First-term Examination (1999/2000)
Level : Form 6
Subject : Chemistry
Full marks : 100 marks
Time allowed : 3 hours
NameClass / Number
This paper must be answered in English
QUESTION-ANSWER BOOK
INSTRUCTIONS
1. There are THREE sections in this paper, Section A, Section B and Section C.
2. Section A carries 20 marks,
Section B carries 20 marks, and
Section C carries 60 marks.
3. All questions in Sections A and B are COMPULSORY. Write your answers in the spaces provided in this Question-Answer Book.
4. Answer ALL question in Section C. Answers are to be written in the extra Answer Book provided.
5. Write your name, class and class number in the spaces provided on this cover.
6. Some useful constants and a Periodic Table are printed on page 12
1
- SECTION A -
Answer ALL questions in this section. Write your answers in the spaces provided.
1. When 0.1 mole of atoms of an element react with chlorine, there is an increase in mass of 7.1 g. The chloride formed has a high melting point. The element could be
A. carbon. B. magnesium.
C. sodium. D. silicon.
E. sulphur. ______
B
2. Which of the following is most likely to form a chloride of the type MCl2?
1st / 2nd / 3rd / 4th / 5thA. / 1090 / 2350 / 4610 / 6220 / 37800
B. / 1400 / 2860 / 4590 / 7480 / 9400
C. / 494 / 4560 / 6940 / 9540 / 13400
D. / 736 / 1450 / 7740 / 10500 / 13600
E. / 1310 / 3390 / 5320 / 7450 / 11000
______
3. 100 cm3 of 0.5 M H2SO4 is added to 400 cm3 of 0.1 M KOH. The final concentration of hydrogen ions is
A. 10-7 M. B. 0.01 M.
C. 0.06 M. D. 0.12 M.
E. 0.24 M. ______
D
4. Archaeologists can determine the age of organic matter by measuring the proportion of 14C present. Assuming that carbon-14 has a half-life of 5600 years, a piece of wood found to contain one-eighth as much carbon-14 as living material is calculated to have an age, in years, of
A. 44 800 B. 16800.
C. 2 800. D. 1 400.
E. 700 ______
5. A commercial production of iodine involves the reduction of a solution of iodate(V) ions (IO3-) with the theoretical quantity of hydrogensulphate(IV) ions (HSO3-). The hydrogensulphate(IV) is oxidised to sulphate(VI) ions while the iodate(V) is reduced to iodine (I2). How many moles of hydrogensulphate(IV) ions are needed to reduce one mole of iodate(V) ions?
A. 0.4 B. 1
C. 2 D. 2.5
E. 5 ______
D
Directions: Questions 6 to 8 refer to the titration of a chloride solution with silver nitration solution. The student measured the chloride solution into a conical flask with a pipette, added chromate indicator and then ran in the silver nitrate solution from a burette.
6. The student did not always read the burette with his eye at the level of the meniscus. This would
A. make his estimate of the chloride concentration too high.
B. make his estimate of the chloride concentration too low.
C. involve an error which reduced the accuracy of his determination in a random way.
D. involve errors which cancel each other out.
E. involve no error of any sort. ______
C
7. At the beginning of the experiment the student had poured the silver nitrate solution into a beaker which he had carefully washed with distilled water only. This would
A. make his estimate of the chloride concentration too high.
B. make his estimate of the chloride concentration too low.
C. involve an error which reduced the accuracy of his determination in a random way.
D. involve errors which cancel each other out.
E. involve no error of any sort. ______
A
8. The jet of the burette was not initially filled with the silver nitrate solution. This would
A. make his estimate of the chloride concentration too high.
B. make his estimate of the chloride concentration too low.
C. involve an error which reduced the accuracy of his determination in a random way.
D. involve errors which cancel each other out.
E. involve no error of any sort. ______
A
9. 0.05 g of a gaseous hydrocarbon occupies 80 cm3 at 380 mmHg and 298 K. What is the number of carbon atoms in each molecule of the hydrocarbon?
(molar volume of gas at 760 mmHg and 298 K = 24 000 cm3)
A. 1 B. 2
C. 3 D. 4
E. 5 ______
B
10. Which of the following solutions contains the greatest number of ions?
A. 0.8 dm3 of 1.0 M CrCl3∙6H2O
B. 0.6 dm3 of 2.0 M CaCl2∙6H2O
C. 0.8 dm3 of 1.0 M Cr2(SO4)3∙18H2O
D. 0.7 dm3 of 0.5 M K2SO4∙Al2(SO4)3∙24H2O
E. 0.8 dm3 of 2.0 M Na2SO4∙10H2O ______
E
11. Which of the following reactions is accompanied by an enthalpy change which is equal to the bond energy for H-I?
A. 2 HI(g) à H2(g) + I2(g)
B. HI(g) à ½ H2(g) + ½ I2(g)
C. HI(g) à ½ H2(g) + ½ I2(s)
D. HI(g) à H(g) + I(g)
E. HI(g) à H+(g) + I-(g) ______
D
12. In which one of the following molecules would you expect to find the smallest angle between two adjacent covalent bonds?
A. BeH2 B. BF3
C. CCl4 D. NH3
E. OH2 ______
E
13. Which of the following analytical techniques makes use of vibration within molecules?
A. electron diffraction B. atomic emission spectroscopy
C. mass spectroscopy D. X-ray diffraction
E. infra-red absorption spectroscopy ______
E
14. The vapour of an organic compound requires three times its own volume of oxygen for complete combustion, and produces twice its own volume of carbon dioxide. Which of the following compounds would give these results?
(1) CH3CHO (2) C2H5OH (3) C2H4
A. (1) only B. (3) only
C. (1) and (2) only D. (2) and (3) only
E. (1), (2) and (3) ______
D
15. The graph below shows the relative abundances of four isotopes of a certain element.
The relative atomic mass will be (to the nearest whole number)
A. 64. B. 65.
C. 66. D. 67.
E. 68. ______
16. Two identical flasks at the same temperature contain 4 g of helium and 4 g of hydrogen respectively. The ratio, in number of molecules of helium to the number of molecules of hydrogen, is
A. 1 : 4 B. 1 : 2
C. 1 : 1 D. 2 : 1
E. 4 : 1 ______
B
17. An element X forms three different compounds. The following table gives the relative molecular mass and percentage of X for the three compounds.
Relative molecular mass / Percentage of XCompound 1 / 100 / 48
Compound 2 / 40 / 40
Compound 3 / 64 / 50
What is the probable relative atomic mass of X?
A. 16 B. 32
C. 40 D. 48
E. 50 ______
A
Directions: Questions 18 and 19 refer to the diagram below. The apparatus shown can be used to determine the relative molecular mass of a volatile liquid L
. 18. The mass of liquid L introduced into the gas syringe would be found by
A. weighing the hypodermic syringe immediately before and after introducing the liquid into the gas syringe.
B. weighing the hypodermic syringe before filling with liquid and again after introducing the liquid into the gas syringe.
C. measuring the volume of liquid used and calculating the mass from its density.
D. measuring the volume of vapour L produced in the gas syringe and calculating the mass using its density.
E. weighing the gas syringe before and after the experiment. ______
A
19. Which of the following liquids could NOT be successfully used in the same way as L in this experiment?
Liquid / Relative molecular mass / Boiling point ( K) / Density (g cm-1)A. / 1,1,1-trichloroethane / 133 / 347 / 1.33
B. / Trichloromethane / 120 / 334 / 1.48
C. / Methylbenzene / 92 / 383 / 0.86
D. / Tetrachloromethane / 154 / 349 / 1.59
E. / Butanone / 72 / 352 / 0.80
C ______
20. Which of the following can accept an electron pair in the formation of a dative covalent bond?
(1) NH3 (2) AlCl3 (3) BF3
A. (1) B. (3) only
C. (1) and (2) only D. (2) and (3) only
E. (1), (2) and (3) ______
D
END OF SECTION A
- SECTION B -
Answer ALL questions in this section. Write your answers in the spaces provided.
1. Bronze is an alloy containing copper and tin. The percentage of tin in the alloy was determined by the method described.
Step 1: 15.0 g of finely powered bronze was warmed with excess dilute sulphuric acid to convert all the tin to tin(II) sulphate. The mixture was then filtered, and the colourless filtrate was made up to 250 cm3.
Step 2:25.0 cm3 portion of the tin(II) sulphate solution was transferred into a conical flask and about 25 cm3 of 1.0 M sulphuric acid was added as well. The mixture was then titrated against 0.0200 M potassium manganate(VII) solution. 28.0 cm3 of potassium manganate(VII) solution was needed to oxidize the tin(II) to tin(IV).
(a) Explain why the mixture was filtered.
(b) Suggest suitable apparatus for
(i) transferring the 25.0 cm3 portion of tin(II) sulphate solution, and
(ii) adding 25 cm3 of 1.0 M sulphuric acid.
(c) Suggest whether dilute nitric acid could be used in this experiment. Explain your answer.
(d) (i) Give the change in oxidation number of manganese
(ii) Write the ionic equation for the reaction of tin(II) with manganate(VII) in an acidic medium.
(iii) Calculate the percentage by mass of tin in the alloy.
(10 marks)
2. (a) Under what conditions of temperature and pressure is the behaviour of real gases most nearly ideal? Explain your answer.
(3 marks)
(b) Using the following data to calculate the apparent molecular mass of a mixture of krypton and xenon obtained from the air. 1.00 dm3 of the mixture at a pressure of 8 x 104 Pa and a temperature of 300 K had the mass of 2.79 g.
(2 marks)
3. Seven sets of experiment were set up. In each set-up, 200 cm3 of a chloride solution of metal M was electrolyzed. The quantity of electricity passed was measured in each case. At the end of each experiment, the cathode was removed from the electrolyte and dried. The results are tabulated:
Set-up / Increase in mass of cathode (g) / Number of coulombs passed / Colour of solution after electrolysis1 / 1.50 / 4 950 / Green
2 / 3.70 / 12 200 / Green
3 / 7.50 / 24 750 / Pale green
4 / 9.40 / 31 000 / Very pale green
5 / 11.71 / 41 000 / Colourless
6 / 11.69 / 44 800 / Colourless
7 / 11.70 / 50 000 / Colourless
(a) Plot a suitable graph to illustrate the Faraday’s First Law of Electrolysis.
(2 marks)
(b) Explain the colour change in the solution in the course of electrolysis.
(1 mark)
(c) Use the graph in (a) to work out the formula of the chloride of M. Given that the relative atomic mass of M is 58.5.
(2 marks)
-- END OF SECTION B --
99-00/Chm/S6/P.4