Chemistry: Molarity and Solubility

Class Meeting Format

• Class will not be for the entire period, likely just half.

• After class, there will be an outing for Spring Flames.

Concentration of Solutions

• Molarity (M) is a key equation for determining the concentration of a solution.

• The formula to memorize:

  [ M = \frac{\text{moles of solute}}{\text{liters of solution}} ]

Using Molarity as a Conversion Factor

• Molarity can help convert between moles and liters.

• Example Problems:

  • Problem 55a:

    • Molarity (M) = 2.3, Volume (L) = 0.556

    • Calculate Moles (m):

      • [ m = M \times V = 2.3 \times 0.556 = 1.28 \text{ moles} ]

  • Problem 56a:

    • Molarity (M) = 0.2, Moles = Given

    • Solve for Volume (V):

      • Answer: 2.25 L

Understanding Molarity

• If given moles and liters, you can solve for molarity.

• If given any two of the three variables, you can find the third.

Dilution Equation

• Formula:

  [ M_1V_1 = M_2V_2 ]

• This equation shows that when diluting, the final concentration (M2) will be less than the original concentration (M1).

• Example Problems:

  • Problem 60:

    • M1 = 4.8, V1 = 3.5L, V2 = 45L, find M2:

      • M2 = 0.37

  • Problem 59:

    • M1 = 1.1, V1 = 123 mL, V2 = 500 mL, find M2:

      • M2 = 0.27

    • Important Note: You can leave measurements in milliliters without converting to liters.

Solubility

• Solubility determines if a compound will dissolve in water (soluble) or not (insoluble).

• Synonyms for soluble: Dissolve

• Example Compounds:

  • Silver Nitrate, Silver Iodide, Potassium Phosphate, Cobalt Carbonate

• Use solubility rules to predict solubility.

• "Soluble" compounds designated with 'aq' (aqueous), while "insoluble" indicated by 's' (solid).

Understanding Electrolytes

• Soluble compounds dissociate into ions and act as electrolytes, conducting electricity.

• Non-soluble compounds do not dissociate and are non-electrolytes.

• Importance of electrolytes for bodily functions (e.g., muscle contractions, nerve signals).

Precipitation Reactions

• Occur when solutions react to form an insoluble product (precipitate).

• Sample Problem Approach:

  • Write the ionic equation and switch partners (double displacement).

  • Determine solubility of products using the solubility rules.

  • Identify which products are insoluble and write the net ionic equation, eliminating spectator ions.

• Definitions:

  • Spectator Ions: Ions that do not participate in the reaction.

  • Ionic Equation: Full representation showing all ions.

  • Net Ionic Equation: Only shows the species that change during the reaction.

Upcoming Exams and Labs

• Class meets again next Tuesday; will cover more material and practice for the exam on April 8th.