Chemistry

(c) 63

Crystalline oxalic acid is $H_2C_2O_4\cdot2H_2O$, molar mass $=126$, basicity $=2$, so equivalent weight $=\frac{126}{2}=63$.

(d) 63

Equivalent weight of the silver salt $=\frac{0.85}{0.54}\times108=170$. Equivalent weight of the acid $=170-108+1=63$.

(a) $H_2O_2$ and $SO_2$

In $H_2O_2$ oxygen is at $-1$ and in $SO_2$ sulphur is at $+4$; both are in intermediate oxidation states, so each can be oxidised or reduced. $HNO_3$ (N at its maximum $+5$) can only be an oxidising agent.

(d) HF

Fluorine is the most electronegative element, so the electronegativity difference in H-F is the largest and the bond has the highest ionic character.

(a) $N^{3-}$

These species are isoelectronic (10 electrons). The size decreases as the nuclear charge increases, so $N^{3-}$ (Z = 7) is the largest.

(a) 1680 L

Moles of $CO_2=\frac{3300}{44}=75$. Volume at NTP $=75\times22.4=1680$ L.

(d) $KIO_4$

Oxidation state of I: KI is $-1$, $KI_3$ is $-\frac13$, $IF_5$ is $+5$, and in $KIO_4$ it is $+1+x-8=0$, so $x=+7$, the highest.

(c) $MCl_2$

$HPO_4^{2-}$ carries a 2- charge, so with $MHPO_4$ the metal is $M^{2+}$. Its chloride is therefore $MCl_2$.

(a) Cu + Sn

Bronze is an alloy of copper and tin (brass is Cu + Zn).

(a) ZnO

China white (Chinese white, zinc white) is zinc oxide, used as a white pigment.

(d) length of carbon atom

Chain isomers have the same molecular formula but differ in the length (branching) of the carbon chain, e.g. n-butane and isobutane.

(d) Wohler

Friedrich Wohler synthesized urea from ammonium cyanate in 1828, disproving the vital force theory.

(b) 5 moles of $N_2$

(a) 50 g. (b) $5\times28=140$ g. (c) $0.1\times35.5=3.55$ g. (d) $\frac{10^{23}}{6.022\times10^{23}}\times12\approx2$ g. The largest is 140 g.

(d) $6.022\times10^{17}$

$[H^+]=10^{-3}$ mol/L, so 1 mL contains $10^{-6}$ mol, i.e. $10^{-6}\times6.022\times10^{23}=6.022\times10^{17}$ ions.

(b) $MO$

Per 100 g of chloride: 71 g Cl and 29 g M, so the equivalent mass of M is $\frac{29}{71}\times35.5=14.5$. For $MCl_n$ the molar mass is $14.5n+35.5n=50n$. With vapour density 50 the molar mass is 100, so $n=2$ and the chloride is $MCl_2$. The oxide of a divalent metal is $MO$.

(a) ethylene glycol

Ethanol with a dehydrating agent such as alcoholic KOH/conc. acid gives ethylene: $C_2H_5OH\to CH_2=CH_2+H_2O$. Cold alkaline $KMnO_4$ (Baeyer's reagent) hydroxylates the double bond to give ethylene glycol, $HOCH_2CH_2OH$.