Molarity and Normality ```Name: Cinda Ross Status: student Age: 16 Location: N/A Country: N/A Date: Around 1999 ``` Question: How do you calculate 1 N of NaOH? The question I am trying to figure out is Describe how to prepare a 1N and a 0.1 N solution of NaOH. Thank you for your help Replies: First of all,you need to understand what molarity and normality are. Molarity refers to the number of molecules of a substance in a solution; a 1M solution contains 1 mole (6.02 x 10^23 molecules or particles) of the substance in 1 liter of solution. Normality refers to compounds that have multiple chemical functionalities, such as sulfuric acid, H2SO4: a 1M solution of H2SO4 will contain only one mole of H2SO4 in 1 liter of solution, but if you titrate the solution with base, you will find that it contains two moles of acid. This is because a single molecule of H2SO4 contains two acidic protons. Thus, a 1M solution of H2SO4 will be 2N. Now, for your specific question: NaOH contains only one significant chemical functionality, which is the basic hydroxide, OH-. So, for NaOH solutions, molarity and normality will be the same thing. So, a 1.0 N solution of NaOH in water is also a 1.0 M solution of NaOH in water, and a 0.1 N solution of NaOH in water is a 0.1 M solution of NaOH in water. How do you make these? The first thing you need to know is the mass of a mole of NaOH. This is just its molecular weight: 40.0 g/mol. (That's what a molecular weight means: the mass in grams of one mole of the substance.) So, to make a 1.0 M (= 1.0 N) solution of NaOH in water, you will want to weigh out 40.0 grams of NaOH, dissolve it in about 0.8 liters of water, and then add water to the solution to take the total volume up to exactly 1.0 liters. You would do the same thing to make a 0.1 M (= 0.1 N) solution: weigh out 0.1 mole of NaOH (= 4.0 g), dissolve it in water, and add enough water to make the total volume equal to exactly 1 liter. If you don't want exactly on liter of these solutions, then you need to change the amounts by the same factor: if you need 0.5 liters of a 1.0 M solution, you use 0.5 moles of the substance and enough solvent to make the solution volume exactly 0.5 liters. Richard Barrans Argonne National Laboratory The 'Normality' of a solution is the 'Molarity' multiplied by the number of equivalents per mole (the number moles of hydroxide or hydronium ions per mole) for the molecule. For NaOH there is one equivalent per mole (one mole of hydroxide ions release per mole of NaOH dissolved in water) so the 'Normality' is the 'Molarity' times 1 eq / mole. The 'Molarity' of a solution is the number of moles of solute in one liter of solution. To make a 1 N solution of NaOH would be the same as making a 1 Molar solution, (1 eq / mole) X (1 mole / liter). To make one liter of a 1 Molar solution, weigh out one mole of NaOH and slowly, with constant stirring and while monitoring the temperature of the solution (by touching the outside of the beaker), add it to about 750 ml of deionized water in a 1 liter beaker. (If the beaker gets warm to the touch, stop adding the NaOH and continue stirring until all the solid is dissolved and you are sure the solution is not overheating.) When all the NaOH has been added, bring the total volume up to 1.0 liter of solution by adding more deionized water. To make a 0.1 N solution of NaOH you could follow the above procedure using 1/10 as much NaOH or you can dilute the above solution by a factor of 10. To do this, measure 100 ml of solution in a graduated cylinder. Slowly, and while stirring, add this to about 750 ml of deionized water in a 1 liter beaker. (ALWAYS add the more concentrated solution to the less concentrated solution!) Again, monitor the temperature of the resulting solution. When all the solution from the graduated cylinder has been added, rinse the graduated cylinder several times with 10 or 20 ml of deionized water and finally, bring the total volume of the solution up to 1 liter. For more accuracy you could use a 1 liter graduated cylinder instead of a beaker. Smaller quantities of solution can be prepared by using the appropriate ratios of NaOH and total solution. Greg Bradburn Click here to return to the Chemistry Archives

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