DIY KH/Alkalinity Test Kit

[okeydokey]

KH Formulation
A reagent
0.04g Bromocresol Green
0.008g Methyl Red
90g DI-Water
1.6g 0.1M NaOH

B reagent
10.12g 1N HCl standard solution
428.7g DI-Water

Procedure
1. Add 4ml of sea water in the vial.
2. Shake th A reagent a few times and add 4 drops in the vial (one drop about 0.032ml)
3. Using 1 ml syringe and add dropwise with 1 ml syringe the B reagent to the water. Continue until the color changes from blue/green to grange/pink color.
4. Read the KH table

Reference
Ind. Eng. Chem. Anal. Ed., 1941, 13 (7), pp 466"“470



KH/Alkalinity Table
Reading in ml, KH value in dKH
0.00, 15.7
0.02, 15.3
0.04, 15.0
0.06, 14.7
0.08, 14.4
0.10, 14.1
0.12, 13.7
0.14, 13.4
0.16, 13.1
0.18, 12.8
0.20, 12.5
0.22, 12.1
0.24, 11.8
0.26, 11.5
0.28, 11.2
0.30, 10.9
0.32, 10.5
0.34, 10.2
0.36, 9.9
0.38, 9.6
0.40, 9.3
0.42, 8.9
0.44, 8.6
0.46, 8.3
0.48, 8.0
0.50, 7.7
0.52, 7.3
0.54, 7.0
0.56, 6.7
0.58, 6.4
0.60, 6.1
0.62, 5.7
0.64, 5.4
0.66, 5.1
0.68, 4.8
0.70, 4.5
0.72, 4.2
0.74, 3.8
0.76, 3.5
0.78, 3.2
0.80, 2.9
0.82, 2.6
0.84, 2.2
0.86, 1.9
0.88, 1.6
0.90, 1.3
0.92, 1.0
0.94, 0.6
0.96, 0.3
0.98, 0

 

[okeydokey]

Compared with commercially products




A and B reagents



Color change before and after titration

 

[okeydokey]

KH table

 

[dartier]

I am not sure of the OP is still on Reef Central, but if they or anyone can comment on the purpose of including the Sodium Hydroxide into the Reagent A in the above recipe I would be most interested.

My best guess is that the PH indicators are weak acids and the Sodium Hydroxide is meant to buffer the indicators.

Dennis

 

[der_wille_zur_macht]

I bet you'd have a much better shot at an answer in the chemistry forum vs here.

 

[dartier]

I agree. I will post a link in the chemistry forum back to this thread.

Dennis

 

[orcafood]

I think dartier is exactly on the money. The dye is a weak acid, many are. Perhaps it has to do with the dye stability.

 

[orcafood]

Methyl red is a weak acid due to a carboxyl group on it. The base is probably added to neutralize the pH change.

 

[SFish]

Nice work

Takes me back to chemistry class