Zn Solubility

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# Zn Solubility - PowerPoint PPT Presentation

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

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### 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.