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:

  1. Place beakers containing distilled water and universal indicator reference set on the overhead projector.
  2.  Add universal indicator to the beakers of water.
  3.  Add a small amount of each salt to a different beaker and stir to dissolve.
  4. 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.