Solutions

Solutions

By Abby Fancsali

Recall

• Mixtures are a combination of substances

  • Can heterogenous or homogenous

    • Heterogenous Mixtures: large particles that ​can be easily seen and separated

      • Suspensions: a heterogenous mixture that separates on its own over time

        • Clay in water

      • Colloids: a heterogenous mixture that does not separate on its own over time

        • Milk

Homogenous solutions are Solutions

• Solution: any mixture that is homogenous on a microscopic level

  • Usually a liquid, but can be solid or gas as well

    • Solid solutions tend to be alloys like brass

  • ​Liquids Solutions have two parts

    • Solvent: The main ingredient that you dissolve substances in

      • Water is called the universal solvent because it dissolves so many things into aqueous solutions

    • Solute: the ingredient you are dissolving

Separating Mixtures-Physical Means

• There are many ways to separate mixtures into their components, and what you do depends on your ultimate goal

  • Physical methods

    • Decanting

    • Centrifuging

    • Filtration

    • Evaporation​

Separating Mixtures- other methods

• Chromatography: separates components of a mixture based on how quickly different molecules dissolved in a mobile phase solvent move along a solid plane

• Distillation Separates mixtures based on evaporation point

Concentration

• In a solution, the solute is distributed evenly throughout the solvent

• Concentration: the ratio of solute to solvent in a solution

  • When a solution has a low concentration it is Diluted

    • Different ways to measure concentration

      • Parts per million

      • Molarity

      • Molality

Calculating Concentration: Parts per million (ppm)

• Parts per million is a measure of concentration used in measuring pollution

  • Involves very low levels of concentration

  • Measures how many grams of solute are in 1 million grams of solution

Calculating Concentration: Parts per million (ppm)

• Sample Problem: A chemical analysis shows that there are 2.2 mg of lead in 500g of a water sample. Convert this measurements to parts per million

  • Step 1: Identify your givens

    • 2.2 mg Pb

    • 500 g H₂O

  • Step 2: Identify what you need to do

    • Need lead in grams

    • convert your ratio to ppm​

Calculating Concentration: Parts per million (ppm)

Calculating Concentration: Molarity (M)

• It is often more useful to describe concentrations in terms of the number of solute particles in a solution rather than the mass of the solute particles

• Molarity: Measures the number of moles of solute that are in one liter of a solution

  • read as "moles per Liter"​

Calculating Concentration: Molarity (M)

• Sample Problem: What is the Molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85 g KCl

  • Step one Identify what you have

    • Volume of substance = 400 mL

    • Mass of Solute= 85 g KCl

  • Step 2: Identify what you need to solve

    • Moles of solute

    • Volume in Liters​

Calculating Concentration: Molarity (M)

• Sample Problem: What is the Molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85 g KCl

  • Step three: plug in your values to the Molarity Equation

Using Molarity in Solution Stoichiometry

• Sample Problem: What volume in mL of a 0.5 M solution of CuSO₄ is needed to react with an excess of aluminum to provide 11.0 g of Copper?

• Molar Mass of Cu = 63.55 g/mol

• 0.5 M solution has 0.5 moles in 1 liter​