ENCE 433 Dr. Alba Torrents

ENVIRONMENTAL ENGINEERING ANALYSIS Spring 2001

Homework Set # 7 SOLUBILITY – 1 Due May 3

Prepare questions before the exam ….May 8

1.

2.

To answer a question like this, we must imagine the "instant of mixing" , and instant before any reaction that may happen has had a chance to take place. We then calculate Q at the instant of mixing, and compare it to the equilibrium constant. Bear in mind than when two solutions are mixed, dilution always occurs.

Because NaNO₃ is a soluble, strong electrolyte the only reaction that can possible occur when these two solutions are mixed is the formation of insoluble BaF₂. Let us calculate both [Ba⁺²] and [F^-] at the instant of mixing.

No. mmol Ba⁺² added = (70 mL) (0.050 mmol L^-1) = 3.50 mmol

Total volume after mixing = 100.00 mL

Hence at the instant of mixing:

This is the reaction whose equilibrium constant is K_sp of BaF₂. The reaction quotient is:

Since Q < K_sp the reaction does not proceed to the left.

The solution is undersaturated and no BaF₂ will form.

3.

If pH decreases, [OH^-] decreases and thus [Fe⁺²] will increase as K_so is constant.

At pH = 5.00 ===> [H⁺] = 10^-5 M ===> [OH^-] = 10^-9 M