Equilibrium II & electrochem  test       [100 points]                          AP chemistry

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer. 

1.  Sketch an acid – base titration curve and label the both axis, include value of specific points to define the graph (show your determination of its values), where add 50.0 mM HNO3 to 45 mL of 25.0 mM KOH.   [15 points]

 

2.  Determine the pH of 45 mL 35 mM HF and 25 mM NaF after the addition of  __.  [15 points]

a.  nothing

b.  15.0 mL of 15 mM KOH

c.  15.0 mL of 15 mM HCl

 

3.   What is the pH of 45 mL, 25 mM boric acid after the addition of 5.0 mL of 45 mM NaOH ?  [15 points]

 

4.  Write the chemical equations involving the following reactants, assume that solutions are aqueous unless otherwise indicated.  Represent substances in solutions as ions if the substances are extensively ionized.  [15 points]


a.  mix aqueous solutions of hydrogen cyanide and sodium carbonate.

b.  add concentrated ammonia to an aqueous solution of Fe(III) choride

c.  add magnesium metal to an acidic solution of potassium permanganate

d.  add strontium metal to an alkaline solution of potassium permanganate

e.  add copper metal to a dilute solution of nitric acid


5.  Sodium carbonate was added to a 75 mL solution of 1.0 mM barium nitrate, 1.25 mM calcium chloride, and 0.1 mM copper (II) sulfate.  Identify the first and last precipitate to be formed.  Justify your answer.  [20 points]


6.   A voltaic cell is setup with 2 Pt electrodes, where an electrode is submerged into an acidic solution containing K2Cr2O7 and the other electrode is put into a solution of KI.  [20 points]

a.  write the spontaneous redox reaction of this system

b.  justify that the above redox reaction is spontaneous

c.  sketch this voltaic cell, identify the content of the solution in the beaker(s), write the appropriate half-reaction at each electrode, show the direction of the current (not electrons) in the system, show the direction of the cation and anion in the salt bridge, and label the anode and cathode.

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Equilibrium II & electrochem  retest     [100 points; 5 ec]                             AP chemistry

 

1.  Sketch an acid – base titration curve and label both axis, include value of specific points to define the graph (show your determination of its values), where add 50.0 mM KOH to 45 mL of 25.0 mM lactic acid.   [25 points]


2.  Determine the pH of 45 mL 35 mM CH3NH2 and 25 mM CH3NH3Cl after the addition of  __.  [15 points]

a.  nothing

b.  15.0 mL of 15 mM KOH

c.  30.0 mL of 55 mM HCl


3.  Determine the molar solubility of calcium hydroxide in water versus in a pH = 11.0 buffer.  Rationalize their relative values.  [15 points]

 

4.  Write the chemical equations involving the following reactants, assume that solutions are aqueous unless otherwise indicated.  Represent substances in solutions as ions if the substances are extensively ionized.  [15 points]


a.  mix solutions of hydrogen fluoride and sodium carbonate.

b.  add concentrated solution of sodium cyanide to a solution of copper (II) nitrate

c.  add magnesium metal to an acidic solution of lithium permanganate

d.  mix aqueous solutions of tin (II) chloride and copper (I) chloride

e.  add iron metal to a concentrated solution of nitric acid


5.  The resting membrane voltage across a nerve cell may be modeled as a potassium concentration cell, where the external potassium concentration is 5.0 mM and internal potassium concentration is about 100.0 mM.  What is the resting membrane voltage in a neuron at 37 °C,  i.e. what is the voltage in this concentration cell ?  [10 points]

 

6.  In regards to the addition of adding solid lead to an aqueous solution of 1.0 M silver nitrate at 35.0 °C.  [10 points]


a.  what is equilibrium constant of the reaction ?

b.  is it a spontaneous reaction ?  justify your answer.


7.  Electrolysis of water.   [15 points]

a.  calculate the minimum voltage for the electrolysis of water.

b.  sketch the electrochemical cell for the electrolysis of water, include:

i.   label the positive & negative pole of the battery
ii.  the half-reaction at each electrode
iii.  label the cathode & anode
iv.  show the direction of the current (not electrons) in the system