How do you calculate Molarity and Normality?

Molarity and NormalityMolarity (M) is defined as the number of moles of solute per liter of solution.

One of the most commonly used concentration units among chemists is the molarity concentration term. It's the handiest measure for most aqueous solutions, since we are usually interested in the number of moles of the solute, but we work with volumes.

The molarity of a solution is calculated by taking the moles of solute and dividing by the liters of solution.

SolutionofLiters

SoluteofMolesMolarity =

A one molar solution is prepared by adding one mole of solute to one liter of solution

Molarity is probably easiest to explain with examples.

Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well mixed, there was exactly 1.00 liter of solution.

What would be the molarity of this solution?

The answer is 1.00 mol/L. Notice that both the units of mol and L remain. Neither cancels.A replacement for mol/L is often used, it is a capital M, so if you write 1.00 M for the answer, then that is correct.

Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's the molarity?

The answer is 2.00 M.Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.022 x 1023 units.

Example #3 - What is the molarity when 0.75 mol is dissolved in 2.50 L of solution?

The answer is 0.300 M.

Now, let's change from using moles to grams. This is much more common. After all, chemists use balances to weigh things and balances give grams, NOT moles.

Example #4 - Suppose you had 58.44 grams of NaCl and you dissolved it in exactly 2.00 L of solution. What would be the molarity of the solution?The solution to this problem involves two steps, which will eventually be merged into one equation.Step One: convert grams to moles.Step Two: divide moles by liters to get molarity.In the above problem, 58.44 grams/mol is the molecular weight of NaCl. (For you technical types, I know it actually is a formula weight, but I'm glossing over the difference for the time being. Remember, this is a nuclear tutorial.)Dividing 58.44 grams by 58.44 grams/mol gives 1.00 mol.Then, dividing 1.00 mol by 2.00 L gives 0.500 mol/L (or 0.500 M). Sometimes, a book will write out the word "molar," as in 0.500-molar.

NormalityThe concentration of a solution can be stated by telling the amount of solute in equivalents rather than moles. This is called normality, which is the number of equivalents of solute per liter of solution, so the formula for normality is:

SolutionofLiter

sEquivalentNormality =

To show normality, you most commonly would find the number of H+ or OH- ions available to make a neutralization. HNO3 has one H+ ion available. Since one mole of HNO3 can donate one mole of H+ ions, it is a 1 N solution.Normality can also be found from molarity and equivalents per mole. Just use this simple formula: N = nM Where N is the normality, n is the number of equivalents per mole, and M is the molarity.

There is a very simple relationship between normality and molarity:N = n x M (where n is an integer)

For an acid solution, n is the number of H+ ions provided by a formula unit of acid.Example: A 3 M H2SO4 solution is the same as a 6 N H2SO4 solution.

For a basic solution, n is the number of OH- ions provided by a formula unit of base.Example: A 1 M Ca(OH)2 solution is the same as a 2N Ca(OH)2

solution.Remember! The normality of a solution is NEVER less than the molarity.

How do you determine the normal concentration of a 0.136 M solution ofPhosphoric acid (assumes all of the hydrogens are to be neutralized)?

For acids involved in neutralization reactions, the number of hydrogen ions produced per mole of acid gives the number of equivalents per mole. If all of the hydrogens in phosphoric acid are neutralized, there are three equivalents per mole. Normality is defined as equivalents per liter.So you have a simple unit conversion to do:

0.136 mol H3PO4/L

3 equiv. = 1 mol

? equiv./L [3]

Therefore 0.136 M H3PO4 = 0.408 N H3PO4

Note that it's possible to have 1 equiv./mol or 2 equiv./mol for other neutralization reactions involving phosphoric acid if not all of the hydrogens get neutralized.

Question - How do you calculate 1 N of NaOH?

Describe how to prepare a 1N and a 0.1 N solution of NaOH. 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.

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 Nsolution 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 one 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.

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.

Copyright: WBF