Zn Solubility

Zn Solubility

Zn2+ in ACSF
• How much ZnCl2 can be added to a
solution of ACSF at a given temperature
before one will observe a precipitate.
• What effect does pH have on solutions.

Formulas
• Zinc Hydroxide in water.
– Zn(OH)2 (s)  Zn2+(aq) + 2OH- (aq)
Ksp= 3.0x10-17
– 2OH-(aq)+ 2 H30+(aq) 4H20(l)
(K1/w= 1.0x1014)2
– Zn(OH)2(s) + H30+ (aq) Zn2+ (aq) +
4H20(l)
Knet= 3.0x10-17 * 1.0x1014 *
1.0x1014 = 3.0x1011

pH determination
• pH can be determined from the
concentration of H30+ from the
following equation:
• pH=-log[H30+]

• From the reaction and the previous
equation, the amount of Zn2+ in
solution based on pH can be
determined from the following
equation:
• 3.0x1011 = [Zn2+]
_______
[H30+]2

Or
• 3.0x1011 * (10-pH)2 = [Zn2+]
• Or
• pH = -log ([Zn2+] / 3.0x1011)-1/2

• Some figured values are
• pH 6: .3 M = [Zn2+]
• pH 7: .003 = [Zn2+]
• pH 8: 3.0x10-5 = [ Zn2+]

Analyzing Solutions
•
•

pH= 7.29
24° C
– 100 µM
• 0/4 solutions had visible precipitations.

– 200 µM
• 0/4 solutions had visible precipitations.

– 300 µM
• 0/4 solutions had visible precipitations.

– 400 µM
• 0/4 solutions had visible precipitations.

– 500 µM
• 0/4 solutions had visible precipitations.

– 600 µM
• 0/4 solutions had visible precipitations.

•
•

Upon sitting, solutions that contained 400 µM to 600 µM ZnCl2 showed
precipitation at the bottom of centrifuge tube.
pH of solution did not decrease significantly. Lowest pH was
measured at 7.23

• pH= 7.19
• 21.6° C
– 300 µM
• 0/3 solutions had visible precipitations.

– 400 µM
• 0/3 solutions had visible precipitations.

– 500 µM
• 0/3 solutions had visible precipitations.

– 600 µM
• 0/3 solutions had visible precipitations.
• Lowest pH was measured at 7.17

At Higher Temperatures
•
•

pH= 7.29
34° C
– 100 µM
• 0/2 solutions had no visible ppt.

– 200 µM
• 0/2 solutions had no visible ppt.

– 300 µM
• 2/2 solutions had visible ppt.

– 400 µM
• 2/2 solutions had visible ppt.

– 500 µM
• 2/2 solutions had visible ppt.

– 600 µM
• 2/2 solutions had visible ppt.

•

All of these solutions had been left overnight in a water bath at 35°
C.

• pH= 7.19
• 35.3° C
– 300 µM
• 0/3 solutions had visible ppt.

– 400 µM
• 0/3 solutions had visible ppt.

– 500 µM
• 0/3 solutions had visible ppt.

– 600 µM
• 0/3 solutions had visible ppt.
•

Solutions had been left standing for approximately 1 hour.