Chemistry Solutions and Concentration Units

Solutions and Concentration Units

• Concentration is the amount of solute in a given amount of solution.
• Molarity (M) = Moles of solute / Liters of solution
• Molarity units are moles per liter (mol/L).
• Percent by mass of solute = (Mass of solute / (Mass of solute + Mass of solvent)) x 100%
• Percent by mass is a unitless ratio.
• Mole fraction of component A (XA) = Moles of A / Sum of moles of all components
• Molality (m) = Moles of solute / Kilograms of solvent
• Molality is the number of moles of solute dissolved in 1 kg of solvent.

Example Calculations (Specific to MgSO4)

• Percent MgSO4: Example calculation showing how to find the percentage of MgSO4 in a solution given masses of MgSO4 and water. The answer is 13.8%.
• Mole Fraction: Example calculation determining the mole fraction of MgSO4, and of H₂O. This demonstrates how to convert mass to moles and then calculating the mole fraction. The answer for MgSO4 is 0.0235 and for H₂O it is 0.977.
• Molality: Example calculation showcasing the calculation of molality. The calculated answer is 1.33m.

Additional Examples (General)

• Example 3: Calculating molality of sulfuric acid (H₂SO₄) in a given amount of water.
• Example 4: Calculating the molality of urea (NH₂₂CO) in a specific amount of water.
• Example 5: Calculating the molality of a 29.7% phosphoric acid (H₃PO₄) solution.
• Example 6: Calculating the molality of a 44.6% sodium chloride (NaCl) solution.
• Example 7: Calculating the molality of a 36.5% hydrochloric acid (HCl) solution given its density.
• Example 7 (part b): Calculating the molarity of the same HCl solution in part a.

Problem Strategies

• Preparing a solution with a specific mass percentage: The strategy for preparing a solution given the desired mass percentage and total mass.
• Demonstrates the calculation involving finding the masses of solute and solvent.
• Exercise: Demonstrating calculation for finding grams of HCl in a given solution, and how many grams of water are present.

Henry's Law (Supplemental)

• Relates gas concentration to gas pressure.
• Gas concentration (c) = k * Pressure (p)

This quiz covers the essential concepts of solutions and concentration units including molarity, percent by mass, mole fraction, and molality. It includes example calculations specific to Magnesium Sulfate (MgSO4) to help reinforce these principles. Ideal for students looking to grasp solution chemistry.