Concept 3.1: WATER BOND Polar Covalent Bonds O is more electronegative polar molecule: unequal distribution of overall charge H & O are held together by polar covalent bond 2 water molecules are together by Hydrogen Bond fragile 1/20 strong as covalent bond form/break a lot Concept 3.2: 4 EMERGENT PROPERTIES OF H2O Cohesion hydrogen bonds hold substance together ex. transport of water and mineral up a plant against gravity Adhesion: clinging of one substance to another ex. water clings on to plant’s cell wall when traveling up against gravity Surface Tension: a measure of how difficult it is to stretch of break the surface of a liquid water has greatest surface tension water and air in ordered arrangement hydrogen bonds created a film on top Moderation of Temperature by water water moderates air temp. by absorbing warm heat from air and releasing stored “cold” heat into the air Heat and Temperature kinetic energy: energy of motion heat: form of energy a measure of the matter’s TOTAL KINETIC ENERGY (depends on matter’s volume) temperature: heat intensity that represents the AVERAGE KINETIC ENERGY (doesn’t depend on matter’s volume) heat es warm to cold till same temperature calorie amount of heat it takes to raise/release 1 g of water by 1 ° C joules…1 cal=4.18 J Water’s high specific heat (unusually high) specific heat: amount of heat that must be absorbed or lost for 1 g of water to change temp by 1 °C
specific heat of water 1 cal/g °C
alcohol has lower specific heat..also iron pot will heat up faster than the water in it water will change its temp less when it absorbs or loses heat heat absorbed break Hydrogen bonds heat released form Hydrogen bonds Evaporative Cooling molecules of liquid stay together due to attraction vaporization/evaporation: liquid to gas Heat of Vaporization: quantity of heat a liquid must absorb for 1 g of it to be converted from liquid to gas emergent property because of hydrogen bonds breaking Evaporative cooling: hottest molecules going to be gas Floating of Ice on liquid water water expands when it solidifies due to hydrogen bonding (molecules moving too slow to break H bonds) 4°C and above water expands as it warms and contract as it cools 0°C crystalline lattice “lock” (each H bonded to 4 partners) H bonds keep molecules are “arms length” far apart makes ice 10% less dense, 10% fewer molecules than H2O 4 °C water’s greatest density Water: The Solvent of Life Solution: homogenous mixture or 2 or more substances (ex. sugar in water) Solvent: dissolving agent of a solution Solute: the stuff that is dissolved
Aqueous solution: water is the solvent. water is NOT the universal solvent (ex. doesn’t dissolve our cells)…water IS the solvent of LIFE hydration shell: sphere of water molecules around each dissolved ion hydrophilic and hydrophobic substances hydrophilic: affinity for water…water loving colloid: stable suspension of fine particles in a liquid (ex. large cells that don’t dissolve in water) hydrophobic: repel water..water fearning nonionic and nonpolar (ex. cell membranes) Solute Concentration in Aqueous Solutions molecular mass: sum of all the atoms in a molecule always use moles…because weighing our small numbers is not practical substances can have difference mass but same # of molecules (6.02e23) to make 1 mol of sucrose dissolved in water324 g of sucrose + 1 L of water = 1 M of sucrose solution Molarity: moles of solute per liter of solution Concept 3.3: Acids and Bases H atom in bond between 2 water molecules …shift from 1 h2o to the other….leaves electron behind...transfers H+ h2o that gained a H+ is hydronium ion (H3O+) ….h2o that lost H+ is hydroxide ion (OH-) H+ ion never exists alone associated with water or hydronium ion H+ and OH- are very reactive changes affect protein and other molecules Acids and bases acids dissolve in water…donate H+….removes OH- forming water bases reduce H+ concentration by accepting H+ ions or dissociating (NaOH Na + OH) both making water neutral solution: H concentration and OH concentration is equal in reversible reaction fixed ratios (weak base= ammonia) (weak acid= carbonic acid) pH scale at 25°C…*H+][OH-]= 10-14 pH= -log[H+] pH declines as H+ concentration increases each pH unit represent 10 fold difference in H+ ions and OH-ions pH 3 to pH 6 means 1000 times difference Buffers pH of human blood= 7.4 stabilizes pH accepts H ions when in excess and donates H ions to the solution when they have been depleted buffer solution = weak acid + corresponding base CO2+H2O=H2CO3 HCO3+H when H rise…HCO3 removes H ions …forming H2CO3 Acidification 25% of CO2 produced by human activity is absorbed by the ocean CO2 dissolves in seawater forms carbonic acid lowers pH ocean acidification acid precipitation= rain,snow, fog with pH lower than 5.2