QUIZ 10 Answers

Chemistry 10 - Dr. Kline

May 23, 2001                                                             

Possibly useful information: pH = -log(H+); (H+)(OH-) = 1.0 x 10-14

QUIZ 10A

1.   5 points Use the following chemical equilibrium to answer the questions that follow. Note that the double-headed arrow («) is meant to represent the equilibrium arrows.

 

CO(g) + 2H2(g) <--> CH3OH(g)  + heat Exothermic

     

    a.  If the reaction is at equilibrium, how will it shift in response to ...

an increase in temperature? LEFT - away from "heat"

the addition of some CO(g)? RIGHT - away from added reactant

b. write the equilibrium expression for the reaction.

2.   5 points A solution has a hydroxide ion concentration, (OH-), 1.2 x 10-8 M.

a. What is the hydrogen ion concentration, (H+)? Show work.
(H+) = 1.0 x 10-14/(OH-) = 1.0 x 10-14/1.2 x 10-10 = 8.3 x 10-7 M
b. What is the pH? Show work.
pH = -log(H+) = -log( 8.3 x 10-7) = 6.08
c. Is the solution acidic, basic or neutral? ACIDIC - pH is less than 7

QUIZ 10B

1.   5 points Use the following chemical equilibrium to answer the questions that follow. Note that the double-headed arrow («) is meant to represent the equilibrium arrows.

 

CO(g) + 2H2(g) <--> CH3OH(g)  + heat Exothermic

     

    a.  If the reaction is at equilibrium, how will it shift in response to ...

a decrease in temperature? RIGHT - towards "heat"

the removal of some CO(g) ? LEFT - towards removed reactant

b. write the equilibrium expression for the reaction.

2.   5 points A solution has a hydroxide ion concentration, (OH-), 5.0 x 10-10 M.

.

a. What is the hydrogen ion concentration, (H+)? Show work.
(H+) = 1.0 x 10-14/(OH-) = 1.0 x 10-14/5.0 x 10-10 = 2.0 x 10-5 M
b. What is the pH? Show work.
pH = -log(H+) = -log( 2.0 x 10-5) = 4.70
c. Is the solution acidic, basic or neutral? - ACIDIC - pH is less than 7


QUIZ 10C

1.   5 points Use the following chemical equilibrium to answer the questions that follow. Note that the double-headed arrow («) is meant to represent the equilibrium arrows.

 

heat + CH3OH(g) <--> CO(g) + 2H2(g)  Endothermic

     

    a.  If the reaction is at equilibrium, how will it shift in response to ...

an increase in temperature? RIGHT - away from "heat"

the addition of some H2(g) ? LEFT - away from added product

b. write the equilibrium expression for the reaction.

2.   5 points A solution has a hydroxide ion concentration, (OH-), 7.8 x 10-5 M.

.

a. What is the hydrogen ion concentration, (H+)? Show work.
(H+) = 1.0 x 10-14/(OH-) = 1.0 x 10-14/7.8 x 10-5 = 1.3 x 10-10 M
b. What is the pH? Show work.
pH = -log(H+) = -log( 1.3 x 10-10) = 9.89
c. Is the solution acidic, basic or neutral? BASIC - pH is greater than 7

Dr. Peggy Kline | Physical Science Department | Santa Monica College | last updated 5/18/01