1) Consider the reaction: HC 2 H 3 O 2 and H 3 O + H 2 O and C 2 H 3 O 2 - H 2 O

Question

1)Consider the reaction:

HC2H3O2 and H3O+

H2O and C2H3O2-

H2O and H3O+

HC2H3O2 and C2H3O2-

all are bases

2)

What would the concentration of H3O+ be if the concentration of OH- was 1 x 10-1M?

[H3O+] x [OH-] = Kw = 1 x 10-14

1 x 10-3

1 x 10-2

1 x 10-4

1 x 1013

None of these

3)Which of the following is the ionization constant expression for water?

Kw = [ H+] [ OH-]

Kw = [ H2O ] [ H2O ]

Kw = [ H2O ]/ [ H+] [ OH-]

Kw = [ H+] [ OH-]/ [ H2O ]

none of these

4)What is the pH of an aqueous solution if the [ H+] = 0.000 000 075 M?

0.88

6.12

6.88

7.12

8.88

5)What is the hydrogen ion concentration of an aqueous acid solution having a pH of zero?

-1 M

0 M

1 M

10 M

none of these

6) Which of the following statements concerning aqueous solutions of salts is FALSE?

For any salt of a strong acid and a strong base, the pH will be about 7.

For any salt of a strong acid and a weak base, the pH will be <7.

For any salt of a weak acid and a strong base, the pH will be >7.

For any salt of a weak acid and a weak base, the pH will be about 7.

none of these

7)

Which of the following could be added to a solution of acetic acid to prepare a buffer?

sodium acetate only

sodium acetate or sodium hydroxide

nitric acid only

hydrofluoric acid or nitric acid

sodium hydroxide only

HC2H3O2 and H3O+

H2O and C2H3O2-

H2O and H3O+

HC2H3O2 and C2H3O2-

all are bases

Explanation / Answer

1. I cannot see the image for question 1, however I can tell for the options that the answer is H2O and C2H3O2-.

Explanation:

HC2H3O2 + H2O -------------> C2H3O2- + H3O+

An acid is a proton (hydrogen ion) donor and a base is a proton (hydrogen ion) acceptor. In this case, the HC2H3O2 is donating a H to the H2O to become H3O+. Therefore, that substance is an acid, and the H2O is accepting the H (the base). On the other hand, the  C2H3O2- becomes the conjugate base of the acid.

2. If Kw = 1x10-14 = [H3O+] x [OH-], then [H3O+] = 1x10-14 / [OH-] so:}

[H3O+] = 1x10-14 / 1x10-1 = 1x10-13 M

3. H2O --------> H+ + OH-   or 2H2O -------> H3O+ + OH-

K = [Products] / [Reactants]

K = [H+] x [OH-] /[H2O] however, concentration of water is near 1, so it's a constant, therefore:

Kw = [H+] x [OH-] or simply [H3O+] [OH-]

4. pH = -log[H+]

pH = -log(0.000000075) = 7.12

5. [H+] = 10-pH

[H+] = 100 = 1 M

6. The fouth option. This is because according to differents sources, the behavior of salts depends on this:

1) A salt of a strong acid and a strong base will produce a solution with pH = 7. Generally speaking, these types of solutions are mentioned, then ignored in deeper discussions.

2) A salt of a weak acid and a strong base will produce a solution with pH greater than 7. In other words, a salt of a weak acid produces a basic solution. Notice also, the mention of a strong base is usually omitted and the phrase "salt of a weak acid" is used. Of course, the strong base had to be present to make the salt, but its presence is assumed.

3) A salt of a weak base and a strong acid will produce a solution with pH less than 7. In other words, a salt of a weak base produces an acidic solution. Notice also, the mention of a strong acid is usually omitted and the phrase "salt of a weak base" is used. Of course, the strong acid had to be present to make the salt, but its presence is assumed.

4) A salt of a weak acid and a weak base produces a solution whose pH depends on the strengths of the acid and base which made the salt. Many times textbooks will show one example calculation only and then not provide any additional problems.

That it's why the fourth option would be the right answer.

7. A buffer consists of a weak acid and its conjugate base:

CH3COOH + H2O --------> CH3COO- + H3O+ where CH3COOH is acetic acid and CH3COO^- is acetate ion, the conjugate base.

If you add the correct amount of NaOH solution, you can convert half of the CH3COOH to CH3COO-

CH3COOH + NaOH --------> CH3COONa + H2O

The option would be Sodium Hydroxide only

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