What is the #"ppm"# concentration of salt in a solution composed of #3.5*g# of salt, and #96.5*g# water?

By definition...#"1 ppm"=(1*mg)/(1*L)#...and we call this ratio #"parts per million"# because there are #1000xx1000*mg-=10^6*mg# IN ONE LITRE VOLUME of water.

...most of the time we can ignore the density because the mass of the solute is miniscule...here we assume that the #96.5*g# of solvent water expresses a volume of #96.5*mL# in the SOLUTION...

And so we take the quotient....

#(3.5*gxx10^3*mg*g^-1)/(96.5*mLxx10^-3*L*mL^-1)=36,269*mg*L^-1-=36,269*"ppm"#.

Do you think this #"ppm"# quotation of concentration is appropriate here?

Note that I have been asked by several posters whether this dissolution reaction of sodium chloride in water represents a physical or chemical reaction. My own very conservative notions of the definition of chemical reaction, INSISTS that such a process, while REVERSIBLE, is CHEMICAL. Chemical change is characterized by the formation of new substances and the making and breaking of chemical bonds. The dissolution reaction certainly qualifies...

#NaCl(s) stackrel(H_2O)rarrNa^+ + Cl^-#

Where the ion is the aquated complex, i.e. #Na^+ -=[Na(OH_2)_6]^+#..