Chua, John Joseph R. 2014-30936
Calculations
Concentration of the standardized HCl solution
M
HCl=
´X mol
primary standard´X L
added titrant=
9.78× 10
−48.47 ×10
−3≈ 0.116 M
Experimental Ksp and Molar Solubility based on Procedure C
2+
¿
Ca
¿¿
s= ´X
¿
K
sp=
s (2 s )
2=
4 s
3=
4 ∙ 0.025
3=6.83 ×10
−5 Error=
|
6.83 ×10
−5−6.5 ×10
−6|
6.5 ×10
−6=
950
Solubility of Ca(OH)2 in Procedure D
2+
¿
Ca
¿¿
s= ´X
¿
Ionic strength of the different KCl solutions in Procedure E
Ionic strength, for easier calculation in this ATQ, is represented by the function f(x,y) wherein x is the concentration of Ca2+ ions and y is the concentration of OH- ions. (Data tabulated in
Excel, attached herewith)
f ( x , y )=
4 x+ y
2
Solubility of Ca(OH)2 in Procedure E (Data tabulated in Excel, attached herewith)
2+
¿
Ca
¿s= ´X
¿
ATQ
1. Write the net ionic reaction for the precipitation of Ca(OH)2 and give the Ksp
a.
−
¿
2+
¿
+
2OH
¿Ca(OH )
2↔ Ca
¿is the net ionic reaction for the precipitation of Ca(OH)2
and the Ksp expression is
2+
¿
Ca
¿¿
−
¿
OH
¿¿
¿
K
sp=
¿
.2. What is the working equation for the determination of the [Ca2+] in the saturated
solution of Ca(OH)2? a.
2+
¿
Ca
¿¿
−
¿
OH
¿=
(
V
added)(
M
titrant)
(
V
analyte)
¿
3. Write the Ksp of Ca(OH)2 in terms of its:
a. Molar solubility i.
2+
¿
Ca
¿¿
−
¿
OH
¿Let s=
¿
∴ K
sp=
s(2 s )
2=4 s
3 b. [OH-] i.2+
¿
Ca
¿¿
−
¿
OH
¿¿
¿
Since
¿
−
¿
OH
¿¿
¿
K
sp=
1
2
∙
¿
c. [Ca2+]i.
−
¿
OH
¿¿
2+
¿
Ca
¿Since
¿
2+
¿
Ca
¿¿
2
¿
K
sp=
¿
4. Discuss the effects of common ion and increasing ionic strength on the solubility of the Ca(OH)2 precipitate. Do they coincide with theoretical effects? Explain.
a. Theoretically, the addition of a common ion decreases the solubility of
Ca(OH)2 because there is addition of Ca2+ ion which, due to the Le Chatelier’s
Priniciple, directs the reaction to the formation of precipitate. In our data, the solubility increased; this may be brought about by random error which is made by wrong measurement of molarity, excessive titration, and
contaminated glassware, among others. Since Ionic strength is the measure of ion concentration, higher values means higher solubility. The results have coincided with the theoretical ones in ionic strength.
5. What are the possible sources of errors and their effect on the calculated parameters? Rationalize.
a. Errors in standardization can cause a large error on all calculations as it is in the concentration of the titrant everything is based. The assumption of the Ksp
at 25oC also increases the error in calculations, especially the relative error
itself because the experiment is not exposed in the said temperature. References
http://www.titrations.info/acid-base-titration-sodium-hydroxide-and-carbonate http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html#top
Determination of Ksp and Solubility of Ca(OH)2
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05
HCl, L 0.0227 0.0219 0.022
[OH] 0.052664 0.050808 0.05104
[Ca] 0.026332 0.025404 0.02552
s 0.026332 0.025404 0.02552
Ksp 7.30317E-05 6.55792E-05 6.64817E-05
s, X bar 0.025752
Ksp, X bar 6.83114E-05
Ksp, Theo. 0.0000065
% Error 950.9438806
Effect of Common Ions on the Solubility of Ca(OH)2
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05 HCl, L 0.025 0.0239 0.0232 [OH] 0.058 0.055448 0.053824 [Ca] 0.029 0.027724 0.026912 s 0.029 0.027724 0.026912 s, X bar 0.027878667 Ksp, X bar 8.66714E-05 Solubility of Ca(OH)2 in 0.010 M KCl
Filtrate, L 0.05 0.05 0.05 HCl, L 0.023 0.0262 0.0232 [OH] 0.05336 0.060784 0.053824 [Ca] 0.02668 0.030392 0.026912 s 0.02668 0.030392 0.026912 Ksp 7.59657E-05 0.000112289 7.79647E-05 s, X bar 0.027994667 Solubility of Ca(OH)2 in 0.050 M KCl
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05 HCl, L 0.0255 0.02445 0.0243 [OH] 0.05916 0.056724 0.056376 [Ca] 0.02958 0.028362 0.028188 s 0.02958 0.028362 0.028188 Ksp 0.000103527 9.12579E-05 8.95886E-05 s, X bar 0.02871 Solubility of Ca(OH)2 in 0.10 M KCl
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05 HCl, L 0.0264 0.0259 0.0255 [OH] 0.061248 0.060088 0.05916 [Ca] 0.030624 0.030044 0.02958 s 0.030624 0.030044 0.02958 Ksp 0.00011488 0.000108476 0.000103527 s, X bar 0.030082667 Solubility of Ca(OH)2 in 0.25 M KCl
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05
HCl, L 0.0284 0.0282 0.028
[OH] 0.065888 0.065424 0.06496
[Ca] 0.032944 0.032712 0.03248
Ksp 0.000143017 0.000140017 0.000137059
s, X bar 0.032712
Solubility of Ca(OH)2 in 0.50 M KCl
Trial 1 Trial 2 Trial 3
Filtrate, L 0.05 0.05 0.05 HCl, L 0.0303 0.0298 0.0294 [OH] 0.070296 0.069136 0.068208 [Ca] 0.035148 0.034568 0.034104 s 0.035148 0.034568 0.034104 Ksp 0.000173685 0.000165228 0.000158663 s, X bar 0.034606667
[KCl] Solubility Ionic Strength 0.01 0.027994667 0.093984 0.05 0.02871 0.13613 0.1 0.030082667 0.190248 0.25 0.032712 0.348136 0.5 0.034606667 0.60382 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.040 0.1 0.2 0.3 0.4 0.5 0.6 0.7 f(x) = 0 exp( 265.87 x ) R² = 0.99 Solubility Ionic Strength
