A 780.0 g hard-water sample contains 276 mg Ca. What is the concentration in parts per million?

353 ppm

Explanation:

PPM also refers to parts per million, it represents a low concentration of a solution. It represents 0.001 gram or a milligram in 1000 mL, equivalent to 1 mg per liter

Given that;

276 mg of Ca in 780.0 g of water

1 ppm = 1 mg/L

780 g = 780 mL = 0.78 L

Therefore;

= 276 mg/ 0.78 L  

=  353.84mg/L

= 353 ppm