Concentrations of Solutions The properties and behavior of solutions often depend not only on the type of solute but also on the concentration of the solute. Concentration: the amount of solute dissolved in a given quantity of solvent or solution many different concentration units (%, ppm, g/L, etc) often expressed as molarity

Concentrations of Solutions Molarity (M): the number of moles of solute per liter of solution Molarity = moles of solute volume of solution in liters 6.0 M HCl 6.0 moles of HCl per liter of solution. 9.0 M HCl 9.0 moles of HCl per liter of solution.

Concentration of Solutions To calculate the molarity of a solution: Convert amount of solute to moles Convert volume to liters Divide amount of solute in moles by volume in liters Units of molarity are mol/L (M)

Concentration of Solutions Example: What is the molarity of a solution prepared by dissolving 225 g of glucose (C6H12O6) in enough water to make 825 mL of solution?

Concentration of Solutions Interconverting Molarity, Moles, and Volume Molarity can be used as a conversion factor. The definition of molarity contains 3 quantities: Molarity = moles of solute volume of solution in liters If you know two of these quantities, you can find the third.

Concentration of Solutions Interconverting Molarity, Moles, and Volume Example: How many moles of HCl are present in 2.5 L of 0.10 M HCl?

Concentration of Solutions Interconverting Molarity, Moles, and Volume Example: What volume (in mL) of a 0.10 M NaOH solution is needed to provide 0.063 mol of NaOH?

Concentration of Solutions Interconverting Molarity, Moles, and Volume Example: How many grams of CuSO4 are needed to prepare 250.0 mL of 1.00 M CuSO4?

Concentrations of Solutions: Preparing solutions from pure solids Steps involved in preparing solutions from pure solids

Concentrations of Solutions: Preparing solutions from pure solids Steps involved in preparing solutions from pure solids Calculate the amount of solid required Weigh out the solid Place in an appropriate volumetric flask Fill flask about half full with water and mix. Fill to the mark with water and invert to mix. You should be able to describe this process (including calculating the mass of solid to use) for any solution I specify.

Concentration of Solutions Dilution Calculations Many laboratory chemicals such as acids are purchased as concentrated solutions (stock solutions). 12 M HCl 12 M H2SO4 More dilute solutions are prepared by taking a certain quantity of the stock solution and diluting it with water.

Concentration of Solutions Dilution Calculations A given volume of a stock solution contains a specific number of moles of solute. 25 mL of 6.0 M HCl contains 0.15 mol HCl (How do you know this???) If 25 mL of 6.0 M HCl is diluted with 25 mL of water, the number of moles of HCl present does not change. Still contains 0.15 mol HCl

Concentration of Solutions Dilution Calculations Moles solute = moles solute before dilution after dilution Although the number of moles of solute does not change, the volume of solution does change. The concentration of the solution will change since Molarity = mol solute Vol soln

Concentration of Solutions Dilution Calculations When a solution is diluted, the concentration of the new solution can be found using: Mi x Vi = Mf x Vf where Mi = initial concentration (mol/L) Vi = initial volume Mf = final concentration (mol/L) Vf = final volume

Concentration of Solutions Dilution Calculations Example: What is the concentration of a solution prepared by diluting 25.0 mL of 6.00 M HCl to a total volume of 50.0 mL?

Concentration of Solutions Dilution Calculations Example: What volume of 1.00 M CuSO4 would be needed to prepare 250.0 mL of 0.100 M CuSO4?

Concentration of Solutions: Preparing dilute solutions from stock solutions Steps involved in preparing a dilute solution from a more concentrated stock solution.

Concentration of Solutions: Preparing dilute solutions from stock solutions Steps involved in preparing a dilute solution from a more concentrated stock solution. Calculate the volume of stock solution needed. Pipet the required amount of stock solution into an appropriate volumetric flask. Dilute to the mark with DI water. Mix well. You should be able to describe this process (including calculating the volume of stock solution to use) for any solution I specify.

Concentration of Solutions Solution Stoichiometry Recall that reactions occur on a mole to mole basis. For pure reactants, we measure reactants using mass For reactants that are added to a reaction as aqueous solutions, we measure the reactants using volume of solution.

Concentration of Solutions Solution Stoichiometry grams A Molar mass moles A Molarity A Vol Soln A Molar ratio Molar mass grams B moles B Molarity B Vol Soln B

Concentration of Solutions Solution Stoichiometry Example: If 25.0 mL of 2.5 M NaOH are needed to neutralize (i.e. react completely with) a solution of H3PO4, how many moles of H3PO4 were present in the solution? 3NaOH (aq) + H3PO4 (aq)  Na3PO4 (aq) + 3H2O(l)

Concentration of Solutions Solution Stoichiometry Example: What mass of aluminum hydroxide is needed to neutralize 12.5 mL of 0.50 M sulfuric acid?

Concentration of Solutions Solution Stoichiometry Example: Calculate the volume of 0.215 M phosphoric acid needed to neutralize 125 mL of 0.103 M sodium hydroxide.

Concentration of Solutions Solution Stoichiometry Solution stoichiometry can be used to determine the concentration of aqueous solutions used in reactions. The concentration of an acid can be determined using a process called titration. reacting a known volume of the acid with a known volume of a standard base solution (i.e. a base whose concentration is known)

Concentration of Solutions Solution Stoichiometry Titration:

Concentration of Solutions Solution Stoichiometry Example: If 35.50 mL of 2.5 M NaOH are needed to neutralize 50.0 mL of an H3PO4 solution, what is the concentration (molarity) of the H3PO4 solution? 3NaOH (aq) + H3PO4 (aq)  Na3PO4 (aq) + 3H2O(l)