Chapter 3

StudyBlue printing of Chapter 3 html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td { margin: 0; padding: 0; border: 0; outline: 0; font-size: 100%; background: transparent; } body { line-height: 1; } blockquote, q { quotes: none; } blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; } /* remember to define focus styles! */ :focus { outline: 0; } /* remember to highlight inserts somehow! */ ins { text-decoration: none; } del { text-decoration: line-through; } /* tables still need 'cellspacing="0"' in the markup */ table { border-collapse: collapse; border-spacing: 0; } /* end RESET */ .header { min-width:800px; } .logo { padding:6px 20px 2px 20px; margin:0; font-size:25px; font-weight:bold; color:#808285; position:relative; border-bottom: 1px solid #c5c5c5; } .logo-blue { color:#70adc4; } .logo-desc { font-weight:normal; font-size:19px; color:#cccccc; margin-top:50px; position:absolute; display: none; } .back-button { position:absolute; top:20px; right:20px; font-size:13px; line-height:25px; color:rgb(0,175,225); font-weight:normal; } .back-button a { color:rgb(0,175,225); } .instructions { padding:0; margin:0; width:100%; position:relative; color:rgb(100,100,100); } .step-holder { border-left:1px solid #ededed; margin-left:20px; } .steps { padding:15px 0; float:left; width:24%; border-right:1px solid #ededed; text-align:center; } .steps-01 { } .steps-02 { } .steps-03 { } .steps-04 { } .label { padding:5px 10px; } .print-button { } .print-button a { background-color:rgb(0,175,225); color:white; line-height: 19px; padding:9px 8px 5px 30px; font-size:14px; text-decoration:none; background-image: url(images/printer.png); background-repeat: no-repeat; background-position: 7px 50%; -moz-border-radius: 5px; -webkit-border-radius: 5px; } .print-button a:hover { background-color:black; } .theNote .content { width: 8.0in !important; margin: 5px auto; padding:20px; background-color:white; } .theNote .header { border-bottom: 1px dashed #C8C8C8; font-size: 17px; padding: 0 0 10px; line-height: 19px; color: #00ADE1; min-width:500px; } .theNote .body { font-size: 14px; line-height: 19px; padding: 10px 0; } .theNote{ padding:6px 0; clear:both; background-color: rgb(200,200,200); } .theNote h3{ color: rgb(100,100,100); } .theNote h1, .theNote h3{ background-color:white; padding:2px 20px; width:8.0in !important; margin: 0 auto; font-size: 15px; } .theNote h1{ padding-top: 10px; font-size: 15px; } .theNote h1:first-child{ font-size: 20px; } .theNote h3 { font-size: 14px; font-weight: normal; } #options { border: 3px double #ccc; padding: 5px 12px; margin: 10px 50px 10px 20px; float: left; } #info { border-top: 1px solid #ccc; padding-top: 5px; font-style: italic; } li { margin: 5px 10px 5px 25px; } ul li { list-style: disc; } ol li { list-style: decimal; } img { border: 0; } table { clear: both; width: 100%; border: 1px solid #c5c5c5; border-width: 1px 0; margin: 0; page-break-after: always; } table#page { page-break-after: auto; } td { text-align: center; font-size: 12px; border-bottom: 1px dashed #c5c5c5; height: 1.75in; width: 50%; padding-left: 15px; } .leftside { border-right: 1px solid #cccccc; padding: 0 15px 0 0; } .bottom td { border-bottom: none; } .clearfix { clear:both; line-height:1px; height:1px; } img { max-width:80%; max-height:150px; margin:20px; } @media print {.header { display: none; } .content .header{ display:inherit; } table { border: 1px dashed #bbb; border-width: 1px 0; } .theNote{ background-color:white; } } Stoichiometry Stoichiometry- the study of quantities of substances consumed and produced in chemical reactions. Atomic mass- the average mass of an atom of an element in atomic mass units (amu) Atomic masses are based on 12 C ("carbon twelve"), which is assigned a value of exactly 12 amu The atomic masses of other elements are determined by comparison to 12 C Mass spectrometer- currently best method for determination of atomic masses of atoms Procedure: atoms or molecules are placed in a beam of high-speed electrons (knocks electrons off the atoms or molecules giving them a positive charge - cations) an electric field is then applied accelerating these cations which causes each cation to create a magnetic field cations pass through an applied magnetic field cations with the least mass are deflected more than heavier cations and masses are determined by comparing amounts of deflection e.g. if, in a mass spectrometer 13 C is found to have a mass 1.0836 times that of 12 C, then the atomic mass of 13 C=1.0836(12 amu)=13.003 amu The mass spectrometer can also be used to determine the isotopic composition of an element. When a sample of an element is placed in a mass spectrometer, a mass spectrum can be obtained which indicates the relative amounts of the various isotopes present in the sample. The average mass of an atom (or mole) of an element is the sum of the fractions of each isotope times their mass e.g. Naturally occurring carbon is composed of two isotopes 12 C (98.89%) and 13 C(1.11%). The average atomic mass for an atom of carbon= (.9889x12 amu)+(.0111x13.003=12.01 amu. The Mole (abbrev. mol)- SI unit for the amount of a substance and is equal to the number of atoms in exactly 12 grams of pure 12 C. Mass spectrometry has determined this number to be 6.02214x10 23 (Avogadro's number)(We will use 4 sig. figs) Calculations involving the mole calculate mass from atoms and vice versa calculate moles from mass and vice versa Molar mass- the mass in grams of one mole of a substance (equals the atomic mass in grams) be able to calculate the molar mass of atoms, ions or molecules or numbers of atoms, ions or molecules from moles or vice versa Mass percent composition- the percent composition of a substance by mass Determining the Formula of a Compound Empirical formula- lowest whole number ratio of the atoms in a compound Determination from percent composition data: Step 1: Determine mass composition (if not given) from percent composition (assume 100g and then percents convert to grams) Step 2: Determine moles of each element in the compound Step 3: Determine the lowest whole number ratio of each element in the compound (empirical formula) Determination of emperical formula from combustion data: Use stoichiometry to determine the grams of C and H from the balanced chemical equation (if the combusted substance contains oxygen, determine the mass of oxygen from the mass of the original compound) Molecular formulas- the actual ratio of the atoms of elements in a compound and are whole number multiples of their empirical formulas. For example if the molecular formula of a compound was N 2 O 4, the empirical formula would be NO 2 . In this case the molecular formula is 2 times the empirical formula (NO 2 x 2= N 2 O 4 ). The mass of the molecular formula is necessarily also 2 times that of the mass of the empirical formula. This relationship can then be used to determine the molecular formula of a compund if the empirical formula and molecular mass of the compund are known. Chemical Equations- represent what happens in a chemical reaction reactant---> products (read "Reactants yield products") conservation of atoms (mass)- atoms are neither created nor destroyed in chemical reaction, they are recombined to form different substances mass is neither created nor destroyed chemical reactions (as opposed to nuclear reactions) Chemical reaction must therefor be balanced- have same kinds and numbers of atoms on both sides of the yields sign The physical states of the substances involved in a chemical reaction are represented by symbols: (aq)- aqueous (dissolved in water) (g)- gas (l)- liquid (s)- solid Balancing chemical equations- usually by inspection it helps to do the most complex substance first never change the correct formulas of reactants or products (change the amounts of the substances represented, do not change the substances) balance by placing coefficients in front of the reactant or product species Stoichiometric Calculations: Amounts of reactants and Products Calculations between moles and mass and moles and numbers of particles have already been covered (moles and volume conversion will be covered later). The only new thing here is the use of the mole ratio in a balanced equation to convert moles of one substance to moles of another Calculations Involving a Limiting Reactant. Stoichiometric quantities- the exact amounts of reactants needed so that no amount of any reactant will be left unused Limiting Reactant- a reactant that there is proportionally less of so that it is used up first and limits the amount of product that can be produced you must first determine which reactant is the limiting reactant when doing stoichiometry problems involving limiting reactants to determine which reactant is limiting arbitrarily choose one reactant and use the mole ratio of reactants to see if you have an excess or not of the other reactant Excess reactant- opposite of limiting reactant- some will remain at the completion of a reaction Theoretical yield- the amount of product a reaction should yield if 100% of the limiting reactant is converted into the product Actual yield- the amount of product that is actually produced when the reaction takes place Percent yield- a measure of the efficiency of a chemical reaction or process Percent yield=(actual/theoretical)x100%