What is the Molarity

Question

Hi I have 100ml of water and 4g of sodium acetate what is the molarity?

Answer 1

Molarity is the solution strength or concentration. It's like how strong your kool aid is, watered down or super strong.

Molarity is defined as the number of moles of (whatever) per liter of solution. So, in your case, to calculate the molarity (M), first calculate the number of moles of sodium acetate you have. then divide that by the amount of water in liters.

Acetate is C₂H₃O₂^- (notice the -1 charge) so Sodium Acetate is NaC₂H₃O₂ (because sodium is a +1 charge). To calculate the number of moles, first calculate the molar mass by adding each of atomic mass times the number of atoms (Na: 1 x 22.99, C: 2 x 12.011, H: 3 x 1.008, O: 2 x 15.999) to get 82.034 g/mol. Now, take the number of grams (4) and divide it by the molar mass (82.034) to get 0.04876 moles.

Finally, take the number of moles (0.04876) divided by the liters of solution [0.100 - because liters = (100 milliliters)/(1000 milliliters/liter)] so the molarity is 0.4876M. But, since there is only 1 significant figure given, round the answer to 0.5M

Answer 2

Molality is moles of solute (sodium acetate) per liter of solution. Assuming the solute does not add to the volume, then you have 100 ml of solution, which is 0.1 liters. The molar mass of sodium acetate is 82 g/mole.

Moles sodium acetate = 4g x 1 mole/82 g = 0.0488 moles

Molarity = 0.0488 moles/0.1 liters = 0.488 M = 0.5 M (1sig fig)