Question

QUESTION 1

Consider a solution prepared by mixing 10.0 mL of 0.200 M formic acid (HCHO₂, pK_a = 3.75) and 5.0 mL of 0.100 M NaOH.

What is the value of K_a for formic acid?

K_a = ___ M

QUESTION 2

Before any reaction occurs, what is present in the solution?

		a) Strong acid + strong base
		b) Strong acid + weak base
		c) Weak acid + strong base
		d) Weak acid + weak base

QUESTION 3

Before considering any equilibria in the mixture one must first ___ .

		a) determine the value of Ka for the weak acid
		b) determine what remains after the complete reaction of the strong base
		c) determine the value of Kb for the weak base
		d) determine what remains after the complete reaction of the strong acid

QUESTION 4

What species are present in the solution that will contribute to the equilibrium?

	a)	Weak acid and its conjugate base
	b)	Weak acid
	c)	Weak base
	d)	Strong base

QUESTION 5

What is the pH of the solution that results from the above mixture?

pH = ___

QUESTION 6

Consider a solution prepared by mixing 10.0 mL of 0.200 M formic acid (HCHO₂, pK_a = 3.75) and 20.0 mL of 0.100 M NaOH.

What species are present in the solution that will contribute to the equilibrium?

a)		Weak acid and its conjugate base
b)		Weak acid
c)		Weak base
d)		Strong base

QUESTION 7

What type of equilibrium must be considered to correctly determine the pH of the resulting solution?

a)		Dissociation of a weak acid
b)		Hydrolysis of a weak base
c)		Weak acid/conjugate base combination, constituting a buffer
d)		An excess of strong base

QUESTION 8

What is the pH of the solution that results from the above mixture?

QUESTION 9

Consider a solution prepared by mixing 10.0 mL of 0.200 M formic acid (HCHO₂, pK_a = 3.75) and 30.0 mL of 0.100 M NaOH.

What species are present in the solution that will contribute to the equilibrium pH?

a)		Weak acid and its conjugate base
b)		Weak acid
c)		Weak base
d)		Strong base

QUESTION 10

What type of equilibrium must be considered to correctly determine the pH of the resulting solution?

a)		Dissociation of a weak acid
b)		Hydrolysis of a weak base
c)		Weak acid/conjugate base combination, constituting a buffer
d)		An excess of strong base

QUESTION 11

What is the pH of the solution that results from the above mixture?

Answer 1

1. HCHO₂ is formic acid with

pKa=3.75

-log Ka= 3.75

Ka=10^-3.75=0.0001778= 1.778x10^-4

2. Formic acid is a weak acid as it doesn't undergo complete dissociation in solution and NaOH is a strong base as it dissociates completely in solution. So before any reaction happens, a weak acid and strong base are present in the solution. So the correct answer is option C.

3. Before considering the equilibria in the mixture, we need to know the species which contribute to the equilibrium and the species which don't. So we must know which species remain in the solution after the complete reaction of the strong base i.e. NaOH in this case. So the correct option in B.

4. The weak acid HCHO₂ dissociates to form HCOO^- (conjugate base) and H₃O⁺.

So both of these contribute to the equilibrium. So correct option is A.