Download Chemistry Problems: Solubility, Hydration, and Reaction Rates - Prof. Jeffrey Weimer and more Assignments Inorganic Chemistry in PDF only on Docsity!
Dr. J. J. Weimer
April 12, 2004
The questions in this set are examples of problems that you should be able to solve by taking the course. While they should cover the key information of the course, they are not meant to be com- plete or exhaustive. Review the summary discussions at the end of each chapter for descriptions of the information you are required to know. Further example problems are provided in the textbook and via the homework.
A solution key for these study problems will not be provided. You are welcome to visit me with your solutions to the problems to discuss whether they are correct.
Solutions
- Which system below is likely to form an immiscible solution over a certain range of concen- tration? CsF(s) in H 2 O(l) CCl 4 (l) in H 2 O(l) H 3 C(CO)CH 3 (l) in H 3 C(CO)OH(l)
- Show a picture that represents how water molecules might be ar- ranged around a sodium ion to hydrate the ion. A sodium ion and water molecule are given to approximate scale.
- A is a species that acts at an oil/water interface to help dissolve oil into water.
- A solution contains exactly 1 molal KCl in water. What is the wt% KCl in the solution? (molar masses: KCl = 74.5510 g/mol, H 2 O = 18.0148 g/mol).
- A doped semiconductor wafer is produced by dissolving 0.2500 g P in 1 kg Si. What is the concentration of P in Si in ppm?
- Consider the two reaction enthalpies shown in the Born-Haber diagram on the right. a) When temperature decreases, will the sol- ubility of MX(s) increase or decrease? b) Show an arrow on the diagram that corre- sponds to the hydration reaction. c) What is the value of the molar enthalpy of hydration of MX?
- The solubility of CO 2 in water is 0.0656 M at 1.50 atm. What is the Henry’s law constant for CO 2 in water?
- The graph on the right shows the solubility of compounds A, B, and C in water. a) For compounds A and B, is ∆ soln H ¯ exothermic or endothermic? b) At 30 o^ C, what is the saturation concen- tration of A in water? Show on the graph the lines you use to read the value. c) What temperature is required to have a solubility limit of 0.25 mol/L of A?
A
B
C
Temperature [oC]
Concentration [mol/L]
- Explain the process of hydration. Illustrate your explaination appropriately.
- What factor(s) will affect the enthalpy of hydration of an ion? a) size of ion, b) shape of ion, c) polarity of solvent, d) shape of solvent molecule, e) charge of ion.
- Consider the following two reactions:
KCl(s)! K+^ (g) + Cl (g) ∆ H ¯ o^ = 950 kJ/mol KCl(s)! KCl(aq, 1m) ∆ H ¯ o^ = 5 kJ/mol Determine the enthalpy of hydration of KCl (kJ/mol).
- The solubility of a gas in a liquid is determined by a) Raoult’s law, b) Henry’s law, c) Le Chatelier’s principle, d) none of these.
- The osmotic pressure of a solution of KCl(aq) at 25 o^ C is 7.75 atm. What is the molar concen- tration of KCl in the solution?
- A solution contains 0.0675 moles ethanol in 1.4325 moles water at 100 o^ C. What is the vapor pressure (atm) of the water in the solution under these conditions? Assume the mixture forms an ideal solution. (Hint: pure water at 1 atm boils at 100 o^ C)
- The freezing point depression constant of KCl in water is 3.54 o^ K/m. Determine the freezing point (o^ C) of a 0.015 m solution of KCl(aq). Assume the van’t Hoff factor is 2, and water freezes at 0 o^ C.
- Explain the differences between a colloid and a solution.
- Water loving colloids are a) hydrophobic or b) hydrophilic?
- Explain how a surfactant works. Illustrate your explaination appropriately.
- The rate of a reaction has SI units of mol/m 3 s. The empirical rate law is overall second order. What are the SI units on the reaction constant?
- At 25 o^ C, a reaction with an activation energy of 120.5 kJ/mol has a rate of 0.742 mol/L s. What is the reaction rate at 30 o^ C?
- What assumption must apply in order to use change in concentration with time as a measure of a reaction rate?
- What two assumptions must apply in order to use change in pressure with time as a measure of reaction rate?
- The graph below on the right shows concentrations of A, B, and C as a function of time. Measured values are shown as circles or squares. The lines are theoretical curves. a) At initial time (t = 0), which species has the greatest rate of formation? b) Determine the average rate of reaction of A measured over the interval from 1 h to 2 h. Circle the points that you use to calculate the value. c) Is the instantaneous theoretical rate of re- action of A at t = 1 h faster or slower than the measured average over the interval from 1 h to 2 h?
A
B
C
Time [h]
Concentration [mol/L]
A
B
C
- The date below are for the reaction 2A + B! C + D. The reaction is known to be first order in A and second order overall. [A] o (mol/L) [B] o (mol/L) rate (mol/L s) 1.00 0.030 2.5 10 ^3 1.00 0. a) Complete the table with the missing value of reaction rate. b) Determine the rate constant from the data given in the above table.
- For a certain reaction that includes species X, a graph of ln[X] versus time in seconds produces a straight line with a constant slope of +2.0 10 ^3 s ^1. a) Is [X] being produced or consumed during the reaction? b) What is the reaction order in [X]?
- An empirical reaction rate expression is always a true expression of the reaction mechanism (True or False)?
- A reaction is inverse first order in [X]. When [X] is doubled, by what factor does the reaction rate change?
- The reaction P + Q! R is zero order in [P] and second order in [Q]. A container starts with [P] o = 1.000 M, [Q] o = 0.100 M, and [R] o = 0. After exactly one minute, the concentration of Q has decreased by 10%. What is the rate constant of the reaction?
- The first order half-life of a certain species is 53.5 yr. How long is required for the concentration of the species to decrease to 25% of its initial value?
- The rate of a reaction doubles when temperature increases from 25 o^ C to 35 o^ C. What is the activation energy of the reaction (kJ/mol)?
- According to collision theory, what three conditions must be satisfied for two molecules to react?
- For a certain reaction at STP, the reactants start at 20 kJ/mol, the activation energy of the forward reaction is 50 kJ/mol, and the activation energy of the reverse reaction is 200 kJ/mol. a) Draw an diagram showing the reaction energy as a function of reaction progress. b) Determine the enthalpy of the forward reaction.
- The two reactions below are elemental steps in an overall reaction.
A + B! C + D fast C + E! B + D slow a) What is the expected empirical expression for the rate of formation of D ( r (^) D )? b) The measured value of r (^) D is 2.5 mol/L min. What is the rate of reaction of A?
- A rate expression derived from a reaction mechanism can always be expressed as a simple empirical rate expression (True or False)?
Equilibrium
- State whether each statement below will always be a true way to tell that a chemical reaction has definitely reached equilibrium. Put yes (Y) or no (N). a) The rate constants of the forward and reverse reactions are equal. b) No chemical reactions are occuring. c) The concentrations of reactants and products are constant.
- Consider the reaction CO(g) + 1/2 O 2 (g) *) CO 2 (g).
a) What is the expression for the reaction quotient Q? b) When total pressure is increased, will reactants or products be favored? c) What is the value of ∆ n is the expression K (^) p = Kc ( RT )∆ n? d) An isotopic labelling experiment is run for the reaction starting only with C^18 O and O 2. If equilibrium was NOT dynamic, which species would NOT be found? Circle all that apply. CO O 18 O C^18 OO C^18 O 18 O 18 O (^2)
- A gas phase reaction system A(g) + 2B(g) *) C(g) + D(g) is allowed to reach equilibrium.
a) The final pressures of components are measured to be p (^) A = 0 :10 bar, p (^) B = 0 :050 bar, pC = 0 :70 bar, and p (^) D = 0 :15 bar. What is the value of Keq ; P? b) Less product is created as temperature increases. Is the reaction endo- or exo-thermic? c) At 25 o^ C, the value of Keq ; C is 2.5 10 13. What is the value of Keq ; P?
- A reaction 2A(l) + 3B(aq) *) C(s) + 2D(aq) is run at 25 o^ C where Keq ; C = 3 : 5 10 ^5. The equilibrium concentration of B is 0.5000 M. What is the equilibrium concentration of D?
- A liquid phase reaction A(aq) + B(aq) *) 2C(aq) starts with [A] = [A] o , [B] = [B] o and [C] = [C] o. The equilibrium constant is Keq ; C. Set up an ICE table and derive the exact equation that should be used to solve this problem for the equilibrium value of [C]. Your equation should be in the form Keq ; C = f (ε), where ε is the unknown extent of reaction.
- Consider the two reactions listed below with their respective equilibrium constants.
2C *) A + B K 1 = 3 : 5 C + B *) D + E K 2 = 0 : 12 What is the equilibrium constant for the reaction A + 3B *) 2D + 2E?
Acids & Bases
- Label each of the following as a Brønstead acid (A), base (B), or neither (N).
NaCl(s) HCl(aq) Cl (aq) Na+^ (aq)
- Explain the difference between monoprotic, polyprotic, and amphiprotic acids. Give an exam- ple of each.
- The pH of a solution is 4.9. What is the value of [H 3 O+^ ]?
- An acid-base is used to show when pH changes because it changes color.
- A student adds 25 ml of 0.100 M carbonic acid to 25 ml of 0.100 M potassium hydroxide.
a) Write the net ionic reaction that occurs. b) Will the final solution pH be less than, equal to, or greater than 7?
- Consider the reaction NaF(aq) + HNO 3 (aq) *) HNO 3 (aq) + HF(aq). Are products or reactants favored?
- What is the pKb of ammonia?
- An aerospace engineer must prepare an etching solution to clean a titanium carbide coating on a jet turbine blade. She adds 0.0450 mol of a base to water to make exactly 1 liter of aqueous solution with a pH of 8.55. a) What is the value of Kb for the base? (Hint: ICE table) b) The pH of the above etching solution is required to be 9.00. Should she add more acid or base to the solution?
- The pH values of two different solutions are to be compared below. Both solutions have the same concentrations. Put one of the symbols <, =, or > between the two solutions to indicate your predication of their relative pH values. a) HOI(aq) HOF(aq) b) NaOCl(aq) NaClO 4 (aq)
- Is AlCl 3 a Lewis acid or Lewis base?
- Explain how metal hydroxides can be acids or bases in water. Show example reactions.
- Explain how an amine can react as a Brønstead base or a Lewis base. Show example reactions.
Acid/Base Aqueous Equlibrium
- What are the two requirements of a useful buffer solution?
- What is the pH of an aqueous ammonium chloride + ammonia buffer solution at its half- equivalence point?
- A crime lab technican must titrate 25.0 ml of 0.0500 M HCN with 0.0750 M NaOH.
a) On the axes on the right, sketch the approximate shape of the titra- tion curve. Be sure your pH val- ues are appropriately placed at the markings for the initial (V added = 0), half-equivalence (heq), and equivalence (eq) points.
pH
Volume NaOH Added (ml)
heq eq
0
b) What volume of titrant is needed to reach the equivalence point (eq)?
- An acid with Ka = 2 : 0 10 ^7 at 0.250 M is titrated with a base at 0.150 M.
a) What is the pH of the solution at the half-equivalence point? b) What is the pH of the solution at the equivalence point?
- The Ksp value of NaNO 3 is 3.7 10 ^11. What concentration of NaNO 3 dissolves in water?
- Water saturated with Pb(OH) 2 (aq) has pH = 9.15. What is the Ksp of Pb(OH) 2 (aq)?
- Consider the three pairs of solutions given below. Answer YES or NO as to whether the pair forms a good buffer solution when mixed. GOOD BUFFER? a) CH 3 CO 2 H (aq) + NaCH 3 CO 2 (aq) b) HCl (aq) + NaOH (aq) c) H 2 SO 4 (aq) + Na 2 SO 4 (aq)
- The concentration of Mg 2 +^ in an aqueous solution is 1: 5 10 ^6 M. Solid NaOH is added. What concentration of NaOH in the final solution will cause Mg(OH) 2 to precipitate? Ksp (Mg(OH) 2 = 5: 6 10 ^12.
- The formation constant of Ag(CN) 2 (aq) is 5: 6 10 18 and Ksp for AgI is 8: 5 10 ^17. What is Keq ; C for dissolving solid AgI in a solution containing CN (aq) to form Ag(CN) 2 (aq)?
- A solution of NH 3 has a concentration of 0.150 M. What concentration of NH 4 Cl solution is needed to make a buffer with a pH of 8.8? pKb (NH 3 ) = 4.74, pKa (NH+ 4 ) = 9.
- A 100.00 ml solution of base at 0.130 M concentration is titrated with an acid at 0.075 M concentration. What volume of acid is needed to reach the equivalence point?
- A saturated solution of BaF 2 has [Ba^2 +^ ] = 3 : 6 10 ^3 M. What is the solubility product of BaF 2?
- a) Using the axes on the right, draw the ap- proximate shape of a titration curve for a weak acid ( Ka = 4 : 0 10 ^7 ) being titrated with a strong base. Mark and label the curve at the half-equivalence and equiva- lence points. b) What is the pH of the solution at the half- equivalence point.
- A reaction has a standard free energy of 16.37 kJ/mol. Calculate the equilibrium constant for the reaction.
- The statement that, entropy of the universe always increases (for a spontaneous process) was first stated in what language?
- Consider the reaction A + 2B! C with data below. A B C S ¯ o^ (J/K mol) 10.0 2.8 7. ∆ H ¯ o^ (kJ/mol) -13.0 -14.0 -11. a) Determine standard entropy change of reaction. b) Determine the standard Gibb’s free energy change of reaction.
- To obtain useful work from a chemical reaction, what must be true under all conditions?
a) The reaction must be exothermic. b) The products must have a higher entropy than the reactants. c) Both of the above statements must always be true. d) None of the above must necessarily be true.
Electrochemistry
- Write the balanced redox reaction for the electrochemical cell notation shown below. (2)
H 2 (g) | H+^ (aq) || Zn^2 +^ (aq) | Zn(s)
- Is a yittrium/zirconium fuel cell used as an oxygen sensor in a car a) an electrolytic or b) a voltaic cell?
- Write a balanced half-cell electrochemical reaction for Fe! Fe(OH) 2 in acidic solutions.
For the next two questions, consider two half-cell reduction reactions
A +^ + e ! A and B +^ + e ! B where E ocell ; A < E (^) cello ; B.
- Which reaction will occur at the cathode of an electrolytic cell?
- Which reactant, A +^ or B +^ , is the stronger oxidizing agent?
- Consider the two reduction half-cell reactions shown below.
A 2 +^ + 2e ! A E (^) cello = 0 :855 V B^3 +^ + e ! B^2 +^ E (^) cello =? The reactions are set up in an electrochemical cell with the reaction of A at the anode and the reaction of B at the cathode. The standard cell potential is measured as -1.110 V. What is the standard half-cell reduction potential of the reaction of B?
- Consider the reaction shown below carried out in aqueous solution.
2Fe^2 +^ (0.25 M) + H 2 O 2 (0.25 M) + 2H 3 O+^ (0.25 M)! 2Fe^3 +^ (0.25 M) + 4H 2 O(l) a) The standard cell potential is 1.15 V. Calculate the measured cell potential. b) The standard cell potential is 1.15 V. What is the equilibrium constant of the reaction?
- The reaction AuCl 4 (aq) + 3 e ! Au(s) +4Cl (aq) produces 2.5 mg of Au and a current of 3.5 A in an electroplating cell. How long did the reaction run? MAu = 196 :9665 g/mol
- An electrochemical cell can contain a salt bridge or a to allow flow of ions between the two chambers.
- Write the balanced net ionic reaction for MnO 4 reacting with Fe^2 +^ to produce Mn 2 +^ and Fe^3 + in acidic solutions.
Main Group Chemistry
- What is the most abundant element in the earth’s crust?
- What is the common oxide formula for the group 6A elements? (1) a) EO b) E 2 O 3 c) EO 2 d) EO (^3)
- What is the chemical formula for the molecular compound formed between Ge and F?
- Label the reaction below as either a) water gas, b) steam reforming, or c) water gas shift.
CH 4 (g) + H 2 O(g)! 3H 2 (g) + CO(g)
- Electrolysis of aqueous NaCl is the basis of one of the largest chemical industries in the US. What is the balanced chemical reaction? NaCl(aq) +! H 2 (g) + +
- The group II elements are called the elements.
- Match one the three names with the formula.
a) limestone, gypsum, or fluorite (1) CaCO (^3) b) talc, asbestos, or dolomite (1) 3MgO 4SiO 2 2H 2 O
- Hydrated aluminum oxide Al 2 O 3 nH 2 O is used to produce aluminum. This form of hydrated aluminum oxide is called.
- Aluminum oxide in cyrstalline form is used in grinding wheels. This form of aluminum oxide is called.
- Silicates are based on what anion?
- Smog contains which one of the following nitrogen oxides that causes the brownish color? a) N 2 O b) NO c) N 2 O 3 d) NO 2 e) N 2 O 4 f) N 2 O (^5)
- What is the color of S 8?
- What is the prefix for the name of the acid HClO 3? a) hypochlorous b) chlorous c) chloric d) perchloric
Transition Metals
- Which reaction produces red-brown rust? a) Fe(s) + H 2 O! Fe(OH) 2 b) Fe(s) + H 2 O + O 2! Fe 3 O 4 H 2 O c) Fe(s) + H 2 O + O 2! Fe 2 O 3 H 2 O
- Which of the above reactions is anaerobic?
- Explain why the density of transition metals varies based on atomic radii and atomic mass.
- Pyrometallurgy is used when a transition metal is typically found in what type of compound as an ore?
- Consider the coordination compound [Ni(NO 2 ) 2 (en) 2 ]Cl.
a) What is the oxidation state of Ni? b) What is the coordination number of Ni?
- Name the compound Na[Pd(NH 3 )(NO 2 ) 3 ], where pallidium is in a 2+ oxidation state.
- Consider the complex [Mn(L) 6 ] x +^ where the ligand L is monodentate. Illustrate the d orbital energy level diagram according to crystal field theory. Label the levels correctly ( d (^) x (^2) y 2 , d (^) z 2 , : : :). Use the space to the right.
- Consider the d orbital energy level diagram for a tetrahe- dral d orbital splitting shown to the right. Label the energy levels and fill in the electrons as spin up or down for a low spin state of Fe^3 +^. Fe: [Ar] 3d 6 4sd 2
- Show the electrons for the same Fe^3 +^ in a complex with tetrahedral binding, high spin state.
