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How to Make 0.25 Molar Solutions

In chemistry, concentration such as molarity is the means to quantitatively describe the amount of a dissolved substance in the solution. Molarity defines the number of moles of a compound dissolved in 1 liter (L) of the solution. In particularly, the molarity of 0.25 indicates that each liter contains 0.25 moles of the substance. Making a solution of a given concentration is a common assignment during the laboratory work in chemistry or biology.

Things You'll Need

Calculator
Beaker
Glass rod

Instructions

- 1
  Divide the volume of the solution in milliliters (ml) by 1,000 to convert it to liters (L). For example, if you need to make 200 ml of the solution it corresponds to 200 ml / 1,000 = 0.2 L.
- 2
  Multiply molarity 0.25 by the volume of the solution to calculate the number of moles of the dissolved compound. In this example, 200 ml of the solution contain 0.25 x 0.2 = 0.05 moles.
- 3
  Calculate the molecular weight of the dissolved compound by multiplying the atomic weight of each element in the molecule by the number of the respective atoms and then adding up all products. For example, if the dissolved compound is sodium chloride, NaCl, its molecular weight is (23 x 1) + (35.5 x 1) = 58.5, where 23 and 35.5 are atomic weights of sodium (Na) and chlorine (Cl) taken from the Periodic Table of Elements.
- 4
  Multiply the molecular weight of the substance by the number of moles to compute the mass of the compound needed to make the solution. In this example, the mass of sodium chloride is 58.5 x 0.05 = 2.925 grams.
- 5
  Weigh the necessary amount of the substance (2.925 grams, in this example) on the scale.
- 6
  Add the compound weighed on the scale to a beaker that contains 200 ml, in this example, of water.
- 7
  Mix the solution in the beaker using a glass rod until the salt is completely dissolved.

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