How do I calculate how much dry powder to add to water to make an X% solution

[jaisol]

I'm trying to figure out how you make a solution that is X% strong, from a dry powder like common salt
eg
I want to make a 5% salt(NaCl) solution.
Do I
a) add 5g of NaCl to 95g of water
b) make a saturated solution of salt water and add 5g of that to 95g of water.
c) ??

 

[dw1305]

Hi all,

I want to make a 5% salt(NaCl) solution.
Do I
a) add 5g of NaCl to 95g of water

Yes. If you want more accuracy (and I'm guessing you don't) take 50g NaCl and add RO water until the solution weighs 1000 grams (1 kg). You could also call this 5% NaCl solution 50 ppt (parts per thousand) NaCl.

To work out the ppm of sodium (Na+) and chloride (Cl-) in your solution you need to know the RMM of NaCl and the RAM of Na and Cl.

Which is: RMM NaCl = 58.4 and that is RAM Na (23) + RAM Cl (35.45). 23 / 58.4 = 39% Na and 35.45 / 58.4 = 61% Cl

I'll just do the sodium (Na) - 50 x 0.39 = 19.5 so you have 19.5g of Na. We know that ppm and mg / L are equivalent, so you have 19.5 x 10^3 milligrams per litre and 19500 ppm Na.

This is about 1.5 times as salty as seawater, so there are approximately 3.5 grams of NaCl in 100g of sea water (35 ppt).

cheers Darrel