Question

Determine which of the following is:

a) the most concentrated, and

b) the most dilute.

(i) 0.45 mol L-1 NaCl

(ii) 4.2 % m/v NaCl

(iii) 41.6g NaCl L-1

(iv) 39950 ppm NaCl

Answer 1

(i) 0.45 mol L-1 NaCl = 0.45 M

(ii) 4.2 % m/v NaCl

means 4.2 g of NaCl present in 100 mL of the solution

           42 g of NaCl present in 1000 mL = 1 L of solution

          So number of moles of NaCl , n =mass/molar mass

                                                        = 42 g / 58.5 (g/mol)

                                                       = 0.718 mol

So concentration = 0.718 mol/1L = 0.718 M

(iii) 41.6g NaCl L-1

Number of moles of NaCl , n = Mass / molar mass

                                         = 41.6 g / 58.5(g/mol)

                                         = 0.711 moles

So concentration of NaCl = 0.711 mol / 1 L = 0.711 M

(iv) 39950 ppm NaCl

means 39950 mg/L NaCl

So number of moles of NaCl , n= mass / molar mass

                                              = (39950mg*10^-3g/mg) / 58.5 (g/mol)

                                              = 0.683 mol

So concentration is 0.683 mol/L = 0.683 M

So (i) is less concentrated

and (ii) is more concentrated