1. Foothill Chemistry

2. Water Water covers ¾ of the Earth’s surface Water is essential to all life on Earth. Water is a polar molecule Water molecules are held together with hydrogen bonds

3. Water Structure Water Molecule One oxygen atom and two hydrogen atoms Polar molecule Water Substance Water molecules are held together by hydrogen bonds Surface Tension Low Vapor Pressure

4. Surface Tension A force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size Causes droplets to take on a spherical shape Capillary action Attraction of the surface of a liquid to the surface of a solid. Tends to pull molecules upward against gravity. Causes meniscus seen in graduated cylinder Surfactants interfere with the hydrogen bonding between molecules and decrease surface tension.

5. Evaporation and Boiling Vaporization – change from liquid state to gaseous state (Equilibrium) Vapor Pressure – pressure from the vapor with its corresponding liquid at a given temperature in a closed system Water has low equilibrium vapor pressure Hydrogen bonds hold water molecules together so that they do not evaporate easily What do you think the difference is between evaporation and boiling? Evaporation has vapor formed only at the surface. Boiling (as evidenced by the bubbles that occur) has vapor formed throughout the liquid. Boiling Point – Temperature at which equilibrium vapor pressure = atmospheric pressure Volatile Liquids (not water) – are liquids that evaporate readily

6. Freezing Change from liquid phase to solid phase. In water, the regular crystal-like shape of the solid holds the water molecules farther apart from one another than the irregular organization of liquid water. 334J of energy are required to melt 1g of ice Freezing point is temperature at which solid and liquid are at equilibrium at 1 atm (760 torr, 101.3kPa).

7. Phase Diagram of Water

8. Aqueous Solutions Water that contains dissolved substances. Solution Homogeneous mixture Solvent – medium in which a substance is dissolved Solute – the dissolved particles The dissolved substance does not settle out readily. The particle size of the dissolved substance is usually less than 1 nm. Cannot be separated by filtration

9. Solvation and Dissociation Solvation - Process by which ions of a solid become surrounded by solvent molecules Dissociation – Separation of ions that occurs when ionic compound dissolves

10. Dissociation Equations NaCl (s) water Na + (aq) + Cl - (aq) 1 mol 1mol 1 mol 1 mole of solid produces 2 moles of aqueous ions CaCl 2(s) water Ca 2+ (aq) + 2 Cl - (aq) 1 mol 1mol 2 mol 1 mole of solid produces 3 moles of aqueous ions Try the equation for dissociation of Al 2 (SO 4 ) 3

11. Solubility Substances that dissolve most readily in water include ionic compounds and polar covalent molecules. Nonpolar covalent molecules, such as methane, and compounds found in oil, grease, and gasoline, do not dissolve in water. “Like Dissolves Like”

12. General Solubility Guidelines 1. Sodium, potassium and ammonium compounds are soluble in water 2. Nitrates, acetates and chlorates are soluble. 3. Most chlorides are soluble except silver, mercury (I), and lead. Lead(II) chloride is soluble in hot water 4. Most sulfates are soluble, except those of barium, strontium, lead, calcium and mercury 5. Most phosphates, carbonates and silicates are insoluble – #1 is exception (Na, K, NH 4 + ) 6. Most sulfides are insoluble except calcium, strontium and #1 (Na, K, NH 4 + )

13. Electrolyte Conducts electricity in an aqueous solution or a molten state All ionic compounds are electrolytes because they dissociate into ions Strong Electrolyte – Electrolyte mostly dissociates to separate ions Weak Electrolyte – Electrolyte only partially dissociates to separate ions Nonelectrolyte – Does not dissociate; is molecular (covalent bond)

14. Hydrates A compound that contains water of hydration Use a dot to connect the formula of the compound and number of water molecules per formula unit CuSO 4 · 5H 2 O copper (II) sulfate pentahydrate Na 2 B 4 O 7 · 10H 2 O Sodium tetraborate decahydrate Ionic compound + prefix (like molecular) + hydrate

15. Hydrate Terms Efflorescent – Vapor pressure of the hydrate is higher than atmospheric, so the hydrate loses water Hygroscopic - Vapor pressure of the hydrate is lower than atmospheric, so the hydrate absorbs water to form higher hydrates Desiccant – Hygroscopic compound that dries out its surrounding area Deliquescent compounds absorb so much moisture from the air that they dissolve.

16. Percent Water in a Hydrate Mass of water in the hydrate x 100% Total mass of hydrate (based on molar mass of the formula) Calculate percent mass of water in washing soda Na 2 CO 3 · 10H 2 O How can this information be helpful?

17. Concentrations of Solutions Concentration is a measure of the amount of solute in a given amount of solvent or solution Molarity – number of moles of solute in 1 L of solution Molality – number of moles in 1 kg of solvent

18. Molarity / Molality Examples 1 M solution of HCl means that for every 1L of solution, there are 36.46g (the molar mass) of HCl How many grams of HCl would there be in a 2M solution of HCl in 2L? Water’s density is 1 kg/L. How many grams of HCl would there be in 1L of a 1m solution?

19. Other Solutions Solution: Homogeneous mixture of two substances in a single phase Solute / Solvent examples Solid / Solid - Metal Alloys Solid / Liquid – Salt in Water Liquid / Solid – Dental Amalgam Liquid / Liquid – Alcohol in Water Gas / Liquid – Carbon Dioxide in Water (soda water) Gas / Gas – Oxygen in Nitrogen (air)

20. Heterogeneous Mixtures Suspensions Particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated. Particles > 1000 nm in diameter Colloids Particles in a solution between solutions and suspensions are called colloidal dispersions or colloids. Particles – Dispersed Phase Solvent – Dispersing Medium

21. Classes of Colloids Class of ColloidPhasesExample SolSolid Dispersed in LiquidPaints, Mud GelSolid Network in LiquidGelatin Liquid EmulsionLiquid Dispersed in LiquidMilk, Mayonnaise FoamGas Dispersed in LiquidShaving Cream, Whipped Cream Solid AerosolSolid Dispersed in GasSmoke, Auto Exhaust Liquid AerosolLiquid Dispersed in GasFog, Mist, Clouds, Aerosol Spray Solid EmulsionLiquid Dispersed in SolidCheese, Butter

22. Tyndall Effect Distinguish a Colloid from a Solution In a Colloid Light is Dispersed by the Particles in the Transparent Medium Like headlights on a foggy night. Suspensions may also disperse light, but they are not transparent. Particle movement seen in Colloid suspensions is called Brownian Motion

23. Colligative Properties Properties that depend on the concentration of solute particles, but not on their identity are colligative properties. Vapor-Pressure Lowering Freezing-Point Depression Boiling-Point Elevation Osmotic Pressure

24. Quiz 1. One characteristic that is unique to a suspension is that the particles in it a) are too small to be seen b) settle due to gravity c) cannot be filtered d) produce the Tyndall Effect 2. Homogenized milk contains finely divided particles that do not settle out rapidly and are not readily filtered. Thus, homogenized milk is a a) solution b) substance c) suspension d) colloid 3. The scattering of light known as the Tyndall effect can be seen in a) suspensions and colloids b) emulsions and solutions c) solutions and suspensions d) colloids and solutions