how to make a 7 dkH NaHCO3 reference solution ?

[Charles Silva]

Hello all

I intent to make a 7 dkH reference using a lab grade sodium bicarbonate (NaHCO3) to cross check my Salifert Alk kit.
Can you kindly review my calculations ?

converting 7 dkH to meq/L
7/ 2.8 = 2.5 meq/L

molar mass sodium bicarbonate = 84.01 grams
1 millimole = 0.08401 grams

2.5 * 0.08401 = 0.21 grams
dissolved in 1 L of RO water = 7 dkH

Should I put first the NaHCO3 then the water to 1 L mark or 1 L of water then the powder or doesn't matter as the mass is insignificant ?

Here I have this jewelry calibration reference (https://www.amazon.com/211-1g-10mg-...ion-Jewelry/dp/B01LCPLMBC#feature-bullets-btf)
so I think if I take 50 times more NaHCO3 I will get 10.5 grams (that will be easier to cross check with my weight calibration reference) I will end up with a solution with 350 dkH /L.

My question is (if my calculations are right) if I take 10 mL of this 350 dkH solution and and dilute in 500 mL of RO water will I get my 7 dkH reference solution ?

or 8 mL of 350 dkH solution diluted in 500 mL of RO water 8.75 dkH ?

regards
Charles Silva
Rio de Janeiro - Brazil

 

[Randy Holmes-Farley Verified Community Expert]

Technically, it is 1 L final volume.

If you make 350 dKH and add 10 m L of this to 490 mL of 0 ppm TDS RO/DI, you will get to 7 dKH.