mass of the solvent (H2O) in kg
D = m / V
1.02 = m / 125
m = 1.02 x 125
m = 127.5 g of H2O
127.5 / 1000 => 0.1275 kg
mass of solute in mg:
1000 x ( 1.86 x 10⁻⁵ ) = 0.0186 mg
ppm = mass of solute in mg / mass of solvent in kg
ppm = 0.0186 / 0.1275
= 0.1458 ppm
hope this helps!
