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How to calculate the molar concentration


How to calculate the molar concentration</a>

What is the molar concentration? This is a quantity that indicates how many moles of a substance are in one liter of solution.

The method for finding the molar mass depends on the conditions of the problem.

You will need

  • - accurate scales-
  • - dimensional capacitance-
  • - salt solubility table-
  • - Periodic table.



For example, you are asked to determine what the molar concentration of the solution is 71 grams of sodium sulfate contained in 450 milliliters of the solution.


First of all, write the exact formula of sulphateSodium: Na2SO4. Write out the atomic weights of all the elements that make up the molecule of this substance: Na-23, S-32, O -16. The total atomic weights are as follows: Na-46, S-32, O-64. Consequently, the molecular weight of sodium sulfate is 142.


Dividing the actual weight of sodium sulfate by molar, find out how many moles of this salt is contained in the solution. This is done as follows: 71/142 = 0.5 mol.


If 71 grams of sodium sulfate were contained in1000 ml of solution, it would be 0.5 molar solution. But you have 450 milliliters, therefore, you need to do the recalculation: 0.5 * 1000/450 = 1,111 or roundly 1.1 molar solution. The problem is solved.


Well, and if you were given (say, on a laboratoryA chemistry workshop) an unknown amount of a substance, for example sodium chloride, a container with an unknown amount of water, and proposed to determine the molar Concentration Solution that has not yet been obtained? And here there is nothing difficult.


Thoroughly weigh sodium chloride, preferably on accurate (laboratory, ideally - analytical) scales. Write down or remember the result.


Pour water into a measuring container (laboratory graduated glass or graduated cylinder), set its volume, and, accordingly, the mass, since the water density is equal to 1.


Make sure, using the salt solubility table, that all sodium chloride will dissolve at this room temperature in such an amount of water.


Dissolve the salt in water and again, using a measuring container, set the exact volume of the solution obtained. Calculate the molar Concentration Solution according to the formula: m * 1000 / (M * V), where m is the actual mass of sodium chloride, M is its molar mass (about 58.5), and V is the volume of the solution in milliliters.


For example, the mass of sodium chloride was 12 grams, the volume of the solution was 270 ml.12000 / (58.5 * 270) = 0.7597. (Approximately 0.76 molar solution).

How to calculate the molar concentration Was last modified: June 21st, 2017 By Douxiasd
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