Question

18. Which H3O+ concentration and classification (acidic vs. basic) are correctly matched for a solution in which the OH- concentration is 5.6 x 10-6 M?

a. 5.6 x 10^-6 M : basic

b. 5.6 x 10^-6 M : acidic

c. 5.6 x 10⁸ M : acidic

d. 1.8 x 10^-9 M : basic

e. 1.8 x 10^-9 M : acidic

19. The solution that will give a pH = 12.00 is (MW: NaOH = 40 g/mol):

a. 4.0 g NaOH in 1.0 L of solution.

b. 12 g NaOH in 1.0 L of solution.                                                                                             

c. 0.20 g NaOH in 2.0 L of solution.

d. 0.20 g NaOH in 0.50 L of solution.

e. 0.40 g NaOH in 0.10 L of solution.

20. What is the K_a of the weak acid HClO₂ if a 0.100 M solution of the acid has a pH = 2.22?

a. 3.6 x 10^-4

b. 6.0 x 10^-3

c. 1.6 x 10^-3    

d. 5.9 x 10^-4

e. 1.3 x 10^-2

Answer 1

[OH-] = 5.6*10^-6

since 10^-7 < [OH]

[H+] = 10^-14)/( 5.6*10^-6) = 1.78571*10^-9

then

this is BASIC

19. The solution that will give a pH = 12.00 is (MW: NaOH = 40 g/mol):

pOH = 14-12 = 2

pOH = -log(OH-)

[OH-] = 10^-2

0.01 mol of NaOH per liter

0.4 g of NaOH per liter

a. 4.0 g NaOH in 1.0 L of solution. --> NOT

b. 12 g NaOH in 1.0 L of solution. --> NOT

c. 0.20 g NaOH in 2.0 L of solution. --> TRUE

d. 0.20 g NaOH in 0.50 L of solution. --> TRUE

e. 0.40 g NaOH in 0.10 L of solution. --> NOT