Total Alkalinity and Sodium Bicarbonate

[easttn]

Well diving deeper into more chemistry. Im looking around at what total alkalinity actually measures and find this page which kind of explains it to me.
http://www.advancedaquarist.com/2002/2/chemistry

1) So when using Sodium Bicarbonate, the bicarbonate is the only part that puts TA in the water, right or wrong?

2) If it is the only part to be concerned about then I should be able to calculate the bicarbonate percentage from the sodium bicarbonate percentage like this:

Example is using a product that has 95% Sodium Bicarbonate.

Molar mass of Sodium Bicarbonate (NaHCO3) = 84.007 g/mol
Molar mass of Bicarbonate (HCO3) = 61.0168 g/mol

61.0168 / 84.007 = 0.7263
0.7263 x 0.95 = 0.6899 ( The Sodium Bicarbonate product is 68.99% Bicarbonate )

3) And furthermore calculate lbs to raise the TA 1ppm in 1,000 gallons like this:

0.008333333 / 0.6899 = 0.012079 LBS of the Sodium Bicarbonate product.

 

[JamesW]

Total Alkalinity is reported in units of calcium carbonate. Adding 1 mole of sodium bicarbonate is equivalent to adding 0.5 moles of calcium carbonate (because calcium carbonate can accept 2 hydrogen ions vs. only 1 for sodium bicarbonate). Adding 84.007 grams of sodium bicarbonate is equivalent to adding 0.5(100.09 grams) of calcium carbonate.

Therefore, adding 100 pounds of sodium bicarbonate is equivalent to adding 59.57 lbs of calcium carbonate.

For example, if you had 1,000,000 pounds of water (about 119,904 gallons) and you added 100 lbs of sodium bicarbonate, you would raise the TA by 59.57.

 

[easttn]

Took me a minute to wrap my head around it but I got it. Thanks.

If CH is measured by units of calcium carbonate and TA is measured by units of calcium carbonate, then how come adding calcium chloride doesnt raise TA and adding sodium bicarbonate doesnt raise CH?

 

[JamesW]

The units of measure are somewhat arbitrarily chosen and not necessarily related to what's being measured.

For example, chlorine is reported in units of chlorine gas and borates are reported in units of boron. It's just a convention that was chosen and somehow become the accepted standard.

 

[easttn]

Oh ok. Thanks again.

 

[onBalance]

Easttn, you are correct that it is the bicarbonate from sodium bicarbonate that adds alkalinity, and not the sodium portion. Soda ash contains "carbonate" that adds alkalinity and twice the equivalent (as James indicated) as does bicarbonate. Hydroxide from caustic soda (sodium hydroxide) also adds alkalinity to the water. James' figures are correct. "Water chemistry" is somewhat different and has a different of rules to follow, so it is confusing that these products are compared to and expressed as "Calcium carbonate" equivalents.

The reason that calcium chloride doesn't raise the TA is because no bicarbonate, carbonate, or hydroxide is being added with the chemical. Sodium bicarbonate doesn't raise CH because no "calcium" is being added.

 

[easttn]

If bleach has a small percentage of sodium hydroxide (lye) in it, then adding bleach would have to add some TA. How much does it add? I suppose its very little.

Is everything expressed as Calcium carbonate in water chemistry such as cya, borates, salt, ph and chlorine? Does it just compare the particle to Calcium carbonate or something?

 

[JamesW]

Test.......equivalent
chlorine ......chlorine gas
TA.................calcium carbonate
calcium. ........calcium carbonate
cya..............cyanuric acid
salt. ...........sodium chloride
borates. ......boron

 

[easttn]

Oh I forgot you already told me chlorine gas and boron.
Thanks guys.

 

[JasonLion]

The amount of lye in most brands of bleach is quite low, low enough to be ignored for most purposes. However occasionally you run into an off brand where there is more lye and it does start to make a difference.

 

[chem geek]

If bleach has a small percentage of sodium hydroxide (lye) in it, then adding bleach would have to add some TA. How much does it add? I suppose its very little.

For high quality 8.25% bleach with a pH of 11.8, it takes roughly 115 ppm FC to raise the TA by 1 ppm from the excess lye.
For high quality 12.5% chlorinating liquid with 0.25% excess lye and a pH of 12.5, it takes roughly 42 ppm FC to raise the TA by 1 ppm from the excess lye.
For low quality 12.5% chlorinating liquid with 0.8% excess lye and a a pH of 13.0, it takes roughly 10 ppm FC to raise the TA by 1 ppm from the excess lye.

So even with low quality product, the rise in TA is pretty negligible though you may start to notice more of a rise in pH. However, generally the rise in pH from carbon dioxide outgassing dominates over the rise from the excess lye.

 

[easttn]

Ok. Good to know. Learn something everyday.