Molarity Chem 11 : Molarity A solution is a mixture of a solute (commonly a solid) dissolved in a solvent (commonly water). The solute is dissolved and the solvent does the dissolving. Molarity is a measure of how strong or weak a solution is. Molarity is defined as the moles of solute dissolved per volume of solution. Commonly it is moles of solute per 1 L of solution. Page

Making a Molar Solution You are asked to make 500 mL of a .25 M solution of NaCl. You will need a 500 mL volumetric flask and balance.

Step 1 : Determine Mass of NaCl Needed .25 M NaCl is .25 mol NaCl / L of solution, a conversion factor. We start with the quantity we must have = 500.0 mL or .5000 L 500.0 mL (.25 mol NaCl)(58.443 g NaCl) = 7.3054 g NaCl needed (1000 mL) ( 1 mol NaCl) Weigh out 7.31 g on a balance.

Step 2 : Put the 7.31 g of NaCl into a clean beaker that has a volume one half to 2/3 the required 500 ml volume. Add distilled water and mix. Pour the salt water from the beaker to the volumetric flask Rinse the stirring rod with distilled water and the beaker with distilled water several times.

Step 3 : Fill the volumetric flask up to the calibration line with washings from the beaker/stirring rod and extra distilled water.

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