Question

Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while the addition of 1 mol of methyl alcohol to 1 litre of water decreases the boiling point.

Hint:

Non-volatile solute → lower vapour pressure → higher bp; volatile solute → higher vapour pressure → lower bp.

Answer 1

To name a coordination compound, name the ligands first in alphabetical order, then the metal with its oxidation state in Roman numerals in brackets. If the complex ion is negative, the metal name ends in '-ate'. Let us do each one.

(i) answer: Take $\mathrm{[PtCl_2(en)_2]SO_4}$. Inside the brackets we have two chloride ligands (named 'dichlorido') and two 'en' ligands. 'en' is ethane-1,2-diamine, and since it already has the prefix 'di' in 'diamine', we use 'bis' to show there are two of them, written 'bis(ethane-1,2-diamine)'. Alphabetically, chlorido comes before ethanediamine, so chlorido is named first. Now the oxidation state of Pt: 'en' is neutral (charge $0$) and each $\mathrm{Cl^-}$ is $-1$, so two chlorides give $-2$. The complex ion carries $+2$ (because the sulphate outside is $-2$), so Pt is $+4$. The full name is dichloridobis(ethane-1,2-diamine)platinum(IV) sulphate.

(ii) answer: Take $\mathrm{(NH_4)_2[CoF_4]}$. Here the complex part $\mathrm{[CoF_4]^{2-}}$ is negative, so the metal name takes the '-ate' ending and cobalt becomes 'cobaltate'. There are four fluoride ligands, named 'tetrafluorido'. For the charge: each $\mathrm{F^-}$ is $-1$, four of them give $-4$, and the whole ion is $-2$ (two ammonium ions outside are $+2$ together), so Co is $+2$. The two $\mathrm{NH_4^+}$ ions are named 'ammonium' and written first. The full name is ammonium tetrafluoridocobaltate(II).