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 to your right; identified as A and B.
- Preparation of sweet solution A
a) We want to add juice crystals to obtain a concentration of 25 g/L in 100 mL of solution. This mass is designated as m crystals.
b) Place the empty weighing boat on the balance and make sure the balance is at zero by pressing the tare button.
c) Adding the crystals : Use a spatula to add juice crystals into the weighing boat until the mass of juice crystals reaches the desired mass.
- Preparation of the solution
a) Measure 50 mL of distilled water using the 50 mL graduated cylinder.
b) Then pour the water into a 100 mL volumetric flask.
c) Transfer the juice crystals from the weighing boat to the volumetric flask using a funnel.
d) Dissolving the crystals : Put the stopper on the volumetric flask and shake with a circular motion until the juice crystals are completely dissolved.
e) Volume adjustment : Top up with distilled water until precisely reaching the final volume of 100 mL.
- Finalizing the solution
a) Put the stopper on the volumetric flask and gently mix the solution.
b) Pour the solution from the volumetric flask (solution A) into the beaker identified A.
- Comparison
a) Visually compare solution A with prepared reference solutions.
Note: Make sure the solutions are in front of a black card, in order to clearly distinguish changes in coloration.
- Preparation of sweet solution B
a) We want to add juice crystals to obtain a concentration of 25 g/L in 100 mL of solution. This mass is designated as m crystals.
b) Place the empty weighing boat on the balance and make sure the balance is at zero by pressing the tare button.
c) Adding the crystals : Use a spatula to add juice crystals into the weighing boat until the mass of juice crystals reaches the desired mass.
- Preparation of the solution
a) Measure 50 mL of distilled water using the 50 mL graduated cylinder.
b) Then pour the water into a 100 mL volumetric flask.
c) Transfer the juice crystals from the weighing boat to the volumetric flask using a funnel.
d) Dissolving the crystals : Put the stopper on the volumetric flask and shake with a circular motion until the juice crystals are completely dissolved.
e) Volume adjustment : Top up with distilled water until precisely reaching the final volume of 100 mL.
- Finalizing the solution
a) Put the stopper on the volumetric flask and gently mix the solution.
b) Pour the solution from the volumetric flask (solution B) into the beaker identified B.
- Comparison
a) Visually compare solution B with prepared reference solutions.
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)