Unit 10 – Solutions Lecture 1: Solutions and Solubility

Solution: A homogeneous mixture (uniform, no distinct phases) 6.3 Solutions Solution: A homogeneous mixture (uniform, no distinct phases) may contain solids, liquids or gasses

Solvents and Solutes A solution is formed when a solute is dissolved in a solvent: SOLUTE: A substance dissolved in a solution Ex: Salt dissolved in water, sugar dissolved in iced tea SOLVENT: The substance that dissolves Ex: Water in a salt-water solution AQUEOUS SOLUTION: water is the solvent

Solvents and Solutes Types Example Solvent Solute Gas Air Nitrogen (78%) Oxygen (21%) Liquid Gas in a liquid Liquid in liquid Solid in liquid Solid Steel Iron Carbon

Dissolving Process Water dissolving table salt (NaCl) http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Dissolving Process According to the kinetic molecular theory, water molecules are in constant motion and collide with the salt crystals. The dipoles of the water molecules attract the positive Na+ and negative Cl-. The water molecules pull apart the salt crystal.

Solubility Solubility, S: The maximum amount of solute needed to form a saturated solution at a specific temperature. Units are: g solute/100 g H2O OR g solute/100 mL H2O (Density of water is ~1 g/mL, so we can use these units interchangeably.) © 2009, Prentice-Hall, Inc.

Types of Solutions Unsaturated Less than the maximum amount of solute for that temperature is dissolved in the solvent. No solid remains in flask. © 2009, Prentice-Hall, Inc.

Types of Solutions Saturated Solvent holds as much solute as is possible at that temperature. © 2009, Prentice-Hall, Inc.

Solubility Chart This chart shows the solubility as a function of temperature. Line represents amount to make a saturated solution In general, increasing temperature means increasing solubility.

Solubility Chart Adding 90 g NaNO3 to 100 g H2O unsaturated Example: At 40°C: Adding 90 g NaNO3 to 100 g H2O unsaturated Adding 105 g NaNO3 to 100 g H2O saturated Adding 120 g NaNO3 to 100 g H2O saturated (15 g solute undissolved)

Factors Affecting Solubility How much solute that can dissolve in a solution depends on: temperature pressure (gasses only)

Factors Affecting Solubility Temperature At higher temperatures, molecules move faster. Increase in collisions between liquid and solid solutes and solvent => INCREASED SOLUBILITY

Solubility of a Gas Pressure Increase P, increase solubility of a gas

Solubility of a Gas Temperature: Increased T, increases the motion of gas solute particles so they escape from the liquid => DECREASED SOLUBILITY What’s more carbonated: Cold or warm soda?

“Like Dissolves Like” Nonpolar solutes dissolve best in nonpolar solvents Fats Oils Gasoline Polar and ionic solutes dissolve best in polar solvents Ionic Compounds Sugars Water Acids

Electronegativity Electronegativity is the ability of an atom of an element to attract electrons in a compound.

Periodic Trends Electronegativity Increases H He Increases O F Properties that vary within groups and across periods include atomic size, ionic size, ionization energy, electronegativity, nuclear charge, and shielding effect. Interpreting Diagrams **Fluorine has the highest electronegativity value

H:H Polarity Compare HF and H2: HF is POLAR – unequal sharing of electrons. H2 is NONPOLAR – equal sharing of electrons. Properties that vary within groups and across periods include atomic size, ionic size, ionization energy, electronegativity, nuclear charge, and shielding effect. Interpreting Diagrams

CO2 Lewis Structures - REVIEW Add up all the valence electrons. Least EN atom in center. Bonds between central atom and outer atoms. Fill outer atom’s octets. Make multiple bonds if needed. CO2 © 2009, Prentice-Hall, Inc.

Polar vs. Non-Polar Molecules Polar molecules: electrons are shared unequally. Polarity depends on symmetry, electronegativity of atoms, lone pairs. Symmetric molecules are non-polar. Asymmetric molecules tend to be polar. F B H O https://www.youtube.com/watch?v=PVL24HAesnc&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=23

“Like Dissolves Like” Nonpolar: Hydrocarbons (only C & H) Polar: Hydrocarbons that contain oxygens or nitrogens

REVIEW What is the intermolecular bond that affects water’s properties? Hydrogen Bonds 2. In a salt-water solution, what is the solvent and what is the solute? Salt: solute water: solvent 3. On a molecular level, how does dissolving of a solute happen? Molecules are in constant motion. When solvent molecules collide with solute, causes solute to distribute through the solvent. Changing the temperature usually affects the solubility of a substance. INTERPRETING GRAPHS a. Describe What happens to the solubility of KNO3 as the temperature increases? b. Identify Which substance shows a decrease in solubility as temperature increases? Which substance exhibits the least change in solubility? c. Apply Concepts Suppose you added some solid sodium chloride (NaCl) to a saturated solution of sodium chloride at 20°C and warmed the mixture to 40°C. What would happen to the added sodium chloride?

REVIEW 4. How does increased temperature affect solubility of solid and liquid solutes? Increased solubility for solid and liquid solutes; decreased solubility for gas solutes Changing the temperature usually affects the solubility of a substance. INTERPRETING GRAPHS a. Describe What happens to the solubility of KNO3 as the temperature increases? b. Identify Which substance shows a decrease in solubility as temperature increases? Which substance exhibits the least change in solubility? c. Apply Concepts Suppose you added some solid sodium chloride (NaCl) to a saturated solution of sodium chloride at 20°C and warmed the mixture to 40°C. What would happen to the added sodium chloride?

REVIEW 1. In a salt-water solution, what is the solvent and what is the solute? Salt: solute water: solvent 2. How does increased temperature affect solubility of a solid in a liquid (salt-water)? Increased solubility for solid and liquid solutes 3. How does increased temperature affect solubility of a solid in a liquid (CO2-water)? Decreased solubility for gas solutes in a liquid Changing the temperature usually affects the solubility of a substance. INTERPRETING GRAPHS a. Describe What happens to the solubility of KNO3 as the temperature increases? b. Identify Which substance shows a decrease in solubility as temperature increases? Which substance exhibits the least change in solubility? c. Apply Concepts Suppose you added some solid sodium chloride (NaCl) to a saturated solution of sodium chloride at 20°C and warmed the mixture to 40°C. What would happen to the added sodium chloride?

REVIEW 4. Define a saturated solution? A solution that contains the maximum amount of solute at a given T. 5. What are two ways to increase solubility? Temperature and pressure for gases Changing the temperature usually affects the solubility of a substance. INTERPRETING GRAPHS a. Describe What happens to the solubility of KNO3 as the temperature increases? b. Identify Which substance shows a decrease in solubility as temperature increases? Which substance exhibits the least change in solubility? c. Apply Concepts Suppose you added some solid sodium chloride (NaCl) to a saturated solution of sodium chloride at 20°C and warmed the mixture to 40°C. What would happen to the added sodium chloride?

A solution is homogeneous. Solutions - Summary A solution is homogeneous. Solute: substance that is dissolved in the solution. Solvent: substance that does the dissolving. “Like Dissolves Like” : Polar solvents dissolve polar or ionic solutes Nonpolar solvents dissolve nonpolar solutes. Solubility: The quantity of solute that will dissolve in a solvent at a given T & P

Solutions – Summary (continued) Saturated solution: contains the maximum amount of solute in a given solvent. Factors affecting solubility: temperature and pressure (gases only).