How do you calculate the mass of NaCl required to prepare 0.5 liters of a 2.5 molar solution of NaCl?
Here's how you can do that.
Your starting point here will be the definition of molarity.
As you know, molarity is defined as the number of moles of solute present in exactly
In your case, a
#0.5 color(red)(cancel(color(black)("L solution"))) * overbrace("2.5 moles NaCl"/(1color(red)(cancel(color(black)("L solution")))))^(color(blue)("required molarity")) = "1.25 moles NaCl"#
Now, to convert this to grams of sodium chloride, you must use the mass of
#1.25 color(red)(cancel(color(black)("moles NaCl"))) * "58.44 g"/(1color(red)(cancel(color(black)("mole NaCl")))) = color(darkgreen)(ul(color(black)("73 g")))#
I'll leave the answer rounded to two sig figs, but keep in mind that you only have one significant figure for the volume of the solution.