Question

Water softeners often replace calcium ions in hard water with sodium ions. since sodium compounds are soluble, the presence of sodium ions in water does not result in the white, scaly residues caused by calcium ions. however, calcium is more beneficial to human health than sodium. calcium is a necessary part of the human diet, while high levels of sodium intake are linked to increases in blood pressure. the food and drug administration (fda) recommends that adults ingest less than 2.4 g of sodium per day. part a how many liters of softened water, containing a sodium concentration of 0.035 % sodium by mass, have to be consumed to exceed the fda recommendation? (assume a density of 1.0 g/ml for water.)

Answer 1

% mass Na = (g Na / g H2O) x 100 
g Na = (% mass Na)(g H2O) / 100 = (5.2 x 10^-4 g Na / g H2O) 

2.4 g Na x (1 g H2O / 5.2 x 10^-4 g Na) = 4600 g Na 

4600 g Na x (1 mL H2O / 1 g H2O) = 4600 mL H2O = 4.6 L H2O which is a little more than a gallon