The mass percent of #"NaCl"# is 75 %. Its mole percent is 79.3 mole %.
The formula for mass percent is
#color(blue)(|bar(ul(color(white)(a/a)"Mass percent" = "mass of component"/"total mass" × 100 %color(white)(a/a)|)))" "#
#"Total mass" = "600 kg + 200 kg" = "800 kg"#
∴ #"Mass % of NaCl" = (600 color(red)(cancel(color(black)("g"))))/(800 color(red)(cancel(color(black)("g")))) × 100 % = "75 % (m/m) NaCl"#
The formula for mole percent is
#color(blue)(|bar(ul(color(white)(a/a)"Mole percent" = "moles of component"/"total moles" × 100 %color(white)(a/a)|)))" "#
#"Moles of NaCl" = 600 color(red)(cancel(color(black)("kg NaCl"))) × "1 kmol NaCl"/(58.44 color(red)(cancel(color(black)("kg NaCl")))) = "10.27 kmol NaCl"#
#"Moles of KCl" = 200 color(red)(cancel(color(black)("kg KCl"))) × "1 kmol KCl"/(74.55 color(red)(cancel(color(black)("kg KCl")))) = "2.683 kmol KCl"#
#"Total moles = 10.27 kmol + 2.683 kmol = 12.95 kmol"#
∴ #"Mole percent of NaCl" = (10.27 color(red)(cancel(color(black)("kmol"))))/(12.95 color(red)(cancel(color(black)("kmol")))) × 100 % = "79.3 mole %"#
