Week 5 of Book Notes
Week 5 of Book Notes Chem 141
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This 6 page Class Notes was uploaded by Cassidy Zirko on Saturday October 3, 2015. The Class Notes belongs to Chem 141 at University of Montana taught by Mark Cracolice (P) in Fall 2015. Since its upload, it has received 41 views. For similar materials see College Chemistry 1 in Chemistry at University of Montana.
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Date Created: 10/03/15
Week 5 Chem 141 Prof Cracolice Chapter 11 How do Chemists Weight and Count Particles 92815 111 How do Chemists Express the Mass of Molecules 0 Subscript numbers used indicate number of atoms or groups of atoms 0 Number one is always omitted when there is only one atom of an element 0 CaN032 1 calcium atom and 2 nitrate molecules 0 How is the Mass of a Molecule or Formula unit Determined 0 O O O O 0 Formula Mass Based on the chemical formula of the compound Could also be called molecular mass to be more precise Molecular mass average mass of molecules or formula units comparted with the mass of an atom of carbon12 which is exactly 12 atomic mass units Formula mas 2 sum atomic mass in the formula unit Ico2 Carbon 1 X 1201 u 1201u C Oxygen X 1600u 1600u O 1201u 1600u 4401u C02 Could be set up 1201u C 21600u O 4401u C02 Usually written horizontally Rounding off formula and molecular masses I 1 Calculate the formula mass using the atomic masses to as many decimals places as they are known too I 2 Round o the answer to the same number of decimal places as the smallest number of decimal places in any atomic mass used in the calculation Usually two places Hydrogen is usually rounded to the third decimal place because that is the known weight on the periodic table The periodic table is rounded to four sig figs for most elements Always use the most precise weight least sig figs 112 How can Atoms be Counted by Weighing 0 Need to know the number of particles of different substances in the reaction 0 You count the number of particles based on the weight of each of the substances 0 What Grouping is used to Count Particles O 0 Use moles Mole is the amount of any substance that contains the same number of units in the number atoms in exactly 12 grams of a carbon 12 atom Mole refers to the number of particles Week 5 Chem 141 Prof Cracolice 60210 23 O 1 mole of any substance 60210 units of that substance 0 Use mole to find how many atoms formula units or molecules are in a substance 0 How is the Mass of a Mole of Particles Determined 0 Molar Mass mas in grams of one mole of a substance 0 This is the bridge between the particulate level and the macroscopic level 0 Molar mass MassMol gmol 0 Definitions of atomic mass mole and molar mass I Mass of an atom of carbon12 the atomic mass of carbon is exactly 12 atomic mass units I The mass of one mole of carbon12 atom is exactly 12 grams its molar mass is exactly 12 gmol Atomic mass and molar mass of a carbon12 atom are numerically equal Differ only in units 0 The molar mass of any substance in grams per mole is numerically equal to the atomic molecular or formula mass of that substance in the atomic mass units 0 Find atomic or formula mass in u I change units to gmol to have molar mass 0 How do you convert the Mass of a Sample to Number of Particles 0 Based on the relationship in molar mass a per relationship grams per mole 0 Per Can be solved using quantity algebra O Moles and grouping units express the number of particles 00 Changes you make Conversion factors used 39 23 M016 DD umtS 602 10 Molecules atoms or formula units Mole II grams Molar mass I What is the Mass Relationship Among Elements in a Compound 0 Percent the amount of one part of a mixture per 100 total parts in the mixture A parts of AEamixture 100 total pats E the mixture 0 Percent composition the percentage by mass of each element in the compound 0 Use the percent composition of a the elements in a compound as the mass of each element I 586 C 586g C 0 You don t necessarily need to know the percent composition of a compound to change between the mass of the element and the compound 0 All ratios of elements can be used a conversion factors I I CO 1 carbon 1 oxygen I 1201g C 2801 grams CO or 1600 g 0 2801g CO Week 5 Chem 141 Prof Cracolice Chapter 12 How are Chemical Formulas Determined 93015 121 How are Chemical Formulas Determined Combustion Analysis a compound burned for the purpose of analyzing its composition Products of a reaction With carbon and hydrogen or carbon hydrogen and oxygen are C02 and H20 Original mass of sample is known for the CHO compound individual mass of carbon hydrogen and oxygen can be determined How is the Ratio of Atoms in a Compound determined 0 0 Empirical Formula simplest formula of a compound I EX two compounds C2H4 and C3H6 have an empirical formula of Crlen n is an integer all compounds in the formula in the empirical formula will have that same ratio empirical formulas can be the molecular formulas for certain chemical compounds I I NOT both molecular and empirical formula How is Percentage Composition used to find an Empirical Formula 0 Procedure I I Find masses of di erent elements in a sample of a compound I 2 Convert the masses into moles I 3Express the moles of atoms as the lowest possible ratio of whole number integers I 4 Write the empirical formula using the number of each atom in the integer ratios as the subscript Set up each problem like this You can think of the percent of an element as the mass of that element per 100 grams of the compound Percentage compositions figure represent the grams of each element in a 100 gram sample of the compound During step 3 divide each number of moles by the smallest number of moles Ratio of atoms of the element in compound ratio of moles of atoms in a compound If either quotient in the mole ratio are not close to a Whole number them multiply by a small number I I mole ratio 1249 this is about 125 so multiply by 4 to get a formula ratio of 5 Which is a Whole number How are Molecular Formulas Determined 0 0 Divide the molar mass of the compound by the molar mass of empirical formula to get how many times the empirical Will go into the actual compound Procedure I 1 Determine the empirical formula Week 5 Chem 141 Prof Cracolice 2 Calculate the molar mas of the empirical formula 39 3 Determine the molar mass of the compound usually given 4 Divide the molar mas of the compound by the molar mass of the empirical formula to get the number of empirical formula units per the molecular given 39 5 Multiply the empirical formula by the factor from step four and write the molecular formula Chapter 13 How is a Chemical Change Expressed Symbolically 10215 131 What Macroscopic Evidence indicates Chemical Change Identity of the substance is destroyed and new substance formed Particles are changes but all of the elements in the reactants will still be the same in the products The number and type of atoms are the same Many chemical reactions are not seen Sensory evidence can be evidence of a physical change as well but not always 132 How are Chemical Equations Written Balanced and Interpreted State symbols indicate the state of each compound and is sometimes omitted 4 state symbols always written as a subscript Aqueous solution a substance that is dissolved into water Most chemical reactions require an energy transfer that is usually is heat so it is omitted form the chemical equation Qualitative Equation an chemical equation that is not balance Balanced placing a coefficient in front of one or more of the formulas indicating it is used more than once A balance equation is both qualitative and quantitative Balance the equation entirely by using coefficients placed before the different chemical formulas Procedure Week 5 Chem 141 Prof Cracolice 0 I Write a qualitative description of the reaction In this step write the formulas based on the reactants and products 0 2 Quantify the description by balancing the equation Done by adding coe icients 0 Chemical equation has provides qualitative description of the reaction 0 Equations interprets the reaction at the particulate level 0 Molar interpretation involves reading coefficients as the number of moles of the reactants and products 0 Molar masses do not give information on the masses 133 What Patterns Characterize a Chemical Change 0 Procedure 0 I Classify the reaction 0 2 Write qualitative description of the reaction write the formulas given Reactants Products 0 3 Quantify the description of the reaction by balancing the reaction 0 What Pattern is Characterized by a Combination Reaction 0 Usually two elements that form a single product but sometimes a compound and an element to create the single product 0 What Pattern is Characterized by a Decomposition reaction O Reactant is a single compound 0 Products are two elements or an element and a compound 0 What Patter is Characterized by a Single Replacement Reaction 0 One kind of oxidationreduction reaction redox reaction Reactants are always an element and a compound Metal will replace a metal or a hydrogen Nonmetal will replace a nonmetal in a compound Polyatomic ions that are unchanged in the reaction can be balanced as a unit rather than as individual elements 0000 0 What Pattern is Characterized by a Burning Reaction 0 Another type of redox reaction 0 A compound containing only carbon and hydrogen or carbon hydrogen and oxygen will burn and react with oxygen in the atmosphere Oxidization means loss of electrons during elector transfer 0 Week 5 Chem 141 Prof Cracolice 0 Products are always C02 and H20 0 What Pattern Characterized a Double Replacement Reaction 0 Q 0000 O Precipitate When solutions of two compounds are mixed positive ion from one compound and the negative ion from the second compound Will combine to form a solid compound that Will settle at the bottom of the container This is a precipitation reaction Double Replacement Reaction ions of two reactants will appear to change partners in the products AX BY I AY BX Acid compound that releases hydrogen ions H to water molecules Base substance that contains a hydroxide ion OH39 Neutralization Reaction When acid is added to an equal amount of base each hydrogen ion reacts With the hydroxide ion to form water The acid and base neutralize each other 0 Acid Base I Water Salt
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