Equilibrium & acid / base  test              [100 points]                          honors 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. 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

                                                                                                Signature:  ___________________

 

1.  Calculate the pH of 5.0 mM benzoic acid, C6 H5 COOH.  [15 points]

 

2.  Fill-in the below table; need not show your work in this problem.  [18 points]

[H+ ]  (M)

[OH- ]  (M)

pH

 

 

7.45

 

2.5 * 10-3

 

5.0 * 10-6

 

 

3.  Methylamine, CH3 NH2 , is a weak base.  [12 points]

a.  write the chemical equation of methylamine reacting with water

b.  identify the conjugate pairs in the above reaction

c.  identify the acid, base, conjugate acid, and conjugate base in the above reaction

 

4.  In the reaction:  N2(g)   +  H2(g)   <-->  NH3(g) , the initial concentration of N2 , H2 , and NH3 is 5.0, 10.0, and 15.0 mM, respectively.  At equilibrium, the concentration of H2 is 4.0 mM.  Based on this information, what is the value of the equilibrium constant, Kc ?  [10 points]

 

5.  Write the algebraic expression of the equilibrium constant for the following reactions:  [10 points]

a.  C2 H6(g)   + O2(g) <-->  CO2(g)   +  H2 O(l)

                Kp =

b.  mixing aqueous solutions of silver nitrate and potassium chloride.

Kc =

6.  Calculate the molar solubility of barium fluoride in water.  [10 points]

 

 

7.  In the reaction:  NO(g)   +  O2(g)   <--> NO2(g)   at equilibrium is disturbed by  ___; what is the subsequent effect on number of moles of O2 ?  justify your response.  [15 points]

a.  add NO2 ; no change in temperature & volume

b.  cool the system only

c.  add helium; no change in temperature & pressure

 

8.  What is / are the condition(s) for a reaction to be at equilibrium ?  [10 points]

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Equilibrium & acid / base  retest           [100 points]                          honors chemistry

 

1.  buffer.   [20 points]

a.  what is a buffer ?

b.  what is the composition of a buffer ?

c.  how does a buffer work ?



2.  What is the pH of  ___.   [25 points]

a.  2.0 mM nitric acid, HNO3

b.  5.0 mM KOH

c. 10.0 mM methylamine

 

3.  What is the pH of a saturated solution of calcium hydroxide ?   [15 points]

 

4.  In the reaction:  N2(g )  +  H2(g)   <-->  NH3(g) , the partial pressure of N2 , H2 , and NH3 is 5.0, 10.0, and 15.0 atm, respectively.  At equilibrium, the partial pressure of H2 is 4.0 atm.  Based on this information, what is the value of the equilibrium constant, Kp ?  [10 points]


5.  In the reaction:  NO(g)   +  O2(g)   <--> NO2(g)  at equilibrium is disturbed by  ___; what is the subsequent effect on number of moles of O2 ?  justify your response.  [20 points]

a.  remove NO; no change in temperature & volume

b.  heat the system only

c.  add neon; no change in temperature & pressure

 

6.  In the reaction:  H2(g)   +  I2(g)   <-->  2 HI (g) ; Kc = 4.0, the initial concentration of H2 , I2 , and HI are 1.0, 2.0, & 3.0 M, respectively.  What is the equilibrium concentration of HI ?  [10 point