ppm = mass of the solute in mg / mass of solvent in kg
a)
0.0020 * 1000 = 2 mg
500.0 / 1000 = 0.5 kg
ppm = 2 / 0.5
= 4 ppm
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b)
0.25 * 1000 = 250 mg
850.0 / 1000 = 0.85 kg
ppm = 250 / 0.85
= 294.117 ppm
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hope this helps!
