Question

What is the concentration, in millimolar, of a 1 mg/ml solution of NaCl (molecular weight = 58 Da)?

Answer 1

Explanation:

Relation between molarity and molar mass is as follows.

             Molarity = $\frac{mass}{\text{molar mass}} \times \frac{1000}{V (in ml)}$

It is given that mass is 1 mg/ml which is also equal to $10^{-3}$ g.

Molecular mass = 58 Da = 58 g/mol

Volume = 1 ml

Therefore, calculate molarity as follows.

         Molarity = $\frac{mass}{\text{molar mass}} \times \frac{1000}{V (in ml)}$

                       = $\frac{10^{-3}g}{58 g/mol} \times \frac{1000}{1 ml}$  

                       = 0.0172 molar

It is known that 1 molar equals 1000 millimolar.

So,               0.0172 molar = $0.0172 molar \times \frac{1000 millimolar}{1 molar}$

                                          = 17.2 millimolar

Thus, we can conclude that the concentration of given solution is 17.2 millimolar.