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chemistry a molecular approach
Questions and Answers of
Chemistry A Molecular Approach
When a suspected drunk driver blows 188 mL of his breath through the fuel-cell breathalyzer described in Section 20.7, the breathalyzer produces an average of 324 mA of current for 10 s.Assuming a
Write a nuclear equation for the indicated decay of each nuclide.a. U-234 (alpha)b. Th-230 (alpha)c. Pb-214 (beta)d. N-13 (positron emission)e. Cr-51 (electron capture)
Two known compounds have the formula H2N2O2. One of them is a weak acid and one is a weak base. The acid, called hyponitrous acid, has two O—H bonds. The base, called nitramide, has no O—H bonds.
A redox reaction has an equilibrium constant of K = 0.055.What is true of ΔG°rxn and E°cell for this reaction?
What is a gamma ray? What happens to the mass number and atomic number of a nuclide that emits a gamma ray?
Fill in the missing particles in each nuclear equation. a. 241 b. Pu 94 c. d. Ne →→→ Se + 34- 2At + He 24 Am + 95- Ne + 73 الاليا As
Fill in the missing particles in each nuclear equation. a. 24 Am 95 b. 2371 c. 233Np 93 d. 3 Br 2371 233Np + 93¹ + e 2331 92 + He 0 + tie
Determine whether or not each nuclide is likely to be stable.State your reasons.a. Mg-26 b. Ne-25c. Co-51 d. Te-124
Determine whether or not each nuclide is likely to be stable.State your reasons.a. Ti-48 b. Cr-63 c. Sn-102 d. Y-88
Calculate the quantity of energy produced per mole of U-235 (atomic mass = 235.043922 amu) for the neutron-induced fission of U-235 to produce Te-137 (atomic mass = 136.9253 amu) and Zr-97 (atomic
The first six elements of the first transition series have the following number of stable isotopes:Explain why Sc, V, and Mn each have only one stable isotope while the other elements have several.
Suppose that an 85.0-gram laboratory animal ingests 10.0 mg of a substance that contained 2.55% by mass Pu-239, an alpha emitter with a half-life of 24,110 years.a. What is the animal’s initial
Describe each kind of reaction.a. Substitution reactionb. Addition reactionc. Elimination reaction
What kinds of reactions are common to alkenes? Give an example of each.
There are 11 structures (ignoring stereoisomerism) with the formula C4H8O that have no carbon branches. Draw the structures and identify the functional groups in each.
A redox reaction employed in an electrochemical cell has a negative ΔG°rxn. Which statement is true?a. E°cell is positive; K < 1b. E°cell is positive; K > 1c. E°cell is negative; K > 1d. E°cell
Calculate ΔG° and K for each reaction the group created in Question 143. For one of the reactions, explain how the sign or magnitude of each quantity (E°cell, ΔG°, and K) is consistent with the
Consider the titration curves (labeled a and b) for two weak bases, both titrated with 0.100 M HCl.i. Which base solution is more concentrated?ii. Which base has the larger Kb?
Phenolphthalein has a pKa of 9.7. It is colorless in its acid form and pink in its basic form. For each of the values of pH, calculate [In–]/[HIn] and predict the color of a phenolphthalein
Find the mass of sodium formate that must be dissolved in 250.0 cm3 of a 1.4 M solution of formic acid to prepare a buffer solution with pH = 3.36.
What relative masses of dimethyl amine and dimethyl ammonium chloride do you need to prepare a buffer solution of pH = 10.43?
What should the molar concentrations of benzoic acid and sodium benzoate be in a solution that is buffered at a pH of 4.55 and has a freezing point of -2.0 °C?
Describe the solubility of CaF2 in each solution compared to its solubility in water.a. In a 0.10 M NaCl solutionb. In a 0.10 M NaF solutionc. In a 0.10 M HCl solution
Estimate the value of the equilibrium constant at 525 K for each reaction in Problem 73.Problem 73Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each
Consider the reaction:Calculate ΔGrxn for the reaction at 25 °C under each of the following conditions:a. Standard conditions b. At equilibrium c. PICl = 2.55 atm; PI2 = 0.325 atm; PCl2 = 0.221
Explain the difference between macrostates (external arrangements of particles) and microstates (internal arrangements of particles).
Living organisms use energy from the metabolism of food to create an energy-rich molecule called adenosine triphosphate (ATP). The ATP acts as an energy source for a variety of reactions that the
The standard free energy change for the hydrolysis of ATP was given in Problem 91. In a particular cell, the concentrations of ATP, ADP, and Pi are 0.0031 M, 0.0014 M, and 0.0048 M,
Calculate ΔG° at 298 K for these reactions and predict the effect on ΔG° of lowering the temperature. a. NH3(g) + HBr(g) → NH4Br(s) b. CaCO3(s) →→→ CaO(s) + CO₂(g) c. CH4(g) + 3
Suppose we redefine the standard state as P = 2 atm. Find the new standard ΔG°f values of each substance.a. HCl(g) b. N2O(g) c. H(g)Explain the results in terms of the relative entropies of
The ΔG for the freezing of H2O(l) at -10 °C is -210 J/mol, and the heat of fusion of ice at this temperature is 5610 J/mol. Find the entropy change of the universe when 1 mol of water freezes at
Consider the reaction that occurs during the Haber process:The equilibrium constant is 3.9 * 105 at 300 K and 1.2 * 10-1 at 500 K. Calculate ΔH°rxn and ΔS°rxn for this reaction. N₂(g) + 3
Calculate ΔG° at 25 °C for the reaction in the previous question. Is this reaction spontaneous under standard conditions? How do you know? What is the determining factor: the change in energy or
Explain the difference between a voltaic (or galvanic) electrochemical cell and an electrolytic cell.
An electrochemical cell is based on these two half-reactions:Calculate the cell potential at 25 °C. 2+ Sn²+ (aq, 2.00 M) + 2 e Ox: Sn(s) Red: ClO₂(g, 0.100 atm) + e- CIO₂ (aq, 2.00 M)
What is a concentration electrochemical cell?
A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ halfcell at 25 °C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively.a. What is the initial cell
A voltaic cell consists of a Pb/Pb2+ half-cell and a Cu/Cu2+ halfcell at 25 °C. The initial concentrations of Pb2+ and Cu2+ are 0.0500 M and 1.50 M, respectively.a. What is the initial cell
Make a sketch of a concentration cell employing two Zn/Zn2+ halfcells.The concentration of Zn2+ in one of the half-cells is 2.0 M, and the concentration in the other half-cell is 1.0 * 10-3 M. Label
A concentration cell consists of two Sn/Sn2+ half-cells. The cell has a potential of 0.10 V at 25 °C. What is the ratio of the Sn2+ concentrations in the two half-cells?
A Cu/Cu2+ concentration cell has a voltage of 0.22 V at 25 °C.The concentration of Cu2+ in one of the half-cells is 1.5 * 10-3 M. What is the concentration of Cu2+ in the other half-cell?
Determine the optimum mass ratio of Zn to MnO2 in an alkaline battery.
Refer to the tabulated values of ΔG°f in Appendix IIB to calculateE°cell for the fuel-cell breathalyzer, which employs the followingreaction. (AG for HC₂H3O₂(g) = -374.2 kJ/mol.)
What mass of lead sulfate is formed in a lead–acid storage battery when 1.00 g of Pb undergoes oxidation?
Refer to the tabulated values of ΔG°f in Appendix IIB to calculate E°cell for a fuel cell that employs the reaction between methane gas (CH4) and oxygen to form carbon dioxide and gaseous water.
Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.a. Zn b. Sn c. Mn
Consider the electrolytic cell: a. Label the anode and the cathode and indicate the halfreactions occurring at each.b. Indicate the direction of electron flow.c. Label the terminals on the battery
Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.a. Mg b. Crc. Cu
Draw an electrolytic cell in which Mn2+ is reduced to Mn and Sn is oxidized to Sn2+. Label the anode and cathode, indicate the direction of electron flow, and write an equation for the halfreaction
Write equations for the half-reactions that occur in the electrolysis of molten potassium bromide.
What products are obtained in the electrolysis of molten NaI?
Write equations for the half-reactions that occur in the electrolysis of a mixture of molten potassium bromide and molten lithium bromide.
What products are obtained in the electrolysis of a molten mixture of KI and KBr?
Write equations for the half-reactions that occur at the anode and cathode for the electrolysis of each aqueous solution.a. NaBr(aq) b. PbI2(aq) c. Na2SO4(aq)
Write equations for the half-reactions that occur at the anode and cathode for the electrolysis of each aqueous solution.a. Ni(NO3)2(aq) b. KCI(aq) c. CuBr2(aq)
Make a sketch of an electrolysis cell that electroplates copper onto other metal surfaces. Label the anode and the cathode and indicate the reactions that occur at each.
Copper can be electroplated at the cathode of an electrolysis cell by the half-reaction:How much time would it take for 325 mg of copper to be plated at a current of 5.6 A? Cu²+ (aq) + 2e →→→
Make a sketch of an electrolysis cell that electroplates nickel onto other metal surfaces. Label the anode and the cathode and indicate the reactions that occur at each.
Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction:What mass of silver would plate onto the cathode if a current of 6.8 A flowed through the cell for 72 min? Ag+
Consider the reaction shown here occurring at 25 °C.Determine the value of E°cell and K for the reaction and complete the table. A(s) + B²+ (aq) A²+ (aq) + B(s) AGx = -14.0 kJ
A major source of sodium metal is the electrolysis of molten sodium chloride. What magnitude of current produces 1.0 kg of sodium metal in 1 hour?
What mass of aluminum metal can be produced per hour in the electrolysis of a molten aluminum salt by a current of 25 A?
Consider the reaction shown here occurring at 25 °C.Determine E°cell, K, and ΔG°rxn for the reaction and complete the table. Cr(s) + Cd²+ (aq) Cr²+ (aq) + Cd(s)
Consider the unbalanced redox reaction:Balance the equation and determine the volume of a 0.500 M KMnO4 solution required to completely react with 2.85 g of Zn. MnO4 (aq) + Zn(s) Mn2+ (aq) + Zn²+
Consider the unbalanced redox reaction:Balance the equation and determine the volume of a 0.850 M K2Cr2O7 solution required to completely react with 5.25 g of Cu. 2+ Cr₂O72 (aq) + Cu(s) Cr³+(aq) +
Consider the molecular views of an Al strip and Cu2+ solution.Draw a similar sketch showing what happens to the atoms and ions after the Al strip is submerged in the solution for a few minutes.
Consider the molecular view of an electrochemical cell involving the overall reaction:Draw a similar sketch of the cell after it has generated a substantial amount of electrical current. Zn(s) +
Determine whether HI can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HI and determine the minimum volume of 3.5 M HI required to
The cell potential of this electrochemical cell depends on the pH of the solution in the anode half-cell.What is the pH of the solution if Ecell is 355 mV? Pt(s) |H₂(g, 1 atm) | H(aq, ? M) || Cu²+
Determine if HNO3 can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HNO3 and determine the minimum volume of 6.0 M HNO3 required to
The cell potential of this electrochemical cell depends on the gold concentration in the cathode half-cell.What is the concentration of Au3+ in the solution if Ecell is 1.22 V? Pt(s) | H₂(g, 1.0
A friend wants you to invest in a new battery she has designed that produces 24 V in a single voltaic cell. Why should you be wary of investing in such a battery?
What voltage can theoretically be achieved in a battery in which lithium metal is oxidized and fluorine gas is reduced?Why might such a battery be difficult to produce?
A battery relies on the oxidation of magnesium and the reduction of Cu2+. The initial concentrations of Mg2+ and Cu2+ are 1.0 * 10-4 M and 1.5 M, respectively, in 1.0-liter half-cells.a. What is the
A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag+ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag+ in the half-cells are
The Ksp of CuI is 1.1 * 10-12. Find Ecell for the cell: Cu(s) | Cul(s) I (aq) (1.0 M) || Cut(aq)(1.0 M) | Cu(s)
If a water electrolysis cell operates at a current of 7.8 A, how long will it take to generate 25.0 L of hydrogen gas at a pressure of 25.0 atm and a temperature of 25 °C?
The Ksp of Zn(OH)2 is 1.8 * 10-14. Find Ecell for the half-reaction: Zn(OH)₂(s) + 2 e Zn(s) + 2OH¯(aq)
Calculate ΔG°rxn and K for each reaction.a. The disproportionation of Mn2+(aq) to Mn(s) and MnO2(s) in acid solution at 25 °C.b. The disproportionation of MnO2(s) to Mn2+(aq) and MnO4¯(aq) in
Calculate ΔG°rxn and K for each reaction.a. The reaction of Cr2+(aq) with Cr2O7 2 ¯(aq) in acid solution to form Cr3+(aq).b. The reaction of Cr3+(aq) and Cr(s) to form Cr2+(aq). [The electrode
The molar mass of a metal (M) is 50.9 g/mol; it forms a chloride of unknown composition. Electrolysis of a sample of the molten chloride with a current of 6.42 A for 23.6 minutes produces 1.20 g of M
A metal forms the fluoride MF3. Electrolysis of the molten fluoride by a current of 3.86 A for 16.2 minutes deposits 1.25 g of the metal. Calculate the molar mass of the metal.
A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn2+. The solution is then titrated with a 0.0448 M solution of NO3¯, which is reduced to NO(g). The
A 0.0251-L sample of a solution of Cu+ requires 0.0322 L of 0.129 M KMnO4 solution to reach the equivalence point. The products of the reaction are Cu2+ and Mn2+. What is the concentration of the
A current of 11.3 A is applied to 1.25 L of a solution of 0.552 M HBr converting some of the H+ to H2(g), which bubbles out of solution. What is the pH of the solution after 73 minutes?
An MnO2(s)/Mn2+(aq) electrode in which the pH is 10.24 is prepared.Find the [Mn2+] necessary to lower the potential of the half-cell to 0.00 V (at 25 °C).
A 215-mL sample of a 0.500 M NaCl solution with an initial pH of 7.00 is subjected to electrolysis. After 15.0 minutes, a 10.0-mL portion (or aliquot) of the solution was removed from the cell and
To what pH should you adjust a standard hydrogen electrode to get an electrode potential of -0.122 V?
Suppose a hydrogen–oxygen fuel-cell generator produces electricity for a house. Use the balanced redox reactions and the standard cell potential to predict the volume of hydrogen gas (at STP)
A voltaic cell designed to measure [Cu2+] is constructed of a standard hydrogen electrode and a copper metal electrode in the Cu2+ solution of interest. If you want to construct a calibration curve
The surface area of an object to be gold plated is 49.8 cm2, and the density of gold is 19.3 g/cm3. A current of 3.25 A is applied to a solution that contains gold in the +3 oxidation state.Calculate
To electrodeposit all the Cu and Cd from a solution of CuSO4 and CdSO4 required 1.20 F of electricity (1 F = 1 mol e-). The mixture of Cu and Cd that was deposited had a mass of 50.36 g.What mass of
Sodium oxalate, Na2C2O4, in solution is oxidized to CO2( g) by MnO4¯, which is reduced to Mn2+. A 50.1-mL volume of a solution of MnO4¯ is required to titrate a 0.339-g sample of sodium oxalate.
Three electrolytic cells are connected in a series. The electrolytes in the cells are aqueous copper(II) sulfate, gold(III) sulfate, and silver nitrate. A current of 2.33 A is applied, and after some
An electrochemical cell has a positive standard cell potential but a negative cell potential. Which statement is true for the cell? a. K> 1;Q> K c. K> 1; Q< K b. K< 1;Q> K d. K< 1; Q< K
Have each group member select a half-reaction from Table 20.1.Each member should calculate the standard cell potential of an electrochemical cell formed between each member’s halfreaction and the
The cell Pt(s) |Cu+(1 M), Cu2+(1 M) II Cu+(1 M) |Cu(s) has E° = 0.364 V. The cell Cu(s) |Cu2+(1 M) II Cu+(1 M) |Cu(s) has E° = 0.182 V. Write the cell reaction for each cell and explain the
Which oxidizing agent will oxidize Br¯ but not Cl¯?a. K2Cr2O7 (in acid) b. KMnO4 (in acid)c. HNO3
Balance the redox reactions by following the steps in the text.Rotate through the group, having each group member do the next step in the process and explain that step to the rest of the group. a.
In this chapter, you have seen that the voltage of an electrochemical cell is sensitive to the concentrations of the reactants and products in the cell. As a result, electrochemical cells can be used
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