Ch. 13/14: Solutions Describing a Solution’s Composition

Concentration  how does it relate to solution saturation? will all higher concentration solutions be more saturated than lower concentration solutions? will all higher concentration solutions be more saturated than lower concentration solutions? with the same or different solutes? with the same or different solutes?

Molarity  is most often used to specify the concentration of a solution  number of moles of solute in one liter of solution  that does not mean solute added to one liter of solvent- WHY?  units: moles/liter = M

Mass Percent  mass of part divided by mass of whole  also called weight percent  percent by mass of the solute in the solution

Mole Fraction  moles of part divided by moles of whole  ratio of number of moles of solute of solution to total number of moles of solution

Molality  number of moles of solute per kg of solvent  units: moles/kilogram = m  like molarity but stays constant with temperature- Why?

Example 1  21.0 g of NaOH is dissolved in enough water to make 500. mL of solution. The density of pure water is 1.00 g/mL but the density of the solution is 1.02 g/mL.

Example 1: Molarity  What is the molarity? find moles from grams find moles from grams total volume of soln is given total volume of soln is given

Example 1: Mass Percent  What is the mass percent? mass of solute is given mass of solute is given calculate the mass of solution using density and volume calculate the mass of solution using density and volume

Example 1: Mole Fraction  What is the mole fraction of NaOH in the solution? find the moles of solute from grams find the moles of solute from grams find the moles of solvent from grams of water find the moles of solvent from grams of water How do we find grams of water? How do we find grams of water?

Example 1: Mole Fraction

Example 1: Molality  What is the molality of the solution? already have the moles of solute already have the moles of solute need to calculate the kg of solvent from mass of water need to calculate the kg of solvent from mass of water

Example 2  3.7 moles of HCl is added to water to make 500. mL of solution. The Density of the solution is 1.10 g/mL.

Example 2: Molarity  What is the molarity? moles are given moles are given total volume of soln is given total volume of soln is given

Example 2: Mass Percent  What is the mass percent? calculate mass of solute from moles calculate mass of solute from moles calculate the mass of solution using density and volume calculate the mass of solution using density and volume

Example 2: Molality  What is the molality of the solution? already have the moles of solute already have the moles of solute need to calculate the kg of solvent from mass of solution and mass of HCl need to calculate the kg of solvent from mass of solution and mass of HCl

Example 2: Mole Fraction  What is the mole fraction of HCl in the solution? given the moles of solute given the moles of solute find the moles of solvent from grams of water find the moles of solvent from grams of water

Example 3  If the HCl solution has a molarity of 12.0 M and a density of 1.13 g/mL,  What is the mass percent? 12.0 M = 12.0 mol of HCl in 1L of soln 12.0 M = 12.0 mol of HCl in 1L of soln mass of HCl: from moles to grams mass of HCl: from moles to grams mass of soln: from volume and density mass of soln: from volume and density

Example 4  If the mass percent of a NaCl solution is 33.0%, what is the molality? 33.0 g of NaCl in g of solution 33.0 g of NaCl in g of solution mass of water = = 67.0 g of water mass of water = = 67.0 g of water moles of NaCl from grams moles of NaCl from grams kilograms of water from grams kilograms of water from grams