1) At 25 °C the solubility product constant, Ksp, for strontium sulfate, SrSO4, is 7.6 x 10¯7. The solubility product constant for strontium fluoride, SrF2, is 7.9 x 10¯10
(a) What is the molar solubility of SrSO4 in pure water at 25 °C?
(b) what is the molar solubility of SrF2 in pure water at 25 °C?
(c) An aqueous solution of Sr(NO3)2 is added slowly to 1.0 liter of a well-stirred solution containing 0.020 mole F¯ and 0.10 mole SO42¯ at 25 °C. (You may assume that the added Sr(NO3)2 solution does not materially affect the total volume of the system.) Which salt precipitates first? What is the concentration of strontium ion, Sr2+, in the solution when the first precipitate begins to form?
(d) As more Sr(NO3)2 is added to the mixture in (c) a second precipitate begins to form. At that stage, what percent of the anion of the first precipitate remains in solution?
(a) Titanium can be reduced in acid solution from TiO2+ to Ti3+ with zinc metal. Write a balanced equation for the reaction of TiO2+ with zinc in acid solution.
(b) What mass of zinc metal is required for the reduction of a 50.00-milliliter sample of a 0.115-molar solution of TiO2+.
(c) Alternatively, the reduction of TiO2+ to Ti3+ can be carried out electrochemically. What is the minimum time, in seconds, required to reduce another 50.00-milliliter sample of the 0.115-molar TiO2+ solution with a direct current of 1.06 amperes?
(d) The standard reduction potential, E°, for TiO2+ to Ti3+ is +0.06 volt. The standard reduction potential, E°, for Zn2+ to Zn(s) is -0.763 volt. Calculate the standard cell potential, E°, and the standard free energy change, DG°, for the reaction described in part(a).
3) The formula and the molecular weight of an unknown hydrocarbon compound are to be determined by elemental analysis and the freezing-point depression method.
(a) The hydrocarbon is found to contain 93.46 percent carbon and 6.54 percent hydrogen. Calculate the empirical formula of the unknown hydrocarbon.
(b) A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene (molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight 128.2). Calculate the molality of the p-dichlorobenzene solution.
(c) The freezing point of pure naphthalene is determined to be 80.2 °C. The solution prepared in (b) is found to have an initial freezing point of 75.7 °C. Calculate the molal freezing-point depression constant of naphthalene.
(d) A solution of 2.43 grams of the unknown hydrocarbon dissolved in 26.7 grams of naphthalene is found to freeze initially at 76.2 °C. Calculate the apparent molecular weight of the unknown hydrocarbon on the basis of the freezing-point depression experiment above.
(e)What is the molecular formula of the unknown hydrocarbon?
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) Sodium metal is added to water.
(b) Dilute sulfuric acid is added to a solution of lithium hydrogen carbonate.
(c) Ethanol and formic acid (methanoic acid) are mixed and warmed.
(d) Excess concentrated potassium hydroxide solution is added to a precipitate of zinc hydroxide.
(e) The gases boron trifluoride and ammonia are mixed.
(f) A solution of tin(II) chloride is added to a solution of iron(III) sulfite.
(g) Phosphorus(V) oxytrichloride is added to water.
(h) An acidified solution of sodium permanganate is added to a solution of sodium sulfite.
5) Properties of the chemical elements often show regular variations with respect to their positions in the periodic table.
(a) Describe the general trend in acid-base character of the oxides of the elements in the third period (Na to Ar). Give examples of one acidic oxide and one basic oxide and show with equations how these oxides react with water.
(b) How does the oxidizing strength of the halogen elements vary down the group? Account for this trend.
(c) How does the reducing strength of the alkali metals vary down the group? Account for this trend.
(a) When liquid water is introduced into an evacuated vessel at 25 °C, some of the water vaporizes. Predict how the enthalpy, entropy, free energy, and temperature change in the system during this process. Explain the basis for each of your predictions.
(b) When a large amount of ammonium chloride is added to water at 25 °C, some of it dissolves and the temperature of the system decrease. Predict how the enthalpy, entropy, and free energy change in the system during this process. Explain the basis for each of your predictions.
(c) If the temperature of the aqueous ammonium chloride system in part (b) were to be increased to 30 °C, predict how the solubility of the ammonium chloride would be affected. Explain the basis for your prediction.
7) Describe a separate laboratory procedure for preparing each of the following.
(a) Pure barium sulfate from an aqueous solution of barium chloride.
(b) A pure aqueous solution of copper(II) nitrate from solid copper(II) carbonate.
(c) A pure aqueous solution of calcium chloride from an aqueous solution of calcium bromide.
8) PCl3(g) + Cl2(g) <===> PCl5(g)
In the equation above, the forward reaction is first order in both PCl5 and Cl2 and the reverse reaction is first order in PCl5
(a) Suppose that 2 moles of PCl3 and 1 mole of Cl2 are mixed in a closed container at constant temperature. Draw a graph that shows how the concentrations of PCl3, Cl2, and PCl5 change with time until after equilibrium has been firmly established.
(b) Give the initial rate law for the forward reaction.
(c) Provide a molecular explanation for the dependence of the rate of the forward reaction on the concentrations of the reactants.
(d) Provide a molecular explanation for the dependence of the rate of the forward reaction on temperature.
| Substance | Melting Point, °C |
| H2 | -129 |
| C3H8 | -190 |
| HF | -92 |
| CsI | 621 |
| LiF | 870 |
| SiC | >2,000 |
(a) Discuss how the trend in the melting points of the substances tabulated above can be explained in terms of the types of attractive forces and/or bonds in these substances.
(b) For any pairs of substances that have the same kind(s) of attractive forces and/or bonds, discuss the factors that cause variation in the strengths of the forces and/or bonds.
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