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IB Chemistry – Structure 1: Particulate Nature of Matter

The mole, atomic structure, electron configurations, ideal gases.

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13 questions  ·  28 marks  ·  answers included  ·  IB Chemistry SL/HL (2023+ syllabus)
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This worksheet covers:

  • The mole concept
  • Atomic structure
  • Electron configurations
  • The ideal gas law from Structure 1

A calculator is required; use $R = 8.31\,\text{J K}^{-1}\text{mol}^{-1}$ and $N_A = 6.02\times10^{23}\,\text{mol}^{-1}$. Ar values are given in each question.

Questions

Section A – Foundations

Short-answer, calculator allowed
1

Define relative atomic mass, $A_r$.

Show answer
The weighted mean mass of an atom of an element relative to $\frac{1}{12}$ of the mass of an atom of $^{12}\text{C}$.
[1]
2

Calculate the molar mass of $\text{Ca(NO}_3\text{)}_2$. ($A_r$: Ca 40.08, N 14.01, O 16.00)

Show answer
$M = 40.08 + 2(14.01 + 3\times16.00) = 164.10\,\text{g mol}^{-1}$
[2]
3

Write the full electron configuration of a chlorine atom ($Z=17$).

Show answer
$1s^2\,2s^2\,2p^6\,3s^2\,3p^5$
[1]
4

State the number of protons, neutrons and electrons in $^{35}_{17}\text{Cl}^-$.

Show answer
Protons $=17$, neutrons $=18$, electrons $=18$.
[2]
5

Calculate the amount, in mol, in 5.00 g of $\text{NaOH}$ ($M = 40.00\,\text{g mol}^{-1}$).

Show answer
$n = \dfrac{5.00}{40.00} = 0.125\,\text{mol}$
[2]

Section B – Applications

Calculator allowed
6

Calculate the volume, in $\text{dm}^3$, occupied by 0.500 mol of an ideal gas at $25\,^\circ\text{C}$ and $100\,\text{kPa}$. Use $PV = nRT$.

Show answer
$T = 298\,\text{K}$; $V = \dfrac{nRT}{P} = \dfrac{0.500\times8.31\times298}{1.00\times10^{5}} = 1.24\times10^{-2}\,\text{m}^3 = 12.4\,\text{dm}^3$
[3]
7

Calculate the number of atoms in 3.60 g of carbon. ($A_r$ C $=12.01$)

Show answer
$n = \dfrac{3.60}{12.01} = 0.300\,\text{mol}$; atoms $= 0.300\times6.02\times10^{23} = 1.80\times10^{23}$
[2]
8

Deduce the full electron configuration of $\text{Fe}^{3+}$ ($Z=26$).

Show answer
$1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^5$ (the $4s$ electrons are removed before the $3d$ electrons)
[2]
9

Explain why there is a large jump between the second and third ionisation energies of magnesium.

Show answer
The first two electrons are removed from the outer $3s$ subshell (n = 3); the third electron must be removed from the $2p$ subshell (n = 2), which is closer to the nucleus and experiences less shielding, so it is held much more strongly, requiring far more energy.
[2]
10

A gas sample occupies $2.00\,\text{dm}^3$ at $20\,^\circ\text{C}$ and $105\,\text{kPa}$. Calculate its volume at STP ($0\,^\circ\text{C}$, $100\,\text{kPa}$), assuming the amount of gas is constant.

Show answer
Using $\dfrac{P_1V_1}{T_1} = \dfrac{P_2V_2}{T_2}$ with $T_1 = 293\,\text{K}$, $T_2 = 273\,\text{K}$: $V_2 = \dfrac{105\times2.00\times273}{293\times100} = 1.96\,\text{dm}^3$
[3]

Section C – Challenge

Calculator allowed
11

A hydrated salt $\text{MgSO}_4\cdot x\text{H}_2\text{O}$ has molar mass $246.47\,\text{g mol}^{-1}$. Determine $x$. ($A_r$: Mg 24.31, S 32.07, O 16.00, H 1.01)

Show answer
$M(\text{MgSO}_4) = 120.38\,\text{g mol}^{-1}$; mass of water $= 246.47 – 120.38 = 126.09\,\text{g mol}^{-1}$; $x = \dfrac{126.09}{18.02} = 7.00$, so $x = 7$
[3]
12

A compound contains 40.0% C, 6.7% H and 53.3% O by mass. Determine its empirical formula. ($A_r$: C 12.01, H 1.01, O 16.00)

Show answer
In 100 g: $n(\text{C}) = 3.33$, $n(\text{H}) = 6.63$, $n(\text{O}) = 3.33$; dividing by the smallest gives ratio $\text{C}:\text{H}:\text{O} = 1:2:1$, so the empirical formula is $\text{CH}_2\text{O}$
[3]
13

Two ideal gas samples at the same temperature and pressure, A (2.00 mol) and B, have volumes in the ratio $V_A:V_B = 3:5$. Calculate the amount, in mol, of gas B.

Show answer
At constant $T$ and $P$, $V \propto n$, so $n_B = 2.00\times\dfrac{5}{3} = 3.33\,\text{mol}$
[2]

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IB Chemistry – Structure 2: Bonding and StructureIB Chemistry – Structure 3: Classification of MatterIB Chemistry – Reactivity 1: What Drives ReactionsIB Chemistry – Reactivity 2: How Much, How Fast, How FarIB Chemistry – Reactivity 3: Mechanisms of ChangeIB Chemistry – Data-Based Questions (Paper 1B)

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