AP CHEMIsTRY LAB:
and the Common Ion Effect
Problem:
1. Determine the solubility product
(K of
2. Determine the effect of a commo ) calcium hydroxide
n ion on the solubility of calcium
hydroxide
Materials:
Buret
200 mL saturated 2
Ca(OH) (aq)
3 250-mL Erlenmeyer flasks
100 mL saturated 2
Ca(OH) (aq) with 2
1.5 g KHP
CaCI
Phenolphthalein indicator
Procedure:
Obtain some filtrate of the saturate
d 2
Ca(OH) solution. Filter
the solution if it isn’t clear.
Prepare a buret by rinsing it with dist
illed water and then with a small
• Weigh three samples of potassi
amount of the filtrate.
um hydrogen phthalate, KHP, of
app
rox
imately 0.25 grams
(to the nearest 0.01 g). Record
each mass. Add each sample
to a separate 250-mL
Erlenmeyer flask and add 25 to 50
mL of distilled water. Swirl to diss
olve; it is not necessary
to dissolve the KHP completely sinc
e it will dissolve as the titration
proceeds.
• Fill the buret with saturated aqu
eous 2
Ca(OH) and record the initial vol
• Add 3 to 4 drops of phenolphthale
ume.
in to the flask.
Titrate until a faint pink color persist
s. Record final volume.
• Repeat with the final two KHP
samples.
• Obtain some filtrate of the satu
rated 2
Ca(OH) containing 2
CaCI Filter the solution if it
.
clear. Prepare a buret by rinsing
isn’t
it with distilled water and then
with some of the filtrate.
(The solution of 2
Ca(OH,) and 2
Caa was prepared by adding 1.1 2
C2
*
aC
H
g0
I per ZOO mL of
saturated solution and allowing the mb
ture to equilibrate for several day
• Weigh two samples of KHP of
s.)
approximately 0.25 grams (to
the nearest 0.01 g). Record
each mass. Add each sample to a
separate 250-mL Erlenmeyer flas
k and add 25 to 50 mL of
distilled water. Swirl to dissolve.
• Fill the buret with saturated aqueou
s2
ca(OH) containing 2
Cad and record the initial vol
• Add 3 to 4 drops of phenolphthale
ume.
in to the flask.
• Titrate until a faint pink color per
sists. Record final volume.
• Repeat with the final KHP sample.
•
Calculations: Create a calculations tabl
e. Be sure to show an example for
each new type of calculation
Prior to calculations
.
• Write the equation for the dissolv
ing of 2
Ca(OH) (s)
• Write the expression for the
of calcium hydroxide
For _
2
Ca
(O.
H)
1. The molar mass of KHP is 204.2
g. Calculate the number of moles
of KHP in each sample.
2. At the equivalence point, the
number of moles of 0H is equal
to the number of moles of
KHP. From this and the volum
e of 2
Ca(Ol-f) used, calculate the
concentration of the
hydroxide ion.
3. Determine the concentration of
calcium ion in each sample.
4. Calculate the value of the
for each trial.
For 2
Ca(OH) with 2
Cad
1. Calculate the number of moles of
KHP in each sample.
2. How many moles of 0H were pre
sent in each trial?
3. Calculate the hydroxide ion con
centration in each trial and calc
ulate the average.
Analysis:
ble?
d (to dissolve the KHP) prior to titration varia
1. Why is the volume of water adde
water? Why
on
hydroxide ion present from the dissociati of
2. Should we be concerned with the
or why not?
CaCI How are they
.
2
Ca(OH) and Ca(OH)z in a solution with
3. Compare the solubility of 2
e?
different? Can you explain this differenc
Ca(QH)
?
wing salts to affect the solubility of 2
follo
the
of
tions
addi
ct
expe
you
ld
wou
How
4.
4IOh
• NaCI
3
• KNO
KHSO
• 4
Prep lob in journal (the usual)
Turn in Calculations and
Analysis on a separate sheet
of paper (1 per lab group)