2018年5月IB化学SL真题下载-Paper2
1. Urea, (H2N)2CO, is excreted by mammals and can be used as a fertilizer.
(a) (i) Calculate the percentage by mass of nitrogen in urea to two decimal places using section 6 of the data booklet.
(ii) Suggest how the percentage of nitrogen affects the cost of transport of fertilizers giving a reason.
(b) The structural formula of urea is shown.
Predict the electron domain and molecular geometries at the nitrogen and carbon atoms, applying the VSEPR theory.
(c) Urea can be made by reacting potassium cyanate, KNCO, with ammonium chloride,NH4Cl.
KNCO (aq) + NH4Cl (aq) → (H2N)2CO (aq) + KCl (aq)
Determine the maximum mass of urea that could be formed from 50.0 cm3 of 0.100 mol dm−3 potassium cyanate solution.
(d) Urea can also be made by the direct combination of ammonia and carbon dioxide gases.
2NH3(g) + CO2(g) ⇔ (H2N)2CO (g) + H2O (g) ΔH < 0
Predict, with a reason, the effect on the equilibrium constant, Kc, when the temperature is increased.
(e) (i) Suggest one reason why urea is a solid and ammonia a gas at room temperature.
(ii) Sketch two different hydrogen bonding interactions between ammonia and water.
(f) The combustion of urea produces water, carbon dioxide and nitrogen.Formulate a balanced equation for the reaction.
(g) The mass spectrum of urea is shown below.
Identify the species responsible for the peaks at m/z = 60 and 44.
60:
44:
(h) The IR spectrum of urea is shown below.
Identify the bonds causing the absorptions at 3450 cm−1 and 1700 cm−1 using section 26 of the data booklet.
3450 cm−1:
1700 cm−1:
(i) Predict the number of signals in the 1H NMR spectrum of urea.
2018年5月IB化学SL真题余下省略！
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