This laboratory session is divided into two significant parts, focusing on the preparation of a concentrated solution of potassium permanganate and its subsequent dilution to achieve a desired concentration. The aim is to impart the skills needed to prepare solutions of specific concentrations through dissolution and then adjust those concentrations via dilution, showcasing fundamental techniques in solution chemistry.
- Preparation of a Concentrated Solution:
To prepare a potassium permanganate solution with a concentration of 80 g/l through the process of dissolution. - Dilution of the Concentrated Solution:
To prepare 250 ml of a diluted potassium permanganate solution with a target concentration of 17.5 g/l.
Educational Goals
- Solution Preparation Techniques: Participants will learn the step-by-step process of dissolving potassium permanganate to create a solution with a specific concentration, enhancing their understanding of solute-solvent interactions.
- Concentration Adjustment via Dilution: The session will demonstrate how to adjust the concentration of a solution by dilution, highlighting the mathematical and practical aspects of dilution techniques.
- Precision in Measurement: Emphasizes the importance of precise measurement and manipulation of measuring instruments in the preparation of chemical solutions, fostering accuracy and attention to detail.
- Understanding of Dissolution and Dilution: Participants will gain insights into the critical roles of dissolution and dilution in achieving desired solution concentrations, understanding the underlying principles of these processes.
Through this laboratory experience, participants will acquire foundational chemistry skills in the preparation and adjustment of solution concentrations. By engaging in the precise preparation of a potassium permanganate solution and its careful dilution, participants will learn to accurately manipulate measuring instruments and appreciate the significance of dissolution and dilution in creating solutions of specific concentrations. This session offers practical application of chemistry principles essential for studies and research in the field, reinforcing the meticulous nature required in scientific experimentation.
Protocol
1. Dissolution
a) Weighing the solute: Use an electronic scale to weigh approximately 8 g of potassium permanganate.
b) Transfer to a volumetric flask: Pour the weighed potassium permanganate into a 100 mL volumetric flask.
c) Adding distilled water: Measure 50 mL of distilled water with a graduated cylinder and pour this water into the flask containing the potassium permanganate.
d) Place a stopper on the flask.
e) Shake the solution to dissolve the solute, then remove the stopper.
f) Volume adjustment: Fill up the volume in the flask to the calibration mark (100 mL) with distilled water.
g) Final mixing: Replace the stopper and shake the flask well by inversion to homogenize the solution.
h) Concentration verification: Compare the color of your solution to that of reference samples to confirm the concentration.
2. Dilution
i) Measure the stock solution: Measure 54.7 mL of the stock potassium permanganate solution (prepared earlier) using a 70 mL graduated cylinder.
j) Transfer to a new volumetric flask: Pour this measured amount into an empty 250 mL volumetric flask.
k) Fill up the flask to 250 mL with distilled water.
l) Place a stopper on the flask and mix well by inversion to homogenize the solution.
m) Concentration verification: Compare the color of the diluted solution to that of reference samples to check the final concentration.
Anticipated Outcomes
- The first steps create a solution of potassium permanganates concentrated at 80g/L (8g/100mL).
- Using 54.7mL of a homogenous solution represents 4.376g of potassium permanganates, in 250mL of liquid.
- The new concentration is therefore 17.51g/L (4.376g/250mL).
- The control solutions of KMnO4 have the following concentrations: #1=17.5g/L (0.11M); #2 = 35g/L (0.22M); #3 = 62.5g/L (0.39M); #4 = 70g/L (0.44M); #5 = 80g/L (0.5M); #6 = 86g/L (0.54M).
- Solution preparation: By dissolving 8 g of potassium permanganate in 100 mL of water, a solution with a concentration of 80 g/L is obtained. This should visually match the color of control solution #5.
- Dilution: The dilution process reduces the concentration from 80 g/L to approximately 17.5 g/L when 54.7 mL of the original solution is diluted to 250 mL. This diluted solution should visually match the color of control solution #1.
Lessons Learned:
- Accuracy and precision: The importance of accurate measurements when weighing the solute and measuring volumes during solution preparation and dilution to achieve the desired concentration.
- Understanding dilution: The dilution process demonstrates how the concentration of a solution changes when the volume of the solvent is increased while the amount of solute remains constant.
- Solution concentration: Learning to calculate and understand different concentrations of solutions and their importance in various chemical applications.
- Observation skills: Developing the ability to compare the color intensity of solutions to determine their concentration, an essential skill in qualitative analysis.
Chemistry Principles:
- Molarity and concentration: The experiment illustrates how to calculate molarity and concentration, fundamental concepts in solution chemistry. Molarity is the number of moles of solute per liter of solution, and concentration is generally the amount of solute dissolved in each volume of solvent.
- Dissolution: This process demonstrates how solutes dissolve in solvents to form solutions, depending on the nature of the solute and solvent, temperature, and other factors.
- Law of conservation of mass: Even though the solution undergoes dilution, the total amount of solute (potassium permanganate) remains constant, illustrating the law of conservation of mass.
- Colorimetric analysis: Using color intensity to determine concentration is an application of colorimetry, a technique often used in chemistry to quantify the concentration of colored compounds in solution.
Through this protocol, students gain hands-on experience with the practical applications of theoretical concepts in solution chemistry, enhancing their understanding and skills in the laboratory.
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 dissolving potassium permanganate, simple demonstrations of dilution, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of solution preparation and concentration adjustment.
- Activities: Preparing a concentrated potassium permanganate solution, performing simple dilution calculations, measuring and adjusting solution concentrations, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced proficiency in solution preparation and precise analytical skills.
- Activities: Accurately preparing an 80 g/l potassium permanganate solution, performing precise dilution to achieve a 17.5 g/l concentration in 250 ml, using advanced measurement techniques, detailed recording and analysis of the process, adhering to advanced safety protocols.
Laboratory essentials
Instruments
Electronic Scale
Gaugeated flask (100ml & 250 ml)
Graduated cylinder (50ml & 70ml)
Spatula
Products
Potassium permanganate (powder)