MEMORIAL UNIVERSITY OF NEWFOUNDLAND CHEMISTRY 1050

Transcription

1 MEMORIAL UNIVERSITY OF NEWFOUNDLAND CHEMISTRY 1050 FINAL EXAMINATION FALL 1997 TIME: 2 hours NAME: MUN STUDENT#: INSTRUCTOR: READ THE FOLLOWING CAREFULLY (1) This examination has 10 pages. Ensure you have a complete paper. (2) The paper must be submitted in its entirety at the end of the examination. Failure to do so may result in disqualification. (3) Your are provided with a Periodic Table and physical constants. These follow the last page of the examination and may be detached for use during the examination. (4) Answer each question in the space provided. Should you require more space, use the back of the previous page and indicate clearly when and where you have done so. (5) When answer problems, show all relevant calculations and justify simplifying assumptions. (6) Numerical answers should be reported to the appropriate number of significant digits. (7) Do not write in the enclosed area below. Question B1 B2 B3 Total Value Part A Part B Mark

2 Page 2 Part A: Short Answers Value 63 marks [2] 1. Complete the following table with the correct IUPAC (systematic) name or formula as appropriate Formula IUPAC (systematic) name LiClO 3 iron(ii)phosphate octahydrate boron nitride H 2 SO 4 (aq) [2] 2. (a) Explain the trend in the first ionization energies for the elements of group 1A. element I 1 /kj.mol -1 Li Na K Rb Cs [2] (b) Arrange the following species in order of increasing ionic radius; Cl -, Ca 2+, Ti 4+, K +, S 2- Smallest r < < < < largest r [6] 3. (a) Complete the following table by indicating the numbers of protons, neutrons and electrons present, the spectroscopic (i.e. spdf) ground state electronic configuration (use the appropriate noble gas core) and the magnetic properties (paramagnetic or diamagnetic) of each species. species 34 S # nuclear protons # nuclear neutrons # electrons ground state electron configuration magnetic properties 34 S 2-56 Fe 56 Fe 3+

3 Page 3 a) [4] (i) Draw a Lewis electron dot structure for CH 2 O. (ii) Sketch the VSEPR shape of CH 2 O clearly indicating the bond angles on your sketch (iii) Draw a diagram to illustrate the bonding in CH 2 O using valence bond theory. Clearly indicate the types of bonds formed (π or σ) and the types of orbitals used to make them. [3] 4. Balance the following redox equation in acidic solution. Fe 2+ (aq) + Cr 2 O 7 2- (aq) Fe 3+ (aq) + Cr 3+ (aq)

4 Page 4 [6] 5. Complete and balance each of the following reactions including the physical states of all products. Write a balanced net ionic equation for each reaction. (a) NH 3 (aq) + H 2 SO 4 (aq) Net ionic: (b) Ca(NO 3 ) 2 (aq) + Na 2 CO 3 (aq) Net ionic: (c) AgNO 3 (aq) + Mg(s). Net ionic: ml of M sodium sulfate solution (Na 2 SO 4 ) and 50.0 ml of M sulfuric acid (H 2 SO 4 ) solution are mixed. Assume solution volumes are additive. [2] (a) Calculate the concentration of sulfate ion in the mixture. [2] (b) If excess lead nitrate is added so that all the sulfate ion is precipitated as lead sulfate, calculate the mass of precipitate formed..

5 Page 5 [4] 7. Write balanced equations to represent: (a) The standard heat of formation, Hÿ f, of oxalic acid, C 2 H 2 O 4 *2H 2 O. (b) The electron affinity of a nitrogen atom. (c) The second ionization energy of a carbon atom. (d) The condensation of ammonia.. [9] 8. Complete the following table: species HCN NO 2 6 SF 4 Lewis structure Sketch of shape Name of shape Approximate bond angles hybridization of central atom [3] 9. Explain why the molecule Be 2 is unstable using molecular orbital theory. Hint Draw a molecular orbital diagram for Be 2.

6 Page 6 [2] 10. (a) Calculate the freezing point and boiling point of m urea, CO(NH 2 ) 2 (aq). Data: K f (H 2 O) = 1.86 ÿc*m -1 K b (H 2 O) = ÿc*m -1 T f (H 2 O) = 0.0 ÿc T b (H 2 O) = ÿc [4] (b) Consider a benzene/toluene mixture with a benzene mole fraction of at 25 ÿc. The vapour pressure of pure benzene at 25 ÿc is 95.1 mmhg and that of pure toluene is 28.4 mm Hg. (i) Calculate the total vapour pressure P T above the benzene/toluene mixture. (ii) Calculate the mole fraction of benzene in the vapour above the benzene/toluene mixture. [3] (c) (i) Calculate the osmotic pressure of a M aqueous solution of sucrose. (ii) Explain how pure drinking water can be obtained from salt water by reverse osmosis.

7 Page 7 [3] 11. (a) Account for the fact that methyl alcohol CH 3 OH is soluble in both water and carbon tetrachloride. [2] (b) Both KBr and MgO have the same sodium chloride crystal structure. (i) Which has the larger lattice energy? Explain briefly. [2] (ii) Which is more likely to be more soluble in water? Explain briefly. [2] (c) The values of the Enthalpy of vaporization H vap of H 2 O and H 2 S at their normal boiling points of 373 K and 212 K are 41.1 and 19 kj*mol -1 respectively. Account for the significantly higher Enthalpy of vaporization of water in terms of intermolecular forces in the liquid state.

8 Page 8 Part B: longer Answer questions Value = 37 marks [12] B1. (a) A 50.0 g sample of aluminum at ÿc is added to 50.0 g of water at 20.0 ÿc in a styrofoam cup. The final temperature of the aluminum and water is 34.2 ÿc. Calculate the specific heat of aluminum. (b) A g sample of quinone (C 6 H 4 O 2 ) is burned in a bomb calorimeter producing a temperature increase of 5.63 ÿc. The heat capacity of the bomb calorimeter is kj*/ÿc. Calculate the heat of combustion of quinone in kj*mol -1. Clearly state any simplifying assumptions made. (c) Using the following thermochemical equations, Fe 2 O 3 (s) + 3 CO(g) 2 Fe(s) + 3 CO 2 (g) H = -28 kj 3 Fe 2 O 3 (s) +CO(g) 2 Fe 3 O 4 (s) + CO 2 (g H = -60 kj FeO(s) + CO(g) Fe(s) + CO 2 (g H = -17 kj calculate H for the following reaction: Fe 3 O 4 (s) + CO(g) 3 FeO(s) + CO 2 (g)

9 Page 9 B2. (a) A sample of benzoic acid, HC 6H 5COO, was dissolved in water and the solution titrated with NaOH(aq) ml of mol L 1 NaOH(aq) were required for neutralization. The neutralization reaction is as follows: HC 6H 5COO(aq) + NaOH(aq) H 2O(l) + NaC 6H 5CO [6] (i) Determine the mass of benzoic acid in the sample. [2] (2) If the actual mass of the sample was g, determine the percent purity of the benzoic acid in the sample. [7] (b) The reaction below can be used as a laboratory method of preparing small quantities of Cl 2(g). If a 57.4 g sample of K 2Cr 2O 7 is allowed to react with 325 ml of HCl(aq) with a density of 1.15 g/ml and 30.1% HCl, by mass, how many grams of Cl 2(g) are produced? Cr 2O H + + 6Cl 2Cr H 2O + 3Cl 2(g)

10 Page 10 [5] B3. (a) Determine the empirical formula of an acid which had the following elemental composition by mass: Carbon %, Hydrogen %, Oxygen %. [5] (b) A flask contains 5 moles of an ideal gas at 25 ºC and 2 atm pressure. The temperature of the gas is raised to 50 ºC. What fraction of the gas must be removed to keep the pressure in the flask constant?