1) A buffer solution contains 0.40 mole of formic acid, HCOOH, and 0.60 mole of sodium formate, HCOONa, in 1.00 liter of solution. The ionization constant, Ka, of formic acid is 1.8 x 10¯4
(a) Calculate the pH of this solution.
(b) If 100. milliliters of this buffer solution is diluted to a volume of 1.00 liter with pure water, the pH does not change. Discuss why the pH remains constant on dilution.
(c) A 5.00-milliliter sample of 1.00-molar HCl is added to 100. milliliters of the original buffer solution. Calculate the [H3O+] of the resulting solution.
(d) A 800-milliliter sample of 2.00-molar formic acid is mixed with 200. milliliters of 4.80-molar NaOH. Calculate the [H3O+] of the resulting solution.
2) When a dilute solution of H2SO4 is electrolyzed, O2(g) is produced at the anode and H2(g) is produced at the cathode.
(a) Write the balanced equations for the anode, cathode, and overall reaction that occur in this cell.
(b) Compute the coulombs of charge passed through the cell in 100.0 minutes at 10.0 amperes.
(c) What number of moles of O2 is produces by the cell when it is operated for 100. minutes at 10.0 amperes?
(d) The standard enthalpy of formation of H2O(g) is -242 kilojoules per mole. How much heat is liberated by the complete combustion, at 298 K and 1.00 atmosphere, of the hydrogen produced by the cell operated as in (c)?
3) Water is added to 4.267 grams of UF6. The only products are 3.730 grams of a solid containing only uranium, oxygen, and fluorine and 0.970 gram of a gas. The gas is 95.0 percent fluorine, and the remainder is hydrogen.
(a) From these data, determine the empirical formula of the gas.
(b) What fraction of the fluorine of the original compound is in the solid and what fraction in the gas after the reaction?
(c) What is the formula of the solid product?
(d) Write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of the gas is the true formula.
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) Hydrogen gas is passed over hot iron(III) oxide.
(b) Solution of potassium iodide and potassium iodate are mixed in acid solution.
(c) Dilute sulfuric acid is added to solid calcium fluoride.
(d) Solid ammonium carbonate is heated.
(e) Methane gas is mixed with an excess of chlorine gas.
(f) A concentrated solution of ammonia is added to a suspension of zinc hydroxide.
(g) Hydrogen peroxide is added to an acidified solution of sodium bromide.
(h) Dilute hydrochloric acid is added to a dilute solution of mercury(I) nitrate.
(a) From the standpoint of the kinetic-molecular theory, discuss briefly the properties of gas molecules that cause deviations from ideal behavior.
(b) At 25 °C and 1 atmosphere pressure, which of the following gases shows the greatest deviation from ideal behavior? Give two reasons for your choice.
| CH4 | SO2 | O2 | H2 |
(c) Real gases approach ideality at low pressure, high temperature, or both. Explain these observations
6) The values of the first three ionization energies (I1, I2, I3) for magnesium and argon [in kJ/mole] are as follows:
| I1 | I2 | I3 | |
| Mg | 735 | 1443 | 7730 |
| Ar | 1525 | 2665 | 3945 |
(a) Give the electronic configuration of Mg and Ar.
(b) In terms of these configurations, explain why the values of the first and second ionization energies of Mg are significantly lower than the values for Ar, whereas the third ionization energy of Mg is much larger than the third ionization energy Ar.
(c) If a sample of Ar in one container and a sample of Mg in another container are each heated and chlorine is passed in to each container, what compounds, if any , will be formed? Explain in terms of the electronic configuration given in part (a).
(d) Element Q has the following first three ionization energies [in kJ/mole]:
| I1 | I2 | I3 | |
| Q | 496 | 4568 | 6920 |
What is the formula for the most likely compound of element Q with chlorine? Explain the choice of formula on the basis of the ionization energies.
7) A solution of barium hydroxide is titrated with 0.1-M sulfuric acid and the electrical conductivity of the solution is measured as the titration proceeds. The data obtained are plotted on the graph below.
(a) For the reaction that occurs during the titration described above, write a balanced net ionic equation.
(b) Explain why the conductivity decreases, passes through a minimum, and then increases as the volume of H2SO4 added to the barium hydroxide is increased.
(c) Calculate the number of moles of barium hydroxide originally present in the solution that is titrated.
(d) Explain why the conductivity does not fall to zero at the equivalence point of this titration.
8) Describe a laboratory procedure needed to carry out each of the following.
(a) Separate a mixture of powdered solid CaCl2 and CaCO3.
(b) Determine the concentration of solute in an aqueous sodium chloride solution and give the concentration units that your method provides.
(c) Separate a mixture of two volatile liquids.
(a) Draw the Lewis electron-dot structures for CO32¯, CO2, and CO, including resonance structures where appropriate.
(b) Which of the three species has the shortest C-O bond length? Explain the reason for your answer.
(c) Predict the molecular shapes for the three species. Explain how you arrived at your predictions.
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