Buffers

Last updated
Save as PDF

Page ID: 127585

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

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