Chemistry 9701 · AS & A Level · States of matter

States of matter — practice question

Chlorine occurs naturally as a blend of two isotopes, $^{35}\text{Cl}$ and $^{37}\text{Cl}$, in the abundance ratio $3 : 1$. Its mass spectrum shows five peaks.
(a(i))

Suggest the mass numbers for these five peaks and state the species responsible.

(a(ii))[4]

Predict the abundance ratios for the three species with the highest mass numbers.

(b(i))

Draw the dot-and-cross diagram for strontium chloride, $\text{SrCl}_2$, showing only the outer-shell electrons.

(b(ii))[5]

Use the data below, together with relevant data from the Data Booklet, to calculate the lattice energy of strontium chloride. You may find it helpful to draw a Born-Haber cycle. Given: Electron affinity per mole of chlorine atoms = $-349\,\text{kJ mol}^{-1}$ Standard enthalpy of atomisation of $\text{Sr}(s)$ = $+164\,\text{kJ mol}^{-1}$ Standard enthalpy of formation of $\text{SrCl}_2(s)$ = $-830\,\text{kJ mol}^{-1}$

(c(i))

Strontium nitrate, $\text{Sr(NO}_3)_2$, can be made readily from strontium carbonate, $\text{SrCO}_3$. Suggest an equation for this preparation of strontium nitrate.

(c(ii))[2]

Write an equation for the reaction that takes place when strontium nitrate is heated.

(d)[3]

Describe and explain the trend in the thermal stabilities of Group II nitrates.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: The correct $m/e$ values are $35, 37, 70, 72, 74$

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