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Question
The structure of aspirin is shown in section 37 of the data booklet.
Salicylic acid
a. Suggest one reactant used to prepare aspirin from salicylic acid.
b. Aspirin, $\mathrm{C}_6 \mathrm{H}_4\left(\mathrm{OCOCH}_3\right) \mathrm{COOH}$, is only slightly soluble in water.
Outline, including an equation, how aspirin can be made more water-soluble. Use section 37 in the data booklet.
▶️Answer/Explanation
Markscheme
a. ethanoic anhydride/acetic anhydride/
OR ethanoyl chloride/acetyl chloride/
NOTE: Accept condensed structural formulas.
Accept “ethanoic acid/acetic acid/ $\mathrm{CH}_3 \mathrm{COOH}^{\mathrm{CO}}$ “.
Accept ” $\mathrm{C}_4 \mathrm{H}_6 \mathrm{O}_3$ ” OR ” $\mathrm{C}_2 \mathrm{H}_3 \mathrm{OCl}$ “.
b. react with sodium hydroxide/NaOH/«strong»
OR
convert to «ionic» salt
NOTE: Accept other suitable bases (eg, $\mathrm{KOH} / \mathrm{NaHCO}_3 / \mathrm{Na}_2 \mathrm{CO}_3$ ) with corresponding equation for chosen base for $\mathrm{M} 2$.
Accept ” $\mathrm{CaCO}_3$ “, although calcium salicylate is not water soluble.
Accept ionic equation.
$$
\mathrm{C}_6 \mathrm{H}_4\left(\mathrm{OCOCH}_3\right) \mathrm{COOH}(\mathrm{s})+\mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{C}_6 \mathrm{H}_4\left(\mathrm{OCOCH}_3\right) \mathrm{COONa}(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(\mathrm{I})
$$
Question
Lanthanum, La, and antimony, Sb, form compounds with bromine that have similar formulas, $\mathrm{LaBr}_3$ and $\mathrm{SbBr}_3$.
a. Determine the type of bond present in $\mathrm{SbBr}_3$, showing your method. Use sections 8 and 29 of the data booklet.
b. Lanthanum has a similar electronegativity to group 2 metals. Explain, in terms of bonding and structure, why crystalline lanthanum bromide is brittle.
▶️Answer/Explanation
Markscheme
a. polar covalent
average electronegativity $«=\frac{1}{2}(3.0+2.0) »=2.5$ AND electronegativity difference $«=3.0-2.0 »=1.0$
[2 marks]
b. ionic bonding
OR
electrostatic forces between ions
«slight» movement brings ions of same charge adjacent to each other «causing the crystal to break» OR
«slight» movement results in repulsion between layers «causing the crystal to break»
Question
Lanthanum, La, and antimony, Sb, form compounds with bromine that have similar formulas, LaBr3 and SbBr3.
Determine the type of bond present in SbBr3, showing your method. Use sections 8 and 29 of the data booklet.
Lanthanum has a similar electronegativity to group 2 metals. Explain, in terms of bonding and structure, why crystalline lanthanum bromide is brittle.
▶️Answer/Explanation
Markscheme
polar covalent
average electronegativity «= \(\frac{1}{2}\)(3.0 + 2.0)» = 2.5 AND electronegativity difference «= 3.0 – 2.0» = 1.0
[2 marks]
ionic bonding
OR
electrostatic forces between ions
«slight» movement brings ions of same charge adjacent to each other «causing the crystal to break»
OR
«slight» movement results in repulsion between layers «causing the crystal to break»
[2 marks]