Buffers
- Page ID
- 127585
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Required Training |
Required PPE |
|---|---|
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
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2- 250ml graduated cylinders |
100ml 1M Acetic Acid 29ml of 17.5 M Acetic Acid, glacial Qs to 500ml |
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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 |
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2-5 g Calcium Carbonate |
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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