In order to prepare a standard 1.00 m solution of oxalic acid from h2c2o4 · 2h2o (126.07 g/mol), 7.564 g of oxalic acid dihydrate should be dissolved in

60.0 ml of distilled water. First determine how many moles of oxalic acid you have by dividing the mass used by the molar mass. So: 7.564 g / 126.07 g/mol = 0.059998414 mol Since you want the molarity of the solution to be 1.00 M and molarity is defined as moles per liter, you want just as many liters of solution as you have moles. So to within 3 significant figures, you want 60.0 ml of solution. You may be tempted to measure out 60.0 ml of water and dissolve the oxalic acid directly, but a much better technique is to dissolve the oxalic acid in a smaller quantity of water such as 55 ml and after the acid is fully dissolved, slowly add more water to the solution until the volume of the solution reaches 60.0 ml. The reason for this is two fold. First, molarity is defined as the number of moles per volume of solution, not volume of solvent. Second, the volume of water changes when solids are dissolved. For instance, when dissolving table salt in water, the volume will first decrease by up to 2.5%, and then increase afterwards as more salt is dissolved. So it's best to dissolve the desired substance in a smaller volume of solvent and after any contraction or expansion has occurred, slowly add more solvent until the desired final volume is reached.