Syllabus Edition

First teaching 2023

First exams 2025

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Ideal Gases (HL IB Chemistry)

Exam Questions

2 hours25 questions
1a
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2 marks

A sample of pure magnesium nitrate, Mg(NO3)2, was decomposed by heating as shown in the equation below

2Mg(NO3)2 (s) → 2MgO (s) + 4NO2 (g) + O(g) 

A 0.75 g sample of Mg(NO3)2 was completely decomposed by heating.

Calculate the amount, in moles, of magnesium nitrate that was decomposed. Give your answer to 2 decimal places.

1b
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2 marks

Calculate the total amount, in moles, of gas produced in the reaction. Give your answer to 2 decimal places. 

1c
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2 marks

Calculate the total volume, in m3, of gas produced at 333 K and 100 kPa. 

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2a
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1 mark

90 cm3 ammonia gas, NH(g), is combusted in oxygen, O(g), to produce nitrogen oxide and water, H2O (l). What is the total volume of gases remaining when 90 cmof ammonia is combusted completely with 50 cm3 of oxygen according to the equation shown?

4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (l)

Deduce the limiting reagent for the combustion of ammonia, 90 cm3 ammonia gas, NH(g), is combusted in oxygen.

2b
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4 marks
Calculate the total volume, in cm3, of gases remaining for the reaction in part (a).
2c1 mark

Sketch a line on the graph below that shows the correct relationship between pressure and begin mathsize 16px style 1 over volume end style

1-2-ib-sl-sq-easy-q5c

2d
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2 marks

At 25 oC and 100 kPa a gas occupies a volume of 35 dm3. Using the equation fraction numerator P subscript italic 1 V subscript italic 1 over denominator T subscript italic 1 end fraction italic equals fraction numerator P subscript italic 2 V subscript italic 2 over denominator T subscript italic 2 end fraction , calculate the new temperature, in oC, of the gas if the volume is decreased to 15 dm3 at constant pressure. 

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3a2 marks

Sodium azide, NaN3, decomposes to form sodium and nitrogen.

Write a balanced symbol equation for this reaction.

3b1 mark

Under certain conditions, 210 g of sodium azide decomposed.

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

3c
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3 marks

The nitrogen formed in this reaction fills a volume of 97 000 cm3 at a pressure of 110 kPa.

Use your answer to part b) and sections 1 and 2 in the Data Booklet to calculate the temperature, in Kelvin, of the nitrogen gas.

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1a4 marks

Astronauts on the Apollo 13 Mission in 1970 avoided disaster by making use of lithium hydroxide canisters, to absorb waste carbon dioxide in their spacecraft through a chemical reaction. The reaction produces lithium carbonate and water as the only products.

 

i)
Write a balanced equation for the reaction between lithium hydroxide and carbon dioxide.
[1]

 

ii)
Determine the mass, in kg, of carbon dioxide absorbed by 4.00 kg of lithium hydroxide.
[3]
1b2 marks

Calculate the percentage yield of lithium carbonate if 5.00 g of lithium hydroxide produces 6.76 g of lithium carbonate.

1c2 marks

Determine the maximum volume, in dm3, of carbon dioxide at 293 K and 100 kPa that can be absorbed by 125.0 g of lithium hydroxide.

1d2 marks

When the astronauts on Apollo 13 were solving the problem of excess carbon dioxide in their spacecraft, they had to be careful with their calculations of the volumes of ideal gases.

Explain what is meant by the term ideal gas and state the conditions under which carbon dioxide shows deviation from ideal gas behaviour.

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2a1 mark

Gas cylinders of helium, like the one shown below, are sometimes used to inflate party balloons.

 

Figure 1

1-2-m-q2-ib-chemistry-sq

A typical 11-inch party balloon has a fully inflated volume of 14.1 dm3. The pressure in the gas cylinders is 20,000 kPa. If the gas cylinder can fill 160 balloons at 298 K and 108 kPa, what is the total volume of helium inside the gas cylinder in dm3?

2b2 marks

Sketch a graph to show the relationship between the volume and temperature of an ideal gas at constant pressure. Describe the relationship between the two variables.

2c2 marks

Deep sea divers sometimes breathe mixtures of helium and oxygen in their scuba diving tanks when the conditions are very deep, so they can avoid nitrogen narcosis.

If a bubble of gas escapes from a scuba tank at 60 m depth where the pressure is 588 kPa and the temperature is 8 oC, determine the increase in the size of the bubble by the time it reaches the surface where the pressure is 100 kPa and the temperature is 20 oC.

2d4 marks

Commercial aircraft are fitted with oxygen cannisters that provide a supply of oxygen in case of the loss of cabin pressure. The cannisters contain sodium chlorate(V) which produces oxygen in the following decomposition reaction.

 

2NaClO3 (s)  2NaCl (s) + 3O2 (g)

Determine the mass of sodium chlorate(V) needed to produce 10.0 dm3 of oxygen at 298 K and 90 kPa.

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3a2 marks

Ammonia and nitrogen monoxide react together according to the following equation:

                        4NH3 (g) + 6NO (g) → 5N2 (g) + 6H2O (g)

50.0 dm3 of ammonia is reacted with 50.0 dm3 of nitrogen monoxide at 150.0 oC and 100 kPa. Identify the limiting reagent and determine the volume of nitrogen produced.

3b2 marks

Determine the volume of excess gas and hence total volume of gas after the reaction has finished.

3c3 marks

What mass of nitrogen is produced in the reaction? Express your answer to an appropriate number of significant figures.

3d1 mark

Explain why calculating the gas volumes in the reaction is likely to be more accurate at 150 oC than at room temperature.

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1a1 mark

Phosphine, PH3, is a gas formed by heating phosphorous acid, H3PO3, in the absence of air, as shown in the equation below.

4H3PO3 (s) → PH3 (g) + 3H3PO(s)

3.45 × 10−2 mol of H3PO3 is completely decomposed by this reaction.

State the expected molecular shape and expected bond angle in PH3 (g).

1b
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5 marks

Calculate the volume of phosphine gas formed, in cm3, at 100 kPa pressure and 210 °C.

1c
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3 marks

1.85 g of white phosphorus was used to make phosphine according to the equation.

P(s) + 3OH− (aq) + 3H2O (l) → PH(g) + 3H2PO2− (aq)

This phosphorus was reacted with 75.00 cm3 of 4.50 mol dm-3 sodium hydroxide solution. Deduce, showing your working, which was the limiting reagent. 

1d
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1 mark

Using section 2 of the Data booklet determine the volume of phosphine, measured in cm3 at standard temperature and pressure, that was produced. Give your answer to 3 significant figures. 

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2a
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4 marks

An empty 1.5 dm3 Tupperware container has been kept in the fridge without a lid at 5 °C. The container is removed from the fridge and allowed to reach a temperature of 21 °C. Using your knowledge of Charles's Law, determine the volume of gas, in cm3, that escaped from the container. 

2b
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2 marks

A balloon contains 2500 mL of helium gas at a temperature of 75 °C. Determine the new volume in mL of the gas when the temperature changes to 55 °C assuming the pressure is constant. Give your answer to three significant figures. 

2c
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2 marks

A 10.0 L container of helium gas with a pressure of 33 000 Pa at 0 °C is heated until the new pressure is 200 000 Pa. Determine the new temperature of the gas assuming the volume remains constant. 

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3a
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2 marks

Oxygen exists as a diatomic gas, O2 (g). A sample of O2 (g) was made during a chemical reaction. When measured at 303 kPa and 28 °C the sample occupied a volume of 95.0 cm3.

Calculate the mass of oxygen formed.

3b2 marks

O2 (g) does not behave as an ideal gas under these conditions. 

Explain why O2 (g) behaves even less ideally at:

  • very high pressures
  • very low temperatures

3c
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5 marks

The homologous series of alkanes undergo combustion with oxygen.

A 2.0 dm3 flask contains 10.84 g of a gaseous alkane, X. The pressure in the flask is 300 kPa and the temperature is 20 oC.

Write an equation for the complete combustion of X.

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