Question

How could I prepare a 1 ppm solution of ammonium chloride in water?

Answer 1

You could dissolve 4 mg of ammonium chloride in 1 L of water.

Explanation:

1 ppm means 1 g of solute in 10⁶ g of solution.

When working with aqueous solutions, it is common to assume that the density of such a dilute solution is 1.00 g/mL.

Therefore, it is common to equate 1 mL of solution with 1 g of solution.

Assume that you want to make 1 L of solution. Then

`1000 cancel("mL soln") × (1 cancel("g soln"))/(1 cancel("mL soln")) × "4 g NH₄Cl"/(10⁶ cancel("g soln")) = "0.004 g NH₄Cl"= "4 mg NH₄Cl"`

You could dissolve 4 mg of NH₄Cl in 1 L of water in a volumetric flask.

It is difficult to measure 4 mg of NH₄Cl accurately.

It would be easier to dissolve 400 mg of NH₄ in 1 L. This would give you a concentration of 400 ppm.

Then you could dilute 10 mL of this solution to 1 L in another volumetric flask to get a final solution with a concentration of 4 ppm.