Water and Solutions Ch. 13

Properties of Water Colorless Odorless Neutral pH; 7 Polar molecule Positive H+ region and Negative O2- region Exists in all 3 phases of matter Solid form is less dense than liquid Why is this important?

Density of Water As water cools, the molecules move closer together Volume decreases and density increases At 4oC water the most dense it can be; almost 1.0g/ml Below 4oC, H-bonds force the molecules in to hexagonal crystals Expanding the ice lowers the density to 0.9984g/ml

Special Properties of Water High Surface Tension 表面张力 Attraction between molecules on the surface of water; cohesion Causes water to bead up; form rain drops

Special Properties of Water Capillary Action 毛细作用 Attraction between molecules in a liquid and the molecules on a surface; adhesion Pulls water upwards against the force of gravity Allows tall trees and plants to exist

Special Properties of Water High Specific Heat Capacity比热容: Amount of energy need to raise the temperature 1 g of substance 1oC Water: 4.178 J/goC Why is this important to living things? Water absorbs the heat produced by biological processes 1 g of sugar produces 16.7 J Water absorbs heat from the sun; keeps the Earth cool during the day and warm as night.

Aqueous Solutions A mixture of water and dissolved minerals Heterogeneous or Homogenous? What are the two parts of a solution called? Solute and Solvent Solution Concentrations Solutions with a high concentration of solute are called concentrated 浓缩的 Solutions with a low concentration of solute are called diluted稀释的

Solubility The concentration of solute in a solvent depends on the solute’s solubility溶解度 Maximum amount of solute that can dissolve in a given solvent Creates 3 levels of concentration: Unsaturated不饱和的 -solute dissolves; more can be added Saturated饱和的 -Past maximum solute level; extra solute can bee seen in solvent Supersaturated过饱和的 - Applying heat dissolves extra solute but solution will crystallize when cooled

Solution Concentration Why are the terms “Concentrated” and “Diluted” not useful in a Chemistry lab? They are relative terms. The solution is “diluted” but compared to what? When doing reactions you need to know the exact concentration of chemicals being used Molarity物质的量浓度(M) Number of moles/L of a substance in a solution Ex. 1 M HCl = 1 mol of HCl/ 1 L of H2O

Calculating Molarity = 349 g KBr M = mol/L M= 0.6784 mol NaCl/ 4.5 L H2O M= 0.15 mol/L = 0.15 M 3 mol KBr 119.0 g KBr 1 L H2O 977.6 mL H2O = 349 g KBr 1 mol KBr 1000 mL H2O 1 L H2O

Formation of Solutions Solubility determine if solutions can form Simple rule for solutions: “Like dissolves Like”相似相溶 Substances with similar properties will dissolve into each other Polar vs. Non-polar Substances Polar substances will dissolve polar substances Salts, Sugars, water, acids… Non-polar dissolve non-polar Oils, fats, hydrocarbons… Non-polar + polar = heterogeneous mixture

Formation of Solutions Factors that effect solubility: Size of solutes Temperature of solvent Stirring or mixing action Solutions cover all phases of matter:

Types of Solutions Electrolytes电解质 Non-electrolytes非电解质 Water dissolves ionic compounds into free floating ions The charged particles allow the conduction of electricity through the water More ions = stronger electrolyte Does pure water conduct electricity? Non-electrolytes非电解质 Molecules and organic compounds do not break into ions in water Cannot conduct electricity

Mixtures with Larger Particles Suspensions悬浮液 Heterogeneous mixtures with particles large and 1 micrometer When stirred the mixture appears homogenous but over time the solid material will settle on the bottom Ex. whole milk, dirty water, paint… Colloids胶体 “Heterogeneous” mixture completely and evenly spread throughout another substance Particles never settle or separate Will glow due to Tyndall effect丁达尔效应 Light particles bounce of particles inside substance Ex. Regular milk, whipped cream, jelly…

Effects of Solutes on Substances Solutes change how particles in solvents interact Boiling Point Elevation沸点升高: Solutes take up space at the top of a liquid solvent Less surface for liquid molecules to escape into gas molecules Temperature must be raised higher than the normal boiling point Freezing Point Depression凝固点降低: Solutes prevent liquid solvent particles from getting close enough to change to a solid state Temperature must be below the normal freezing point