Structure: Models of the Particulate Nature of Matter — Free IB Chemistry HL Practice Questions

1FoundationMCQProperties of matter1 markPaper 1~2 min

A student tests three unlabelled solids: iodine (

\text{I}_2

), sodium chloride (NaCl), and copper (Cu). A small sample of each is added to water; the electrical conductivity of each mixture is then measured. Iodine is insoluble and its mixture does not conduct; sodium chloride dissolves and its solution conducts; copper is insoluble and its mixture does not conduct. Which explanation accounts for all three observations?

Solutions

2MasteryMCQProperties of matter1 markPaper 1~2 min

A drop of food colouring is placed into a beaker of cold water and an identical drop into a beaker of hot water. The colouring disperses throughout the hot water significantly faster. Which statement correctly explains this observation in terms of kinetic particle theory?

Solutions

3FoundationMCQProperties of matter1 markPaper 1~2 min

A pure substance is heated at constant pressure from

-50\ ^\circ\text{C}

to

150\ ^\circ\text{C}

. A temperature–time graph shows two horizontal plateaus: one at

0\ ^\circ\text{C}

, where solid and liquid coexist, and one at

100\ ^\circ\text{C}

, where liquid and gas coexist. Which row correctly identifies the phase change occurring at each plateau and the substance?

Solutions

4FoundationMCQProperties of matter1 markPaper 1~2 min

A student measures the mass of a 25.0 cm³ sample of an unknown liquid at 20 °C and finds it to be 19.75 g. She transfers the liquid into a 50.0 cm³ volumetric flask and adds distilled water to the graduation mark. The resulting solution has a density of 1.02 g cm⁻³. What is the density of the original liquid?

Solutions

5FoundationMCQStructure of the atom: Protons, neutrons, electrons1 markPaper 1~2 min

Lithium has atomic number 3. A sample contains two types of electrically neutral lithium atoms: one type has 3 neutrons and the other has 4 neutrons. Which statement correctly describes these two types of atom?

Solutions

6MasteryMCQStructure of the atom: Protons, neutrons, electrons1 markPaper 1~2 min

A sample of potassium is analysed by mass spectrometry, giving two peaks:

m/z = 39

(relative abundance 93.1%) and

m/z = 41

(relative abundance 6.9%). The proton number of potassium is 19. How many neutrons are present in the isotope responsible for the peak at

m/z = 41

?

Solutions

7FoundationMCQStructure of the atom: Protons, neutrons, electrons1 markPaper 1~2 min

A sample of chlorine gas is analysed in a mass spectrometer, giving peaks at

m/z = 35

(relative abundance 75.8%) and

m/z = 37

(relative abundance 24.2%). The atomic number of chlorine is 17. How many neutrons are present in the lighter isotope?

Solutions

8FoundationMCQStructure of the atom: Protons, neutrons, electrons1 markPaper 1~2 min

Two atoms of neon each have 10 protons. One atom has 10 neutrons and the other has 12 neutrons. Which statement correctly describes the relationship between these two atoms?

Solutions

9FoundationMCQAufbau principle, Pauli exclusion principle, Hund's rule1 markPaper 1~2 min

Phosphorus has atomic number 15 and electron configuration

1s^2\, 2p^6\, 3s^2\, 3p^3

. Using the Aufbau principle, Pauli exclusion principle, and Hund's rule, and filling the

3p

orbitals in order of increasing

m_l

(-1, 0, +1)

, what are the quantum numbers

(n,\, l,\, m_s)

of the last electron added?

Solutions

10MasteryMCQPeriodicity of electron configurations1 markPaper 1~2 min

A neutral chromium atom (atomic number 24) has anomalous ground-state electron configuration. Which of the following correctly represents this configuration?

Solutions

11FoundationMCQAufbau principle, Pauli exclusion principle, Hund's rule1 markPaper 1~2 min

A vanadium atom (atomic number 23) has the electron configuration

\text{[Ar] }4s^2\, 3d^3

. A student instead writes the configuration as

\text{[Ar] }3d^5

, keeping the total electron count correct. Which principle is most directly violated by the student's configuration?

Solutions

12FoundationMCQAufbau principle, Pauli exclusion principle, Hund's rule1 markPaper 1~2 min

The ground-state electron configuration of oxygen (

Z = 8

) is

\text{1s}^2\text{ 2p}^4

. How many unpaired electrons does an oxygen atom have in its ground state?

Solutions

13FoundationMCQConversions between moles, mass, and number of particles1 markPaper 1~2 min

A student dissolves

12.485 \text{ g}

of hydrated copper(II) sulfate,

\text{CuSO}_4 \cdot 5\text{H}_2\text{O}

(molar mass

= 249.7 \text{ g mol}^{-1}

), in water. Excess sodium hydroxide solution is added, precipitating all copper(II) ions according to:

\text{Cu}^{2+}(\text{aq}) + 2\text{OH}^-(\text{aq}) \rightarrow \text{Cu(OH)}_2(\text{s})

What is the maximum number of moles of

\text{Cu(OH)}_2

produced?

Solutions

14MasteryMCQConversions between moles, mass, and number of particles1 markPaper 1~2 min

A student heats a 2.50 g sample of hydrated copper(II) sulfate,

\text{CuSO}_4 \cdot x\text{H}_2\text{O}

, to constant mass and obtains 1.60 g of anhydrous

\text{CuSO}_4

. Using

M(\text{CuSO}_4) = 159.6 \text{ g mol}^{-1}

and

M(\text{H}_2\text{O}) = 18.0 \text{ g mol}^{-1}

, what is the value of

x

?

Solutions

15FoundationMCQConversions between moles, mass, and number of particles1 markPaper 1~2 min

A technician obtains

3.024 \text{ g}

of pure paracetamol (

\text{C}_8\text{H}_9\text{NO}_2

, molar mass

= 151.2 \text{ g mol}^{-1}

) after recrystallisation. How many molecules of paracetamol are present in this sample? (

N_A = 6.02 \times 10^{23} \text{ mol}^{-1}

)

Solutions

16FoundationMCQConversions between moles, mass, and number of particles1 markPaper 1~2 min

A sample of dry air contains

3.01 \times 10^{20}

molecules of carbon dioxide. What is the mass of

\text{CO}_2

in this sample? (Molar mass of

\text{CO}_2 = 44.01 \text{ g mol}^{-1}

;

N_A = 6.02 \times 10^{23} \text{ mol}^{-1}

)

Solutions

17FoundationMCQIdeal gas law (PV = nRT)1 markPaper 1~2 min

A fixed amount of nitrogen gas is maintained at 298 K. A student plots pressure

P

against

\dfrac{1}{V}

and obtains a straight line passing through the origin. Which conclusion is consistent with this observation?

Solutions

18MasteryMCQGas laws: Boyle's law, Charles's law, Avogadro's law1 markPaper 1~2 min

A sample of nitrogen gas occupies

250 \text{ cm}^3

at

101 \text{ kPa}

and

25 \text{ °C}

. It is transferred into a sealed container of volume

500 \text{ cm}^3

at the same temperature. What is the pressure of the gas in the new container?

Solutions

19FoundationMCQIdeal gas law (PV = nRT)1 markPaper 1~2 min

A weather balloon contains

0.50\ \text{mol}

of helium gas at

101\ \text{kPa}

and

300\ \text{K}

. The balloon rises to an altitude where the pressure is

50\ \text{kPa}

and the temperature is

250\ \text{K}

. Which statement correctly describes the change in volume of the balloon?

Solutions

20FoundationMCQIdeal gas law (PV = nRT)1 markPaper 1~2 min

A student uses the ideal gas equation

PV = nRT

to determine the molar mass of an unknown gas. She measures the mass of a sample and its volume at

101\ \text{kPa}

and

298\ \text{K}

, obtaining a molar mass of

44\ \text{g mol}^{-1}

. Which gas is most consistent with this result?

Solutions

21MasterySAQ-SSolid, liquid, gas phases and changes of state5 marksPaper 2~8 min

A student examines a sample of bromine,

\text{Br}_2

, at room temperature (

25\,^\circ\text{C}

). Bromine is a dark red liquid that evaporates readily, producing a toxic orange vapour. The melting point of bromine is

-7.2\,^\circ\text{C}

and its boiling point is

58.8\,^\circ\text{C}

.

(a)

State the name of the change of state occurring when liquid bromine at

25\,^\circ\text{C}

produces orange vapour. [1 mark]

(b)

Describe the changes in particle arrangement and energy as liquid bromine solidifies. [2 marks]

(c)

A student claims that a sample of bromine stored at

30\,^\circ\text{C}

is entirely in the gaseous state. Evaluate this claim, referring to the data above. [2 marks]

Solutions

22MasterySAQ-SSolid, liquid, gas phases and changes of state8 marksPaper 2~12 min

A student compresses a sample of carbon dioxide gas in a syringe at a constant temperature of

20\,^{\circ}\text{C}

. The initial volume is

50\,\text{cm}^3

at a pressure of

1.0\,\text{atm}

.

(a)

State Boyle's Law as a mathematical expression, defining all symbols used. [1 mark]

(b)

Calculate the pressure of the gas after the volume is reduced to

25\,\text{cm}^3

, assuming ideal behaviour. [2 marks]

(c)

Using kinetic molecular theory, explain why reducing the volume at constant temperature causes the pressure to increase. [2 marks]

(d)

At very high pressures, the actual pressure of

\text{CO}_2

deviates from the value predicted by Boyle's Law. Deduce and explain the direction of this deviation for

\text{CO}_2

, referring to intermolecular forces and molecular volume. [3 marks]

Solutions

23ChallengeSAQ-LSolid, liquid, gas phases and changes of state7 marksPaper 2~11 min

Iodine (

\text{I}_2

) is a solid at room temperature (

25\,^\circ\text{C}

) and standard pressure (

1\,\text{atm}

). Selected phase data for iodine are given below. Feature — Temperature — Pressure Triple point —

113.6\,^\circ\text{C}

—

0.12\,\text{atm}

Normal melting point —

113.6\,^\circ\text{C}

—

1\,\text{atm}

Normal boiling point —

184.3\,^\circ\text{C}

—

1\,\text{atm}

Critical point —

546\,^\circ\text{C}

—

115\,\text{atm}

(a)

State the phase of iodine present at each of the following conditions. In each case, identify which region of the phase the point occupies. - (i)

25\,^\circ\text{C}

and

1\,\text{atm}

\hspace{12em}

[1] -
(ii)

200\,^\circ\text{C}

and

1\,\text{atm}

\hspace{12em}

[1] -
(iii)

200\,^\circ\text{C}

and

80\,\text{atm}

\hspace{11.5em}

[1 mark]

(b)

Explain why the density of solid iodine is much greater than that of gaseous iodine, and why liquid iodine has a density closer to the solid than to the gas. [2 marks]

(c)

A student claims: *"At

1\,\text{atm}

, liquid iodine can exist over a range of temperatures."* Evaluate this claim using the phase data, and identify one industrial application that exploits the phase behaviour of iodine at

1\,\text{atm}

. [2 marks]

Solutions

24MasterySAQ-SSolid, liquid, gas phases and changes of state5 marksPaper 2~8 min

A student seals a bag of chips at sea level where the atmospheric pressure is

1.00\,\text{atm}

. The sealed portion of the bag contains

0.0120\,\text{mol}

of nitrogen gas occupying a volume of

0.295\,\text{L}

at

25\,°\text{C}

. The student hikes to high altitude where the atmospheric pressure drops to

0.700\,\text{atm}

at the same temperature.

(a)

State Boyle's Law, including its mathematical form. [1 mark]

(b)

Explain why the bag puffs up when the student reaches high altitude. [2 marks]

(c)

Calculate the volume of nitrogen gas in the bag at high altitude, and hence determine the percentage increase in volume of the gas. [2 marks]

Solutions

25MasterySAQ-SAtomic number, mass number, isotopes5 marksPaper 2~8 min

An element X exists as three naturally occurring isotopes. The mass spectrum of X shows three peaks: Peak — Mass number — Relative abundance 1 — 24 —

79.0\%

25 —

10.0\%

3 — 26 —

11.0\%

(a)

State the relationship between mass number, atomic number, and number of neutrons. [1 mark]

(b)

Calculate the relative atomic mass of element X. [2 marks]

(c)

The element X has atomic number 12. Deduce, with reference to its electron configuration, why X forms an ion with a charge of

2+

. [2 marks]

Solutions

26MasterySAQ-SAtomic number, mass number, isotopes5 marksPaper 2~8 min

An unknown element Q has three isotopes. Data obtained from a mass spectrometer are shown below. Isotope — Relative atomic mass — Abundance /

\%

^{28}

Q —

28

—

92.23

^{29}

Q —

29

—

4.67

^{30}

Q —

30

—

3.10

(a)

State what the notation

^{28}

Q indicates about the mass number of this isotope, and explain why the atomic number is not shown in this notation. [1 mark]

(b)

Calculate the relative atomic mass of element Q. [2 marks]

(c)

The first ionization energy of element Q is

786\,\text{kJ mol}^{-1}

. Explain why the second ionization energy of Q is significantly larger than the first. [2 marks]

Solutions

27ChallengeSAQ-LAtomic models: Bohr model, quantum model7 marksPaper 2~11 min

Data

\dfrac{1}{\lambda} = R_H\!\left(\dfrac{1}{n_1^2} - \dfrac{1}{n_2^2}\right)

A student measures the wavelength of the second line in the Balmer series of atomic hydrogen and obtains a value of

486\,\text{nm}

.

(a)

Determine the value of

n

for the upper energy level involved in this transition. Use

R_H = 1.097 \times 10^7\,\text{m}^{-1}

. [2 marks]

(b)

Explain why the Bohr model successfully predicts the spectral lines of hydrogen but fails to predict the spectrum of helium. Refer to specific structural features of each atom. [2 marks]

(c)

A student claims: *"The principal quantum number

n

in the quantum mechanical model has exactly the same physical meaning as the orbit number

n

in the Bohr model."* Evaluate this claim. In your answer, identify one way in which the two uses of

n

are equivalent and one way in which they are fundamentally different, and use the concept of radial nodes to justify your conclusion. [3 marks]

Solutions

28MasterySAQ-SAtomic models: Bohr model, quantum model5 marksPaper 2~8 min

The quantum mechanical model of the atom describes electrons in terms of orbitals rather than fixed circular orbits.

(a)

State one difference between the Bohr model and the quantum mechanical model in how each describes the motion of an electron. [1 mark]

(b)

Define probability density,

\psi^2

, and explain why the quantum mechanical model cannot assign a precise distance from the nucleus to the electron in the

1s

orbital of hydrogen. [2 marks]

(c)

The Bohr model successfully predicts the emission spectrum of hydrogen but fails for helium. Explain why the quantum mechanical model can predict the emission spectrum of helium while the Bohr model cannot, referring to electron–electron interactions and orbital energy levels. [2 marks]

Solutions

29ChallengeSAQ-LElectron arrangement and atomic orbitals7 marksPaper 2~11 min

Data

- Speed of light:

c = 3.00 \times 10^{8}\,\text{m s}^{-1}

- Planck constant:

h = 6.63 \times 10^{-34}\,\text{J s}

- Rydberg constant:

R_H = 1.097 \times 10^{7}\,\text{m}^{-1}

A student investigates the emission spectrum of atomic hydrogen. A spectral line is observed at

486\,\text{nm}

, corresponding to the transition from

n = 4

to

n = 2

(Balmer series).

(a)

Calculate the energy, in J, of the photon emitted during the

n = 4

to

n = 2

transition. [2 marks]

(b)

Using the Rydberg equation, determine the value of

n_2

for a transition that emits a photon of wavelength

434\,\text{nm}

(another line in the Balmer series, where

n_1 = 2

). [2 marks]

(c)

State the physical significance of the integer

n_2

in the quantum mechanical model of the hydrogen atom. [1 mark]

(d)

Evaluate two limitations of the Bohr model of the hydrogen atom when applied to multi-electron atoms such as iron (Fe,

Z = 26

). In your answer, refer to atomic orbitals and the quantum mechanical model. Relevant equations:

E = h\nu \qquad c = \lambda\nu \qquad \frac{1}{\lambda} = R_H\!\left(\frac{1}{n_1^2} - \frac{1}{n_2^2}\right)

[2 marks]

Solutions

30MasterySAQ-SAufbau principle, Pauli exclusion principle, Hund's rule12 marksPaper 2~18 min

Data

First ionisation energy of Fe

= 762\,\text{kJ mol}^{-1}

; atomic radius of Fe

= 126\,\text{pm}

. (Note: the data line above is removed — no orphaned data present in this question. Stem is self-contained.) (Clean stem — no data line needed) Iron (Fe,

Z = 26

) is a transition metal essential for haemoglobin. The ground-state electron configuration of iron is

[\text{Ar}]\,3d^6\,4s^2

. (a) State the Aufbau principle. [1] (b) Using the Aufbau principle, explain why the

4s

orbital is filled before the

3d

orbitals in neutral iron. [2] (c) Evaluate the statement: *"The

4s

orbital is always lower in energy than the

3d

orbitals for all elements and all ions."* Use the ionisation of iron to support your answer. [2] (d) Deduce the electron configuration of the

\text{Fe}^{2+}

ion. [1]

Iron (Fe,

Z = 26

) is a transition metal essential for haemoglobin. The ground-state electron configuration of iron is

[\text{Ar}]\,3d^6\,4s^2

.

(a)

State the Aufbau principle. [1 mark]

(b)

Using the Aufbau principle, explain why the

4s

orbital is filled before the

3d

orbitals in neutral iron. [2 marks]

(c)

Evaluate the statement: *"The

4s

orbital is always lower in energy than the

3d

orbitals for all elements and all ions."* Use the ionisation of iron to support your answer. [2 marks]

(d)

Deduce the full electron configuration of the

\text{Fe}^{2+}

ion. [1 mark]

Solutions

31ChallengeSAQ-LElectron arrangement and atomic orbitals7 marksPaper 2~11 min

First ionization energies (

\text{IE}_1

) for Period 2 elements in

\text{kJ mol}^{-1}

: Li — Be — B — C — N — O — F — Ne 520 — 900 — 801 — 1086 — 1402 — 1314 — 1681 — 2081

(a)

State the full ground-state electron configurations of boron (B,

Z = 5

) and oxygen (O,

Z = 8

). Explain the observed decrease in

\text{IE}_1

from beryllium to boron. [3 marks]

(b)

The successive ionization energies of nitrogen in

\text{kJ mol}^{-1}

are:

\text{IE}_1 = 1402,\quad \text{IE}_2 = 2856,\quad \text{IE}_3 = 4578,\quad \text{IE}_4 = 7475,\quad \text{IE}_5 = 9445

Identify between which two successive ionization energies the largest jump occurs. Explain this jump in terms of electron configuration and orbital energy levels. [2 marks]

(c)

The aufbau principle predicts the ground-state electron configuration of chromium (Cr,

Z = 24

) to be

[\text{Ar}]\,4s^2\,3d^4

. State the actual ground-state configuration of chromium and explain why it differs from the aufbau prediction. [2 marks]

Solutions

32ChallengeSAQ-LElectron arrangement and atomic orbitals7 marksPaper 2~11 min

A student prepares aqueous solutions of two transition metal salts: copper(II) sulfate (

\text{CuSO}_4

) and zinc sulfate (

\text{ZnSO}_4

). The

\text{CuSO}_4

solution is blue and paramagnetic, while the

\text{ZnSO}_4

solution is colourless and diamagnetic. Atomic numbers:

\text{Cu} = 29

,

\text{Zn} = 30

(a)

Determine the ground-state electron configuration of the

\text{Cu}^{2+}

ion. Explain, using the concept of atomic orbitals and Hund's rule, why

\text{Cu}^{2+}

is paramagnetic. [3 marks]

(b)

Determine the ground-state electron configuration of the

\text{Zn}^{2+}

ion. Explain, in terms of the occupancy of the 3d orbitals, why

\text{Zn}^{2+}(\text{aq})

is colourless. [2 marks]

(c)

When excess ammonia is added to

\text{Cu}^{2+}(\text{aq})

, the solution changes from pale blue to deep blue-violet. Deduce, using the quantum mechanical model and the concept of d–d transitions, why replacing water ligands with ammonia ligands changes the colour of the complex. [2 marks]

Solutions

33ChallengeSAQ-LDefinition of the mole and Avogadro's constant10 marksPaper 2~15 min

Data

M(\text{Ti}) = 47.9\,\text{g mol}^{-1}

,

M(\text{O}) = 16.0\,\text{g mol}^{-1}

,

N_A = 6.02 \times 10^{23}\,\text{mol}^{-1}

A sample of pure titanium(IV) oxide,

\text{TiO}_2

, used as a white pigment in paint, has a mass of

7.99\,\text{g}

.

(a)

Show that the molar mass of

\text{TiO}_2

is

79.9\,\text{g mol}^{-1}

, and hence determine the number of moles of

\text{TiO}_2

in the

7.99\,\text{g}

sample. [2 marks]

(b)

Calculate the number of titanium atoms in the

7.99\,\text{g}

sample of

\text{TiO}_2

. [2 marks]

(c)

The mole is described as a "bridge" between the atomic scale and the macroscopic scale. Using the relationship between the mass of one

\text{TiO}_2

formula unit in atomic mass units and the molar mass of

\text{TiO}_2

in grams, explain what this bridging role means and why it is necessary for quantitative chemistry. [3 marks]

(d)

A student claims that a

7.99\,\text{g}

sample of pure titanium metal contains more atoms than the

7.99\,\text{g}

sample of

\text{TiO}_2

. Evaluate this claim using calculations, and explain why any difference arises in terms of molar mass. [3 marks]

Solutions

34ChallengeSAQ-LDefinition of the mole and Avogadro's constant10 marksPaper 2~15 min

Aspirin (acetylsalicylic acid,

\text{C}_9\text{H}_8\text{O}_4

) is synthesised by reacting salicylic acid (

\text{C}_7\text{H}_6\text{O}_3

) with ethanoic anhydride (

\text{C}_4\text{H}_6\text{O}_3

). In a laboratory preparation, a student uses

13.8\,\text{g}

of salicylic acid an excess of ethanoic anhydride.

\text{C}_7\text{H}_6\text{O}_3 + \text{C}_4\text{H}_6\text{O}_3 \rightarrow \text{C}_9\text{H}_8\text{O}_4 + \text{CH}_3\text{COOH}

(a)

Calculate the number of moles of salicylic acid used. [1 mark]

(b)

Calculate theoretical yield, in grams, of aspirin. [2 marks]

(c)

After purification,

15.0\,\text{g}

of aspirin is obtained. Determine the percentage yield of aspirin. [1 mark]

(d)

Explain why the mass of aspirin obtained (

15.0\,\text{g}

) can be greater than the mass of salicylic acid used (

13.8\,\text{g}

), with reference to the mole concept and the law of conservation of mass. [3] (e) A student claims that recrystallisation from hot ethanol is sufficient to remove all unreacted salicylic acid from the crude aspirin product, because salicylic acid and aspirin have similar solubilities. Evaluate this claim, referring to the physical properties of the two compounds and the principles of recrystallisation. *Molar masses /

\text{g mol}^{-1}

: H = 1.01, C = 12.0, O = 16.0* *

N_A = 6.02 \times 10^{23}\,\text{mol}^{-1}

* *

n = \dfrac{m}{M}

* *Percentage yield

= \dfrac{\text{actual yield}}{\text{theoretical yield}} \times 100

* [3 marks]

Solutions

35ChallengeSAQ-LDefinition of the mole and Avogadro's constant8 marksPaper 2~12 min

Data

M(\text{C}) = 12.0\,\text{g\,mol}^{-1}

;

M(\text{O}) = 16.0\,\text{g\,mol}^{-1}

;

N_A = 6.02 \times 10^{23}\,\text{mol}^{-1}

An atmospheric scientist collects an air sample in a remote location. Analysis shows the sample contains

4.40 \times 10^{-4}\,\text{g}

of carbon dioxide (

\text{CO}_2

) per litre of air. Molar mass

(a)

Calculate the number of moles of

\text{CO}_2

in one litre of this air sample. [1 mark]

(b)

Determine the number of

\text{CO}_2

molecules in one litre of this air sample. [2 marks]

(c)

Explain why the mole acts a 'bridge' between a mass-based concentration (

\text{g\,L}^{-1}

) and a number-based concentration (molecules

\text{L}^{-1}

), and state what property of

\text{CO}_2

makes this conversion exact. [2 marks]

(d)

A second air sample from an urban area contains

8.80 \times 10^{-4}\,\text{g}

of

\text{CO}_2

per litre. A student claims: "Doubling the mass concentration always doubles the number of molecules per litre, regardless of which gas is present." Evaluate this claim. [3 marks]

Solutions

36ChallengeSAQ-LDefinition of the mole and Avogadro's constant8 marksPaper 2~12 min

Data

\left(c = 3.00 \times 10^8\,\text{m s}^{-1}\right)

A pure diamond gemstone has a mass of

0.586\,\text{g}

. Diamond is a giant covalent lattice consisting entirely of carbon atoms.

(a)

Calculate the number of carbon atoms present in this diamond. [2 marks]

(b)

The diamond is completely combusted in excess pure oxygen according to:

\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)}

Explain why the number of

\text{CO}_2

molecules produced is exactly equal to the number of carbon atoms originally present in the diamond. In your answer, refer to moles and Avogadro's constant. [2 marks]

(c)

The diamond is vaporised into individual gaseous carbon atoms at

2500\,°\text{C}

. The average bond enthalpy of a C–C bond is

+346\,\text{kJ mol}^{-1}

; assume each carbon atom breaks an average of two such bonds during vaporisation, giving a total energy input of approximately

3.4\,\text{kJ}

for this sample. A student claims: *"The total mass of the gaseous carbon atoms will be less than

0.586\,\text{g}

because the energy absorbed to break the covalent bonds comes from the mass of the atoms, via*

E = mc^2

." Evaluate this claim. Your answer must include a calculation of the predicted mass change

\Delta m

and a comparison with the original mass of the diamond. [4 marks]

Solutions

37ChallengeSAQ-LIdeal gas law (PV = nRT)9 marksPaper 2~14 min

A

500\,\text{mL}

sealed glass flask contains a mixture of

\text{N}_2(\text{g})

and

\text{O}_2(\text{g})

at a total pressure of

2.50 \times 10^5\,\text{Pa}

and

300\,\text{K}

. The flask contains

0.0200\,\text{mol}

of

\text{N}_2

.

R = 8.31\,\text{J K}^{-1}\text{mol}^{-1}

(a)

(i) Calculate the partial pressure of

\text{N}_2

in the flask. [2]
(ii) Determine the number of moles of

\text{O}_2

in the flask. [2 marks]

(b)

Explain, using the assumptions of the ideal gas model, why the total pressure of a gas mixture equals the sum of the partial pressures of its components. [2 marks]

(c)

Evaluate whether the ideal gas law would accurately predict the pressure in the flask if it were cooled to

50\,\text{K}

. Justify your answer with reference to two assumptions of the kinetic molecular theory. [3 marks]

Solutions

38MasterySAQ-SReal gases vs ideal gases6 marksPaper 2~9 min

Data

PV = nRT \qquad R = 0.0821\,\text{L\,atm\,mol}^{-1}\text{K}^{-1} \qquad T(\text{K}) = T(^\circ\text{C}) + 273

A student compresses carbon dioxide gas in a syringe at

25\,^\circ\text{C}

. At pressures below

5\,\text{atm}

, the product

PV

is approximately constant. At pressures around

50\,\text{atm}

, the

PV

product falls significantly below the ideal value. At pressures above

500\,\text{atm}

, the

PV

product rises above the ideal value.

(a)

State two assumptions of the kinetic molecular theory that define an ideal gas. [2 marks]

(b)

Calculate the volume occupied by

0.500\,\text{mol}

of carbon dioxide at

25\,^\circ\text{C}

and

1.00\,\text{atm}

, assuming ideal behaviour. Give your answer to three significant figures. [2 marks]

(c)

Explain why the

PV

product for carbon dioxide decreases at moderate pressures (around

50\,\text{atm}

) but increases at very high pressures (around

500\,\text{atm}

). [2 marks]

Solutions

39ChallengeSAQ-LGas laws: Boyle's law, Charles's law, Avogadro's law7 marksPaper 2~11 min

Data

- Initial volume:

V_1 = 50.0\,\text{cm}^3

- Initial pressure:

P_1 = 1.00 \times 10^5\,\text{Pa}

- Final volume:

V_2 = 25.0\,\text{cm}^3

- Measured final pressure:

P_\text{exp} = 2.05 \times 10^5\,\text{Pa}

A student investigates the relationship between pressure and volume of a fixed mass of nitrogen gas,

\text{N}_2\text{(g)}

, at a constant temperature of

25\,°\text{C}

. The student uses a gas syringe and a pressure sensor, recording the following

(a)

Calculate the pressure expected at

V_2 = 25.0\,\text{cm}^3

, assuming ideal gas behaviour. [2 marks]

(b)

Explain, in terms of kinetic molecular theory, why reducing the volume of a fixed mass of gas at constant temperature increases its pressure. [2 marks]

(c)

The measured pressure (

2.05 \times 10^5\,\text{Pa}

) differs from the ideal value calculated in (a). Evaluate whether this difference is best explained by the limitations of the ideal gas model or by experimental error. In your answer, refer to the assumptions of kinetic molecular theory and the magnitude of the deviation. [3 marks]

Solutions

40ChallengeSAQ-LGas laws: Boyle's law, Charles's law, Avogadro's law7 marksPaper 2~11 min

Data

PV = nRT

;

R = 8.31\,\text{J}\,\text{mol}^{-1}\,\text{K}^{-1}

;

T(\text{K}) = T(°\text{C}) + 273

*

A weather balloon is filled with

2.50\,\text{mol}

of helium gas at ground level, where the temperature is

20.0\,°\text{C}

and the pressure is

1.00 \times 10^{5}\,\text{Pa}

. The balloon rises to an altitude where the temperature is

-10.0\,°\text{C}

and the pressure is

0.500 \times 10^{5}\,\text{Pa}

. *

(a)

Calculate the volume of the balloon at ground level and at the higher altitude. [3 marks]

(b)

The two effects of altitude — decreasing temperature and decreasing pressure — act in opposite directions on the balloon volume. Using Charles's law and Boyle's law, deduce which effect dominates and explain why the volume increases overall. [2 marks]

(c)

The balloon material can withstand a maximum volume of

0.250\,\text{m}^{3}

. A second balloon is filled with

5.00\,\text{mol}

of helium under the same ground-level conditions and rises to the same altitude. Evaluate whether this second balloon would burst. [2 marks]

Solutions

41ChallengeLAQProperties of matter15 marksPaper 3~23 min

An industrial chemist is investigating two crystalline substances, A and B, for use in a high-temperature furnace lining. Substance A: brittle; melting point

1565\,^\circ\text{C}

; does not conduct electricity when solid, conducts when molten; density

5.24\,\text{g cm}^{-3}

. Substance B: malleable and ductile; melting point

962\,^\circ\text{C}

; conducts electricity well in both solid and molten states; density

10.49\,\text{g cm}^{-3}

.

(a)

State the type of bonding and structure present in each of Substance A and Substance B. [2 marks]

(b)

Explain how the bonding and structure of Substance A account for its brittleness, high melting point, and electrical conductivity behaviour. [3 marks]

(c)

Explain how the bonding and structure of Substance B account for its malleability, electrical conductivity, and high density. [3 marks]

(d)

When Substance A is heated in a stream of hydrogen gas, it slowly loses mass and a new substance C forms. Substance C is a grey, lustrous solid that conducts electricity well in both solid and molten states and has a melting point of

1538\,^\circ\text{C}

. - (i) Identify Substance A and Substance C. [1] -
(ii) Write a balanced equation, including state symbols, for the reaction of Substance A with hydrogen gas. [2] (e) Evaluate which of the three substances — A, B, or C — is most suitable for use as a high-temperature furnace lining. In your answer, refer to at least two physical properties and the bonding and structure of your chosen substance. Identify one limitation of your chosen substance and explain why it remains the best choice. [4 marks]

Solutions

42ChallengeLAQProperties of matter17 marksPaper 3~26 min

A student investigates the physical properties of four unknown substances, W, X, Y, and Z, to classify their bonding and structure. The observations are recorded below. - Substance W: colourless liquid at room temperature (

\text{bp} = 78\,°\text{C}

,

\text{mp} = -114\,°\text{C}

); does not conduct electricity in any state; miscible with water in all proportions. - Substance X: white crystalline solid (

\text{mp} = 801\,°\text{C}

,

\text{bp} = 1413\,°\text{C}

); does not conduct electricity when solid; aqueous solution and molten state both conduct electricity well. - Substance Y: black, shiny solid (

\text{mp} = 3550\,°\text{C}

, sublimes at

3825\,°\text{C}

); does not conduct electricity at any temperature; insoluble in water and all common organic solvents. - Substance Z: pale yellow-green gas at room temperature (

\text{bp} = -34\,°\text{C}

,

\text{mp} = -101\,°\text{C}

); does not conduct electricity in any state; slightly soluble in water, forming a pale green solution that does not conduct electricity.

(a)

State the type of bonding and structure present in each of W, X, Y, and Z. [4 marks]

(b)

For Substance W, explain how its bonding and structure account for each of the following properties: - its low melting point - its non-conductivity in all states - its miscibility with water [3 marks]

(c)

For Substance X, explain how its bonding and structure account for each of the following properties: - its high melting point - its non-conductivity when solid - its conductivity when molten or dissolved in water [3 marks]

(d)

For Substance Y, explain how its bonding and structure account for each of the following properties: - its very high melting point - its non-conductivity at all temperatures - its insolubility in water and organic solvents [3] (e) For Substance Z, explain how its bonding and structure account for each of the following properties: - its low boiling point - its non-conductivity in all states - its only slight solubility in water [2] (f) Substance Z is cooled to

-120\,°\text{C}

, forming a solid. Evaluate whether solid Z at this temperature would conduct electricity. [2 marks]

Solutions

43ChallengeLAQAtomic number, mass number, isotopes15 marksPaper 3~23 min

Data

N = N_0\,e^{-\lambda t}, \qquad t_{1/2} = \frac{\ln 2}{\lambda}, \qquad L = 6.02 \times 10^{23}\,\text{mol}^{-1}

Technetium does not occur naturally on Earth. The synthetic radioisotope

^{99\text{m}}_{43}\text{Tc}

(metastable technetium-99) is widely used in medical diagnostic imaging. It decays by gamma emission with a half-life of

6.01\,\text{h}

to form technetium-99 (

^{99}_{43}\text{Tc}

), which subsequently undergoes beta-minus decay with a half-life of

2.11 \times 10^{5}\,\text{years}

to form ruthenium-99 (

^{99}_{44}\text{Ru}

).

(a)

State the number of protons, neutrons, and electrons in a neutral atom of

^{99\text{m}}_{43}\text{Tc}

. [1 mark]

(b)

The notation "

^{99\text{m}}_{43}\text{Tc}

" and "

^{99}_{43}\text{Tc}

" represent two distinct nuclear species. Explain why they are classified as isotopes of the same element, and state what the superscript "m" indicates about the nucleus of

^{99\text{m}}_{43}\text{Tc}

. [3 marks]

(c)

A patient is injected with

2.0 \times 10^{-8}\,\text{mol}

of

^{99\text{m}}_{43}\text{Tc}

. The molar mass of

^{99\text{m}}_{43}\text{Tc}

is

99.0\,\text{g mol}^{-1}

. Calculate the mass, in grams, of

^{99\text{m}}_{43}\text{Tc}

remaining in the patient

12.0\,\text{h}

after injection. Assume no biological excretion. [4 marks]

(d)

Evaluate the suitability of

^{99\text{m}}_{43}\text{Tc}

as a medical imaging agent, considering the properties of both steps in the decay chain

^{99\text{m}}_{43}\text{Tc} \rightarrow\, ^{99}_{44}\text{Ru}

. Your answer must include a reasoned overall judgement that weighs the benefits of the first decay step against any risks arising from the second. [7 marks]

Solutions

44ChallengeLAQAtomic number, mass number, isotopes15 marksPaper 3~23 min

A sample of lead ore from a uranium-rich mine contains four stable isotopes with the following relative abundances: Isotope —

^{204}\text{Pb}

—

^{206}\text{Pb}

—

^{207}\text{Pb}

—

^{208}\text{Pb}

Abundance / % —

1.4

—

24.1

—

22.1

—

52.4

(a)

Calculate the relative atomic mass of this lead sample to four significant figures. [2 marks]

(b)

A lead sample from a thorium-rich mine has the following abundances:

^{204}\text{Pb}\ 1.4\%

,

^{206}\text{Pb}\ 20.5\%

,

^{207}\text{Pb}\ 20.5\%

,

^{208}\text{Pb}\ 57.6\%

. Explain why the abundance of

^{206}\text{Pb}

is lower and the abundance of

^{208}\text{Pb}

is higher in the thorium-rich sample compared with the uranium-rich sample. [3 marks]

(c)

In a mass spectrometer, lead ions are detected at

m/z = 204,\ 206,\ 207,

and

208

. (i) State which two peaks have the greatest height and justify your answer using the data in the table above. [2]
(ii) The mass spectrometer uses a magnetic field of strength

B

and an accelerating voltage

V

. Ions travel in a circular path of radius

r

according to:

\frac{m}{z} = \frac{B^2 r^2}{2V}

The accelerating voltage is doubled while

B

and the detected radius

r

remain fixed. Deduce what happens to the

m/z

value of ions that now reach the detector, and identify which isotope, if any, is detected. [2 marks]

(d)

The ratios

^{206}\text{Pb}/^{204}\text{Pb}

and

^{208}\text{Pb}/^{204}\text{Pb}

are used in radiometric dating of geological samples. The relevant decay series and half-lives are: -

^{238}\text{U} \rightarrow\ ^{206}\text{Pb}

,

t_{1/2} = 4.47 \times 10^{9}\ \text{yr}

-

^{235}\text{U} \rightarrow\ ^{207}\text{Pb}

,

t_{1/2} = 7.04 \times 10^{8}\ \text{yr}

-

^{232}\text{Th} \rightarrow\ ^{208}\text{Pb}

,

t_{1/2} = 1.40 \times 10^{10}\ \text{yr}

Evaluate the reliability of lead isotope ratio dating, addressing: the role of

^{204}\text{Pb}

as a reference isotope; the validity of the assumption that no radiogenic lead was present when the rock formed; the suitability of the method for rocks of different ages; and one geochemical factor that could compromise the results. [6 marks]

Solutions

45ChallengeLAQElectron arrangement and atomic orbitals15 marksPaper 3~23 min

Technetium (Tc,

Z = 43

) is a synthetic transition metal with no stable isotopes. Its ground-state electron configuration presents a well-known anomaly relative to the simple Aufbau principle.

(a)

State the ground-state electron configuration of technetium as predicted by the Aufbau principle, and the actual experimentally observed configuration. [2 marks]

(b)

Explain why the actual configuration

[\text{Kr}]\,4d^5\,5s^1

is more stable than the Aufbau-predicted configuration

[\text{Kr}]\,4d^5\,5s^2

. [3 marks]

(c)

The element immediately below technetium in Group 7 is rhenium (

Z = 75

). Predict whether rhenium exhibits the same type of electron configuration anomaly. Justify your prediction using the concepts of orbital energy and exchange energy. [3 marks]

(d)

For the highest-energy electron in the anomalous ground-state configuration of technetium, deduce all four quantum numbers

n

,

l

,

m_l

, and

m_s

. [3] (e) A student claims: *"In a technetium atom, the

4d

and

5s

orbitals have the same energy because

4d

belongs to the

n = 4

shell and

5s

belongs to the

n = 5

shell, so they are simply ordered by principal quantum number."* Evaluate this claim using the concepts of penetration and shielding. [4 marks]

Solutions

46ChallengeLAQPeriodicity of electron configurations15 marksPaper 3~23 min

A student investigates the magnetic and spectroscopic properties of first-row transition metal ions. She prepares aqueous solutions of the nitrate salts of vanadium, chromium, and manganese, each at

0.100\,\text{mol}\,\text{dm}^{-3}

. She adds excess zinc powder to each solution in acidic conditions, reducing the metal ions stepwise to the

+2

oxidation state. She records the following colour changes: - Vanadium: yellow

\to

blue

\to

green

\to

violet - Chromium: orange

\to

green

\to

blue - Manganese: purple

\to

very pale pink (effectively colourless) Atomic numbers:

\text{V} = 23

,

\text{Cr} = 24

,

\text{Mn} = 25

.

(a)

State the full electron configuration of the vanadium ion present in the yellow solution. [1 mark]

(b)

Explain the sequence of colour changes observed for vanadium by reference to the successive electron configurations of each vanadium ion formed. [3 marks]

(c)

Evaluate the student's claim that the blue

\text{Cr}^{2+}

ion and the colourless

\text{Mn}^{2+}

ion are isoelectronic. In your answer: - determine the electron configurations of

\text{Cr}^{2+}

and

\text{Mn}^{2+}

- state whether the claim is correct - compare the number of unpaired electrons in each ion and calculate the spin-only magnetic moment,

\mu

, for each, using

\mu = \sqrt{n(n+2)}\,\text{BM}

[5 marks]

(d)

\text{Cr}^{2+}_{(\text{aq})}

is blue, whereas

\text{Mn}^{2+}_{(\text{aq})}

is effectively colourless, even though both ions have

d

-electrons available in principle for

d

–

d

transitions. Using your electron configurations from (c), explain this observation. In your answer refer to: - the Pauli Exclusion Principle and spin selection rule - the concept of crystal field splitting (

\Delta_o

) and how the magnitude of

\Delta_o

differs between

\text{Cr}^{2+}

and

\text{Mn}^{2+}

in an octahedral aqua complex - the consequence for the molar absorption coefficient and the observed colour [6 marks]

Solutions

47ChallengeLAQConversions between moles, mass, and number of particles15 marksPaper 3~23 min

Data

M(\text{Cu}) = 63.55

,

M(\text{S}) = 32.07

,

M(\text{O}) = 16.00

,

M(\text{H}) = 1.01

;

n = \dfrac{m}{M}

;

n = cV

A student investigates the composition of a sample of hydrated copper(II) sulfate,

\text{CuSO}_4 \cdot x\text{H}_2\text{O}

. The student heats a

4.990\,\text{g}

sample in a crucible until constant mass, obtaining

3.190\,\text{g}

of anhydrous

\text{CuSO}_4

. The student dissolves the anhydrous salt in deionised water and makes the solution up to

250.0\,\text{cm}^3

in a volumetric flask. A

25.00\,\text{cm}^3

aliquot is reacted with excess aqueous KI, producing iodine:

2\text{Cu}^{2+}(\text{aq}) + 4\text{I}^-(\text{aq}) \rightarrow 2\text{CuI}(\text{s}) + \text{I}_2(\text{aq})

The iodine is titrated with

0.100\,\text{mol\,dm}^{-3}

sodium thiosulfate,

\text{Na}_2\text{S}_2\text{O}_3

, using starch indicator. The mean titre is

19.98\,\text{cm}^3

. The relevant half-equation is:

\text{I}_2(\text{aq}) + 2\text{S}_2\text{O}_3^{2-}(\text{aq}) \rightarrow 2\text{I}^-(\text{aq}) + \text{S}_4\text{O}_6^{2-}(\text{aq})

(a)

Calculate the value of

x

in

\text{CuSO}_4 \cdot x\text{H}_2\text{O}

using the mass data from the heating experiment. [3 marks]

(b)

Calculate the number of moles of

\text{Cu}^{2+}

ions in the original

4.990\,\text{g}

sample using the titration data. [3 marks]

(c)

Explain whether the titration data confirms the value of

x

calculated in (a). [3 marks]

(d)

The student prepares a second

\text{CuSO}_4

solution of unknown concentration. A

10.00\,\text{cm}^3

sample is treated with excess KI and the iodine produced requires

15.60\,\text{cm}^3

of

0.100\,\text{mol\,dm}^{-3}

\text{Na}_2\text{S}_2\text{O}_3

for complete reaction. The solubility of

\text{CuSO}_4

at

25\,°\text{C}

is

32.0\,\text{g}

per

100\,\text{g}

of water, and the density of a saturated solution at

25\,°\text{C}

is

1.21\,\text{g\,cm}^{-3}

. Evaluate whether this unknown solution could be a saturated solution of

\text{CuSO}_4

at

25\,°\text{C}

. [6 marks]

Solutions

48ChallengeLAQDefinition of the mole and Avogadro's constant13 marksPaper 3~20 min

Data

N_A = 6.02 \times 10^{23}\,\text{mol}^{-1}

;

R = 8.31\,\text{J K}^{-1}\text{mol}^{-1}

Nitrogen dioxide (

\text{NO}_2

) is a brown, toxic gas that contributes to photochemical smog. In a controlled laboratory experiment, a student collects a pure sample of

\text{NO}_2

gas in a sealed container of volume

2.50 \times 10^{-4}\,\text{m}^3

at a pressure of

1.01 \times 10^5\,\text{Pa}

and a temperature of

298\,\text{K}

. The molar mass of

\text{NO}_2

is

46.01\,\text{g mol}^{-1}

.

(a)

Calculate the number of moles of

\text{NO}_2

gas in the container. [2 marks]

(b)

The student decomposes the

\text{NO}_2

sample completely into nitrogen and oxygen gases. (i) Deduce the balanced chemical equation for this decomposition. [1]
(ii) The sealed container is maintained at

298\,\text{K}

throughout the decomposition. Calculate the pressure inside the container after decomposition is complete. [2 marks]

(c)

The mole is defined such that

N_A = 6.02214076 \times 10^{23}\,\text{mol}^{-1}

exactly. A classmate argues that this definition is arbitrary and that any sufficiently large number could serve the same purpose. Evaluate this claim, with reference to: - the relationship between

N_A

, atomic mass units, and measurable molar masses; - the consequences for the molar mass of carbon-12 if

N_A

were instead fixed at

1.00 \times 10^{24}\,\text{mol}^{-1}

; - the practical role of the mole industrial stoichiometry, using the Ostwald process (

\text{NH}_3 \rightarrow \text{NO} \rightarrow \text{HNO}_3

) as an example. [8 marks]

Solutions

49ChallengeLAQIdeal gas law (PV = nRT)14 marksPaper 3~21 min

The Haber–Bosch process for ammonia synthesis,

\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}

, is typically operated at pressures between

150

and

250\,\text{atm}

and temperatures around

400

–

500\,°\text{C}

. Data (not in IB Data Booklet): At

400\,°\text{C}

and

200\,\text{atm}

, the compressibility factor

Z

for the reacting gas mixture is

1.12

.

R = 0.08206\,\text{L\,atm\,mol}^{-1}\,\text{K}^{-1}

(a)

State three assumptions of the kinetic molecular theory (KMT) that underpin the ideal gas law. For each assumption, explain how it breaks down at the high-pressure conditions of the Haber–Bosch process, and state whether each breakdown causes the actual pressure to be higher or lower than the ideal pressure at fixed

n

,

V

, and

T

. [6 marks]

(b)

A reactor vessel of volume

5000\,\text{L}

at

400\,°\text{C}

contains a stoichiometric

\text{N}_2/\text{H}_2

mixture at a total pressure of

200\,\text{atm}

. (i) Using the ideal gas law

PV = nRT

, calculate the total number of moles of gas in the vessel. [2 marks]
(ii) Using the compressibility factor

Z = \dfrac{PV}{nRT}

, determine the actual number of moles present. [1 mark]
(iii) The value of

Z

is greater than

1

at these conditions. Explain, with reference to one KMT assumption from part (a), why the ideal gas law overestimates the number of moles of gas. [1 mark]

(c)

As the reaction proceeds, the total number of moles of gas decreases. A process engineer proposes increasing the operating pressure from

200\,\text{atm}

to

300\,\text{atm}

to improve ammonia yield. Evaluate this proposal. In your answer: - use Le Chatelier's principle to justify the yield benefit, - use the compressibility factor concept to identify one specific engineering consequence of increased non-ideality at

300\,\text{atm}

, - conclude whether the proposal is justified, given that

Z

increases further above

1

as pressure rises. [4 marks]

Solutions

50ChallengeLAQIdeal gas law (PV = nRT)15 marksPaper 3~23 min

A student investigates thermal decomposition of dinitrogen monoxide according to:

2\text{N}_2\text{O}(\text{g}) \rightarrow 2\text{N}_2(\text{g}) + \text{O}_2(\text{g})

A sample of pure

\text{N}_2\text{O}

is placed in a rigid

1.00\,\text{L}

container at

25.0\,°\text{C}

. The initial pressure is

1.50\,\text{atm}

. The container is heated to

500\,°\text{C}

and the pressure is measured again. The student assumes ideal gas behaviour throughout. Data (not in IB Data Booklet):

R = 0.08206\,\text{L}\,\text{atm}\,\text{mol}^{-1}\,\text{K}^{-1}

(a)

State two assumptions of the kinetic molecular theory (KMT) that justify treating

\text{N}_2\text{O}

as an ideal gas at

25.0\,°\text{C}

and

1.50\,\text{atm}

. For each assumption, explain why it becomes less valid as the gas is heated to

500\,°\text{C}

in the rigid container. [4 marks]

(b)

(i) Calculate the initial number of moles of

\text{N}_2\text{O}

in the container at

25.0\,°\text{C}

. [2]
(ii) Assuming complete decomposition at

500\,°\text{C}

, calculate the total pressure in the container after the reaction. [3 marks]

(c)

The student's measured pressure after decomposition is

6.10\,\text{atm}

, which is higher than your calculated value from (b)(ii). Evaluate this discrepancy by suggesting one reason related to non-ideal gas behaviour and one reason related to the chemical system. In each case, state whether the reason would cause the measured pressure to be higher or lower than the ideal calculated value, and justify your answer. [6 marks]

Solutions

Structure: Models of the Particulate Nature of Matter — Free Chemistry HL Practice Questions