2 Hydrofluoric acid HF F H Ka 10

2. 化學沈降法基本原理 Hydrofluoric acid HF F- + H+ Ka = 10 -3. 17 CT = [HF] + [F-] From eqs. (1) and (2) (1) (2) (3) (4) Nearly 100% ionized F- is formed when p. H is maintained at greater than 6. 0.

2. 化學沈降法基本原理 Calcium fluoride Ca. F 2(s) ⇌ Ca 2+ + 2 FKs 0 = 10 -10. 3 (5) S 2 S From eq. (5) S = solubility = = 2. 32 10 -4 mole/L = [Ca 2+] (6) [F-] = 2 S = 2 2. 32 10 -4 mole/L (7) = 4. 64 10 -4 mole/L = 4. 64 10 -4 mole/L 19000 mg/mole = 8. 8 mg/L

重要觀念 Ca. F 2(s) ⇌ Ca 2+ + 2 F- Ks 0 = 10 -10. 3 (5) Precipitation occurs when Q > Ks 0 where Q = [Ca 2+]actual[F-]2 actual If Q is too much larger than Ks 0, nucleation predominates (i. e. , too many small nuclei) If Q is relatively larger than Ks 0, particle growth predominates (i. e. , relatively larger particles)