Question

How to calculate the mass of solid sodium hydroxide needed to prepare 200 ml of a 0.040m solution. if one pellet of sodium hydroxide weighs 0.170g, how many pellets should be dissolved?

Answer 1

0.496 g of NaOH required 3 pellets. First, determine the molar mass of NaOH. Atomic weight sodium = 22.989769 Atomic weight hydrogen = 22.989769 Atomic weight oxygen = 15.999 Molar mass NaOH = 22.989769 + 22.989769 + 15.999 = 61.978538 g/mol Now determine how many moles of NaOH we need. Multiply desired volume by desired molarity. So 0.200 l * 0.040 mol/l= 0.008 mol To get the mass, then multiply by the molar mass, so 0.008 mol * 61.978538 g/mol = 0.495828304 g Since we have the NaOH in pellet form, divide the desired mass by the mass of each pellet. So 0.495828304 g / 0.170 g/pellet = 2.916637082 pellets You'll need 3 pellets. To get closer to the desired molarity, I would recommend increasing the amount of solution being prepared if you can accurately measure the larger volume.