Experiment 9: Determination of the Solubility Product Constant of KHT
Reading Chemistry 2.0, OpenStax, Sec. 15,1: Precipitation and Dissolution
OBJECTIVE
To use the technique of titration to determine the K.o of a solid.
INTRODUCTION
When solid potassium hydrogen tartrate, KHCiH,OG, (KHT) is added to water, it dissociates into the ions
K* and HT (hydrogen tartrate; HCH.O). The structure formula of KHT is:
HO
OH OH 0
H
KHCaH40ss)
(KHT)
C
H
-0 K*
KHTis the salt of an organic a cid commonly known as cream of tartar by cooks and is used as a stabilizer,
thickener, leavening agent (used in baking powder), and pH control agent. It is also formed as a
precipitate during the fermentation of grapes during the wine making process.
Na Ranes
As KHT dissolves in water the concentrations of K* and HT increase and the rates of dissociation
(forward reaction) and solid formation (reverse reaction) become equal. Thus, a dynamic equili
ium
is reached as represented by the equili
ium reaction in equation 1. At this point the concentration of
ions is maximized, i.e., the solution is saturated.
K'pg) + HCaH40s (a)
(HT)
The equili
ium constant expression for this reaction is: Ksp = (K*][HCAH,0s]
9-1
(1)
(2)
where sp stands for solubility product and the (K'] and [HT] symbolize the molar con centrations (M =
mo/L) of K* and HT, respectively. The amount of solid does not affect the equili
ium concentrations
as long as some is present. Therefore, concentrations of solids are not included in the equili
ium
constant expression; they are assigned values of 1.0.
Equation 2 shows that when one mole of KHCaH4Os dissolves, one mole of K* and one mole of HCaH405
are present in the solution. Therefore, the molar ratio of reaction species is 1:1:1 and if the moles of K*
or HCHe0s in a saturated solution can be determined then the moles of KHT dissolved can be
determined since they wil be the same for this reaction.
You will determine the number of moles of HT present in a saturated solution of KHT using the titration
technique. HT (a monoprotic acid) will be titrated with NaOH via the net-ionic reaction
(3)
Because one mole of sodiun hydroxide neutralizes one mole of HT ions, the number of moles of
sodium hydroxide used in the titration will equal the number of moles of HT. The (HT] will be equal
Two Videos What is K,? (Solubility Product Constant) & Solubility Equili
ia
Concentration of standard NaOH
Volume of saturated KHT solution
Temperature of KHT solution
Initial buret reading
Final buret reading
Volume of NaOH delivered
Moles of NaOH used
Moles of HT titrated
Show one calculation in the space below.
Trial I
Tnal a
Trial 3
Trial 1
Show one calculation in the space
elow.
(HT] in KHT(ag) in each trial
50m
0.03
(K] in KHT(ag) in each trial
Show one calculation in the space
elow.
Show one calculation in the space below.
Trial 2
O.03
9-3
Trial 3
5Uml
Ksp
Show one calculation in the space below.
Average Ksp
Show calculation in the space below.
In this experiment, a volume of NaOH is used to titrate a solution of KHT. Explain how it is possible to use the moles of NaOH required in the titration to determine the Ksp of KHT.
9-4
Additional Questions
1) Write the equili
ium reaction for the dissociation of solid copper(!) sulfide, Cu;S in water.
2) Write the equili
ium constant expression, K,o, for the CuzS reaction.
3) Applying Le Chatelier's Principle., how will the addition of the following substances affect
the
equilibium reaction written in #1 and how will the equili
ium be restored? Explain.
In completing your answer, complete the following equations to show how these compounds
exist
when in water.
a) NazS(s)
) CuCl(s)
c) NaCl(s)
water
e) CuzS(s)
Water
Water
d) Temperature is increased (reaction is endothermic)
4) Using the information from 1 and 2 above, calculate the concentrations of [Cu'] and (S?-] if the Kso of
CuS(s) is 6.0 x10-", Hint: Assume (Cut] = 2x and [S]=x and then solve for x after setting up the
equili
ium constant expression.
9-5
Name:
Experiment 9: Determination of the Solublity Product Constant of KHT
Na kainos
Quiz Practice Questions
1. Consider solid aluminum ca
onate, Al;(Co;)1(s).
Instructor:
(a) Write a balanced equili
ium reaction equation for the dissociation of the compound.
Sec:
(b) Write an equili
ium constant expression (the solubility product constant, Kso) for the for the aqueous dissociation of the compound.
2. Write the equili
ium reaction and solubility product constant (Ksp) for the dissolution of Hg,Cl,(s). Caiculate the Ksp Value if the experimentally determined equili
ium concentrations are: (Hg,*] = 1.78 x 10 M and [CI= 3.97 x 10 M, respectively.
9-6
3. Write the equili
ium reaction and solubility product constant (Ksp) for the dissolution of solid Zna( PO.)2. Calculate the zinc ion and phosphate ion concentrations. the Ksp Of Zn,(PO.), is 9.1 x10-33