Notes
1) A 0.682-gram sample of an unknown weak monoprotic organic acid, HA, was dissolved in sufficient water to make 50 milliliters of solution and was titrated with a 0.135-molar NaOH solution. After the addition of 10.6 milliliters of base, a pH of 5.65 was recorded. The equivalence point (end point) was reached after the addition of 27.4 milliliters of the 0.135-molar NaOH.
(a) Calculate the number of moles of acid in the original sample.
(b) Calculate the molecular weight of the acid HA.
(c) Calculate the number of moles of unreacted HA remaining in solution when the pH was 5.65.
(d) Calculate the [H3O+] at pH = 5.65.
(e) Calculate the value of the ionization constant, Ka, of the acid HA.
(a) When 300.0 milliliters of a solution of 0.200-molar AgNO3 is mixed with 100.0 milliliters of a 0.0500-molar CaCl2 solution, what is the concentration of silver ion after the reaction has gone to completion?
(b) Write the net cell reaction for a cell formed by placing a silver electrode in the solution remaining from the reaction above and connecting it to a standard hydrogen electrode.
(c) Calculate the voltage of a cell of this type in which the silver ion concentration is 4 x 10¯2 M.
(d) Calculate the value of the standard free energy change DG° for the following half-reaction:
Ag+ (1 M) + e¯ <===> Ag°
| Substance | Standard Entropy, Joule °C¯1 mole¯1 |
| N2(g) | 192 |
| H2(g) | 130 |
| NH3(g) | 192 |
Ammonia can be produced by the following reaction:
N2(g) + 3 H2(g) <===> 2 NH3(g)
The Gibbs free energy of formation DGf° of NH3 (g) is -16.5 kilojoules per mole.
(a) Calculate the value for DH° for the reaction above at 298 K.
(b) Can the yield of ammonia be increased by raising the temperature? Explain.
(c) What is the equilibrium constant for the reaction above at 298 K?
(d) If 235 milliliters of H2 gas measured at 25 °C and 570 millimeters Hg were completely converted to ammonia and the ammonia were dissolved in sufficient water to make 0.500 liter of solution, what would be the molarity of the resulting solution?
4) Use appropriate ionic and molecular formulas to show the reactants and the products for the following, each of which occurs in aqueous solution except as indicated. Omit formulas for any ionic or molecular species that do not take part in the reaction. You need not balance. In all cases a reaction occurs.
(a) Gaseous silane, SiH4, is burned in oxygen.
(b) Equal volumes of 0.1-molar hydrochloric acid and 0.1-molar disodium monohydrogen phosphate are mixed.
(c) Hydrogen sulfide gas is bubbled through a solution of lead(II) nitrate.
(d) Solid zinc strips are added to a solution of copper sulfate.
(e) Solid lithium oxide is added to excess water.
(f) Copper(II) sulfide is oxidized by dilute nitric acid.
(g) Silver chloride is dissolved in excess ammonia solution.
(h) Propene reacts with water in the presence of a catalyst.
5) The freezing point and electrical conductivities of three aqueous solutions are given below.
| Solution | Freezing Point | Electrical Conductivity |
| 0.010-molal sucrose | -0.0186 °C | almost zero |
| 0.010-molal formic acid | -0.0213 °C | low |
| 0.010-molal sodium formate | -0.0361 °C | high |
Explain the relationship between the freezing point and electrical conductivity for each of the solutions above. Account for the difference in the freezing point among the three solutions.
6) Predict whether solutions of each of the following salts are acidic, basic, or neutral. Explain your prediction in each case.
(a) Al(NO3)3
(b) K2CO3
(c) NaBr
7) State precisely what is meant by each of the following four terms. Then distinguish clearly between each of the two terms in part (a) and between each of the two terms in part (b) , using chemical equations or examples where helpful.
(a) Bond polarity and molecular polarity (dipole moment)
(b) For a metal M, ionization energy and electrode potential
8) Dehydration of 3-hexanol yields a mixture of four isomers each with the molecular formula C6H12. Draw structures of the four isomers and name each of them.
9) The postulates of the Bohr model of the hydrogen atom can be stated as follows:
(I) The electron can exist only in discrete states, each with a definite energy.
(II) The electron can exist only in certain circular orbits.
(III) The angular momentum of the electron is nh/2p where n is any positive integer.
(IV) Radiation is emitted by the atom only when an electron makes a transition from a state of higher energy to one of lower energy.
(a) State whether each of these postulates is currently considered to be correct, according to the wave mechanical description of the hydrogen atom.
(b) Give the wave mechanical description that has replaced one of the postulates now considered to be incorrect.
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