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S1.5 Ideal gases

Practice exam-style IB Chemistry questions for Ideal gases, aligned with the syllabus and grouped by topic.

Verified by Dennis M.
Verified by Dennis M.
Paper
Difficulty
Status
Level
Question 1
SL • Paper 1A
Easy
Calculator Permitted
SL • Paper 1A
Easy
Calculator Permitted

An assumption used in the ideal gas model is that gas particles have

A.

strong attractive forces between neighbouring particles.

B.

negligible volume compared with the volume of the container.

C.

collisions in which total kinetic energy decreases.

D.

fixed positions except when the container is heated.

Question 2
SL • Paper 1A
Easy
Calculator Permitted
SL • Paper 1A
Easy
Calculator Permitted

A fixed amount of ideal gas is heated in a rigid sealed container. The pressure increases because the particles

A.

expand in size and occupy a greater fraction of the container.

B.

move faster and collide more forcefully with the container walls.

C.

attract one another more strongly at the higher temperature.

D.

collide inelastically and transfer energy to the container walls.

Question 3
SL • Paper 1A
Easy
Calculator Permitted
SL • Paper 1A
Easy
Calculator Permitted

The conditions under which a real gas is expected to behave most like an ideal gas are

A.

high temperature and low pressure.

B.

low temperature and low pressure.

C.

low temperature and high pressure.

D.

high temperature and high pressure.

Question 4
SL • Paper 1A
Easy
Calculator Permitted
SL • Paper 1A
Easy
Calculator Permitted

The volume occupied by 0.500 mol0.500\ \text{mol} of an ideal gas at STP is

A.

22.7 dm322.7\ \text{dm}^3

B.

5.68 dm35.68\ \text{dm}^3

C.

45.4 dm345.4\ \text{dm}^3

D.

11.35 dm311.35\ \text{dm}^3

Question 5
SL • Paper 1A
Easy
Calculator Permitted
SL • Paper 1A
Easy
Calculator Permitted

A fixed amount of ideal gas occupies 3.00 dm33.00\ \text{dm}^3 at 300 K300\ \text{K}. The gas is heated to 450 K450\ \text{K} at constant pressure. Its final volume is

A.

4.50 dm34.50\ \text{dm}^3

B.

6.00 dm36.00\ \text{dm}^3

C.

2.00 dm32.00\ \text{dm}^3

D.

3.00 dm33.00\ \text{dm}^3

Question 6
HL • Paper 1A
Easy
Calculator Permitted
HL • Paper 1A
Easy
Calculator Permitted

A gas is collected over water at 25 C25\ ^\circ\text{C}. The total pressure is 101.3 kPa101.3\ \text{kPa} and the water vapour pressure is 3.2 kPa3.2\ \text{kPa}. The pressure to use for the dry gas in PV=nRTPV=nRT is

A.

3.2 kPa3.2\ \text{kPa}

B.

98.1 kPa98.1\ \text{kPa}

C.

104.5 kPa104.5\ \text{kPa}

D.

101.3 kPa101.3\ \text{kPa}

Question 7
SL • Paper 2
Easy
Calculator Permitted
SL • Paper 2
Easy
Calculator Permitted

A sealed container holds a sample of gas that is modelled as ideal.

A

Outline two assumptions made in the ideal gas model.

[2]
Question 8
SL • Paper 2
Easy
Calculator Permitted
SL • Paper 2
Easy
Calculator Permitted

A sample of ethene, C2H4C_2H_4, has a volume of 5.68 dm35.68\ \text{dm}^3 at STP. The molar volume of an ideal gas at STP is 22.7 dm3 mol122.7\ \text{dm}^3\ \text{mol}^{-1}.

A

Calculate the amount, in mol, of ethene in the sample.

[1]
B

Calculate the mass of ethene in the sample.

[2]
Question 9
SL • Paper 1A
Medium
Calculator Permitted
SL • Paper 1A
Medium
Calculator Permitted

An ideal gas has a volume of 24.9 dm324.9\ \text{dm}^3 at 100 kPa100\ \text{kPa} and 300 K300\ \text{K}. Using R=8.31 J K1mol1R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}, the amount of gas is

A.

0.0100 mol0.0100\ \text{mol}

B.

0.100 mol0.100\ \text{mol}

C.

10.0 mol10.0\ \text{mol}

D.

1.00 mol1.00\ \text{mol}

Question 10
HL • Paper 1A
Medium
Calculator Permitted
HL • Paper 1A
Medium
Calculator Permitted

Under the same conditions of temperature and pressure, the gas expected to deviate most from ideal behaviour is

A.

Ne\text{Ne}

B.

CH4\text{CH}_4

C.

NH3\text{NH}_3

D.

He\text{He}

Question 11
HL • Paper 1A
Medium
Calculator Permitted
HL • Paper 1A
Medium
Calculator Permitted

The graph shows results from an investigation using a fixed amount of ideal gas at constant temperature.

The relationship shown is best interpreted as

Pressure-volume data for a gas sample at constant temperature.
A.

PP is directly proportional to V2V^2.

B.

PP is independent of VV.

C.

PP is directly proportional to VV.

D.

PP is directly proportional to 1V\dfrac{1}{V}.

Question 12
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A fixed amount of a real gas is compressed and cooled.

A

State the conditions under which a real gas deviates most from ideal behaviour.

[1]
B

Explain why these conditions cause greater deviation from ideal behaviour.

[2]
Question 13
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A student investigates the pressure of a fixed amount of gas at constant temperature by changing the volume of the container.

Gas pressure measured at different reciprocal volumes.
A

Identify the independent variable in this investigation.

[1]
B

State the relationship between pressure and volume for this gas sample.

[1]
C

Explain, using the particle model, why the pressure changes when the volume is decreased.

[1]
Question 14
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A balloon contains 0.150 mol0.150\ \text{mol} of helium at 25.0 C25.0\ ^\circ\text{C} and 1.20×105 Pa1.20\times 10^5\ \text{Pa}. Assume ideal gas behaviour.

A

Convert the temperature to kelvin.

[1]
B

Calculate the volume of helium in m3\text{m}^3.

[2]
Question 15
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A fixed mass of gas is sealed in a rigid metal cylinder. Its pressure is 1.01×105 Pa1.01\times 10^5\ \text{Pa} at 20.0 C20.0\ ^\circ\text{C}. The cylinder is warmed to 60.0 C60.0\ ^\circ\text{C}.

A

Calculate the final pressure of the gas, assuming ideal behaviour.

[2]
B

State why temperature must be converted to kelvin in this calculation.

[1]
Question 16
SL • Paper 1B
Medium
Calculator Permitted
SL • Paper 1B
Medium
Calculator Permitted

A fixed amount of an ideal gas was kept at constant temperature while the volume of the container was changed. The graph shows the measured pressure at each volume, with one point labelled A.

Measured pressure of a fixed gas sample.
A

Describe the relationship shown by the graph.

[1]
B

Use point A to calculate the value of PVPV for the gas sample.

[1]
C

Explain, using the particle model, why the pressure increases when the volume is decreased at constant temperature.

[2]
Question 17
SL • Paper 1B
Medium
Calculator Permitted
SL • Paper 1B
Medium
Calculator Permitted

Different gases were measured at standard temperature and pressure, STP. The table shows the amount of gas and the volume occupied by each sample.

Sample

Amount / mol

Volume / dm3\text{dm}^{3}

A

0.150

3.41

B

0.500

11.35

C

0.750

17.0

A

Calculate the molar volume using the data for sample B.

[1]
B

State why the gases have similar molar volumes even though their particles have different masses.

[1]
C

A fourth sample contains 0.0750 mol0.0750\ \text{mol} of an ideal gas at STP. Calculate its volume in dm3\text{dm}^3.

[2]
Question 18
HL • Paper 1A
Medium
Calculator Permitted
HL • Paper 1A
Medium
Calculator Permitted

A 0.440 g0.440\ \text{g} sample of gas occupies 2.49×104 m32.49\times10^{-4}\ \text{m}^3 at 100 kPa100\ \text{kPa} and 300 K300\ \text{K}. Using R=8.31 J K1mol1R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}, the molar mass of the gas is

A.

88.0 g mol188.0\ \text{g mol}^{-1}

B.

4.40 g mol14.40\ \text{g mol}^{-1}

C.

22.0 g mol122.0\ \text{g mol}^{-1}

D.

44.0 g mol144.0\ \text{g mol}^{-1}

Question 19
HL • Paper 1A
Medium
Calculator Permitted
HL • Paper 1A
Medium
Calculator Permitted

A fixed amount of ideal gas changes from 120 kPa120\ \text{kPa}, 1.50 dm31.50\ \text{dm}^3 and 290 K290\ \text{K} to 1.00 dm31.00\ \text{dm}^3 and 348 K348\ \text{K}. The final pressure is

A.

216 kPa216\ \text{kPa}

B.

261 kPa261\ \text{kPa}

C.

100 kPa100\ \text{kPa}

D.

145 kPa145\ \text{kPa}

Question 20
HL • Paper 1A
Medium
Calculator Permitted
HL • Paper 1A
Medium
Calculator Permitted

In an experiment to determine the molar mass of a gas, some gas escapes before its volume is measured. The mass loss of the gas source is measured correctly. The calculated molar mass will be

A.

too high, because the calculated amount of gas is too high.

B.

too low, because the calculated amount of gas is too high.

C.

too high, because the calculated amount of gas is too low.

D.

too low, because the calculated amount of gas is too low.

Question 21
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

A volatile liquid is vaporized and the gas is collected over water. The mass of liquid vaporized is 0.108 g0.108\ \text{g}. The gas volume is 4.86×105 m34.86\times 10^{-5}\ \text{m}^3 at 296 K296\ \text{K}. The total pressure is 1.012×105 Pa1.012\times 10^5\ \text{Pa} and the water vapour pressure at 296 K296\ \text{K} is 2.80×103 Pa2.80\times 10^3\ \text{Pa}.

A

Calculate the pressure of the dry gas.

[1]
B

Determine the molar mass of the volatile liquid.

[3]
Question 22
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

An impure sample of calcium carbonate decomposes on heating according to the equation:

CaCO3(s)CaO(s)+CO2(g)\text{CaCO}_3(s)\to \text{CaO}(s)+CO_2(g)

A 0.842 g0.842\ \text{g} sample produces 1.68×104 m31.68\times 10^{-4}\ \text{m}^3 of CO2CO_2 at 298 K298\ \text{K} and 1.00×105 Pa1.00\times 10^5\ \text{Pa}. Assume ideal gas behaviour.

A

Calculate the amount, in mol, of CO2CO_2 produced.

[2]
B

Calculate the percentage by mass of calcium carbonate in the impure sample.

[2]
Question 23
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

Ammonia, NH3NH_3, and nitrogen, N2N_2, are compared under the same conditions of 250 K250\ \text{K} and 5.00×105 Pa5.00\times 10^5\ \text{Pa}.

A

Identify which gas is expected to deviate more from ideal behaviour.

[1]
B

Explain your answer in terms of the ideal gas model.

[2]
Question 24
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

A rigid vessel of volume 2.50×103 m32.50\times 10^{-3}\ \text{m}^3 contains 0.0300 mol0.0300\ \text{mol} of argon at 298 K298\ \text{K}. A further 0.0100 mol0.0100\ \text{mol} of argon is added and the vessel is then heated to 350 K350\ \text{K}. Assume ideal gas behaviour.

A

Calculate the initial pressure in the vessel.

[2]
B

Calculate the final pressure in the vessel.

[2]
Question 25
SL • Paper 1B
Medium
Calculator Permitted
SL • Paper 1B
Medium
Calculator Permitted

The compressibility factor, ZZ, is equal to PV/(nRT)PV/(nRT). For an ideal gas, Z=1Z=1. The table shows values of ZZ for nitrogen at different temperatures and pressures.

TT / K

1.0 MPa

5.0 MPa

10.0 MPa

200

0.98

0.88

0.76

300

0.99

0.94

0.86

400

1.00

0.98

0.95

A

Identify the conditions in the table under which nitrogen shows the greatest deviation from ideal behaviour.

[1]
B

Describe the effect of increasing temperature on the value of ZZ at the same pressure.

[1]
C

Explain why real gases deviate more from ideal behaviour under the conditions identified in part (a).

[2]
Question 26
SL • Paper 1B
Medium
Calculator Permitted
SL • Paper 1B
Medium
Calculator Permitted

Oxygen gas was collected in a gas syringe during the decomposition of hydrogen peroxide. The table shows the final gas volume and the conditions in the laboratory.

Quantity

Value

Final oxygen volume / cm3\text{cm}^{3}

72.0

Pressure / kPa

101

Temperature / K

295

A

Calculate the amount, in mol, of oxygen collected at the end of the experiment.

[3]
B

State one variable, other than amount of gas, that must be measured to use the ideal gas equation for this sample.

[1]
C

Suggest one reason why the calculated amount of oxygen could be lower than the amount actually produced.

[1]
Question 27
SL • Paper 1B
Medium
Calculator Permitted
SL • Paper 1B
Medium
Calculator Permitted

A gas sample in a sealed piston was changed from state 1 to state 2. The diagram gives the pressure, volume and temperature for state 1, and the volume and temperature for state 2.

Annotated piston diagram showing two states of the same sealed gas sample. Labels must include initial pressure, initial volume and initial temperature, and final volume and final temperature, with consistent units.
A

Calculate the pressure of the gas in state 2.

[3]
B

Explain why temperature values in gas calculations must be in kelvin rather than degrees Celsius.

[1]
Question 28
HL • Paper 1B
Medium
Calculator Permitted
HL • Paper 1B
Medium
Calculator Permitted

A fixed amount of gas was sealed in a rigid container. The pressure was recorded at different temperatures. The graph shows pressure plotted against temperature in degrees Celsius.

Pressure of a fixed gas plotted against temperature in a rigid container.
A

Identify the independent variable, the dependent variable and one controlled variable in this investigation.

[2]
B

Use the extrapolated line to estimate the temperature at which the pressure would be zero.

[1]
C

Explain the linear relationship shown by the graph using the ideal gas equation.

[2]
Question 29
HL • Paper 1B
Medium
Calculator Permitted
HL • Paper 1B
Medium
Calculator Permitted

Students used measured values of pressure, volume, amount and temperature for an ideal gas to calculate the gas constant, RR. The table and plot show their results from several trials.

Trial

Pressure / kPa

Volume / dm3\text{dm}^{3}

Amount / mol

Temperature / K

A

99.8

0.250

0.0100

300

B

100.1

0.249

0.0100

300

C

99.4

0.251

0.0100

300

D

120.0

0.250

0.0100

300

A

Calculate RR for trial A using the data in the table.

[2]
B

Identify the anomalous trial.

[1]
C

Evaluate whether the results support the ideal gas model.

[1]
Question 30
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

The graph shows pressure against temperature for a fixed amount of gas in a container of constant volume. The ideal prediction and experimental results for a real gas are shown.

Ideal and real gas pressure-temperature data.
A

State the relationship predicted by the ideal gas model for this experiment.

[1]
B

Explain why the experimental pressure may be lower than the ideal prediction at lower temperatures.

[2]
C

Suggest why an accurately plotted graph is more useful than a sketch graph for this investigation.

[1]
Question 31
HL • Paper 2
Medium
Calculator Permitted
HL • Paper 2
Medium
Calculator Permitted

A student determines the molar volume of hydrogen gas by reacting magnesium with excess hydrochloric acid and collecting the hydrogen in a gas syringe. A 0.0450 g0.0450\ \text{g} strip of magnesium produces 4.50×105 m34.50\times 10^{-5}\ \text{m}^3 of hydrogen at room temperature and pressure.

Mg(s)+2HCl(aq)MgCl2(aq)+H2(g)\text{Mg}(s)+2HCl(aq)\to \text{MgCl}_2(aq)+H_2(g)

An apparatus diagram showing magnesium reacting with hydrochloric acid in a conical flask connected by a delivery tube to a gas syringe used to collect hydrogen gas.
A

Calculate the experimental molar volume of hydrogen in m3 mol1\text{m}^3\ \text{mol}^{-1}.

[2]
B

Suggest one systematic error that would make the calculated molar volume too low.

[1]
C

Suggest one improvement to increase the reliability or validity of the result.

[1]
Question 32
SL • Paper 1B
Hard
Calculator Permitted
SL • Paper 1B
Hard
Calculator Permitted

A gas was collected over water and used to determine the molar mass of a volatile compound. The table shows the experimental data. The total pressure is the pressure of the dry gas plus the pressure of water vapour.

Quantity

Value

Unit

Total pressure

100.8

kPa

Pressure of water vapour

3.17

kPa

Volume of gas collected

72.4

cm3\text{cm}^3

Temperature

298

K

Mass of volatile compound

0.118

g

A

Determine the pressure of the dry gas.

[1]
B

Calculate the amount, in mol, of dry gas collected.

[2]
C

Calculate the molar mass of the gas and suggest one source of systematic error if the water vapour pressure were not subtracted.

[2]
Question 33
HL • Paper 1B
Hard
Calculator Permitted
HL • Paper 1B
Hard
Calculator Permitted

The table shows compressibility factors for methane, carbon dioxide and ammonia under comparable conditions. An ideal gas has Z=1Z=1.

Condition

Methane

Carbon dioxide

Ammonia

300 K, 5.0 MPa

0.86

0.68

0.50

500 K, 1.0 MPa

0.98

0.94

0.89

A

Identify the gas and conditions in the table that are closest to ideal behaviour.

[1]
B

Compare the deviations of carbon dioxide and ammonia at low temperature and high pressure.

[2]
C

Suggest why ammonia deviates more from ideal behaviour than methane under comparable conditions.

[2]
Question 34
HL • Paper 1B
Hard
Calculator Permitted
HL • Paper 1B
Hard
Calculator Permitted

The molar mass of a volatile liquid was determined by vaporizing it in a flask of known volume. The apparatus and data are shown.

Annotated diagram of a flask containing vaporized volatile liquid in a hot water bath, with a data table showing flask volume, bath temperature, atmospheric pressure and mass of vapour filling the flask.
A

Calculate the amount of vapour in the flask, assuming ideal behaviour.

[3]
B

Calculate the molar mass of the volatile liquid.

[1]
C

Suggest one reason why the calculated molar mass would be too high if some liquid remained unevaporated in the flask.

[1]
Question 35
HL • Paper 1B
Hard
Calculator Permitted
HL • Paper 1B
Hard
Calculator Permitted

A fixed amount of gas was compressed at constant temperature. The data were processed by plotting pressure against the reciprocal of volume, 1/V1/V. The best-fit line has a gradient shown on the graph.

Pressure against reciprocal volume for a gas at constant temperature.
A

State the evidence from the graph that pressure is inversely proportional to volume.

[1]
B

Use the gradient of the graph to calculate the amount of gas in the sample at 298 K298\ \text{K}.

[3]
C

Suggest why the data might curve away from the straight line at very small volumes for a real gas.

[1]
Question 36
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A student reacts 0.0400 g0.0400\ \text{g} of magnesium ribbon with excess dilute hydrochloric acid and collects the hydrogen gas in a gas syringe. The collected gas is saturated with water vapour at 25.0 C25.0\ ^\circ\text{C}. The atmospheric pressure is 101.2 kPa101.2\ \text{kPa}. The vapour pressure of water at this temperature is 2.8 kPa2.8\ \text{kPa}.

A labelled apparatus diagram showing a conical flask containing magnesium and excess hydrochloric acid connected by delivery tubing to a gas syringe. Labels should include magnesium ribbon, hydrochloric acid, delivery tube and gas syringe. The diagram must not include any calculated gas volume.
A

The mass of magnesium used is 0.0400 g0.0400\ \text{g}.

I.

Calculate the amount, in mol, of magnesium used.

[1]
II.

Calculate the volume, in cm3\text{cm}^3, of dry hydrogen expected.

[3]
B

The student actually collects 38.6 cm338.6\ \text{cm}^3 of gas. Evaluate one experimental reason, other than measurement uncertainty in mass, for the lower volume.

[2]
C

Explain why hydrogen is expected to behave nearly ideally under these conditions.

[2]
Question 37
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A fixed amount of gas is placed in a sealed syringe at 300 K300\ \text{K}. The pressure is measured at different volumes.

Pressure of a fixed amount of gas measured at different volumes at 300 K.
A

The pressure is 124.7 kPa124.7\ \text{kPa} when the volume is 1.00 dm31.00\ \text{dm}^3.

I.

Calculate the amount of gas in the syringe.

[2]
II.

Predict the pressure when the volume is increased to 2.50 dm32.50\ \text{dm}^3 at the same temperature.

[1]
B

Explain, using the particle model, why the pressure decreases when the volume is increased at constant temperature.

[2]
C

Discuss one advantage and one limitation of using the plotted data rather than only a sketch graph for this investigation.

[2]
Question 38
SL • Paper 2
Hard
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SL • Paper 2
Hard
Calculator Permitted

A sealed metal aerosol can contains a fixed amount of propellant gas. At 20.0 C20.0\ ^\circ\text{C} the gas pressure inside the can is 100 kPa100\ \text{kPa}. The can volume is constant.

A

The can is heated to 50.0 C50.0\ ^\circ\text{C}.

I.

State why the combined gas law can be applied to this change.

[1]
II.

Calculate the pressure in the can at 50.0 C50.0\ ^\circ\text{C}.

[2]
B

The can is designed to rupture at 125 kPa125\ \text{kPa}. Determine the temperature, in C^\circ\text{C}, at which rupture would be expected if the gas behaved ideally.

[2]
C

Explain why using temperature in C^\circ\text{C} directly in the combined gas law would give an invalid prediction.

[2]
Question 39
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

Helium, carbon dioxide and ammonia are stored separately in identical cylinders at the same temperature and pressure. The cylinders are then cooled and compressed.

A

Compare the expected deviations from ideal gas behaviour for helium and ammonia under the cooled, compressed conditions.

I.

Identify which gas is expected to deviate more from ideal behaviour.

[1]
II.

Explain your answer in terms of the ideal gas model.

[2]
B

Explain why low temperature and high pressure both increase deviation from ideal behaviour.

[2]
C

State one assumption of the ideal gas model that is least valid for carbon dioxide at high pressure.

[1]
Question 40
HL • Paper 1B
Hard
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HL • Paper 1B
Hard
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A fixed amount of gas in a rigid metal flask was cooled. The graph compares the measured pressure with the pressure predicted by the ideal gas equation.

Measured and predicted pressure for a fixed gas sample.
A

Using the ideal gas model, calculate the predicted pressure at 250 K250\ \text{K} if the pressure is 120 kPa120\ \text{kPa} at 300 K300\ \text{K}.

[2]
B

Compare the measured pressure at 250 K250\ \text{K} with the ideal prediction.

[1]
C

Evaluate the suitability of the ideal gas model for these data.

[2]
Question 41
SL • Paper 2
Hard
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SL • Paper 2
Hard
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A volatile liquid is vaporized in a sealed 125 cm3125\ \text{cm}^3 flask at 100.0 C100.0\ ^\circ\text{C}. After cooling, the mass of condensed liquid in the flask is found to be 0.246 g0.246\ \text{g}. The pressure of the vapour before cooling is 100.5 kPa100.5\ \text{kPa}.

An apparatus diagram for determining molar mass by vaporizing a volatile liquid in a small flask immersed in a hot water bath. Labels should include flask, hot water bath, volatile liquid vapour, thermometer and pressure reading. No numerical answer should be shown.
A

Use the data to determine the molar mass of the volatile liquid.

I.

Calculate the amount, in mol, of vapour in the flask.

[3]
II.

Calculate the molar mass of the liquid.

[1]
B

The empirical formula of the liquid is CH2OCH_2O. Determine its molecular formula.

[2]
C

Suggest two improvements to increase the reliability or accuracy of the molar mass determination.

[2]
Question 42
SL • Paper 2
Hard
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SL • Paper 2
Hard
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A sample of impure calcium carbonate is reacted with excess hydrochloric acid. The carbon dioxide produced is collected and measured at 25.0 C25.0\ ^\circ\text{C} and 101 kPa101\ \text{kPa}. A 2.50 g2.50\ \text{g} sample produces 0.510 dm30.510\ \text{dm}^3 of carbon dioxide.

A

A 2.50 g2.50\ \text{g} sample produces 0.510 dm30.510\ \text{dm}^3 of carbon dioxide.

I.

Calculate the amount, in mol, of carbon dioxide produced.

[2]
II.

Calculate the percentage by mass of calcium carbonate in the sample.

[2]
B

Calculate the volume of carbon dioxide, in dm3\text{dm}^3, that would be produced at STP if the 2.50 g2.50\ \text{g} sample were pure calcium carbonate.

[2]
C

State one reason why the measured volume in part (a) should not be compared directly with the STP volume in part (b) without calculation.

[1]
Question 43
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
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A gaseous hydrocarbon is collected over water to determine its molar mass. The mass of gas collected is 0.134 g0.134\ \text{g}, the gas volume is 58.0 cm358.0\ \text{cm}^3, the temperature is 25.0 C25.0\ ^\circ\text{C} and the total pressure is 101.6 kPa101.6\ \text{kPa}. The vapour pressure of water at 25.0 C25.0\ ^\circ\text{C} is 3.17 kPa3.17\ \text{kPa}.

A gas collection over water setup with an inverted measuring cylinder in a water trough connected by a delivery tube to a gas source. Labels should include water trough, inverted measuring cylinder, delivery tube, collected gas plus water vapour, gas source and water level. The visual must not include calculated dry gas pressure or molar mass.
A

Determine the molar mass of the hydrocarbon.

I.

Calculate the pressure of the dry hydrocarbon gas.

[1]
II.

Calculate the amount, in mol, of hydrocarbon gas.

[2]
III.

Calculate the molar mass of the hydrocarbon.

[2]
B

Evaluate the effect on the calculated molar mass if the vapour pressure of water were not subtracted.

[2]
C

Suggest why the hydrocarbon may still not behave perfectly ideally in this experiment.

[1]
Question 44
HL • Paper 2
Hard
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HL • Paper 2
Hard
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In an experiment, carbon dioxide is generated and collected in a 250.0 cm3250.0\ \text{cm}^3 gas syringe at constant temperature. At RTP, one mole of gas occupies 24.0 dm3 mol124.0\ \text{dm}^3\ \text{mol}^{-1}. A graph of mass lost by the reaction flask against gas volume is used to determine the molar mass of the gas.

Mass lost vs gas volume scatter graph with a best-fit line.
A

At RTP, where the molar volume of a gas is 24.0 dm3 mol124.0\ \text{dm}^3\ \text{mol}^{-1}, the best-fit line shows that 0.180 g0.180\ \text{g} of carbon dioxide corresponds to 100.0 cm3100.0\ \text{cm}^3 of gas.

I.

Calculate the amount, in mol, in 100.0 cm3100.0\ \text{cm}^3 of gas.

[2]
II.

Use the value from (a)(i) to calculate the molar mass of the gas.

[2]
B

Explain why a best-fit line is preferable to using one individual data point from the graph.

[2]
C

Suggest one systematic error that would make the calculated molar mass too high.

[1]
Question 45
HL • Paper 2
Hard
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HL • Paper 2
Hard
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Sodium azide, NaN3NaN_3, can decompose rapidly to form sodium and nitrogen gas in an inflator. The simplified equation is:

2NaN3(s)2Na(s)+3N2(g)2NaN_3(s)\to2Na(s)+3N_2(g)

A sealed test chamber of volume 12.0 dm312.0\ \text{dm}^3 contains nitrogen produced by decomposing 5.00 g5.00\ \text{g} of sodium azide. The gas temperature immediately after decomposition is 450 K450\ \text{K}.

A

A sealed test chamber of volume 12.0 dm312.0\ \text{dm}^3 contains nitrogen produced by decomposing 5.00 g5.00\ \text{g} of sodium azide. The gas temperature immediately after decomposition is 450 K450\ \text{K}.

I.

Calculate the amount, in mol, of sodium azide decomposed.

[1]
II.

Calculate the amount, in mol, of nitrogen gas produced.

[1]
III.

Calculate the pressure, in kPa\text{kPa}, due to the nitrogen gas.

[3]
B

Discuss two assumptions made when applying the ideal gas equation to the nitrogen immediately after decomposition.

[2]
C

Suggest why the pressure calculated in (a)(iii) may differ from the pressure measured in a real inflator.

[1]
Question 46
HL • Paper 2
Hard
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HL • Paper 2
Hard
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A 600 cm3600\ \text{cm}^3 sample of the mixture decreases to 420 cm3420\ \text{cm}^3 after treatment with excess aqueous potassium hydroxide. Carbon dioxide is removed completely by passing the mixture through excess aqueous potassium hydroxide. All gas volumes are measured at the same temperature and pressure unless stated otherwise.

A

A 600 cm3600\ \text{cm}^3 sample of the mixture decreases to 420 cm3420\ \text{cm}^3 after treatment with potassium hydroxide.

I.

Determine the volume of carbon dioxide in the original mixture.

[1]
II.

Determine the mole fraction of carbon dioxide in the original mixture.

[2]
III.

State one assumption needed for the volume decrease to represent only carbon dioxide.

[1]
B

The remaining oxygen, volume 420 cm3420\ \text{cm}^3, is initially at 100 kPa100\ \text{kPa} and 298 K298\ \text{K}. It is compressed to 150 cm3150\ \text{cm}^3 and heated to 350 K350\ \text{K}. Calculate the final pressure.

[3]
C

Explain why the calculation in (b) would be less reliable if the oxygen were compressed to a much smaller volume at low temperature.

[1]
Question 47
HL • Paper 2
Hard
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HL • Paper 2
Hard
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The quantity PV/(nRT)PV/(nRT) is equal to 1.001.00 for an ideal gas. A student measures this quantity for two real gases at 298 K298\ \text{K} as pressure is increased. The plotted values are hypothetical gas-phase data used to illustrate deviation from ideal behaviour.

Compressibility factor PV/nRT for methane and ammonia as pressure increases at 298 K.
A

Use the graph to compare the behaviour of methane and ammonia.

I.

Identify which gas behaves more ideally over the pressure range shown.

[1]
II.

Explain the difference in behaviour in terms of intermolecular forces.

[2]
B

Explain why increasing pressure generally increases deviation from ideal gas behaviour.

[2]
C

Evaluate whether a mathematical correction for real gases is required by the ideal gas model in this syllabus context.

[3]
Question 48
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
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A student uses a computer simulation to investigate a fixed amount of ideal gas. The simulation can hold either pressure, volume or temperature constant while the other variables are changed.

A schematic computer simulation screen showing a box of moving gas particles with adjustable sliders labelled pressure, volume and temperature, plus a data table area. The image should not display any specific results or final graphs.
A

The student wants to test the relationship between pressure and absolute temperature.

I.

Identify the independent, dependent and controlled variables for a valid investigation.

[2]
II.

State the expected graphical relationship for an ideal gas.

[1]
B

The student plots pressure against temperature in C^\circ\text{C} and obtains a straight line that does not pass through the origin. Evaluate this graph as evidence for the ideal gas model.

[3]
C

Suggest one advantage of using a simulation and one limitation compared with a laboratory experiment using real gases.

[1]

S1.4 Counting particles, mass. The mole

S2.1 The ionic model