Ch 3 Terms to know Polar Covalent Bonds a covalent bond between atoms that differ in electronegativity Polar Molecule overall charge is evenly distributed Cohesion the hydrogen bonds hold the substance together Adhesion the clinging of one surface to another Surface tension a measure of how difficult it is to stretch or break the surface of a liquid Kinetic energy the energy of motion Heat a form of energy Temperature a measure of heat intensity that represents the average kinetic energy of the molecules regardless of volume Celsius scale a temperature scale that measure the freezing point of water at 0 degrees celsius and the boiling point of water at 100 degrees celcius Calorie cal The amount of heat it takes to raise the temperature of 1 g of water by 1 degree Celsius Kilocalorie kcal 1 000 cal is the quantity of heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius Joule J one Joule 0 239 cal one calorie equals 4 184 J Specific Heat the amount of heat that must be absorbed or lost for 1 g of that substance to change it s temperature by 1 degree Celsius Heat of Vaporization the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state Evaporative Cooling occurs because the hottest molecules those with the greatest kinetic energy are the most likely to leave as a gas Solution a liquid that is completely homogenous Solvent the dissolving agent of a solution Solute the substance that is dissolved Aqueous solution one in which water is the solvent Hydration shell the sphere of water molecules around each dissolved ion Hydrophilic any substance that has an affinity for water Colloid molecules suspended in the aqueous liquid of a cell Hydrophobic repels water water hating Molecular Mass sum of the masses of all atoms in a molecule Mole mol represents an exactnumber of objects 6 02x1023 Molarity the number of mols of solute per liter of solution Hydrogen ion H a single proton with the charge of 1 Hydroxide ion OH which has a charge of 1 Hydronium ion H3O Acid a substance that increases the hydrogen ion concentration of a solution Base substance that reduces the hydrogen ion concentration of a substance pH the negative logarithm base 10 of the hydrogen ion concentration pH log H Buffer a substance that minimizes changes in the concentrations of H and OH in a solution Ocean acidification when CO2 dissolves in sea water it reacts with water to form carbonic acid which lowers ocean pH Emergent properties new properties that arise with each step upward in the hierarchy of life owing to the arrangement and interactions of parts as complexity increases Concepts to know 1 Water s two hydrogen atoms are bonded to the oxygen atom by single covalent bonds a Because oxygen is more electronegative than hydrogen the electrons of the covalent bonds spend more time closer to oxygen this is because it is polar covalent 2 The oxygen region of the molecule has a partial negative charge and each hydrogen has a partial positive charge 3 When water is in liquid form hydrogen bonds are very fragile 4 4 emergent properties of water a Cohesive behavior b Ability to moderate temperature c Expansion upon freezing d Versatility as a solvent 5 The fact that water is held together by multiple hydrogen bonds makes it more structured than other liquids 6 Real life example of cohesion transport of water and dissolved nutrients against gravity in plants when the water reaches the leaves and evaporates hydrogen bonds which cause water molecules leaving the veins to tug on molecules further down and the upward pull is transmitted through the water conducting cells all the way to the root a Because of this water will change its temperature less when it absorbs a given 7 Water has a high specific heat amount of heat when it absorbs or releases heat released when hydrogen bonds form a gas 8 Specific heat can be thought of as how well a substance resists changing its temperature 9 Heat must be absorbed in order to break a hydrogen bond by the same token heat is 10 Evaporative cooling occurs because the hottest molecules are the most likely to leave as 11 Water is a versatile solvent because of its polarity 12 When salt is dissolved in water the result is a solution of two solutes sodium cations and chloride anions homogenously mixed with water the solvent 13 A compound doesn t need to be ionic to be dissolved in water a Nonionic polar molecules such as sugar can dissolve in water i This is because water molecules surround each of the solute molecules forming hydrogen bonds with them 14 Calculating molecular Mass Ex table sugar sucrose C12H22O11 a In round numbers of daltons the mass of a carbon atom is 12 hydrogen is 1 and oxygen is 16 b So the sucrose molecule has a molecular mass of 12x12 22x1 11x16 342 daltons 15 There are 6 02 x 1023 daltons in 1 g a This is relevant because once we determine the molecular mass of sucrose we can use the same number but with the unit gram to represent the mass 16 How would you make 1 L of solution consisting of 1 mol of sucrose dissolved In water a Measure out 342 g of sucrose and then gradually add water while stirring until the sugar was completely dissolved then ad enough water to bring the total volume of the solution up to 1 liter At that point we d have a 1 molar solution of sucrose 17 Occassionally a hydrogen atom participating in a hydrogen bond between two water molecules shifts from 1 molecule to another when this happens the hydrogen atom leaves its electron behind and what is transferred is the hydrogen ion H The water molecule that lost a proton is now a hydroxideion OH 18 You use a pH scale to determine how acidic or basic a solution is a When acids dissolve in water they donate additional H to the solution i For example when hydrochloric acid is added to water hydrogen ions dissociate from cholride ions 1 This source of H results in an acidic solution one having more H than OH 19 pH log H concentrations ii Some bases reduce the H concentration directly by accepting hydrogen ions a Remember that each pH unit represents a tenfold difference in H and OH i A solution of 3 is 1 000 times more acidic than a pH of 6 Ch 4 Terms to know Organic chemistry branch of chemistry that specializes in the study of carbon compounds Hydrocarbons organic molecules consisting of only carbon and hydrogen Isomers compounds that have the same numbers of atoms of the same elements but different structures and properties
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