[Q] piper diagram help

[emmas]

i have to plot points on a piper diagram,

i have the cation and anions concentration in mg l-1

and to plot the points i have to convert these concentrations into percentages.

to plot on the diagram,

been trying for ages, do i have to convert to mol then to percentage ??

this is the part i'm having trouble with,

it says to get the mols i divide the mass 14.3 mg l-1 by 40.1 relative ionic mass = 0.36 mol l-1

then i have to change the 0.36 mol l-1 into percentage to plot

if i'm barking up the wrong tree could someone please point me the right way

many thanks

em.