Question

Since soap and detergent action is hindered by hard water, laundry formulations usually include water softeners-called builders-designed to remove hard water ions (especially Ca2+ and Mg2+) from the water. A common builder used in North America is sodium carbonate. Suppose that the hard water used to do laundry contains 75 ppm CaCO3 and 55 ppm MgCO3 (by mass).

What mass of Na2CO3 is required to remove 90.0% of these ions from 10.0 L of laundry water?

Answers on other posts that have been incorrect: 1.3g, 1.4g, .668g