Easy Chemistry for All: Solution Concentration Part Two

Introduction

• Encouragement to subscribe, share, and benefit from the Easy Chemistry for All channel.
• Continuation of Module 13: Mixtures and Solutions from The Inspired Mystery book.
• Focus on solution concentration, particularly molality and mole fraction.

Learning Outcomes

• Solve concentration problems, perform calculations with moles, and express results in various units (mole per liter, molarity, mole per kilogram, molality, parts per million, percent by mass, percent by volume).
• Practically prepare solutions with specific concentrations by dissolving solids or diluting concentrated solutions.

Key Concepts

Review of Part One

• Concentration explained in terms of percent and moles.
• Definitions of concentration and molarity.

New Topics in Part Two

• Molality: Number of moles of solute per kilogram of solvent.
• Mole Fraction: Ratio of moles of a solute or solvent to total moles in the solution.

Calculating Molar Solutions

• Example: Prepare a 1L solution of NaCl with 0.5 Molar concentration.
  • Calculate moles using molarity and volume.
  • Determine mass: Multiply moles by molar mass (29.25g NaCl).
  • Add measured NaCl to a 1L volumetric flask, dissolve, and fill to the mark with water.

Correct Technique for Solution Preparation

• Add correct amount of water to solute, not vice versa to avoid exceeding desired volume.

Dilution of Molar Solutions

• Diluting Stock Solutions: Lower concentration by adding water, keeping moles of solute constant.
• Equation: M1V1 = M2V2.

Example: Dilute NaCl Solution

• Reduce 4 molar NaCl to 2 molar NaCl by adding water.

Mathematical Methods for Concentration

Molarity

• Moles of solute per liter of solution.

Molality

• Used when temperature affects molarity (volume changes).
• Example: Calculate molality for CaCl2 in water.
  • Convert mass to kilograms and apply formula.

Mole Fractions

• Express concentration using moles of solute and solvent.
• Example: Calculate mole fractions in HCl and water solution.

True or False Review

• Diluted Solution: Contains less solute than concentrated.
• Concentration: Described relatively and quantitatively (True).
• Molarity Definition: Moles per liter of solution, not solvent (False).
• Molality: Useful when temperature changes (True).
• Sum of Mole Fractions: Equals one (True).

Conclusion

• Summary of Parts 1 and 2:
  • Concentration measured qualitatively and quantitatively.
  • Molarity and molality distinctions.
  • Moles constant in dilution.
• Encourage filling out the L part of the KW chart (What you have learned).