2016年5月IB化学SL真题下载-Paper2
1. Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3.
(a) (i) Draw a Lewis (electron dot) structure of phosphine.
(ii) Outline whether you expect the bonds in phosphine to be polar or non-polar, giving a brief reason.
(iii) Explain why the phosphine molecule is not planar.
(iv) Phosphine has a much greater molar mass than ammonia. Explain why phosphine has a significantly lower boiling point than ammonia.
(b) Phosphine is usually prepared by heating white phosphorus, one of the allotropes of phosphorus, with concentrated aqueous sodium hydroxide. The equation for the
reaction is:
P4 (s) + 3OH− (aq) + 3H2O (l) → PH3 (g) + 3H2PO2 −(aq)
(i) Identify one other element that has allotropes and list two of its allotropes.
Element:
Allotrope 1:
Allotrope 2:
(ii) The first reagent is written as P4, not 4P. Describe the difference between P4 and 4P.
(iii) The ion H2PO2− is amphiprotic. Outline what is meant by amphiprotic, giving the formulas of both species it is converted to when it behaves in this manner.
(iv) State the oxidation state of phosphorus in P4 and H2PO2−.
P4:
H2PO2−:
(v) Oxidation is now defined in terms of change of oxidation number. Explore how earlier definitions of oxidation and reduction may have led to conflicting answers for the conversion of P4 to H2PO2− and the way in which the use of oxidation numbers has resolved this.
(c) 2.478 g of white phosphorus was used to make phosphine according to the equation:
P4 (s) + 3OH− (aq) + 3H2O (l) → PH3 (g) + 3H2PO2−(aq)
(i) Calculate the amount, in mol, of white phosphorus used.
(ii) This phosphorus was reacted with 100.0 cm3 of 5.00 mol dm−3 aqueous sodium hydroxide. Deduce, showing your working, which was the limiting reagent.
(iii) Determine the excess amount, in mol, of the other reagent.
(iv) Determine the volume of phosphine, measured in cm3 at standard temperature and pressure, that was produced.
2. Impurities cause phosphine to ignite spontaneously in air to form an oxide of phosphorus and water.
(a) (i) 200.0 g of air was heated by the energy from the complete combustion of 1.00 mol phosphine. Calculate the temperature rise using section 1 of the data booklet and the data below.
Standard enthalpy of combustion of phosphine, ΔHØc= −750 kJ mol−1
Specific heat capacity of air = 1.00 J g−1 K−1 = 1.00 kJ kg−1 K−1
(ii) The oxide formed in the reaction with air contains 43.6 % phosphorus by mass.Determine the empirical formula of the oxide, showing your method.
(iii) The molar mass of the oxide is approximately 285 g mol−1.Determine the molecular formula of the oxide.
(b) (i) State the equation for the reaction of this oxide of phosphorus with water.
(ii) Predict how dissolving an oxide of phosphorus would affect the pH and electrical conductivity of water.
pH:
Electrical conductivity:
(iii) Suggest why oxides of phosphorus are not major contributors to acid deposition.
(iv) The levels of sulfur dioxide, a major contributor to acid deposition, can be minimized by either pre-combustion and post-combustion methods. Outline one technique of each method.
Pre-combustion:
Post-combustion:
2016年5月IB化学SL真题余下省略！
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