Calculating Molar Solutions

Dear Professor Cram:

How many grams of NaCl would you dissolve in water to make a 0.5 M NaCl solution with 500 mL final volume? What are the steps in finding the answer?

Anneka L.

Thank you for using and for your chemistry question.

This requires a multi-step process to determine the answer. First, we need to note that the "M" in a 0.5 M NaCl solution means there are 0.5 moles of NaCl per 1 liter of solution. Since there is in fact only 500mL of solution (i.e., half a liter), you really have only 0.25 moles of NaCl (half of 0.5).

Next, you can use our Mole Conversions Cramlet™ to find how many grams it takes to produce this solution. Using your Periodic Table, you can determine the molar mass of one mole of NaCl by adding the atomic masses of the two elements:

  • 22.98977 + 35.453 = 58.44277 grams/mole

Now multiply this by the number of moles of NaCl you have (0.25, as we found above) to find the number of grams of NaCl we needed to start with:

  • (58.44277 grams/mole)(.25 moles) = 14.611 grams

I hope this helps. Let us know if you need anything else.

Good studying,

Professor Cram

P.S. Need more practice on this? Try our Bottomless Worksheet of Mole Conversions