First, convert the mass of sulfate from grams to milligrams:
125g = 125000mg
Next, need to find the total mass of the solution in milligrams:
1kg = 1000000mg
Now calculate the concentration of sulfate in ppm:
Concentration (ppm) = (mass of solute / mass of solution) x 10^6
Concentration (ppm) = (125000mg / 1000000mg) x 10^6
Concentration (ppm) = 125
Therefore, the concentration of sulfate in water is 125 ppm.