Why can't I make a certain molarity of NaOH solution by weighing solid NaOH and adding the right amount of water? How would I make it?
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Who says you can't do that? That is exactly how it is done. One problem however. NaOH solid is what is known as a hydroscopic substance. That means that the solid form absorbs water from the air. So when you are weighing out NaOH to create a solution with a certain molarity, there will always be a certain amount of error. Your solution will be WEAKER than you expect. To overcome this you must titrate your NaOH solution against an acid for which you KNOW the concentration.