Precipitates of NaHCO3

[Slimymadness]

Hi all,

been trying to mix my own calcium and alkalinity additive but the NaHCO3 seems to have some precipitation. I am afraid these are the unused carbonate thus i want to make sure everything is dissolved in the concentrate.

Now i know that NaHCO3 + H2O -> CO2 + NaOH + H2O. Thus the white precipitation is just NaOH. Am i able to solve this by adding small amount of CH3COOH (vinegar)?

The equation would be CH3COOH + NaOH = CH3COONa + H2O, which i believe will be without precipitation.

Am i correct in this equation?

[limsc]

Hi all,

been trying to mix my own calcium and alkalinity additive but the NaHCO3 seems to have some precipitation. I am afraid these are the unused carbonate thus i want to make sure everything is dissolved in the concentrate.

Now i know that NaHCO3 + H2O -> CO2 + NaOH + H2O. Thus the white precipitation is just NaOH. Am i able to solve this by adding small amount of CH3COOH (vinegar)?

The equation would be CH3COOH + NaOH = CH3COONa + H2O, which i believe will be without precipitation.

Am i correct in this equation?

Hi bro, not too well versed in chemistry.

But I believe that the precipitate could be some form of impurities.

Even if it is NaOH as suggested, personally, I won't add vinegar just to get the small amount of precipitate into solution.

I would just discard the precipitate or pour everything into tank, but definitely not adding vinegar. My 2cents.

[Slimymadness]

I did a read up and indeed adding vinegar might not be

good due to possible bacteria build up and ultimately leading to algae. It just bugs me if a reaction does not equates! Hahahah

[Slimymadness]

OK for those who are experiencing the same problem as me, the vinegar can actually be added into the mixture to aid higher dissolution.

The acetate acid will lower ph but still able to maintain carbonate hardness of solution. For those who are afraid that the ph will shoot up with NaHCO3, might want to consider this at your own risk.

I am experimenting the equation and hopefully things will turn out well. I will document findings in this thread for all to know more!

Vinegar And Limewater To Boost Limewater Potency

Another potentially useful attribute of vinegar is that it can be used to help dissolve additional solid lime into limewater. It does this by reducing the hydroxide concentration in the limewater:

10. CH3OOH � CH3COO- + H+

The H+ combines with OH- in the limewater:

11. H+ + OH- � H2O

The actual dissolution of Ca(OH)2 is limited by the multiplication product of the calcium and hydroxide concentrations in the limewater as shown below:

12. Ca(OH)2 � Ca++ + 2OH-

13. [Ca++] x [OH-] x [OH-] � 5.5 x 10-6

where [Ca++] is the concentration of calcium (in moles/L) and [OH-] is the concentration of hydroxide (in moles/L). Consequently, if you reduce the concentration of OH- via equations (10) and (11), then more Ca(OH)2 can dissolve into solution and still meet the equation (13) requirement.

This would seem like a concern, however, since losing OH- might reduce the amount of alkalinity delivered by the limewater. Luckily, this is not the case. While the OH- is temporarily reduced by the acetic acid in the vinegar, when bacteria metabolize the acetate, they release it back to the water:

14. CH3COO- + 2O2 � 2CO2 + H2O + OH-

Consequently, additional solid lime can be dissolved into limewater using vinegar.

How much can be used? The more vinegar that is used, the lower the pH of both the limewater and the aquarium will be. One reasonable point to shoot for is to add about the same amount of total CO2 via the vinegar as is needed by the lime to form HCO3-. This balance is roughly matched by using three level teaspoons of solid lime per gallon of limewater, and 45 ml of vinegar per gallon of limewater. For those aquarists choosing to use vinegar in limewater, these values are a suitable starting point. Note that the pH of the limewater is still quite high, so slow dosing is usually required.

more reading can be done here.