The picture above is showing you how to correctly make a 1.00 molar saline solution, 1.00 M NaCl(aq).
First, think about what molarity is, and what it means. Molarity is the most common unit for
concentration in chemistry. Molarity is equal to the amount of solute in moles, divided by the total
volume of the solution in Liters… so M = mol of solute/L of solution. The units are important, and it is
important that you understand what they mean. In this case, moles of solute is the amount of NaCl that
you are placing in the water solvent. What does a mole actually mean? It is the amount 6.02x1023 of
whatever you are talking about. So for example, when you find the molar mass of NaCl, and you look up
the mass of sodium and chlorine on your periodic table and add those two values together, you should
end up with the same mass stated above, 58.44 g. What this really means is that it takes 6.02x1023
sodium ions and 6.02x1023 chloride ions to weigh 58.44 g, or it takes 1.00 mole of NaCl to weigh 58.44 g,
or NaCl has a molar mass of 58.44 g/mol. Okay, now for the volume. Be careful, the volume here is the
volume of solution in liters… that means that it’s the combined volume of the salt solute and the water
solvent. This is why the picture above shows the salt first being dissolved in the water, before it is filled
to the 1.00 L mark. Okay but why did we place 58.44 g NaCl in a volumetric flask (always create
solutions in a volumetric flask) and once dissolved, fill it to 1.00 L? This picture is showing you how to
make 1.00 L of a 1.00 M NaCl solution. If we rearrange the formula above to solve for moles, we will see
that moles of NaCl = Molarity x volume = 1.00 M x 1.00 L = 1.00 mol NaCl and we know that 1.00 mol
NaCl weighs 58.44 g NaCl.
See if you can write out a procedure, with values and units, to create 0.500 L of 3.00 M NaCl. Hint: you
would have to use a 500 mL volumetric flask.