IB Chemistry

Question 1

Which statements about mixtures are correct?

I. The components may be elements or compounds.

II. All components must be in the same phase.

III. The components retain their individual properties.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Answer: B. I and III only

A. Incorrect:
Although statement I is correct, statement II is false. Mixtures can exist in more than
one phase — for example, oil and water form a heterogeneous mixture with two distinct
layers.

B. Correct:
Statement I is true because mixtures can contain elements (e.g., oxygen and nitrogen in
air) or compounds (e.g., salt and water in saltwater).
Statement III is true because substances in a mixture are physically combined, so each
retains its own properties — for example, in a mixture of iron and sulfur, the iron
remains magnetic.

C. Incorrect:
Statement II is false because not all components must be in the same phase (oil and
water are two separate phases). Therefore, “II and III only” is not correct.

D. Incorrect:
Statement II is false, so not all three statements (I, II, and III) are correct.

Question 2

Which is correct?

A. Mixtures are either homogeneous or heterogeneous and their chemical properties are an average of the individual component properties.

B. Mixtures are never heterogenous and their chemical properties are an average of the individual component properties

C. Mixtures are either homogeneous or heterogeneous and the components retain their individual chemical properties.

D. Mixtures are never homogeneous and the components retain their individual chemical properties.

Answer: C. Mixtures are either homogeneous or heterogeneous and the components retain their individual chemical properties.

A. Incorrect:

Mixtures do not have average chemical properties because no chemical reaction occurs between the components. Each substance keeps its own chemical identity.

B. Incorrect:

Mixtures can be heterogeneous (e.g., sand and water) as well as homogeneous (e.g., saltwater), so this statement is false.

C. Correct:

Mixtures can be homogeneous (uniform composition, e.g., saltwater) or heterogeneous (non-uniform composition, e.g., sand and water). The substances are physically combined, not chemically bonded, so each retains its own chemical properties — for example, in a mixture of iron and sulfur, iron remains magnetic and sulfur remains yellow.

D. Incorrect:

Mixtures can indeed be homogeneous, such as air or saltwater, so this statement is false.

Question 3

Which physical processes could be used to separate decane (C₁₀H₂₂) and water. The two liquids are immiscible and have different boiling points.

1. Distillation

2. Filtration

3. Sublimation

4. Use of a separating funnel

A. 1, 2, 3 and 4

B. 1, 2 and 3 only

C. 1 and 2 only

D. 1 and 4 only

Answer: D. 1 and 4 only

A. Incorrect:

Filtration and sublimation are not suitable methods. Filtration separates solids from liquids, and sublimation applies only to solids turning into gas.

B. Incorrect:

Includes sublimation, which is irrelevant because both substances (decane and water) are liquids, not solids.

C. Incorrect:

Filtration is only used to separate insoluble solids from liquids, not two immiscible liquids like decane and water.

D. Correct:

Distillation works because the liquids have different boiling points — heating will vaporize one liquid first, which can then be condensed and collected.

A separating funnel is also effective because the liquids are immiscible and form two distinct layers, allowing one to be drained from the other.

Question 4

A colourless solid crystalline sample was heated from a temperature of 25 °C (standard conditions) until it completely melted to form a colourless liquid. As the temperature starts to rise again the state change is complete.

State which of the following statements best explains the shape of the graph at region Z.

A. There was no further heating.

B. The particles do not have any kinetic and potential energy.

C. A chemical reaction has taken place as the solid was melted.

D. Heat energy is used to separate the solid particles from their fixed positions in the lattice.

Answer: D. Heat energy is used to separate the solid particles from their fixed positions in the lattice.

A. Incorrect:

Heating continues during region Z, but the temperature does not increase because the energy is being used for the state change, not for raising temperature.

B. Incorrect:

Particles always possess both kinetic and potential energy. During melting, their potential energy increases as they move apart.

C. Incorrect:

Melting is a physical change, not a chemical reaction - no new substances are formed.

D. Correct:

At region Z, the temperature remains constant while the solid melts. The heat energy absorbed is used to overcome the forces holding the particles in their fixed lattice positions, allowing them to move freely as a liquid. All the heat goes into breaking these intermolecular forces rather than increasing kinetic energy.

Question 5

Benzenecarboxylic acid is widely used in the food industry as a food preservative. The melting and boiling points of benzenecarboxylic acid are given below.

Melting point of 122 °C

Boiling point of 249 °C

Which of the following will occur to the molecules of benzenecarboxylic acid when it is cooled from 260 °C to 100 °C?

	Distance between molecules	Kinetic energy of particles
A	decreases	decreases
B	increases	decreases
C	increases	increases
D	decreases	increases

Answer: A. Distance between molecules decreases; kinetic energy decreases.

A. Correct:

At 260 °C, benzenecarboxylic acid is a gas (above its boiling point). As it cools below 249 °C, it condenses into a liquid, and below 122 °C, it freezes into a solid.

● During cooling, temperature and kinetic energy both decrease.

● The distance between molecules decreases as gas → liquid → solid, since particles move closer together.

B. Incorrect:

Although kinetic energy decreases during cooling, the distance between molecules actually decreases, not increases.

C. Incorrect:

Both kinetic energy and distance decrease, not increase, because the temperature is dropping.

D. Incorrect:

Kinetic energy does not increase during cooling; it decreases as the particles lose energy and move more slowly.

Question 6

Which of the following is not true about the Kelvin scale of temperature?

A. The values on the absolute scale are directly proportional to the average kinetic energy of the particles.

B. To convert a temperature on the Celsius scale to the absolute scale, subtract 273.15 from the Celsius temperature.

C. A kelvin has the same size as Celsius degree.

D. Absolute zero corresponds to the absence of molecular movement.

Answer: B. To convert a temperature on the Celsius scale to the absolute scale, subtract 273.15 from the Celsius temperature.

A. Correct:

Kelvin values are directly proportional to the average kinetic energy of particles — higher Kelvin means higher average kinetic energy.

B. Incorrect:

To convert Celsius to Kelvin, we add 273.15, not subtract.

K=°C+273.15K = °C + 273.15K=°C+273.15

Therefore, the statement is false.

C. Correct:

One kelvin (K) has the same size interval as one degree Celsius (°C).

D. Correct:

At absolute zero (0 K), molecular motion theoretically stops — particles have minimum possible energy.

Question 7

The black and white balls represent atoms of different elements.

null

Answer: C

A. Incorrect:

This diagram shows a mixture of compounds — some are triatomic (black–white–black) and some are diatomic (black–black or white–white). This indicates that new substances have already formed, meaning the reaction is complete, not in progress.

B. Incorrect:

Shows separate diatomic molecules of both elements (black–black and white–white). This represents unreacted elements, meaning no chemical reaction occurred.

C. Correct:

This diagram shows both reactants (diatomic molecules: black–black and white–white) and products (combined molecules: black–white). This means a chemical reaction is taking place and is partially complete, showing rearrangement of atoms into new combinations.

D. Incorrect:

Shows only diatomic molecules (black–black and white–white) again, indicating no reaction — the elements remain unreacted.

Question 8

The diagrams below show the arrangement of particles in a substance at the same pressure and at temperatures −90 °C and −70 °C.

Which of the following could be the property of the substance?

	Melting point / °C	Boiling point / °C
A	-100	-75
B	-110	-65
C	-66	-32
D	-80	-60

Answer: A. Melting point −100 °C; Boiling point −75 °C

A. Correct:

At −90 °C, the particles are closely packed but not in a fixed position → liquid state. At −70 °C, the particles are far apart → gas state.

This means the boiling point must lie between −90 °C and −70 °C. Only option A (boiling point −75 °C) fits this pattern.

Thus, the substance melts at −100 °C, boils at −75 °C, and changes from liquid to gas between −90 °C and −70 °C.

B. Incorrect:

Boiling point (−65 °C) is higher than −70 °C, meaning at −70 °C the substance would still be liquid — inconsistent with the diagram showing a gas.

C. Incorrect:

Both melting and boiling points are too high; the substance would be solid at both −90 °C and −70 °C.

D. Incorrect:

With a boiling point of −60 °C, the substance would still be liquid at −70 °C — not gas as shown.

Question 9

Substances W, X, Y and Z have the physical properties shown below:

When these substances are mixed, physical methods of separating them may include: filtration, sublimation, simple distillation, fractional distillation, chromatography, separating funnel, crystallization, evaporation to dryness

Substance	Melting point / °C	Boiling point / °C	Solubility in water
W	−114	78	soluble
X	−6	300	insoluble
Y	801	1413	soluble
Z	Sublimes at 340 °C		soluble

State the best method(s) to separate the following mixtures:

a. A mixture of W and X

b. A mixture of X and Y

c. A mixture of Y and Z

d. A mixture of W, X and water

a. Mixture of W and X

At 25°C, both W (ethanol-like, boiling point 78°C) and X (high-boiling organic liquid, b.p. 300°C) are liquids.

Since their boiling points differ significantly, they can be separated by fractional distillation.

Fractional distillation allows components with different boiling points to vaporize and condense at different stages in the column. W (the more volatile substance) will distill off first, followed by X.

Answer: Fractional distillation

b. Mixture of X and Y

At 25°C, X is a liquid (melting point −6°C), while Y is a solid (melting point 801°C). Since Y is a solid and insoluble in X, the two substances can be separated easily by filtration.

Filtration allows the solid particles of Y to remain on the filter paper, while liquid X passes through as the filtrate.

Answer: Filtration

c. Mixture of Y and Z

At 25°C, both Y and Z are solids. However, Z is known to sublime at 340°C, meaning it can change directly from solid to gas without melting.

Therefore, when the mixture is gently heated, Z will sublime and leave Y behind as a solid residue.

The vapour of Z can then be cooled and collected again as a solid by sublimation.

Answer: Sublimation

d. Mixture of W, X, and water

Here, W (soluble in water) and X (insoluble in water) are both liquids.

Step 1: Use a separating funnel to remove X, since it forms a separate immiscible layer on top of or below the aqueous layer.

Step 2: The mixture of W and water (both miscible liquids with boiling points 78°C and 100°C, respectively) can then be separated by fractional distillation. The substance with the lower boiling point (W) will distill first, followed by water.

Answer: Separating funnel (for X) → Fractional distillation (for W and water)

Question 10

The solid can be made by allowing liquid carbon dioxide, at 298 K and 4053 kPa to evaporate rapidly (by reducing the pressure to 100 kPa).

a. Convert −78 °C to kelvin and 298 K to Celsius.

Give both answers to the nearest integer.

b. State and explain whether the change

CO₂ (l) → CO₂ (g) is exothermic or endothermic.

c. Suggest why the rapid expansion of liquid CO₂ produces some solid CO₂.

d. Explain why the gaseous carbon dioxide produced by the reaction occupies a significantly greater volume than the liquid carbon dioxide it was formed from.

e. State two physical differences between liquid and gaseous carbon dioxide.

f. Carbon dioxide gas reacts with calcium hydroxide solution to form solid calcium carbonate and water. Add state symbols to the equation below:

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

a. Convert –78°C to kelvin and 298 K to Celsius

Formula:

K = °C + 273.15 and °C = K - 273.15

Calculations:

–78°C + 273.15 = 195 K

298 K – 273.15 = 25°C

Answer:

–78°C = 195 K (nearest integer)

298 K = 25°C (nearest integer)

b. State and explain whether the change CO₂(l) → CO₂(g) is exothermic or endothermic

Answer:

The process is endothermic because heat energy is taken in to overcome the forces holding the liquid molecules together and allow them to move freely as a gas.

c. Suggest why the rapid expansion of liquid CO₂ produces some solid CO₂. When liquid CO₂ expands rapidly, the gas formed expands quickly and does work against the surroundings, causing a rapid drop in temperature (cooling effect). This sudden cooling lowers the temperature below the freezing point, so some of the carbon dioxide solidifies into dry ice.

Answer:

Rapid expansion causes cooling due to energy loss during expansion, lowering the temperature enough for some CO₂ to freeze into solid form.

d. Explain why the gaseous carbon dioxide occupies a significantly greater volume than the liquid carbon dioxide it was formed from

In the gaseous state, CO₂ molecules are much farther apart than in the liquid state. For the same mass, gas particles occupy a much larger space because the intermolecular forces are very weak, allowing molecules to spread out widely.

Answer:

The gas has particles that are far apart with negligible intermolecular forces, so the same number of molecules occupy a much greater volume than in the liquid state.

e. State two physical differences between liquid and gaseous carbon dioxide

Density: The liquid is much denser than the gas.

Compressibility: The gas is highly compressible, while the liquid is almost incompressible.

(Alternative differences: the gas has no fixed volume or shape; the liquid has a fixed volume but no fixed shape.)

Answer:

Liquid CO₂ has a much higher density than gaseous CO₂.

Liquid CO₂ is almost incompressible, whereas gaseous CO₂ is easily compressed.

f. Add state symbols to the equation

CO₂+ Ca(OH)₂ → CaCO₃ +H₂O

Answer:

CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s) + H₂O(l)

Question 1

Which statements about mixtures are correct?

I. The components may be elements or compounds.

II. All components must be in the same phase.

III. The components retain their individual properties.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 2

Which is correct?

A. Mixtures are either homogeneous or heterogeneous and their chemical properties are an average of the individual component properties.

B. Mixtures are never heterogenous and their chemical properties are an average of the individual component properties

C. Mixtures are either homogeneous or heterogeneous and the components retain their individual chemical properties.

D. Mixtures are never homogeneous and the components retain their individual chemical properties.

Question 3

Which physical processes could be used to separate decane (C₁₀H₂₂) and water. The two liquids are immiscible and have different boiling points.

1. Distillation

2. Filtration

3. Sublimation

4. Use of a separating funnel

A. 1, 2, 3 and 4

B. 1, 2 and 3 only

C. 1 and 2 only

D. 1 and 4 only

Question 4

A colourless solid crystalline sample was heated from a temperature of 25 °C (standard conditions) until it completely melted to form a colourless liquid. As the temperature starts to rise again the state change is complete.

State which of the following statements best explains the shape of the graph at region Z.

A. There was no further heating.

B. The particles do not have any kinetic and potential energy.

C. A chemical reaction has taken place as the solid was melted.

D. Heat energy is used to separate the solid particles from their fixed positions in the lattice.

Question 5

Benzenecarboxylic acid is widely used in the food industry as a food preservative. The melting and boiling points of benzenecarboxylic acid are given below.

Melting point of 122 °C

Boiling point of 249 °C

Which of the following will occur to the molecules of benzenecarboxylic acid when it is cooled from 260 °C to 100 °C?

	Distance between molecules	Kinetic energy of particles
A	decreases	decreases
B	increases	decreases
C	increases	increases
D	decreases	increases

Question 6

Which of the following is not true about the Kelvin scale of temperature?

A. The values on the absolute scale are directly proportional to the average kinetic energy of the particles.

B. To convert a temperature on the Celsius scale to the absolute scale, subtract 273.15 from the Celsius temperature.

C. A kelvin has the same size as Celsius degree.

D. Absolute zero corresponds to the absence of molecular movement.

Question 7

The black and white balls represent atoms of different elements.

null

Question 8

The diagrams below show the arrangement of particles in a substance at the same pressure and at temperatures −90 °C and −70 °C.

Which of the following could be the property of the substance?

	Melting point / °C	Boiling point / °C
A	-100	-75
B	-110	-65
C	-66	-32
D	-80	-60

Question 9

Substances W, X, Y and Z have the physical properties shown below:

When these substances are mixed, physical methods of separating them may include: filtration, sublimation, simple distillation, fractional distillation, chromatography, separating funnel, crystallization, evaporation to dryness

Substance	Melting point / °C	Boiling point / °C	Solubility in water
W	−114	78	soluble
X	−6	300	insoluble
Y	801	1413	soluble
Z	Sublimes at 340 °C		soluble

State the best method(s) to separate the following mixtures:

a. A mixture of W and X

b. A mixture of X and Y

c. A mixture of Y and Z

d. A mixture of W, X and water

Question 10

The solid can be made by allowing liquid carbon dioxide, at 298 K and 4053 kPa to evaporate rapidly (by reducing the pressure to 100 kPa).

a. Convert −78 °C to kelvin and 298 K to Celsius.

Give both answers to the nearest integer.

b. State and explain whether the change

CO₂ (l) → CO₂ (g) is exothermic or endothermic.

c. Suggest why the rapid expansion of liquid CO₂ produces some solid CO₂.

d. Explain why the gaseous carbon dioxide produced by the reaction occupies a significantly greater volume than the liquid carbon dioxide it was formed from.

e. State two physical differences between liquid and gaseous carbon dioxide.

f. Carbon dioxide gas reacts with calcium hydroxide solution to form solid calcium carbonate and water. Add state symbols to the equation below:

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Structure 1.1. The models of particulate nature of matter

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