CHE1303 – Chemistry Lab Lab 4: Solution Preparation from Solid Risk Assessment Completed by: Vernon Mussgnug Date Risk Assessment Completed: 19-JUL-23 Objectives In Labs 4-6 you will: 1. demonstrate the ability to carry out calculations related to solution preparation. 2. accurately prepare molar solutions with specified volume and solute strength. 3. demonstrate the ability to use proper technique with the analytical balance, and volumetric glassware when preparing solutions (analytical transfers). 4. operate a Spec 20 to measure absorbance. 5. use a conductivity meter to measure conductivity. 6. use volumetric instruments in order to prepare analytical standards from stock solution (via dilution). 7. perform serial dilution. Introduction Solution preparation is a core skill that must be mastered by any good laboratory technologist. A laboratory technologist should be able to quickly and accurately prepare any volume of solution (large or small) at any concentration (large or small) that is required. This is a skill that must be mastered to find and keep employment in the field at the end of your studies. By definition a solution is a homogeneous mixture of two or more components. A solution is comprised of a solvent (the major component of a mixture), and at least one solute (the minor component of a mixture). The most common solvent used in the preparation of solutions is distilled water. Solution preparation involves mastering a core set of essential skills: • Ability to select and use correct volumetric tools (volumetric flasks, pipettes). • Accurately measure mass using analytical balance. CHE1303, ASET Department, Algonquin College Page 1 CHE1303 – Chemistry Lab • Ability to verify calibration of lab equipment (balances and volumetric tools). • Develop comfort level working with prefix multipliers (ex. mL, µg, nmol). • Understand and work with solution concentration unit descriptions (Molarity (M), mass %, ppm, ppb, etc). • Perform key chemistry calculations of molarity, moles, mass, volume, etc. Understanding Solution Descriptions In chemistry or biology, when we prepare solutions, we always label the solution with respect to the strength or concentration of the solute that is in that solution. Consider the following solutions: 1. 0.5 M NaOH 2. 5% (m/m) sucrose 3. 10 ppm NaCl 4. 10 g/L C6H12O6 Notice for these four solutions, the solvent is not mentioned (we assume in these cases that water is the solvent). For each of the solutions, the minor component in solution (the solute) is identified (NaOH, sucrose, NaCl, C6H12O6), as well as a numerical value and unit (M for molarity, mass % (% m/m), ppm (parts per million), grams per L) that describes the strength of the solute. Solution Preparation Requires Practice Students often find solution preparation to be a challenging task because confusion can arise over the various units (and there are many!) that are used to describe solution strength. Students may also struggle with the equations and mathematics involved in solution preparation. The best way to become proficient in solution preparation is to PRACTICE! CHE1303, ASET Department, Algonquin College Page 2 CHE1303 – Chemistry Lab Figure: Solution Concentration Terms (Source: Principles of Chemistry, Nivaldo and Tro) Molarity In today’s lab, we will focus on molarity to describe solute strength (concentration) in a solution. Molarity (M) Is the most common unit used in solutions for chemistry and biology. Molarity, represented by M, defines the moles of solute (mol) per litre (L) of solution. CHE1303, ASET Department, Algonquin College Page 3 CHE1303 – Chemistry Lab Materials/Reagents 25 mL, 50 mL, 100 mL volumetric flasks with stoppers 10 mL graduated pipette and pipette pump Transfer pipettes Beakers (approx. 150 mL) Top loading and analytical balance Weigh boats Spec 20 Scoopula Cuvettes Kim wipes Conductivity meter Table 4.1 – Laboratory Reagents Reagent Handling Personal Protective Equipment Disposal CuSO4 ●5H2O DO NOT dispose of down the drain Place waste into "Inorganic Waste” container located in the fumehood. NaCl Solutions may be disposed of down the drain. DI Water Solutions may be disposed of down the drain. 1 Personal Protective Equipment Safety Data Sheet 3 Applied Science and Environmental Technology 4 Refer to ASET Laboratory Safety Program Manual 2 CHE1303, ASET Department, Algonquin College Page 4 CHE1303 – Chemistry Lab Protocol Part I: Solution Preparation Worksheet 1. Complete the questions in the Solution Preparation Worksheet. We will complete some of these as a class and some in small groups. Part II: Preparing Solutions from Solid Reagent 1. Determine the mass of solute required. 2. Prepare each solution, recording in detail the method and glassware used. 3. For copper sulfate solutions, transfer about 5 mL into a cuvette and obtain the absorbance from the Spec 20 located at the front of the class. a. Ensure the wavelength is set to 690nm. b. Place the cuvette in the Spec 20. c. Close the lid. d. Record the absorbance. 4. For sodium chloride solutions, transfer the entire solution to a small beaker and obtain the conductivity using one of the provided conductivity meters. a. Turn on the meter. b. Rince with distilled water. c. Submerge in beaker containing your NaCl solution. d. Obtain reading. e. Rinse meter with water. Note: If the instrument reads”3999” your solution is overrange and you should record it as such. CHE1303, ASET Department, Algonquin College Page 5 CHE1303 – Chemistry Lab Part 1: Solution Preparation Worksheet Molarity (M, mol/L) For each problem: 1. Identify the solute/solvent. 2. Calculate the molar mass of the solute (use periodic table). 3. Identify the required concentration. 4. Identify the volume of solution required. 5. Complete the calculation. A) Calculate the mass of NaOH required to prepare 500 mL of a 0.250 M NaOH solution. B) Calculate the mass of NaCl required to prepare 10 L of a 1.5 mM NaCl solution. CHE1303, ASET Department, Algonquin College Page 6 CHE1303 – Chemistry Lab C) Calculate the mass of CuSO4●5H2O required to prepare 100 mL of a 0.1M solution. D) Calculate the mass of CuSO4●5H2O required to prepare 50 mL of a 0.1M solution. CHE1303, ASET Department, Algonquin College Page 7 CHE1303 – Chemistry Lab Results/Lab Report Part 2: Preparing Solutions from Solid Reagent Solution 1: 25 mL of 0.1 M CuSO4●5H2O Calculations: Method of Preparation: Measured absorbance at 690 nm: ___________________________ Solution 2: 50 mL of 0.025 M CuSO4●5H2O Calculations: Method of Preparation: Measured absorbance at 690 nm: ___________________________ CHE1303, ASET Department, Algonquin College Page 8 CHE1303 – Chemistry Lab Solution 3: 25 mL of 0.05 M NaCl Calculations: Method of Preparation: Measured conductivity: ________________________ Solution 4: 50 mL of 0.02 M NaCl Calculations: Method of Preparation: Measured conductivity: __________________________ CHE1303, ASET Department, Algonquin College Page 9 CHE1303 – Chemistry Lab Solution 5: 100 mL of 0.1 M NaCl Calculations: Method of Preparation: Measured conductivity: ________________________ Solution 6: 100 mL of 0.03 M NaCl Calculations: Method of Preparation: Measured conductivity: __________________ CHE1303, ASET Department, Algonquin College Page 10
