Chemistry Lab/Aqueous Solutions

This page refers to the 2011 focus of Chem Lab.

This topic focused on the concentrations of solutions and how chemical properties of solutions are changed when mixed. This topic is very broad, considering that many substances used in chemistry are in aqueous form, including Acids and Bases, which are a slightly different focus.

Solution Concentration
There are a number of ways to determine solute concentration:
 * Molarity=(number of moles of solute)/(Liters of solution)
 * Molality=(number of moles of solute)/(kilograms of solvent)
 * Mass Percentage=massA/(massA+massB+...)
 * Parts Per Million=Mass Percentage*10,000

Conversion Between Units

 * Molarity->Molality: Multiply by Liters of solution, divide by kilograms of solvent (approximately equal for dilute solutions).
 * Molality->Mass Percentage: Multiply by mass of solute, then divide by moles of solute, then multiply by kilograms of solvent, and divide by kilograms of solution (can be appromimated by multiplying by molar mass).

Solubility Rules
There are certain rules that dictate which substances dissolve in water and which ones precipitate out.


 * Always dissolve
 * Nitrate ($$NO_3^-$$)
 * Acetate ($$CH_3COO^-$$)
 * Cations of alkali metals (e.g. sodium, potassium, etc.)
 * Sometimes dissolve
 * Sulfate ($${SO_4}^{2-}$$)
 * Precipitates with barium, calcium, lead, silver, strontium and mercury (I)
 * Halides (except fluoride)
 * Precipitate with silver, lead, and mercury (I)
 * Sulfides
 * Rarely dissolve
 * Carbonates ($${CO_3}^{2-}$$)
 * Hydroxides ($$OH^-$$)
 * Phosphates ($${PO_4}^{3-}$$)

Sample Questions
Questions in the kinetics section might involve...
 * 1) Solution Concentration (Molarity, Molality, Mass Percentage, Parts Per Million)
 * 2) Conversion Between Units (at state and national levels)
 * 3) Determining Concentration using Density, Beer's Law or Titration
 * 4) Freezing Point Depression and Boiling Point Elevation
 * 5) Factors Affecting Solution Formation
 * 6) Solubility