Calculating Ks.........

Calculating the ion concentration on solution using Ks....

Equilibrium

Equilibrium

When a salt dissolves an equilibrium is set up.

example: PbI2(s) --> Pb2+(aq) + 2I-(aq)

The equilibrium constant Kc is a ration of [products]/[reactants] at equilibrium

When you write a Kc expression, you never include solids or water when it is present as a solvent.

Qs is the reaction quotent for the dissolving process when a solution is formed that is NOT a saturated solution.

Ks is the solubility product and is for the dissolving process when a solution is formed that IS saturated.

Ks(BaSO4) = [Ba2+] [SO42-]

Titration Hints

When you are doing a titration you must always do the following:

A) Recording results:

1. Always record the first titration as rough and never use this volume in the average titre calcualtion.

2. Record the titre volumes to 0.05mL

3. You need at least 3 titres within 0.2mL of eachother.

4. Always record your results in a table form as follows:


rough 1 2 3 4

Final volume (mL)
initial volume (mL)
Volume used (mL)

B) Experimental technique

1. Rinse the conical flasks with distilled water.

2. Rinse the burette with the test solution you are going to use in it.

3. Rinse the pipette with the solution you are going to measure in it.

Disproportionation

This occurs when a reactant is both reduced and oxidised in the same reaction.

eg: H2O2 --> H2O + O2

here H2O2 is reduced to water and oxidised to O2

H2O2 + 2H+ + 2e- --> 2H2O reduction

H2O2 --> O2 + 2H+ + 2e- Oxidation

Another example:

Cl2 --> HCl + HOCl

Here the oxidation number of Cl goes from 0 to -1 in HCl, indicating a gain of electrons = reduction
And from 0 to +1 in HOCl, indicating a loss of electrons = oxidation