of 298K.

The kinetic data for the reaction A + 2B → C at a certain temperature is shown in the following table. Experiment 1 2 3

Initial cencentration [A]o [B]o a b 2a b a 2b

Initial rate of reaction r 4r r

What is the rate of the reaction? A 12

k[A]2

B k[B]2

C k[A][B]2

D k[A]2[B]

A 2.0 dm3 stoppered flask at T oC contains 0.50 mol of SO2, 0.010 mol of O2 and 4.6 mol of SO3 at equilibrium. Calculate Kc for the following equilibrium at T oC. 2SO2 (g) + O2 (g) A B C D

5.9 x 10-5 dm3 mol-1 9.2 x 102 dm3 mol-1 8.5 x 103 dm3 mol-1 1.7 x 104 dm3 mol-1

2SO3 (g)

6 13

Which underlined molecule reacts as a Lewis base? A B C D

14

The solubility product, Ksp of magnesium hydroxide in pure water at 25 oC is 2.0 x 10-11 mol3 dm-9. What is the solubility of magnesium hydroxide when an excess of solid magnesium hydroxide is shaken in 1 dm3 of 0.1 mol dm-3 sodium hydroxide? A B C D

15

K2O + SO3 → K2SO4 BF3 + NH3 → H3N.BF3 OH- + CO2 → HCO3CH3Cl + FeCl3 → CH3+ + FeCl4-

2.0 x 10-13 mol dm-3 4.0 x 10-12 mol dm-3 4.0 x 10-11 mol dm-3 2.0 x 10-9 mol dm-3

The phase diagram of a mixture of two liquids P and Q is as follows: Vapour pressure / atm

1.0

1.0

Mole fraction

Q

P

What could P and Q be? P A B C D

Trichloromethane Benzene Ethanol Carbon disulphide

Q Propanone Methylbenzene Water Propanone

7 SECTION B [15 marks] Answer all questions in this section. 16

The mass spectrum of a gaseous compound is shown below.

Percentage abundance

(a)

Write the formula of ions responsible for each of the peaks labelled A, B, C and D. [2 marks]

(b)

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

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

C: ------------------------------

D: ---------------------------------

(i)

Write a possible formula for the compound with m/e value of 92 [2 marks] ------------------------------------------------------------------------------------------

(ii)

Name the compound -------------------------------------------------------------------------------------------

(c)

The four naturally occurring stable isotopes of iron are given in the table below. Relative atomic mass Relative abundance / %

53.94 5.82

Determine the relative atomic mass of iron.

55.93 91.80

56.94 2.10

57.93 0.28 [2 marks]

8 17.

The diagram below represents the energy levels of the orbitals in atoms of the third period.

Energy

(a)

Indicate the type of orbitals at each energy level electrons in the diagram above. [2 marks]

(b)

Draw and label all the possible shapes of orbitals at the energy level, n = 2. [4 marks]

(c)

In the above diagram, mark the valence electron configuration for phosphorus, using arrows to represent electrons in the diagram above. [3 marks]

9 SECTION C [30 marks] Answer any two questions in this section. 18

(a)

Ammonia is a colourless gas with a pungent smell. It reacts with hydrogen ions in acids to form ammonium ions, NH4+. Draw a Lewis structure for ammonia and the ammonium ion. [2 marks]

(b)

The H—N—H bond angles in ammonia and ammonium ion are 107° and 109.5° respectively. Explain the difference in these bond angles. [4 marks]

(c)

The reaction between fluorine and nitrogen dioxide was carried out at T K. F2(g) + 2NO2(g)

2NO2F(g)

The following data were obtained when the reaction was carried out using different concentrations of the gases.

What is the order of the reaction with respect to (i) (ii) (iii) 19.

(a)

fluorine and nitrogen dioxide? Write the rate equation for the reaction. Propose a possible mechanism for this reaction.

[4 marks] [ 1 mark ] [4 marks]

Nitrogen monoxide, NO can be prepared from the reaction between nitrogen and oxygen. N2(g) + O2(g)

2NO(g)+

∆H = +180.5 kJ

State how (i) Kc and (ii) the amount of NO will change when an equilibrium mixture of N 2, O2 and NO is subjected to the following changes. (i) (ii) (iii) (iv)

More O2 is added The volume is increased The temperature is decreased A catalyst is used [8 marks]

(b)

Carbon monoxide can be used to reduce steam to hydrogen. CO(g) + H2O(g)

H2(g) + CO2(g)

2.20 mol of CO(g) and 1.71 mol of H2O are placed in an empty 1.00 dm3 flask at T °C. After equilibrium was reached, the concentration of CO was 0.78 mol dm -3. Calculate (i) (ii) (iii)

the concentration of H2O(g) at equilibrium the value of Kc at T °C for the above reaction the value of Kc at T °C for the reaction, H2(g) + CO2(g) CO(g) + H2O(g)

[2 marks] [2 marks] [3 marks]

10 20.

(a)

(i) (ii)

(b)

A 25.0 cm3 sample of saturated, aqueous magnesium hydroxide required 19.2 cm3 of 0.050 mol dm-3 hydrochloric acid for neutralisation. Calculate (i) (iii)

What do you understand by the term solubility product? [2 marks] Write an expression for the solubility product of magnesium hydroxide, Mg(OH) 2. [2 marks]

the hydroxide ion concentration of the saturated solution, a value for the solubility product of magnesium hydroxide, stating the units.

[2 marks] [2 marks]

(c)

The buffer system, H2PO4 - / HPO4 2- in blood helps to keep the pH of blood at about 7.40. (i) (ii)

Calculate the [H2PO4 -] / [ HPO42- ] ratio at the normal pH of blood. [Ka H2PO4 - : 6.2 x 10-8 mol dm -3] Using a suitable equation, explain what happens when;

[3 marks]

I) a small amount of strong acid is added to this buffer system. II) a small amount of strong base is added to this buffer system. [4 marks]

END OF QUESTION PAPER

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