Biochemical Calculations Biochemistry Department, Faculty of Science University of Tabuk

Molarity (M) Another way of expressing concentration is called molarity. Molarity is the number of moles of solute dissolved in one liter of solution. The units, therefore are moles per liter, specifically it's moles of solute per liter of solution.

Molarity (M) Molarity = moles of solute liter of solution Molarity is abbreviated as M or M. M = wt X 1000 MW X Vml

Normality (N) Used to compare solutions on the basis of concentration of specific ions or the amount of charge that the ions have. No. of equivalent weight per liter of solution. Eq.wt = molecular weight (MW) Valance

Normality (N) Normality is abbreviated to (N). N = wt X 1000 Eq.wt X Vml

Problems To Solve: 1- How many grams of glucose are needed to make 100 ml of a 0.6 mol/l solution? (MW glucose = 180). 2- How can you prepare 0.1 M NaOH solution? 3- Describe the preparation of 5 L of 0.1 M Na2CO3 (MW = 105.99) from the primary standard solid.

Percent Concentration (%) 1-Volume percent: It is usually used when the solution is made by mixing two liquids. The use of % is a common way of expressing the concentration of a solution.

Percent Concentration (%) The % can be calculated using volumes as well as weights, or even both together. Volume percent (v/v) = volume of solute X 100 volume of solution

Example: Rubbing alcohol is generally 70% by volume isopropyl alcohol. This means that 100 ml of solution contains 70 ml of isopropyl alcohol. That also means that a liter (or 1000 ml) of this solution has 700 ml of isopropyl alcohol plus enough water to bring it up a total volume of 1 liter, or 1000 ml.

Percent Concentration (%) 2- Weight percent: is expressing the concentration of a solution in weight percent (or mass percent). Weight percent (w/w) = weight of solute X 100 weight of solution

Question What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?

Analysis To get weight percent we need the weight of the solute and the total weight of the solution. Determine total weight of solution: 4.6 g+ 145.2 g = 149.8 g

solution Calculate percent: Weight % glucose = 4.6 g glucose x 100 149.8 g solution = 3.1% glucose.

Percent Concentration (%) 3- Weight- volume percent: Another variation on % concentration is weight/volume percent or mass/volume percent. This variation measures the amount of solute in grams but measures the amount of solution in milliliters.

Percent Concentration (%) An example would be a 5 %( w/v) NaCl solution. It contains 5 g of NaCl for every 100 mL of solution. Weight-Volume percent (w/v) =   weight of solute  X 100 volume of solution