Introduction
The pH of acidic, basic, and neutral aqueous solutions of salts is shown with ammonium chloride, sodium acetate, and sodium chloride.
Equations:
NaCl(aq) → Na+(aq) + Cl-(aq)
|
no effect on pH |
C2H3O2-(aq) + H2O(l) → HC2H3O2(aq) +OH-(aq) (Kb for acetate is 5.6x10-10) |
basic |
NH4+(aq) → NH3(aq) + H+(aq) (Ka for ammonia is 5.6x10-10) |
acidic |
To Conduct Demonstration:
- Place beakers containing distilled water and universal indicator reference set on the overhead projector.
- Add universal indicator to the beakers of water.
- Add a small amount of each salt to a different beaker and stir to dissolve.
- Compare the colors to the reference set.
Note: the NaCl will not be pH 7, but rather approximately pH 5 due to dissolved CO2in the water. A procedure to prepare the buffers to eliminate the CO2 follows, but was found to be relatively ineffective, so is not used often.
Demo Time: ~5 - 10 minutes
Reference:
S.S. Zumdahl, Chemistry, pp 644-650, 1989.
Acknowledgment:
Margaret Asirvatham, Spring 1990.