sk016 past year examination questions unit 5 unit 5

SK016

Past Year Examination Questions Unit 5

40

Unit 5: States of Matter

The Gaseous State

Jun 99

1. A group of matriculation students had done an experiment to determine the relative molecular

mass of gas X.

The table below shows the experimental data obtained at 25C.

Pressure (atm) 0.25 0.50 0.75 1.00 1.25

Density (g/L) 0.60 1.24 1.78 2.35 2.96

a) Determine the relative molecular mass of gas X using graph.

b) i. State the ideal gas equation and the van der Waals equation for real gas.

ii. Explain the differences between both equations.

Jan 99

2. The table below shows the changes in volume for 0.39g of gas A at temperature 25C.

Pressure, P/(kNm-2) Volume, V/(x 102 cm3)

20 3.53

40 1.76

60 1.18

80 0.88

100 0.71

i. Plot a graph of P values against 1/V.

ii. State the gas law that was obeyed by A. Explain.

iii. Based on the plotted graph, determine the molar mass of gas A.

Jan 00

3. Derive the ideal gas equation from the gas laws.

A 0.112-g sample of gas occupies 81.8 mL at temperature 127C and pressure 1 atm. Calculate

the relative molecular mass of the gas. <44.9>

Jun 00

4. In another experiment, 1.490 g of zinc reacted with excess hydrochloric acid. The released

hydrogen gas was collected using the water displacement method at temperature 23C and

pressure 99.99 kN m2. The vapour pressure of water at this temperature is 2.81 kN m2.

Calculate the volume of the dry hydrogen gas collected.

[Ar Zn=65; H=1; Cl=35.5] <0.580 L>

5. Give the three assumptions underlying the Kinetic Molecular Theory of gases. Hence explain

the Boyle’s law by using this theory.

Explain the conditions whereby gases would behave ideally.

SK016


41

MST 01

6. State the characteristics of ideal gas.

a) The density of a gas at temperature 27C and pressure 1.5 atm is 1.35 g L1. Calculate the

relative molecular mass of this gas.

b) This gas occupies 5.0 L at temperature 26C. If the temperature is raised to 300C,

calculate the change in volume of the gas at constant pressure. <9.6>

7. The total pressure exerted by a mixture of gases consisting of 3.20 g methane, CH4, 0.60 g

hydrogen, H2, and 11.20 g nitrogen, N2 at 25C is 2.20 atm. Calculate

i. the volume of the gas container. <10.00>

ii. the partial pressure of each gas. <0.49; 0.73; 0.98>

iii. the total number of molecules of gases in the mixture. <5.42x1023>

Mac 01

8. Silver oxide, Ag2O, when heated, it decomposes to form silver and oxygen gas.

i. Write a balanced equation for the decomposition of silver oxide.

ii. Calculate the volume of gas released at temperature 28.3C and pressure 749 torr if 4.262 g

of Ag2O decomposed completely.

[Ar Ag=108; O=16] <0.23>

UPS Jun 02

9. A 2-litre flask contains 4.40 g carbon dioxide gas, CO2 and 1.00 g nitrogen gas, N2 at 27C.

i. What is the partial pressure of each gas component in the flask? <1.23; 0.44>

ii. Calculate the total pressure in the flask. <1.67>

10. Name three gas laws and write down their mathematical expressions used in derivation of the

ideal gas equation.

11. A sample of an oxide of nitrogen separated from a car exhaust has a mass of 0.571 g and

occupy 1.00 litre at 356 torr and temperature 27C.

Determine its relative molecular mass and hence identify whether the oxide is NO or NO2. <30>

Mac 02

12. The van der Waals equation for 1 mol of real gas is as follow:

(P + 2V

a )(V b) = RT

Determine and explain whether

i. H2 molecule or H2S molecule has a higher value of a and b.

ii. a or b value that can be related to the boiling point.

MST Jul 03

13. a) State 2 differences between an ideal gas and a real gas.

b) The density of a gas is 3.73 g L1 at 120C and 960 mmHg.

Calculate the relative molecular mass of the gas.

SK016


42

Sept 03

14. The van der Waals equation for n moles of a real gas is

(P + 2

2

V

an)(V – nb) = nRT

where a and b are van der Waals’ constants. The values of a and b for gas A, B and C are given

in the following table.

Gas Molar volume/L Van der Waals’ constants / arbitrary unit

a B

A 22.398 0.034 0.02370

B 22.413 1.390 0.03913

C 22.414 3.592 0.04276

i. Derive the units for the constants a and b.

ii. Arrange the three gases in the above table with respect to increasing ideal gas behaviour.

iii. Gas C is more ideal at elevated temperatures. Explain.

iv. Almost all gases behave almost ideally at low pressures. Explain.

15. An experiment was carried out under high pressure and low temperature to determine the

relative molecular mass of CO2 gas. The following data were obtained.

Mass of empty bulb 25.40 g

Mass of bulb filled with CO2 gas at temperature 170C and

pressure 1.1x 103 atm 26.50 g

Mass of bulb filled with water 619.50 g

Calculate the relative molecular mass of CO2 gas. <0.04>

There is difference in value of the relative molecular mass between the one calculated above

and the one calculated from the molecular formula. Explain.

MST Jul 04

16. (a) What is the volume of 0.125 M HClO4 is required to neutralise 40 ml of 0.065 M NaOH.

The reaction that takes place is as follows:

HClO4 (aq) + NaOH(aq) NaClO4 (aq) + H2O()

(b) Give two differences between ideal gas and real gas.

(c) A mixture of gases contain 4.46 moles of neon (Ne), 0.74 mole of argon and 2.15 moles of

xenon (Xe). Calculate the partial pressures of the gases if the total pressure is 2.00 atm at a

certain temperature.

Oct 04

17. Sketch a graph of PV against T and T

PV against P for a constant number of moles of an ideal

gas. Explain both graphs.

SK016


43

MST Jul 05

18. A sample of 1.650 g Ag2O decomposed on heating and the oxygen produced was collected by

displacement of water at 25C and 750 mmHg. The equation of the reaction is,

2Ag2O(s) O2(g) + 4Ag(s)

If the vapour pressure of water at 25C is 23.8 mmHg, what is the volume of oxygen in litre.

Oct 05

19. Define Dalton’s law of partial pressures.

A certain mass of nitrogen gas is added to an vessel of 405 mL containing 0.52 g oxygen. The

gas pressure is increased from 745 mmHg to 980 mmHg. Assuming the temperature remains

constant and that the nitrogen gas does not react with oxygen gas, calculate the mass of the

added nitrogen. <0.144>

What will happen to the pressure of the closed vessel of nitrogen and oxygen if the temperature

is increased? Explain.

MST July 06

20. 2 moles of hydrogen gas are allowed to react with 1 mole of nitrogen gas in a 30 L container at

25 oC . If all hydrogen gas are converted to ammonia.

i. write a balanced equation for the above reaction.

ii. Calculate the total pressure after the reaction is completed.

Oct 06

21. (a) Gas C with a mass of 8 g at 0oC and 0.87 atm occupies a volume which is equal to volume

of 11 g CO2 at STP. Calculate the density and the molar mass of the gas.

What would be the pressure if the volume of the gas is doubled while the temperature is

kept constant ?

(b) A mixture containing 28 g of Ar and 14 g of Hbr gases are placed in an 8.0 L container at

30 oC . Determine the partial pressure of each gas and the total pressure inside the container.

Assume the gases are ideal.

MST July 07

22. Calcium carbonate, CaCO3, decomposes upon heating according to the following equation.

CaCO3(s) CaO(s) + CO2(g)

0.20 mol of CaCO3 is heated in a 2.0 dm3 vessel. After heating, it is found that the pressure of the

gas is 44.08 kPa at 30oC. Determine

i. the number of moles of gas formed from the decomposition of CaCO3.

ii. the mass of CaCO3 left after the reaction was completed.

iii. the partial pressure of hydrogen gas in the vessel when 0.10 mol of hydrogen gas is added to

the vessel at the same temperature.

SK016


44

Oct 07

23. State Charles`s law. Explain Charles`s law from a kinetic perspective.

A piston-cylinder holds 7.00 g of CO2 at 160 oC and 110 kPa. How many grams of CO2 will it

hold at 27 oC under the same pressure?

Oct 08

24. What is an ideal gas?

When 17.75g of Cl2 gas is filled into a 3L closed container at 27°C, the internal pressure of the

container increased to 1.6 atm. Determine whether Cl2 gas behaves as an ideal gas at this

condition. State the conditions when a gas deviates from an ideal behaviour. Explain your

answer. [ 8 marks]

MST Jul 08

25. b) Ammonium nitrous, NH4NO2 decomposes upon heating to form nitrogen gas.

NH4NO2 (s) →N2(g) + 2H2O(l)

When a sample of NH4NO2 was decomposed in a test tube, 0.511 L of nitrogen gas was

collected over water at 26°C and 745 torr. How many grams of NH4NO2 were decomposed?

[Vapour pressure of water at 26°C = 25 torr]

[Molar mass of NH4NO2 = 64.0 gmol-1]

[6 marks]

MST 09/10

26. (a) A sample of nitrogen at 25° C and 95.0 kPa contains moisture.

(i) Determine the partial pressure of nitrogen if the vapour pressure of water is 3.3 kPa

(ii) If the volume of the mixture is 4.5 dm3 , what is the mass of nitrogen in the mixture?

(b) (i) State the characteristics of an ideal gas.

(ii) Give the conditions that cause real gases to deviate from ideal behaviour?

(iii) FIGURE 1 shows a graph of PV/RT against pressure, P, for one mole of hydrogen

gas at a constant temperature.

FIGURE 1

Redraw the above figure and sketch lines to show the behaviour of one mole of an

ideal gas and one mole of ammonia at the same temperature.

[5 marks]

PV/RT

1.0

P

H2

SK016


45

2009/2010

27. (a) Derive the ideal gas equation from Boyle’s law, Charles’s Law and Avogadro’s principle.

[7 marks]

(b) Using the ideal gas equation, derive an expression which relates density, ρ, and pressure,

P of a particular gas. Calculate the value of the gas constant, R, if the density of oxygen

gas at STP is 1.428 g dm-3. [5 marks]

(c) What would be the possible temperature of a gas as P approaches 0 atm ? [3 marks]

MST 2010/2011

28. (a) FIGURE 1 shows three chambers with equal volume, connected by closed valves. Each

chamber contain helium gas at a constant temperature.

chamber A chamber B chamber C

1 mole of Helium

FIGURE 1

(i) State the chamber that has the highest pressure.

(ii) The initial pressure in chamber B is 1.0 atm. When all the valves are opened, the gas

from chamber A and C is forced into chamber B. What will be the new pressure of

chamber B? [ 5 marks]

(b) (i) Define boiling point.

(ii) TABLE 1 shows the vapour pressure of compound A and B at T °C.

TABLE 1

Compound Vapour pressure (torr)

A 55.3

B 92.0

Which compound has a higher boiling point? Explain. [ 5 marks]

SK016


46

2010/2011

29. Define Boyle’s law

A closed cylinder contains hydrogen gas under a pressure of 4.27 atm at a temperature of 25°

C . When the gas is allowed to expand to a final volume of 10.5 L, the pressure drops to 1.63

atm at the same temperature. Determine the original volume of the gas.

A mixture of 8.27 g of N2 and 20.4 of O2 is confined to a volume of 5.0 L at 25° C in another

closed cylinder. Determine the total pressure and the partial pressure of N2 and O2 in the

cylinder. State the law used for the calculation. [15 marks]

The Liquid State

Jun 99

30. What do you understand by the term boiling point.

“The boiling point of a liquid increases with increasing intermolecular attractive forces”.

Explain the above statement.

MST Jul 03

31. State the properties of liquid.

The following table shows the boiling points for a few liquids.

Liquid Ethanal,

CH3CHO

Ethanol,

CH3CH2OH

Methanol,

CH3OH

Boiling point/C 20 78 65

Arrange these liquids in order of increasing vapour pressure. Explain.

MST Jun 02

32. Using the kinetic theory, explain the changes that occur when ice was left at room

temperature.

MST Jul 06

33. i. Define boiling point of a liquid.

ii. State two factors affecting the boiling point.

MST Jul 07

34. i. What is the relationship between intermolecular forces and surface tension?

ii. Predict, with reasons, which liquid has a greater surface tension, ethanol (CH3CH2OH) or

dimethyl ether (CH3OCH3).

SK016


47

MST Jul 08

35 .a) Boiling points of benzene, water and butanol are 80°C. 100°C and 120°C

respectively at 1 atmospheric pressure. The graph below shows the variations of the

saturated vapour pressure of the three liquids against temperature.

Pressure (atm)

Temperature (°C)

Label the three liquids on the graph given in APPENDIX 1. Mark on the graph the

boiling point of each liquid.

[4 marks ] Oct 08

36. What is vapour pressure of a liquid?

Explain why vaporization occurs only on the surface of a liquid before the boiling

point temperature is reached.

[ 7 marks]

The Solid State

Oct 04

37. i. Define melting point and normal melting point of a substance.

ii. Describe the melting process in terms of the molecular kinetic theory.

Oct 07

38. When a solid is heated in a closed container, it undergoes phase changes. Describe the

process.

The Phase Diagram

Jan 00

39. Carbon dioxide has a triple point at temperature 57C and pressure 5 atm while its critical

point is at temperature 31C and pressure 73 atm.

Sketch a labelled phase diagram for carbon dioxide and explain how the melting point of

carbon dioxide changes with increasing pressure.

SK016


48

Aug 02

40. The following diagram represents the vapour pressure for substance Y.

Pressure

(mmHg) u

760

p q r s t

v

temperature

Explain the points u and v. State the phases that exist at points q and r.

Oct 04

41. Table below shows data phase equilibrium diagram for carbon dioxide.

Pressure (atm) Temperature (C)

Triple point 5.2 57

Critical point 73 31

a) Sketch a phase diagram for carbon dioxide.

b) By referring to the phase diagram, explain why solid carbon dioxide at ordinary

temperature and pressure does not melt, instead it sublimes.

c) Explain the phase changes that could possibly occur when a sample of carbon dioxide in a

closed vessel under 1 atm pressure and a temperature of -78C is pressurised isothermally

to 10 atm, followed by isobaric heating to 20C.

Oct 07

42. (a) TABLE 2 shows phase equilibrium data for substance D.

TABLE 2

Pressure (atm) Temperature (oC)

Sublimation point 2.5 - 80

Triple point 5.0 - 60

Critical point 40.0 30

Melting point 1 15.0 - 30

Melting point 2 35.0 - 15

Boiling point 1 20.0 10

Boiling point 2 30.0 25

Plot and label a phase diagram for D. Does D sublime at 20 atm? Explain your answer.

2011/2012

43. (a) Copy TABLE 1 into your answer booklet. Give a brief comparison between a solid

and a liquid according to the properties given in TABLE 1 by filling in the blank.

TABLE 1

Properties Solid Liquid

Shape

SK016


49

Surface tension

Viscosity

Compressibility

[8 marks]

(b) (i) Write the ideal gas equation for one mole of gas.

(ii) State two assumption made in the ideal gas equation.

(iii) Explain how assumption in (b) (ii) are addressed for the real gas in

the van der Waals equation,

where a and b are the van der Waals constants.

[7 marks]

44. Using copper, diamond, sulphur and sodium chloride to represent various crystalline

solids, identify the types of interparticle bonding that forms the state of the matter.

[ 8 marks ]

2012/2013

45. Carbon dioxide, CO2, has triple point at 5.2 atm and -57°C and a critical point at 72.9

atm and 31°C. Sketch a phase diagram of CO2. Based on the diagram, explain the

formation of solid CO2 (dried ice) at room condition and how liquid CO2 can be

obtained.

[8 marks]

46. (a) In the offshore base oil drilling operation, methane gas, CH4, was found at

the bottom of the sea at 480 °C and a pressure of 12.8 atm. (i) Calculate the volume of the gas needed to be transfer to a container in the

refinery mill with a volume of 1.8 x 103 L at a pressure of 1.0 atm and

temperature of 22°C.

(ii) Determine the mass of the gas being transferred. [ 7 marks]

(b) (i) Define vapour pressure and boiling point

(ii) Based on TABLE 2, arrange the compound in order of increasing

strength of intermolecular forces. Explain your answer.

TABLE 2

Compound Boiling Point/ K

Propane, CH3CH2CH3 231

Ethanol, CH3CH2OH 351

Dimethyl ether, CH3OCH3 313

Ethanoic acid, CH3COOH 391

[ 8 marks]

SK016


50

2013/2014

47. (a) (i) Define equilibrium vapour pressure

(ii) Explain how temperature affects the vapour pressure of a liquid.

[ 4 marks]

(b) (i) State Dalton’s law of partial pressure.

(iii) FIGURE 1 shows two connecting vessels containing different gases.

When the valve between the vessels is opened, the gases are allowed to

mix. Ignoring the volume taken by the valve, calculate the partial

pressure of each gas and the final pressure of the mixture at 25C.

FIGURE 1

(c) Differentiate between a crystalline solid and amorphous solid in terms of their

particle arrangement. Draw the structures and state the types of crystal for

diamond and sodium chloride.

[ 6 marks ]

48. State the relationships of the volume of an ideal gas with its pressure,

absolute temperature and the amount of gas respectively.

A student added an amount of hydrochloric acid to a rock sample and

observed the fizzing action indicating a gas being released. At 25 0C, the

gas collected in a 0.220 L gas bulb was 0.300 g and at a pressure of 0.757

atm. Calculate the molar mass and the density of this gas.

[12 marks] 2014/2015

49. (a) Limestone, CaCO3, decomposed to solid calcium oxide and carbon dioxide

gas when heated at high temperature. At 300C, a volume of 107.3 mL of the

gas was collected by displacement of water with a total pressure of 1 atm.

Calculate;

(i) The number of moles of carbon dioxide produced. [5 marks]

(ii) The mass of limestone decomposed. [4 marks]

[Vapour pressure of water at 300C is 31.8 mmHg]

(b) Briefly describe three types of crystalline solids in terms of their interparticle

forces.

SK016


51

2015/2016

50. (a) A gas mixture contain 82% (w/w) methane, CH4 and 18% (w/w) ethane, C2H6.

If a 15.50 g sample of the gas mixture is placed in a 15-L container at 20.0 º C,

calculate

(i) the total moles of gases

(ii) the total pressure (atm) and

(iv) The partial pressure of each gas in the container.

[7 marks]

(b) Explain each of the following observations:

(i) Methane, CH4 (16 g mol-1) has lower boiling point than propane, C3H8

(44 g mol-1) whereas water, H2O (18 g mol-1) has higher boiling point

than hydrogen sulphide, H2S (34 g mol-1).

(ii) Carbon dioxide, CO2, molecule and diamond are both covalently

bonded. However, solid CO2, is softer and exhibits lower melting point

as compared to diamond.

[8 marks]

2016/2017

51. a) A sample of potassium chlorate, KClO3, was decomposed upon heating,

producing potassium chloride, KCl and oxygen gas, O2. The volume of gas

collected by displacement of water was 0.250 L at 26°C and a pressure of 765

mmHg. Given water vapour pressure at 26°C is 25.2 mmHg, calculate

(i) the partial pressure of O2.

(ii) the moles of O2 collected.

(iii) the amount of KClO3 (in g) decomposed.

[10 marks]

(b) Nitrogen gas is real gas that deviates from ideality. It is the most abundant gas

found in the atmosphere.

(i) Why does nitrogen gas behave as real gas at room temperature?

(ii) State the conditions under which nitrogen gas can be liquefied.

(iii) How can nitrogen gas be made to behave an ideal gas?

[5 marks ]

52. Ethane, C2H6, burns in the air according to the equation below:

2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)

A mixture of C2H6 and O2 at 30 mmHg and 124 mmHg, respectively, was added into

a 7.5L flask at a temperature of 27 °C. The combustion reaction was carried out until

completion. Calculate the total pressure of the gas mixture obtained at the end of the

reaction, at the same temperature. Give your answer in mmHg.

[11 marks]

SK016


52

2017/2018

53. A 3.0 L flask at 298 K contains a mixture of 2.0 mol helium gas and 3.0 mol xenon

gas. The van der Waals constants for helium and xenon are given in TABLE 3.

TABLE 3

Gas a (L2 atm mol-2) b (L mol-1)

Helium 0.03421 0.02370

Xenon 4.194 0.05105

Given the van der Waals equation:

(a) State two (2) postulates of the kinetic molecular theory of an ideal gas in

relationship to parameters a and b as in TABLE 3. [2 marks]

(b) Which gas is expected to behave ideally and which gas exhibits a marked

deviation from ideal behaviour. [2 marks]

(c) Explain your answer in 3 (b) by referring to the significance of a and b values in

TABLE 3. [5 marks]

(d) Calculate total pressure of the gas in the mixture using an ideal gas equation.

[3 marks]

(e) Using the van der Waals equation, the total pressure of the system is calculated to

be 38.1 atm. Explain the reasons behind the differences between this value and the

pressure calculated in 3(d). [3 marks]

54. Carbon dioxide can be used to extract caffeine under supercritical condition. Some of

the physical properties of carbon dioxide are shown below.

What is meant by triple point and critical point?

Using the data given above, sketch a labelled phase diagram for carbon dioxide.

Show the supercritical point in the diagram.

Using the phase diagram, under what condition can dry ice be formed to act as

coolants?

[10 marks]

Triple point temperature -51° C

Triple point pressure 5 atm

Critical temperature 31° C

Critical pressure 73 atm

sk016 past year examination questions unit 5 unit 5

Documents