Solutions/ Concentrations Georgia Performance Standard SC7: Students will characterize the properties that describe solutions and the nature of acids and bases.

Polar bonds & polar overall The Water Molecule Triatomic Covalent Polar bonds & polar overall Bent at 105° angle

Intermolecular Forces Polar molecules are attracted to one another by dipole forces Water is attracted to other water molecules by a special dipole force, a hydrogen bond

Solution=Homogeneous Mixture Water Solutions “Chemically pure water never exists in nature because water dissolves so many substances.” textbook Universal solvent Aqueous solutions Solution=Homogeneous Mixture

What happened to the ionic compound? Water Solutions Ionic compounds most readily dissolve in water due to extreme polarity Polar covalent compounds also dissolve in water Nonpolar compounds don’t What happened to the ionic compound?

Solvation of Ionic Compounds

A Few Exceptions... Calcium carbonate Remember the solubility rules... In some ionic compounds, the ions are so attracted to each other that they won’t break apart and dissolve. These are INSOLUBLE ionic compounds. Calcium carbonate

Solvation of Covalent Compounds Covalent compounds do NOT break apart in water when dissolving. Solvation of covalent compounds means that each solute molecule is surrounded by water molecules.

Conductors In general, aqueous solutions of ionic compounds are electrolytes. Generally, aqueous solutions of covalent compounds are nonelectrolytes.

Solution Vocabulary Solute: Dissolves in the solvent Soluble: Able to be dissolved in the solvent (applicable to any states of matter) Insoluble: Unable to be dissolved in the solvent (applicable to any states of matter) Miscible: Able to be dissolved in the solvent (applicable to liquid/liquid solutions) Immiscible: Unable to be dissolved in the solvent (applicable to liquid/liquid solutions)

Solubility Vocab Unsaturated: less than maximum amount of solute is dissolved in the solvent Saturated: maximum amount of solute is dissolved in the solvent Supersaturated: special conditions have been created to dissolve more than maximum amount of solute in the solvent

Determines IF Solute Will Dissolve... The nature of the solvent and solute governs whether a solute will solvate in a particular solvent. Specifically, the nature of the intramolecular bond. Polar molecules will solvate with polar molecules. Nonpolar molecules will solvate with nonpolar molecules. BUT, polar and nonpolar will not form solutions together.

Determines Speed of Dissolving BRING SOLUTE IN CONTACT WITH SOLVENT Agitation: Create more collisions mechanically Temperature: More kinetic energy creates more collisions Surface Area: Dissolving process is a surface phenomenon, the more surface of the solute that is exposed the faster the solvation

Determines How Much Will Dissolve SOLUBILITY: HOW MUCH WILL DISSOLVE Temperature: solubility of solid solute increases as the temp. increases; solubility of gaseous solute decreases as temp increases ex. Hot water bubbles, thermal pollution 2. Pressure: solubility of gaseous solute increases as the pressure increases -Henry’s Law ex. Soft drinks

Temperature & Solubility Higher the temperature, the more solid will dissolve in a liquid Higher the temperature, the less gas will dissolve in a liquid Why do soft drinks taste better cold?

Henry’s Law: Pressure & Solubility At a given temperature, the solubility of a gas is proportional to the pressure of the gas above the liquid. Page 506 The higher the pressure, the more carbon dioxide will dissolve in the syrup giving a less “flat” taste.

Solubility Graph

Concentration of Solutions The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution. Molarity: most common units of solution concentration; # of moles solute dissolved in one liter of the solution

Molarity: moles of solute liter of solution If given grams, remember to change it to moles.

Example 15.3 (page 531) Example 15.4 (page 532) Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50L of solution. Example 15.4 (page 532) Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8 mL of solution.

molality: moles of solute kg of solvent The most common concentration term in chemistry is Molarity (M), but chemists also report concentration in molality (m) sometimes. molality: moles of solute kg of solvent If given grams, remember to change it to moles.

Practice Molality The front of the last page in the calculations packet refers to Molality. Complete 1 (a), 2 (a), 3 (b), and 4 (b). NOTE: Questions 3 and 4 will require you to manipulate the equation. Question 4 might even require that you change the units of your answer at the end of the calculation.

Preparing a Solution in the Lab You’ve learned about concentration (Molarity and molality). Therefore, you should be able to create your own solutions for use in the lab from now on. Example: 0.5 M HCl reacts with Mg(s) If I gave you HCl powder, what would you do to make the solution? Watch these kids, and assess your plan. Choose a lab group and station. Draw an assignment from the cup, and make the solution. Write your steps (including materials) as you go. ALSO: Solve 15-2 Practice Problems WS 6, 8, 10-12, 14-16.

Diluting Solutions If you already have a solution molarity, but you want a different molarity: Example: Your lab asks you to use 250 mL of 0.25M HCl, but you only find a jug of 6M HCl in the stockroom. USE THIS EQUATION: M1V1 = M2V2

Example 15.8 (page 539) What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H2SO4 solution? *Be sure to solve the Dilution Worksheet in your practice packet!

Using Molarity as a Conversion Factor You have learned to calculate molarity using the equation: Molarity = moles of solute / liter of solution Did you realize that the calculation is simply a ratio of solute to solution? Ratios (ie mole ratios, energy to mole ratios) can be used as conversion factors in stoichiometry. THEREFORE, molarity can be written into our dimensional analysis charts to solve stoichiometry problems.

Solutions Stoichiometry What volume of 1.5 M HCl is needed to react with 21.5 grams of NaOH? What is the molarity of a solution of H2S if 48.5mL are required to titrate 35.6mL of 0.35M Fe(OH)3 solution? A white precipitate forms when 200 mL of 0.200M K3PO4 solution is mixed with 300 mL of 0.250 M CaCl2 solution. What mass of precipitate will form? BE SURE TO SOLVE THE PRACTICE PROBLEMS IN YOUR PACKET!

Diluting A Solution Lab MUST HAVE NOTEBOOK APPROVED BEFORE MOVING TO STATION Purpose: See group assignment Materials: What else would you need? Safety: What should you think about? Procedure: Part One: Making the solution from “scratch”. Part Two: Dilution. Write it out step by step! Results & Conclusions: How do you need to revise your procedure?

Colligative Properties Vapor Pressure lowering Freezing Point Depression Boiling Point Elevation Physical properties of solution are different from the physical properties of the solvent. Some properties are different simply because there are “foreign” particles (solute) in the solvent. Colligative properties of solutions depend only on the number of solute particles. Colligative Properties

More solute particles means less solvent particles able to escape to become vapor!

Boiling Point Elevation More solute particles means that vapor pressure is lower which means that more kinetic energy is needed to make vapor pressure equal atmospheric pressure! Change in temperature is calculated: ∆Tb = Kb m i Since boiling point increases...ADD the change. Kb will be given.

Freezing Point Depression Liquid particles get into an orderly pattern to become a solid. The solute particles disrupt the orderly pattern causing more kinetic energy to be drawn from the solution for it to freeze! ∆Tf = Kf m i Since freezing point decreases...SUBTRACT the change. Kf will be given

About.com Chemistry Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using 'ice cream salt', which is just salt sold as large crystals instead of the small crystals you see in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.

Molality Another unit for concentration m=moles of solute per kilogram of solvent page 520

Solutions Stoichiometry A white precipitate forms when 200 mL of 0.200M K3PO4 solution is mixed with 300 mL of 0.250 M CaCl2 solution. What mass of precipitate will form? What volume of 1.5 M HCl is needed to react with 21.5 grams of NaOH? What is the molarity of a solution of H2S if 48.5mL are required to titrate 35.6mL of 0.35M Fe(OH)3 solution?