AS & A Level Chemistry - 9701 Paper 2 2021 Winter Zone 2

Hydrogen iodide, HI, is a colourless gas at room temperature.

(a) (i) Explain why HI has a higher boiling point than HCl and HBr.
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(ii) The bar chart shows the boiling points of HCl, HBr and HI. The boiling point of HF is not shown.



Hydrogen bonds form between HF molecules. Draw a bar on the bar chart to predict the boiling point of HF. Explain your answer.
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(b) The standard enthalpy change of formation, $\Delta H^\circ_f$, of HI(g) is +26.5 kJ mol$^{-1}$. Define the term standard enthalpy change of formation.
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(c) HI(g) can be formed by reacting H$_2$(g) with I$_2$(g). The reaction is reversible, and an equilibrium forms quickly at high temperatures.
$$\text{H$_2$(g)} + \text{I$_2$(g)} \rightleftharpoons 2\text{HI(g)}$$

(i) Construct an expression for the equilibrium constant, $K_p$, for the reaction of H$_2$(g) and I$_2$(g) to form HI(g).

$K_p =$ ....................................................................................................................................... [1]

(ii) The equilibrium partial pressures of the gases at 200°C are as follows.
$p_{\text{H$_2$(g)}}$ = 895 Pa
$p_{\text{I$_2$(g)}}$ = 895 Pa
$p_{\text{HI(g)}}$ = 4800 Pa

Calculate $K_p$ for this reaction.

$K_p =$ ..................................................................................................... [1]

(iii) State how the value of $K_p$ would change, if at all, if the reaction were carried out at 100°C rather than 200°C. Explain your answer.
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(d) HI reacts with oxygen to form iodine and water.

(i) Construct an equation for the reaction of HI with oxygen.
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(ii) Explain, with reference to oxidation numbers, why this reaction is a redox reaction.
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(e) HI(g) can also be formed by the reaction of I$_2$(g) with hydrazine, N$_2$H$_4$(g).
$$2\text{I$_2$(g)} + \text{N$_2$H$_4$(g)} \rightarrow 4\text{HI(g)} + \text{N$_2$(g)}$$
State the change in pressure that would occur when 2 mol I$_2$(g) fully reacts with 1 mol N$_2$H$_4$(g) in a sealed container at constant temperature. Explain your answer.
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(f) In the laboratory, HI(aq) can be formed in a two-step process.
$$\text{step 1 } 3\text{I$_2$(s)} + 2\text{P(s)} \rightarrow 2\text{PI$_3$(s)}$$
$$\text{step 2 } \text{PI$_3$(s)} + 3\text{H$_2$O(l)} \rightarrow \text{H$_3$PO$_3$(aq)} + 3\text{HI(aq)}$$

(i) Draw a 'dot-and-cross' diagram of a P$I_3$ molecule.

[2]

(ii) Name the type of reaction in step 2.
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(iii) H$_3$PO$_3$(aq) and HI(aq) are both strong Brønsted–Lowry acids. Give the meaning of the term strong Brønsted–Lowry acid.
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(iv) Give the formula of the conjugate base of H$_3$PO$_3$.
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(g) HI(g) reacts with propene, CH$_3$CH=CH$_2$(g) to form a mixture of 1-iodopropane and 2-iodopropane.

(i) Identify which of 1-iodopropane and 2-iodopropane is the major product of this reaction. Explain your answer.
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(ii) Complete the diagram to show the mechanism of the reaction between HI and CH$_3$CH=CH$_2$ that forms the major product identified in (g)(i).
Include curly arrows, lone pairs of electrons and charges as necessary.

[3]

[Total: 26]

(a) Table 1 gives physical data for some of the Period 3 elements.

[Table_1:
atomic number, Z | 11 | 12 | 13 | 14 | 15 | 16 | 17
bonding present in element | M | | | C
first ionisation energy / kJ mol^-1 | 494 | 736 | 577 | 786 | 1060 | 1000 | 1260
maximum oxidation number | | | | | | | +7
anionic radius / nm | | | | 0.271 | 0.212 | 0.184 | 0.181]

(i) Complete the row in the table labelled 'bonding present in element'.
Use C = covalent, I = ionic, M = metallic, as appropriate. [1]

(ii) Explain the difference between the first ionisation energies of the elements with atomic numbers 11 and 17. [2]

(iii) Explain the difference between the first ionisation energies of the elements with atomic numbers 15 and 16. [2]

(iv) Complete the row in the table labelled 'maximum oxidation number'. [1]

(v) Explain the variation in anionic radius for the elements with atomic numbers 14 to 17. [2]

(b) Use the axes to sketch a graph that shows the trend in melting points of the elements with atomic numbers 11 to 17. [2]

(c) Dmitri Mendeleev published the first Periodic Table in 1869.
Mendeleev used his knowledge of chemical periodicity to propose the properties of gallium, ₃₁Ga, a Group 13 element.
Table 2 gives some chemical and physical data of elements in Group 13.

[Table_2:
element | density / g cm^-3 | boiling point / K | cationic radius / nm
₅B | 2.34 | 3930 | 0.020
₁₃Al | | 2470 | 0.050
₃₁Ga | 5.91 | 2400 |
₄₉In | 7.30 | | 0.081
₈₁Tl | 11.8 | 1460 | 0.095]

Complete the table by predicting values for the missing data. [3]

(d) Indium and aluminium are elements in Group 13 of the Periodic Table.
Indium has very similar chemical properties to aluminium.
- Indium reacts vigorously with hydrochloric acid to form a colourless gas and a salt in solution.
- Indium oxide, In₂O₃, is amphoteric.
- Gaseous indium bromide has the formula In₂Br₆. This molecule contains coordinate bonds.

(i) Identify the formula of the salt formed when indium reacts with hydrochloric acid. [1]

(ii) Construct an equation for the reaction of In₂O₃ with excess aqueous NaOH. [1]

(iii) Draw a diagram that clearly shows the types of bond present in In₂Br₆(g). [2]

[Total: 17]

Compound T is an isomer of $C_6H_{12}$. T (a) Name T. .............................................................................................................................................

(b) Draw the skeletal formula of a structural isomer of T that shows cis-trans (geometrical) isomerism.

(c) Each carbon atom in T forms a sigma $(\sigma)$ bond to at least one other carbon atom, as shown. (i) On the diagram, draw the orbitals that represent the pi $(\pi)$ bond that is also present in T. (ii) State the hybridisation of the two carbon atoms between which the pi $(\pi)$ bond forms. .............................................................................................................................................

(d) A reaction scheme starting with T is shown. Reaction 2 occurs in the presence of a catalyst; knowledge of the mechanism for this reaction is not required. (i) Give the reagent(s) and conditions for reaction 1. ............................................................................................................................
(ii) State and explain how 2,4-dinitrophenylhydrazine (2,4-DNPH) can be used to detect the presence of V as a product of reaction 2. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(iii) The progress of reaction 2 can be monitored by infrared spectroscopy. The absorption caused by O—H bonds is always present because water is used as a solvent. Identify two absorptions, and the bonds responsible for these absorptions, whose appearance will change significantly during the reaction. 1 ........................................................................................................................................ 2 ........................................................................................................................................

(e) V is used in a wide range of organic reactions. Some reactions of V are shown. (i) V and W are colourless and soluble in water. State what you would observe in reaction 3. ............................................................................................................................
(ii) Reaction 3 is a redox reaction. Identify which of the reactants is reduced in this reaction. ............................................................................................................................

(iii) Construct an equation for reaction 4. Use [H] in the equation to represent an atom of hydrogen from NaBH$_4$. $C_6H_{12}O$ + ....................................................................................................................

(iv) X is a mixture of two optical isomers. Draw the two optical isomers in the boxes provided.

(v) Both optical isomers of X can be dehydrated to form a single product, Y. Give the reagent(s) and conditions required for reaction 5. ............................................................................................................................

(vi) Y can form an addition polymer Z. Draw one repeat unit of Z.

(vii) Reaction 6 does not proceed quickly at room temperature. Suggest why this is the case. ............................................................................................................................ ............................................................................................................................