IBDP Chemistry -Structure 3.1 The periodic table: Classification of elements - IB Style Questions For SL Paper 2 -FA 2025
▶️ Answer/Explanation
(a)
(i)
From section 7, thallium has atomic number \(81\).
Isotope has \(122\) neutrons, so mass number \(A = 81 + 122 = 203\).
Nuclear symbol: \(\boxed{{}^{203}\text{Tl}}\)
(ii)
Two isotopes: \({}^{203}\text{Tl}\) (30%) and \({}^{205}\text{Tl}\) (70%) since \(81+124=205\).
\[ A_r = (0.30 \times 203) + (0.70 \times 205) \] \[ A_r = 60.9 + 143.5 = \boxed{204.40} \]
(iii)
Lead has a higher nuclear charge (\(Z=82\)) than thallium (\(Z=81\)).
The shielding of the outer electron is similar (both are period 6 with many inner shells), so the effective nuclear attraction is slightly lower in thallium.
Therefore, the outer electron in thallium is held less strongly, so its first ionization energy is lower than that of lead.
(b)
(i)
• Covalent bonds: within the sulfate ion, between \(\text{S}\) and \(\text{O}\) atoms in \(\text{SO}_4^{2-}\).
• Ionic bonds: between \(\text{Tl}^+\) ions and \(\text{SO}_4^{2-}\) ions.
(ii)
• Covalent bonding: atoms share pairs of valence electrons.
• Ionic bonding: electrons are transferred (forming cations and anions), then ions are held by electrostatic attraction.
(iii)
\[ 2\text{TlOH}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Tl}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l) \]
(iv)
From section 7: \(\text{Tl} = 204.38\), \(\text{O} = 16.00\), \(\text{H} = 1.01\).
\[ M_r(\text{TlOH}) = 204.38 + 16.00 + 1.01 = 221.39\ \text{g mol}^{-1} \] \[ n(\text{TlOH}) = \frac{10.0}{221.39} = 0.0452\ \text{mol} \] From the equation, \(2\ \text{mol TlOH}\) react with \(1\ \text{mol H}_2\text{SO}_4\):
\[ n(\text{H}_2\text{SO}_4) = \frac{0.0452}{2} = 0.0226\ \text{mol} \] \[ V = \frac{n}{c} = \frac{0.0226}{2.00} = 0.0113\ \text{dm}^3 = \boxed{11.3\ \text{cm}^3} \]
(v)
No. Thallium is a metal (group 13, lower down the group shows strong metallic character), so \(\text{TlOH}\) is expected to be mainly basic rather than amphoteric.
(vi)
Set up two displacement tests:
• Place thallium metal in aqueous copper(II) sulfate and observe whether copper is displaced (copper deposits / solution colour decreases).
• Place copper metal in aqueous thallium(I) sulfate and observe whether thallium is displaced.
The metal that displaces the other metal from its sulfate solution is the more reactive metal.