Ch. 16 acid, base, pH, & buffer                      90 points                                                          honors chemistry
           
Show your work in an organized manner, include (i) any relevant equation (or formula), (ii) conversion factor(s), (iii) put the proper units in your calculations and answer, and (iv) have the proper number of significant figures in your answer.

1. Fill-in the blank.  [15 points; based on HW 16.13]

a. If [H+] = 2.5 * 10 -4 M, then pH = ___.

b. If [H+] = 2.5 * 10 -4 M, then [OH-] = __.

c. If [OH-] = 6.9 * 10 -8 M, then pH = __.

2. Calculate the pH of __.  [15 points; based on HW 16.31]

a. 1.8 * 10 -4 M HBr

b. 1.02 g of HNO3 in 250. mL

c. A solution containing 10.0 mL of 0.0100 M HBr and 20.0 mL of 2.5 * 10 -3 M HCl.

3.  Calculate [OH-] and pH of 1.50 g LiOH in 250. mL of solution.  [10 points; based on HW 16.33]

4. A buffer contains acetic acid, HC2H3O2, and sodium acetate, NaC2H3O2.  Write the chemical equation (or net ionic equation) describing the reaction that occurs when add a few drops of __ to the buffer.  [10 points; based on HW 17.13]

a. Hydrochloric acid

b. Sodium hydroxide

5. In regards to a buffer,  [10 points]

a. define / describe a buffer

b. What’s its composition ?

c. How does it work ?

6. A 0.10  M aqueous solution of a weak acid, HA, has a pH = 2.44.   What is the dissociation constant of the acid ?    [15 points; based on HW 16.39]

7. A buffer was prepared by adding 20.0 g of acetic acid, HC2H3O2, and 20.0 g of sodium acetate, NaC2H3O2, to enough water to make a 2.0 L solution; what is the pH of the buffer ?  [15 points;  based on HW 17.13]