CHEMICAL EQUILIBRIA
Introduction
The reactions we use in analytical chemistry never actually result in complete
conversion of reactants to products. Instead, they proceed to a state of chemical
equilibrium in which their ratio of concentrations of reactants and products is constant.
Equilibrium constant expressions are algebraic equations that describe the
concentration relationship that exists among reactants and products at equilibrium.
Among other things, equilibrium constant expressions permit us to calculate the error
that result from the any unrelated analyte remaining when equilibrium has been
reached.
Laboratory Activity
1. Briefly explain why there is no term in an equilibrium-constant expression for water or
for a pure solid, even though one (or both) appears in the balanced net ionic equation
for the equilibrium.
2. Silver sulfide is formed by the interaction of silver and hydrogen sulfide based on the
equation below. What is the pH of a 300 mL solution with 6.32 mol of hydrogen sulfide
and 30M of silver sulfide? (Ka of H2S 9.6 x 10-8)
Ag + H2S Ag2S + H2
3. Define buffer capacity.
4. Is the following statement true or false or both? Define your answer with equations,
examples, or graphs. “A buffer maintains the pH of a solution constant.”
5. Explain the importance of pH detection in diagnosing acid-base imbalance.
6. What Arterial Blood Gas Study lab results are to be expected when the patient has
metabolic acidosis? Metabolic alkalosis? Respiratory acidosis? Respiratory alkalosis?