Question

General Chemistry II Laboratory Manual After addition: H,O 82PH 4 656 pH 7 8.1 pH 10 o Explain the results. Discuss the change in pH for water and contrast it to the change in pH of the buffer systems Acid Addition Base Addition 3. Buffer Preparation Assigned buffer pH S.5 L a. Calculate the amount of sodium acetate required to make the buffer. Show all your work. 5.5 Cen? Ka 1.2x l Ce.2 PKaz-(1.970 H.74 Actual pH of the buffer solution prepared 5.2 6.69 pH after addition of 2 drops 6M HCI 14 pH after addition of 2 drops 6M NaOH Discuss: How well you prepared your buffer (actual pH vs. target pH). (The word good" is not a discussion). How well your buffer worked upon the addition of acid and base. 74

i need help explaining this,

explain the results. discuss the change in pH for water and contrast it to the change in pH of the buffer system

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Answer 1

Solution:

A buffer solution resists the change in pH on addition of small amount of acid or base.

1) Acid addition:

Addition of HCl in buffer does not contribute a significant change in pH because acetate ion (CH3COO-) present in buffer reacts with HCl and forms weak acetic acid (CH3COOH) and therefore no significant change in pH observed.

HCl + CH3COONa = NaCl + CH3COOH (weak acid)

The addition of HCl in water increases H+ concentration by the formation of hydronium ion (H3O+) which is a strong acid and therefore pH decreases.

HCl + H2O = H3O+ (strong acid) + Cl-

2) Base addition:

Addition of base (NaOH) in buffer does not contribute a significant change in pH because acetic acid (CH3COOH) present in buffer reacts with NaOH and forms sodium acetate (CH3COONa) and unionized water molecule, therefore no significant change in pH observed.

NaOH + CH3COOH = CH3COONa + H2O (unionized)

When NaOH added in water, it increases OH- concentration therefore increases pH of water.

NaOH + H2O = Na+ + OH-