Chemistry Lecture 3: Preparation of Solutions PDF

Chemistry Lecture 3: Areej A. M. Osman MSc. Pharm. Chem. U of K 2020 BSc. Pharmacy U of K 2014 Learning outcomes By the end of this lecture the student should be able to: Describe the preparation of solutions Prepare solutions from solid samples and liquid samples Define dilution Appl...

Chemistry Lecture 3: Areej A. M. Osman MSc. Pharm. Chem. U of K 2020 BSc. Pharmacy U of K 2014 Learning outcomes By the end of this lecture the student should be able to: Describe the preparation of solutions Prepare solutions from solid samples and liquid samples Define dilution Apply the dilution process in preparing solutions Calculate the concentration of diluted solutions 10/14/2024 Areej A. M. Osman 2 Preparing solutions Preparing solutions is a fundamental skill in chemistry, involving the accurate measurement and mixing of solutes and solvents. Solution is a mixture of solute and solvent. There must be a specific amount of solute in a specific amount of solution (concentration). 10/14/2024 Areej A. M. Osman 2 Preparing solutions Steps for preparing solutions: First: calculations 1- Determine the concentration needed and the volume needed. 2- Find the amount of solute must be taken. 3- Find the volume of solvent must be added. Second: preparation 1- Weigh the solid or measure the liquid solute 2- Dissolve or mix the solute with the solvent. 10/14/2024 Areej A. M. Osman 2 Basic Concepts Molarity (M): Molarity is defined as the number of moles of solute per liter of solution. Formula: M = n ÷ V Percent Solutions: These can be expressed in three ways: Mass percent: grams of solute per 100 grams of solution. Volume percent: milliliters of solute per 100 mL of solution. Mass/Volume percent (w/v%): grams of solute per 100 mL of solution. Dilution: It is the process of adding more solvent to a solution. When a concentrated solution is diluted, the number of moles remains constant while the volume increases. n1 = n2 M1V1 = M2V2 M1, V1 are the molarity and volume of the concentrated solution M2, V2 are the molarity and volume of the diluted solution. Examples How can you prepare a 500 mL solution of NaCl 0.9% w/v? Calculation: Volume of solution = 500 mL Percent = mass of solute ÷ volume of solution x 100 Mass of solute = percent x volume of solution ÷ 100 Mass of solute = 0.9 x 500 ÷ 100 = 4.5 grams Volume of solution (add water up to 500 mL). 10/14/2024 Areej A. M. Osman 2 Examples Preparation: Weigh 4.5 grams of NaCl using sensitive balance. Accurately transfer the weight to a 500 ml volumetric flask. Add a suitable volume of water to dissolve the powder and shake the volumetric flask to aid dissolution. Complete the volume to the mark with water. Close the volumetric flask and mix carefully. 10/14/2024 Areej A. M. Osman 2 Examples Prepare 2 Liters of a solution of NaOH (0.5 M). Calculations: Volume needed = 2 L Mass of NaOH = M x Mwt x Volume (L) Mass of NaOH = 0.5 x 40 x 2 = 40 grams Preparation: Weigh 40 g of NaOH, transfer to 2 L volumetric flask and make up the volume to 2 L. 10/14/2024 Areej A. M. Osman 2 Examples To prepare 800 mL (0.8 L) of a 2 M sodium chloride (NaCl) solution: Calculate grams needed: Mwt of NaCl = 58.45 g/mol Mass = M x Mwt x Volume (L) = 2 x 58.45 x 0.8 = 93.52 grams Dissolve 93.52 g in about 400 mL of distilled water, then add more water until reaching a total volume of 800 mL. 10/14/2024 Areej A. M. Osman 2 Examples To prepare 100 mL (0.1 L) of a 1.0 M hydrochloric acid (HCl) from a concentrated solution (12.1 M): Use the dilution formula: M1 = 12.1 , V1 = ? M2 = 1 , V2 = 0.1L M1V1 = M2V2, V1 = M2V2/M1 V1 = 1 x 0.1 / 12.1 = 0.00826 L = 8.26 mL Add 8.26 mL of concentrated HCl to about 50 mL of distilled water, then dilute to a final volume of 100 mL. 10/14/2024 Areej A. M. Osman 2 Examples Prepare a standard solution 500 mL of Na2CO3 (0.1M) Na=23, C = 12 , O = 16 Answer = 5.3 grams in 500 mL 10/14/2024 Areej A. M. Osman 2 Examples A 3500 mL solution of potassium permanganate (0.08 M) is needed. How can you prepare it? Mwt = 158 Answer = 44.24 grams in 3500 mL 10/14/2024 Areej A. M. Osman 2  Any question? 10/14/2024 Areej A. M. Osman 2