Question

Consider a solution which is 0.10M in CH3COOH and 0.20M in NaCH3COO. Choose ALL of the following that are true. If Ca(CH3COO)2 is added, the pH becomes more basic. If a small amount of HCl is added, the pH becomes slightly more acidic. If HCl is added, the H ions react with the CH3COOH. If a small amount of NaOH is added, the pH becomes slightly more acidic. If NaOH is added, the OH- ions react with the CH3COO- ions.

Answer 1

In a buffer solution of acetic acid and sodium acetate, the addition of either calcium acetate or NaOH will cause the pH to become more basic, while the addition of HCl will make the solution more acidic. The respective ions react with components of the buffer to mitigate significant changes in pH.

Step-by-step explanation:

Considering a solution that is 0.10M in CH3COOH (acetic acid) and 0.20M in NaCH3COO (sodium acetate), certain actions will cause the pH to change. This system is a buffer solution, which can resist changes in pH when small amounts of an acid or a base are added. The following outcomes are true:

• If Ca(CH3COO)2 is added, the pH becomes more basic due to the introduction of acetate ions which form with the hydronium ions to create more acetic acid, thus reducing hydronium ion concentration.
• If a small amount of HCl is added, the pH becomes slightly more acidic with the hydronium ions from the HCl reacting with acetate ions to form more acetic acid.
• If HCl is added, the H+ ions interact primarily with the acetate ions, not the acetic acid itself, due to Le Chatelier's Principle, where the reaction adjusts to minimize the change caused by the addition of the HCl.
• If a small amount of NaOH is added, the pH becomes slightly more basic, as the OH- ions will react with the hydronium ions, decreasing the hydronium concentration.
• If NaOH is added, the OH- ions react with the hydronium ions produced by the acetic acid in the solution.

Answer 2

The first 2 statements are correct. The others are false.

If Ca(CH3COO)2 is added, the pH becomes more basic.

If a small amount of HCl is added, the pH becomes slightly more acidic.

Step-by-step explanation:

Step 1: Data given

Molarity of a CH3COOH solution = 0.10 M

⇒CH3COOH is a weak acid

Molarity of a NaCH3COO solution = 0.20 M

Step 2: If Ca(CH3COO)2 is added, the pH becomes more basic.

Ca(CH3COO)2 → Ca^2+ + 2CH3COO-

This means when we add Ca(CH3COO)2, the amount of CH3COO- will be increased.

CH3COO- is the conjugate base of the acid CH3COOH.

By increasing the amount of the conjugate base CH3COO- the pH will become more basic.

The first statement is true.

Step 3: If a small amount of HCl is added, the pH becomes slightly more acidic

This is true. By adding a strong acid, the pH will become more acid.

Step 4: If HCl is added, the H ions react with the CH3COOH.

When the strong acid HCl is added. The H+ ions will react with a negative charged compound. This will not be CH3COOH but it's conjugate base CH3COO-

This statement will be false.

Step 5: If a small amount of NaOH is added, the pH becomes slightly more acidic.

When we add HCl, ste pH will become more acid. NaOH is a strong base. When adding a strong base, the pH will become (slightly) more basic, not more acid.

This statement is false.

Step 6: If NaOH is added, the OH- ions react with the CH3COO- ions.

The OH- ions of NaOH are negative charged, they will not react with the CH3COO- ions because those are also negative charged.

This statement is false?

The first 2 statements are correct. The others are false.

If Ca(CH3COO)2 is added, the pH becomes more basic.

If a small amount of HCl is added, the pH becomes slightly more acidic.