Find the Molarity

Question

Find the molarity of 3.76 g NaCl in 900 mL of water

 

.Find the molarity of 1.15 g KF in 150 mL of water

Answer 1

Molarity is determined as number of moles of a substance (or solute) dissolved in 1 L (1000 ml) of solution. The formula for molarity is

The first step is to determine the molar mass of the solute. By looking on the periodic table you can see that Na has an atomic mass of 22.990 g/mol. Cl has an atomic mass of 35.453 g/mol.

So NaCl would be 22.990 + 35.453 = 58.443 g/mol

Next convert the g to moles.

3.76 g NaCl x 1 mol NaCl = 0.064 moles NaCl

58.443 g NaCl

Now use the molarity formula to get your answer. Convert 900 mL to L first.

900 mL x 1 L = 0.9 L

1000 mL

0.064 moles NaCl = 0.071 Molarity solution

0.9 L water

Follow these same steps to solve your second equation, using the molar mass for KF in 150 mL of water.