Question

What is the molarity of a 2.0 L sodium hydroxide solution containing 10.0 grams of solute? 0.80 M 0.13 M 5.0 M 0.25 M

Answer 1

Explanation:

Molarity is defined as the number of moles divided by one liter of solution.

Mathematically,      Molarity = $\frac{\text{no. of moles}}{\text{volume in liter}}$

As it is given that volume is 2.0 L and mass is 10.0 grams. Therefore, first we will calculate the number of moles as follows.

           No. of moles = $\frac{mass}{\text{molar mass of NaOH}}$

                                 = $\frac{10.0}{40 g/mol}$            (molar mass of NaOH = 40 g/mol)

                                 = 0.25 mol

Hence, calculate the molarity of the solution as follows.

            Molarity = $\frac{\text{no. of moles}}{\text{volume in liter}}$  

                           = $\frac{0.25}{2.0 L}$

                           = 0.125 M

Thus, we can conclude that molarity of given solution is 0.125 M.  

Answer 2

Molarity is moles of solute per litre of solvent. We're given mass of solute, but can convert to moles using the molar mass of NaOH (40 g/mol). There are 10 g / 40 g/mol = 0.25 mol of NaOH in the solution.

M = 0.25 mol / 2.0 L = 0.125M

The second answer (0.13M) is the correct one.