Experiment 3.pdf

EXPERIMENT 3: EFFECT OF BUFFER SOLUTION ON pH OBJECTIVES 1. To understand the nature of a buffer. 2. To prepare a buffer from acetic acid and sodium acetate. 3. To test the ability of buffered and unbuffered solutions to resist pH changes when strong acids and bases are added.

EQUIPMENT/APPARATUS Beakers, distilled water, sodium chloride, solid sodium acetate, acetic acid, stirring rod, hydrochloric acid, pipette, pH meter, magnetic stirrer, spin bar, sodium hydroxide

PROCEDURES Required PPE : Goggles/safety glass, Lab Coat, Shoes, Gloves NO SEQUENCE OF STEPS POTENTIAL HAZARDS i HCl : Corrosive Chemicals NaCl : Irritant sodium chloride (NaCl) NaOH : Corrosive solid sodium acetate (CH3COONa) Sodium acetate : acetic acid (CH3COOH) Irritant hydrochloric acid (HCl) Acetic acid : Irritant sodium hydroxide (NaOH)

PREVENTATIVE MEASURES i . Wear proper PPE ii. Handle chemicals carefully to avoid spillage iii. Safety Briefing prior start the class iv. Use fume hood

A. The preparation of the Buffer Solution 1

Label 7 beakers of 100 ml as 1 until 7.

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2

Add 50 ml distilled water into beaker 1 and i . Spillage 6 and 50 ml 0.1 M sodium chloride into beaker 2 and 7.

3

Weigh 1 g solid sodium acetate (CH3COONa) and transfer into beaker 3.

i . Spillage

Nil i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE i. Handle chemicals carefully to avoid spillage ii. Wear proper PPE

Weigh 5 g solid sodium acetate (CH3COONa) and transfer into beaker 4. Weigh 10 g solid sodium acetate (CH3COONa) and transfer into beaker 5. 1

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Prepare 250 ml of 0.1 M acetic acid in i . Spillage another beaker. ii. Hazardous chemical

7

Add 50 ml 0.1 M acetic acid to beaker 3, 4 i . Spillage and 5. Stir the solution until all the solid ii. Hazardous chemical dissolve.

i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE

B. The Determination of Buffering Action toward Acid 8

Use pH paper to measure the pH value.

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9

Determine the pH value of distilled water Nil in beaker 1.

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Record the value. (Note: Rinse the pH probe with distilled water before each measurement). 10

Prepare 200 ml of 3.0 M HCl.

i . Spillage ii. Extremely Add 1 ml 3.0 M hydrochloric acid into hazardous chemical beaker 1 until 5.

11

Mix the solution and determine the pH i . Spillage value of the solution by using pH paper. ii. Extremely Record the pH value in a table format. hazardous chemical Repeat Step 11 until there is only a slight change in the pH value (at least 4 times)

i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE

C. The Determination of Buffering Action Toward Base 12

Repeat all the steps in Section A by i . Spillage replacing 3.0 M hydrochloric acid with 3.0 ii. Hazardous chemical M sodium hydroxide into beaker 1 until 5.

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Record your pH reading at least 4 times in Nil a table format.

i . Training on handling of pipette ii. Handle chemicals carefully to avoid spillage iii. Wear proper PPE Nil

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EXERCISE 1. From your results in this experiment, which solution of those you tested had the greatest buffer capacity: i. Toward strong acid? ii. Toward strong base? Discuss. 2. Why was distilled water used to rinse off the pH probe? 3. Define buffer solution. 4. Specify which of these systems can be classified as a a buffer system: 5.

KCl/HCl

b.

NH3/NH4NO3

c. NaHPO4/NaH2PO4

6. Calculate the pH of the buffer system 0.15M NH3 / 0.35 M NH4C

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