[raccoon]

You guys were so helpful last time I thought I'd try again. I have a couple titration questions that I want to make sure I am doing correctly. The answers are to be in both mol H+/L and then ppm CaCO3.

Determination of Alkalinity (in both mol H+/L and then ppm CaCO3):

Volume HCl used for titration: 7 mL

Conc'n HCl: 0.05 M

In 250 mL water using methyl orange. Do I need the K_a value?

K_a = [H+][CO3]/[HCO3] = 4.7 x 10-11 @ 25C

    Determination of Calcium Ion Content

Volume Na2EDTA used: 1 mL

Conc'n HCl: 0.025 M

In 250 mL water using Eriochrome Black T.

    Determination of Oxygen Content (Winkler Method)

Sodium thiosulfate volume used: 5 mL

Conc'n sodium thiosulfate: 0.01 M

250 mL water sample

Not sure if we use:

Kh = [O2 (aq)]/P of O2 = 1.3 x 10-4 mol/L

    Determ'n of Chloride Ion Content

Silver nitrate volume used: 3 mL

Conc'n sodium thiosulfate: 0.05 M

25 mL water sample


So, for #1:

7 mL HCl x (0.05 mol/L) x (1 mL/1000 mL) = 0.0035mol

(0.0035mol/250 mL water) x (1000 mL/L) = 0.0014 mol/L

Is that correct at all? How do I get mol H+/L and ppm CaCO3?

[Borek]

As usual, start with the reaction equations.

[raccoon]

Perfect. Again, more than helpful website. Thanks so much!