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Buffers

Last updated

Aug 15, 2020
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- Bubble Machine
- B-Z Oscillating Reaction (Cerium Catalyzed)

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Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
2- 250ml graduated cylinders	100ml 1M Acetic Acid 29ml of 17.5 M Acetic Acid, glacial Qs to 500ml
Splash pan.	100ml Buffered Acetic Acid (1M acetic acid/1M Sodium Acetate) 136.1g Sodium Acetate Trihydrate + 57ml of 17.5 M Acetic Acid, glacial Qs to 1000ml
	2-5 g Calcium Carbonate

Procedure:

Add 100ml 1M acetic acid to a 250ml Graduate cylinder.
Add 100ml buffered acetic acid to a 250ml Graduate cylinder.
Pour 5 g calcium carbonate into each graduated cylinder.
Observe the difference between the reactions of the acid solution and the buffered acid solution.

Discussion:

How it works:

A buffered solution is one that resist change in its pH when an acid or base is added to it. Buffers typically contain a weak acid and a salt of the weak acid, or a weak base and salt of the weak base.

This demo shows that a solution containing both acetic acid and sodium acetate resist changes to pH when the calcium carbonate is added. First a small amount of carbonate is added to an acid, the pH changes dramatically and the reaction can be observed through the formation of calcium acetate and carbon dioxide.

${\mathrm{CH}}_\mathrm{3}\mathrm{COOH\;+\;Ca}{\mathrm{CO}}_\mathrm{3}\;→\;\mathrm{Ca}\left({\mathrm{CH}}_\mathrm{3}\mathrm{COO} \right)_\mathrm{2}\;\mathrm{+}\;CO2\;+\;H2O$

When the same amount of acid is added to the buffer solutions the pH does not change dramatically thus there is an absence of the visual reaction.

Hazards:

Wear gloves and splash goggles. Caution: Acetic acid is a weak acid.

SOP

N/A

Disposal (by Storeroom)

Once neutralized the solutions may be rinsed down the drain with copious amounts of water.

Acknoledgement and adapted from:

B. Z. Shakhashiri Chemical Demonstrations; A Handbook for Teachers of Chemistry Vol.3, Wisconsin, 1989, Vol.3, p.173-185

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