Chemistry Midterm.docx

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University of Toronto Scarborough
Heinz- Bernhard Kraatz

Chemistry Midterm Chapter 1: Matter, Measurement and Problem Solving Chemistry: the study of matter and how it changes (chemical behaviour of atoms, molecules and ions) Physical Change: a change that alters only the state or appearance of a substance but not its chemical composition Chemical Change: a change that alters the molecular composition of a substance Mass (g): measure of the amount of matter present in an object Time (s): measure of the duration of an event Temperature: measure of the average amount of kinetic energy caused by motion of the particles – high temperature = larger average kinetic energy Chapter 2: Atoms and Elements Ions: formed when atoms gain or lose electron  Proton and neutron count stays the same  Charges are changed (+ve charge = lose electrons, -ve charge = gain electrons) Isotopes:  of an element are chemically identical and have the same number of protons  have different masses and different number of neutrons  identified by their mass number Chapter 3: Compounds, Molecules, and Chemical Equations Organic Compounds: compounds containing carbon, along with hydrogen, oxygen, nitrogen and sulfur Inorganic Compounds: all the rest! – include ionic compounds (including hydrates) and molecular compounds (including acids/bases) Molecular Compounds: made up of discreet units called molecules  aggregates of two or more atoms in a definite arrangement held together by chemical forces Ionic Compounds: composed of cations and anions arranged in a lattice (no molecules!)  held together by electrostatic forces  cation is usually from a metallic element  anion is usually from a non-metallic element  sum of charges is equal to zero 1 Polyatomic Ions: are single ions that contain more than one atom Molecular Mass (MM): mass of a molecule in amu Formula Mass (FM): mass of a formula unit in amu Molar Mass: mass of one mole of compound (6.022x10 molecules/formula units) – same as molecule mass except with unit; g/mol Combustion: a reaction in which a substance reacts with oxygen to form oxygen containing compounds and heat (ex: combustion of natural gas (methane) produces carbon dioxide and water)  mass of combustions products (carbon dioxide and water) provides relative amounts of C and H in original sample – used to determine empirical formula Chapter 4: Chemical Quantities and Aqueous Reactions Chemical Reaction: conversion of one or more substances into one or more new substances – represented with a balanced chemical equation Limiting Reagent: determines how much product can be formed from a given reaction  rare to have the correct stoichiometric proportions for a reaction  in a reaction; one reagent is limiting and the other(s) are in excess Theoretical Yield: the amount of product that would result if all of the limiting reagent reacted Actual Yield: the amount of product actually obtained from a reaction – cannot be calculated ! Percent Yield: actual yield as a percentage of the theoretical yield Electrolyte: a solute which produces an aqueous solution that conducts electricity  dissociates into their cations (+) and anions (-) in solutions  movement of cations to negative electrode and anions to positive electrode establishes current Precipitate Reaction: soluble ions can combine to form an insoluble compound – precipitate forms Acid: yield H (H 3 ) when dissolved in water (Arrhenius Theory)  sour taste  cause colour change in plant dyes (litmus =pink) +  react with certain metals to produce H gas  react with carbonates to produce CO ga2  acidic aqueous solutions conduct electricity 2 - Base: yield OH ions when dissolved in water  bitter taste  feel slippery (soap)  litmus paper: blue  cause colour change in plant dyes (litmus= blue)  react with acids to produce salts  basic aqueous solutions conduct electricity Strong acids/bases: ionize completely in solution Weak acids/bases: only partially ionize in solution Neutralization Reaction: # of moles of H = # of moles of OH - Titration: a solution of known concentration is added to a solution of unknown concentration  ends when stoichiometric equivalence has been reach (equivalence point) – colour change Redox Reactions: involve the transfer of electrons between reacting species  types of redox reactions include; combination, decomposition, combustion, displacement, and disproportionation reaction – substance is both oxidized and reduced (decomposition of H O2) 2  oxidation – loss of electrons: atoms oxidation state increases o reactant being oxidized is known as the reducing agent  reduction – gain of electrons: atoms oxidation state decreases o reactant being reduced is known as the oxidizing agent Oxidation State: the charge an atom would have in a compound/ion if electrons were completely transferred from one atom to another Oxidizing Agent: causes oxidation of another species Reducing Agent: Causes reduction of another species Chapter 5: Gases Gases:  very low density  assume volume and shape of their container  highly compressible  mix evenly and completely when combined  important properties: pressure, volume, temperature, quantity 3 Kinetic Molecular Theory:  gases composed of small particles moving in constant, random, straight-line motion  have negligible volume  separated by great distances  collisions are rapid and elastic  no attractive or repulsive forces  average kinetic energy is proportional to the temperature in K Pressure: force per unit area  pressure exerted by a liquid depends on the height and density of the column of liquid Pressure- Volume Relationship:  1650: Townele observes yan increase in gas sample size at higher altitudes  1660s: Boyle and Hooke quantify Townealy’s observation o As P increases, V decreases by the same factor Boyle’s Law: for a fixed amount of gas at a constant temperature, pressure is inversely proportional to the volume Pressure- Temperature Relationship: Charles’s Law: for a fixed amount of gas at a constant pressure, volume is directly proportional to temperature in units of Kelvin Avagadro’s Law: at constant temperature and pressure of an ideal gas is directly proportional to its molar amount Molar Volume: 1 mol of any gas occupies 22.4L at STP (1 atm, 25 C) Gas Density: direc
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