This document provides information on assessing various chemical equilibrium concepts including ionic equilibrium, solubility product (Ksp), and the effect of temperature on the equilibrium constant (Kc). It describes experiments that could be performed to investigate these concepts including determining Ksp for calcium hydroxide by titrating a saturated solution and determining Kc for the silver-iron redox reaction at different concentrations. Procedures are outlined for preparing solutions, collecting data, and calculating equilibrium constants from experimental results.

1. Equilibrium
Planning skills

2. Possible areas of assessment
 Ionic equilibrium
– Solubility in different solvents
– Effect of common ion on solubility of a
sparingly soluble compound
– Solubility product, Ksp
 Chemical equilibrium
– Kc of homogeneous aq / liquid system

3. Ionic equilibrium - Solubility
 Dependent variable:
– Amount of precipitate formed;
– Amount of sparingly soluble salt left;
 Independent variable:
– Amount of common ion added.
– Types of solvents;
 Constant:
– Mass of water;
– Temperature;

4. Solubility
As the no. of moles of NaCl increases,
the number of moles of PbCl2(s) increases.
Fixing amount of Pb(NO3)2, varying the amount
of NaCl added..

5. Graph
PbCl2 / mol
 NaCl / mol

6. Preparation of standard solution
 Weigh accurately about 8.275 g of solid Pb(NO3)2 into an
empty weighing bottle.
 Transfer and dissolve it in some distilled water in a 100 cm3
beaker.
 Rinse weighing bottle with distilled water and transfer the
washings to the beaker.
 Ensure all solid has dissolved.
 Transfer to a 250 cm3 volumetric flask using a funnel and
glass rod.
 Rinse beaker with distilled water and transfer the washings
to the flask.
 Add distilled water to the volumetric flask to the 250 cm3
mark.
 Shake thoroughly to ensure a homogenous mixing

7. Investigating solubility
 Measure 40 cm3 of Pb(NO3)2 into an beaker using a
50 cm3 measuring cylinder.
 Measure 5 cm3 of NaCl using a 10 cm3 measuring
cylinder.
 Filter out PbCl2(s). Dry the precipitate by drying the
precipitate between filter papers.

8. Table of data
Exp
t
Vol. of
Pb(NO3)2 /
cm3
Vol. of
NaCl /
cm3
Mass
of
PbCl2/
g
No. of
moles
of
PbCl2
No. of
moles
of
NaCl
1 40 5
2 40 10
3 40 15
4 40 20
5 40 25

9. Reliability
 Idea from gravimetry.
 Repeat drying/heating process until a
constant mass is obtained.

10. Q2: Solubility Product (Ksp)
 Using a 50.00 cm3 burette, run 32.00 cm3
of 0.200 mol dm 3 HCl into a 250 cm3
volumetric flask.
 Add de-ionised water and make up to the
mark using deionised water.
 Stopper the volumetric flask and shake
well to obtain a homogeneous solution.

11. Preparation of saturated solution
 Using a 100 cm3 measuring cylinder, place
about 150 cm3 of 0.100 mol dm 3 CaCl2 into a
250 cm3 dry conical flask.
 Add a large spatula of Ca(OH)2(s) into the flask
and shake. Continue to add more solid and swirl,
until some Ca(OH)2 remains undissolved to
ensure a saturated solution is obtained.
 Filter the saturated solution using a dry filter
funnel and dry filter paper into dry conical
flask/beaker.

12. Titration
 Pipette 25.0 cm3 of saturated Ca(OH)2
solution into another conical flask. Add 1-4
drops of methyl orange indicator. Titrate with
the diluted HCl from the burette until the
colour of the solution changes from yellow to
orange.

 Repeat the titration/step 4 to obtain two
consistent titres/results.

13. Determination of Kc
 Ag+ + Fe2+ Ag + Fe3+
overnight
Left to stand
overnight
Establish equilibrium Analysis
Constant temp

14. Ag+ + Fe2+ Ag + Fe3+
KSCN
Ag+, Fe2+, Fe3+
When SCN- is added, AgSCN(s) is precipita
out immediately.
Ag+ + SCN- AgSCN(s)
When Ag+ is used up, Fe3+ will form blood-re
complex with SCN-.
[Fe(H2O)6] 3+ + SCN-
[Fe(H2O5)(SCN)]2+ + H2O
Titration results give the amount of Ag+ left in
eqm mixture. Use ICE table to determine the
amt of Fe2+ and Fe3+.

15. Ag+ + Fe2+ Ag + Fe3+
 Using separate clean pipettes, transfer 25.0cm3 of
each of 0.100 mol dm-3 silver nitrate solution and
0.100 mol dm-3 iron(II) sulfate solution into a dry
100cm3 conical flask. Stopper the flask and place
the flask in a 25 oC water bath. Leave it to stand
overnight.
 Using a pipette, transfer 10.0cm3 of the solution into
another conical flask, taking care not to disturb the
precipitate of silver.
 Titrate the sample with 0.0200 mol dm-3 potassium
thiocyanate. The end-point is marked by the first
permanent brown/red colour. Repeat the titration
sampling

16. Ag+ + Fe2+ Ag + Fe3+
[Ag+] 0.100 0.100 0.100 0.100
[Fe2+] 0.100 0.200 0.300 0.400
Different
samples
[Ag+] 0.100 0.200 0.300 0.400
[Fe2+] 0.100 0.100 0.100 0.100

17. Effect of temperature on Kc
 CH3CO2H + C2H5OH CH3CO2C2H5 + H2O
 Weigh accurately about 1.200 g of CH3CO2H, 0.920
g of C2H5OH into a 100 cm3 conical flask.
 Add 0.490 g of concentrated H2SO4 to the mixture.
 Stopper the flask and place the flask in a 25 oC
water bath. Leave it to stand for 5 days.
 Titrate the remaining CH3CO2H against 1 mol dm-3
NaOH(aq). Phenolphthalein was used as an
indicator.
 Repeat procedure by placing reaction mixtures at
different temperatures, e.g. 35 oC, 40 oC and 45 oC.