Question #11d9c

The problem doesn't provide you with the number of moles of sodium chloride, #"NaCl"#, because it wants you to convert the given mass to moles by using the compound's molar mass.

A compound's molar mass tells you the mass of one mole of that compound. This means that if you know the molar mass, you can use it a conversion factor to go from moles to grams or vice versa.

In this case, sodium chloride has a molar mass of #"58.44 g mol"^(-1)#. This means that one mole of sodium chloride has a mass of #"58.44 g"#.

Use this value to convert the mass of the sample to moles

#58color(red)(cancel(color(black)("g"))) * overbrace("1 mole NaCl"/(58.44color(red)(cancel(color(black)("g")))))^(color(purple)("molar mass of NaCl")) = "0.9925 moles NaCl"#

Now, to find the molarity of the solution, simply divide the number of moles by the volume of the solution.

#color(blue)(|bar(ul(color(white)(a/a)c = n_"solute"/V_"solution"color(white)(a/a)|)))#

In your case, you will have

#c = "0.9925 moles"/"1.0 L" = color(green)(|bar(ul(color(white)(a/a)"0.99 M"color(white)(a/a)|)))#

The answer is rounded to two sig figs.