Physical Pharmacy Lab2.pdf

Practical Physical Fundamentals of Pharmacy-I Pharmaceutical Calculations For 2nd year students Concentration Expressions, Preparation and Dilution of Solutions and Mixtures Lab 2: Objectives...

Practical Physical Fundamentals of Pharmacy-I Pharmaceutical Calculations For 2nd year students Concentration Expressions, Preparation and Dilution of Solutions and Mixtures Lab 2: Objectives Define solutions and learn how to prepare them Define concentration, and learn the methods used to express concentration Learn how to dilute prepared solutions Practical experiments: Preparation of solutions/mixtures in different concentrations Definitions Solute: The substance which is dissolved, or has gone into solution (typically a solid). Solvent: The substance which does the dissolving (typically a liquid, such as water or alcohol). Must be greater than 50% of the solution. Solution: is uniform homogeneous mixture of two or more substances. The individual substances may be present in varying amounts.  Solution preparation steps 1. Weigh an appropriate amount of solute and place it in a beaker. 2. Add enough solvent and stir to dissolve 3. Transfer the solution to a volumetric flask. Rinse the beaker with more solvent and transfer to the volumetric flask. 4. Add more solvent to the volumetric flask carefully until an accurately calibrated final volume is reached. 5. Stopper your volumetric flask, shake it then put a suitable label. Solution preparation steps Concentration is expression referring to the amount (volume or mass) of solute that is present in a given amount (volume or mass) of solution. Expressing Concentrations 1. Qualitative methods Concentrated solution Diluted solution Darker in color Lighter in color Stronger in taste and odor Milder in taste and odor More solute Less solute Less solvent More solvent Expressing Concentrations 2. Quantitative methods There are many ways to express concentrations of solute in a solution, the most common being: A. Molar concentration B. Normal concentration C. Percentage concentrations Expressing Concentrations 2. Quantitative methods A. Molarity (M): is the number of moles of solute dissolved in one liter (1000 mL) of solution. Molarity, therefore, is a ratio between moles of solute and liters of solution. Typical units of molarity are mol/L (or M) o To determine molarity, the molecular weight or molar mass of the solute is needed. So: Or: Example: Prepare (50 ml) of (0.5 M) sodium chloride solution (M.wt NaCl is 58.5 gm/mol) Answer: using the equation Weight =??? 0.5 58.5 50 Weigh and dissolve 1.46 gm NaCl in about 40 ml of DW in beaker, stir until dissolve, transfer to a volumetric flask and complete the volume by DW up to 50 ml. Expressing Concentrations 2. Quantitative methods B. Normality (N): is the number of gram equivalent weights of solute dissolved in one liter of solution. Typical units of molarity are mol/L or N. So: Or: the equivalent weight is defined Or: as the molecular weight of the acid or base divided by the number of replaceable hydrogen or hydroxyl ions  Example: Prepare (50 ml) of (0.5 N) sodium carbonate solution (M.wt Na2CO3 is 106 gm/mol). Answer: using the equation Weight =??? 0.5 50 Weigh and dissolve 1.325 gm Na2CO3 in about 40 ml of DW in beaker, stir until dissolve, transfer to a volumetric flask and complete the volume by DW up to 50 ml.  ExpressingConcentrations 2. Quantitative methods If % concentration type is not C. Percent (%) Concentration Expressions mentioned, assume it as % (w/v) Percent weight by volume Percent volume by volume Percent weight by weight (w/v) (v/v) (w/w) Gram of solute present in Milliliters of solute present Gram of solute present in 100 ml of solution in 100 ml of solution 100 gm of solution/mixture Used in preparing solutions of Used in preparing solutions of Used in preparing of mixtures solid solute in liquids liquid solute in liquids of solid solute in solids (as in Example: ointments, creams, etc.), or Example: gases in liquids, or 0.9% sodium chloride 5% v/v methanol solution is concentrated commercial solution is a solution a solution containing 5 ml aq. reagents (HCl is sold as a containing 0.9 g of sodium of methanol dissolved in 37% w/w solution, which chloride dissolved in sufficient water to make means that the reagent sufficient water to make 100 100 ml of solution contains 37 g of HCl per 100 g ml of solution of solution). To determine the % of solutions, we use the following equations:  Dilution and Concentration To prepare a dilute solution from a concentrated solution: stock solution is a strong A suitable amount of stock solution is pipetted into a solutions from which clean volumetric flask and solvent added to the mark weaker solutions are made  Dilution Law C1V1 = C2V2 Or C1W1= C2W2 C1 = initial concentration expressed as a percentage (stock solution or mixture) C2 = final, or desired, concentration expressed as a percentage (final solution or mixture) V1 or W1= initial volume (or weight) from stock to be used V2 or W2 = final, or desired volume or quantity of solution or mixture to be prepared Example: How can you prepare 250 ml of 4% w/v glucose solution from 20% w/v glucose solution using DW as a solvent ? Answer: Measure 5 ml of 20% glucose solution C1V1 = C2V2 and transfer it to a volumetric flask, 20%x V1 = 4% x 250 then add enough DW up to the mark V1 = 5 ml of 250 ml. Shake an put a suitable label. Experimental work Prepare the following solution using volumetric flask _____________________________________________ 1-100 ml of 0.5 M NaCl 2-100 ml of 2N NaCl 3-100 ml of 0.1N Na₂CO₃ 4-100 ml of 0.1 M Na₂CO₃ 5-100 ml of 2% w/v NaCl 6-100 ml of 5% v/v Alcohol