KEY2CHEM

Molarity

Molarity is a concentration term defined as moles of solute per liter of solution. The greater the amount of solute particles in a given volume of solution, the higher the molarity (meaning, the more concentrated the solution). Since ionic compounds dissociate into ions when dissolved in aqueous solution (for example, $$\require{mhchem}\ce{NaCl -> Na+ + Cl-}$$), the number of ions corresponds to the number of solute particles.

Example 1.

Which $$100.0\text{ mL}$$ sample of aqueous solution contains the greatest number of solute particles?

A. $$1.0 \text{ M sucrose }(\require{mhchem}\ce{C12H22O11})$$

B. $$0.8\text{ M } \require{mhchem}\ce{NaCl}$$

C. $$1.2\text{ M glucose }(\require{mhchem}\ce{C6H12O6})$$

Solution

C. $$\require{mhchem}\ce{CH3OH}$$

The ionic compound will release 2 moles solute particles per mole of dissolved solute, so its concentration of solute particles is the greatest.

Example 2.

What is the molarity of the solution below? Assume$$\text{ each circle} = 0.10\text{ mol solute}$$.

A. $$0.007\text{ M}$$

B. $$0.07\text{ M}$$

C. $$7\text{ M}$$

Solution

C. $$7\text{ M}$$

$$\text{ Molarity} = \frac{\text{ mol solute}}{\text{ L solution}} = \frac{0.7\text{ mol}}{0.1000\text{ L}} = 7 \text{ M}$$

Example 3.

Molarity is defined as moles of _______ per liters of _________.

A. solute, solvent

B. solute, solution

C. solvent, solution

Solution

B. solute, solution

Molarity is defined as moles of solute per liters of solution.