Assume you have 1 L of seawater.
Step 1. Calculate the mass of the seawater
#"Mass of seawater" = 1000 color(red)(cancel(color(black)("mL seawater"))) × "1.025 g seawater"/(1 color(red)(cancel(color(black)("mL seawater")))) = "1025 g seawater"#
Step 2. Calculate the mass of #"NaCl"#
#"Mass of NaCl" = 1025 color(red)(cancel(color(black)("g seawater"))) × "3.50 g NaCl"/(100 color(red)(cancel(color(black)("g seawater")))) = "35.88 g NaCl"#
Step 3. Calculate the moles of #"NaCl"#
#"Moles of NaCl" = 35.88 color(red)(cancel(color(black)("g NaCl"))) × "1 mol NaCl"/(58.44 color(red)(cancel(color(black)("g NaCl")))) = "0.6139 mol NaCl"#
Step 4. Calculate the molarity of #"NaCl"#
#" Molarity" = "0.6139 mol"/"1 L" = "0.614 mol/L"#
