This laboratory session is designed to introduce participants to fundamental chemistry techniques through the preparation of a sweet solution with a specific concentration of 25 g/l in a final volume of 100 ml. The focus is on teaching the essential skills of calculating the necessary quantities to achieve a desired concentration, accurately weighing solids using laboratory scales, and mastering the methods for dissolving and diluting solutes in solvents. The main goal is to guide participants through the process of preparing a 25 g/l sugar solution in a 100 ml volume, emphasizing the calculation of solute mass, precise weighing, solution preparation, and dilution techniques. This exercise aims to underline the importance of accuracy and methodology in chemical solution preparation
Educational Goals
- Chemical Calculation Proficiency: Participants will learn how to calculate the mass of solute needed to prepare a solution of a specific concentration, enhancing their understanding of molarity and solution preparation.
- Precision Weighing Skills: The session aims to develop skills in using a balance for precise weighing of solutes, highlighting the importance of accuracy in the mass measurement of substances.
- Solution Preparation Techniques: Introduces participants to the techniques for dissolving solutes effectively in solvents to achieve a uniform solution, focusing on the initial dissolution in a lesser volume and subsequent dilution to the final desired volume.
- Dilution and Mixing Methods: Emphasizes the importance of thorough mixing and accurate volume adjustment to ensure a homogeneous solution, teaching participants the practical aspects of solution dilution.
- Application of Solution Chemistry Principles: Through hands-on practice, participants will apply fundamental principles of solution chemistry, gaining insights into the preparation and characterization of chemical solutions.
- This laboratory session not only imparts the basics of solution preparation and concentration calculation but also offers invaluable hands-on experience. By preparing a sugar solution with specific concentration, participants will gain a comprehensive understanding of the meticulous nature of chemical solution preparation, from the initial calculations to the final dilution and mixing. This practical application of chemistry principles is essential for studies and research in the field, fostering a deeper appreciation for the precision and methodology required in scientific experimentation.
Protocol
Two 100 mL beakers are on your right, identified as A and B.
1. Preparation of solution A
a) Calculation of the necessary mass of crystals: Calculate the mass of juice crystals needed to achieve a concentration of 25 g/L in 100 mL of solution. This mass is designated by m_crystals.
b) Preparation of the Balance: Ensure the balance scale is zeroed before beginning.
c) Weighing the Boat: Weigh the empty boat on the balance scale and note its mass (m_boat).
d) Adjustment of the Sliders: Set the balance sliders to correspond to the sum of the mass of the boat and the required mass of sugar crystals (m_boat + m_crystals).
e) Adding the Crystals: Use a spatula to add sugar crystals into the boat until equilibrium is achieved (the needle aligned with zero).
2. Preparation of the solution:
a) Pour about 50 mL of water into a 100 mL volumetric flask.
b) Transfer the sugar crystals from the boat to the volumetric flask using a funnel.
c) Dissolving the Sugar: Place the stopper on the volumetric flask and shake in a circular motion until the sugar crystals are completely dissolved.
d) Adjustment of Volume: Top up with water to precisely reach the final volume of 100 mL. Use a dropper for accurate adjustments.
3. Finalization of the solution:
a) Place the stopper on the volumetric flask and gently mix the solution.
b) Pour Solution A into the beaker labeled A.
4. Comparison and cleaning:
a) Visually compare Solution A with prepared control solutions.
b) Rinse the volumetric flask after use to prepare it for future experiments.
c) Repeat the experiment, with beaker B, to prepare a 5% w/v solution with a final volume of 100 mL
Anticipated Outcomes
The first solution (Solution A) should have a concentration of 25 g/L, achieved by dissolving 2.5 g of sugar crystals in 100 mL of water.
The second solution (Solution B) should have a 5% m/v concentration, which means 5 g of sugar crystals are dissolved in enough water to make 100 mL of the final solution.
Participants should be able to visually compare Solution A with control solutions to understand concentration differences.
Observing the dissolving process, noting how sugar crystals integrate into the water to form a homogeneous solution.
Lessons Learned:
Precision in measurement: Understanding the importance of accurately measuring mass and volume to achieve desired concentrations.
Proper use of equipment: Gaining familiarity with laboratory equipment like balances, volumetric flasks, and pipettes, and learning their correct usage.
Solution preparation: Learning the step-by-step process of dissolving solids in liquids to create solutions with specific concentrations.
Chemistry principles:
Molarity and percent solutions: Understanding these two ways of expressing concentration – molarity (g/L in this case) and percent mass/volume (m/v) – and how to calculate the amount of solute needed for a desired concentration.
Dissolution: Observing the process by which a solid (sugar crystals) dissolves in a solvent (water) to form a solution, which is a physical change.
Mixtures: Recognizing that solutions are homogeneous mixtures where the solute is evenly distributed within the solvent. This experience is a hands-on way to learn about solution preparation, a fundamental skill in chemistry, while also emphasizing the importance of methodical and safe laboratory practices.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to solution preparation and simple measurements.
- Activities: Observing the process of preparing a sugar solution, basic weighing and mixing, simple calculations, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of solution preparation techniques and measurements.
- Activities: Calculating solute mass, weighing sugar, preparing and mixing solutions, observing the importance of precision and thorough mixing, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced proficiency in solution preparation and precise analytical skills.
- Activities: Calculating the exact mass of solute needed, using precision balances, preparing and diluting solutions, ensuring accurate volume adjustments, detailed recording and analysis of the process, adhering to advanced safety protocols.
Laboratory essentials
Instruments
Beaker (50ml, 100ml, 250ml & 1000ml)
Dropper
Erlenmeyer (25 ml)
Funnel
Gaugeated flask (100ml)
Glass Rod
Graduated Cylinders (10ml & 50ml)
Spatulas
Test tubes
Triple beam scale
Products
Juice crystals (powder)