Lab 27 - Determination of Ksp for a
Sparingly Soluble Salt
Introduction
Inorganic substances are broadly classified as
acids, bases, or salts. With few exceptions, all
common salts are strong electrolytes. However,
the solubilities of salts span a broad spectrum,
ranging from slightly or sparingly soluble to very
soluble.
 This
experiment is concerned with
heterogeneous equilibria of slightly
soluble salts. For true equilibrium to
exist between a solid and solution, the
solution must be saturated. Thus the
solubility equilibrium constant can be
expressed solely on the concentrations
of the ions.
 The
rule for writing the solubility product
expression states that Ksp is equal to the
product of the concentration of the ions
in solution, each raised to the power of
the coefficient in the equilibrium
equation.
For the salt MA, the dissociation proceeds
as:
MA  M+ + A- Ksp = [M+][A-]
For the salt MA2, the dissociation proceeds as:
MA2  M+ + 2A- Ksp = [M+][A-]2
To determine the Ksp for a
sparingly soluble salt

we need only determine the concentration of one
of the ions, because the concentration of the
other ion is related to the first ion s concentration
by a simple stoichiometric relationship. In this
experiment, we will determine the Ksp for silver
chromate, Ag2CrO4, by measuring the
concentration of the yellow chromate ion, CrO42-,
using a spectrophotometer.
 Ag2CrO4(s)
 for
 2Ag+(aq)
+ CrO42-(aq)
which the Ksp = [Ag+]2 [CrO42-].
A. Preparation of
calibration curve
 Initial
[CrO4-2] 0.0024M
Volume of
0.0024 M
K2CrO4
Total
volume
[CrO4-2]
Absorbance
1 ml
100 ml
2.4e-5
.041
5 ml
100 ml
.37
10 mll
100 ml
.85
15 ml
100 ml
1.13
Molar absorption
 Absorption
/ molarity
1. 0.041 / 2.4e-5 = 1708
plot the absorbance versus concentration to
construct the calibration curve
B. Determining Ksp of Ag2CrO4
 1. Using pipettes, accurately prepare 3 separate
solutions,
• in a 150 mm test tube 5 mL of 0.004 M AgNO3
to 5 mL of 0.0024 M K2CrO4. Stopper each
test tube. Shake the solution thoroughly at
periodic intervals over a 10 min period. This
will establish equilibrium between the solid
phase and ions in solution.
B. Determining Ksp of Ag2CrO4
 2.
Transfer approximately 3 mL of each
solution and most of the insoluble
Ag2CrO4 to 75 mm test tubes and spin in
a centrifuge for two minutes. Discard the
supernatant and retain the precipitate.
B. Determining Ksp of Ag2CrO4
 3.
To the test tube add 2 mL of 0.25 M
NaNO3. Shake as before, then
centrifuge.
B. Determining Ksp of Ag2CrO4
 4.
Transfer the clear, pale yellow
supernatant liquid from the test tube to a
clean, dry cuvette. Measure and record
the absorbance of the solution. Using
the calibration curve, calculate the molar
concentration of CrO42- in the solution
Analysis
 Using
the calibration curve, calculate the
molar concentration of CrO42- in the
solution.
Lab 28 – Heat of neutralization
Introduction
Most chemical reactions are accompanied by a chance in
energy, usually in the form of heat. The energy change of
a reaction is called the heat of reaction or enthalpy. The
symbol, DH, is used to denote the enthalpy change. A
chemical change that has heat given off during the reaction
is said to be exothermic and DH is negative (<0); if heat is
absorbed, the reaction is endothermic and DH is positive
(>0).

In this experiment you will measure the heat of
neutralization when an acid and a base react to
form water. The quantity of heat given off during
the exothermic reaction will be estimated using a
thermally insulated vessel called a calorimeter.
The temperature change of the calorimeter and
its contents is measured before and after the
reaction. The change in enthalpy, DH, is equal to
the negative product of the temperature change,
DT, times the heat capacity (C) of the calorimeter
and its contents
. Heat Capacity of the
Calorimeter
 Procedures
 1.
Your instructor (me) has determined
the heat capacity (C) of the styrofoam
calorimeter in J/K.
 For each degree rise in temperature, the
calorimeter gains 10.2 Joules of energy.
Heat of Neutralization of HCl –
NaOH
 1.
Add exactly 50 mL of 1 M NaOH to
the dry calorimeter. Measure out exactly
50 mL of 1 M HCl and place it near the
calorimeter. Wait 3-4 minutes.
Heat of Neutralization of HCl –
NaOH
 2.
Measure the temperature of the acid;
rinse the thermometer with tap water and
wipe dry.
 Insert the thermometer into the
calorimeter and measure the
temperature of the NaOH solution. The
temperatures of the two solutions should
not differ by no more than 0.5oC.
Heat of Neutralization of HCl –
NaOH
 Lift
the lid and carefully add the 1.0 M
HCl all at once.
 Stir the solution carefully with the
thermometer and record the highest
temperature.
 Calculate the heat of neutralization per
mole of water formed.

calculations
Heat gained by soln
• T x mass x specific heat (4.18 J/k-g)
Heat gained by calorimeter
• T x heat capacity of calorimeter
(10.2J / K)