Question

the weight of kcl required to prepare 100 ml 7.8ppm potassium ion solution is
k=39 cl=35.5

Answer 1

1 ppm = 1 mg/L

\(\rho=\dfrac{m}{V}\rightarrow 7.8~mg/L=\dfrac{m}{0.1~L}\)

So you need 0.78 mg of potassium ion, factor in the mass of \(Cl^-\) to get the mass of KCl.