Chapter 6 Chemical Accounting

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Chapter 6 - Chemical Accounting

• Equations, Moles, Solutions, Molarity
• Note We will not cover the gas laws.

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Homework and Quizzes

• Homework, Chapter 6 Pages 181 187
• 10 13, 17 19, 21, 22, 24, 35 39, 41, 43,
• 45 47, 49, 67, 69, 71, 74, 75
• Blackboard Graded Quiz

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I. Chemical Equations Review

• A chemical equation is the representation of a
  chemical reaction (rxn) in terms of chemical
  formulas.
• Example 2 Mg 1 O2 -----) 2 MgO
• Notes - Mg O2 are called reactants
• - MgO is called a product
• - ------) goes to give
• - 2s understood 1s are balancing
  coefficients
• Balancing Coefficients can be molecules/atoms
  or they can represent moles of compounds/atoms.

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I. Chemical Equations Review

• Why do rxns occur? Reactions may occur in order
  to produce more stable products.
• How do rxns occur? Molecules or atoms are
  traveling at high speeds in gas or in solution.
  If they collide with enough energy, then the
  valence electrons are rearranged old bonds break
  and new ones form, which results in new
  compounds.
• Note May need a catalyst to enable a chemical
  reaction to take place. Catalyst substance
  which speeds up a chemical reaction but is not
  consumed.
• A biochemical catalyst is called an enzyme.
  Examples Pepsin, Trypsin and Chymotrypsin
  digestive enzymes which catalyze the cleavage of
  proteins.

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I. Chemical Equations Review

• - Mass is neither lost or gained in a chemical
  reaction so, we need to balance the equation
  without changing the identity of the reactants or
  products - change only coefficients. Only give
  the smallest set of whole s.
• This is done by inspection however, on difficult
  reactions it is best to first balance the
  elements which occur the fewest times.
  Examples
• ___Al ___Cl2 ---------) ___AlCl3
• ___Ca ___H2O --------) ___Ca(OH)2
  ___H2
• ___HCl ___Al(OH)3 ---) ___AlCl3
  ___H2O
• ___C2H4 ___O2 ---------) ___CO2
  ___H2O

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II. Mole A. Review

• Chemists devised a new term called a mole or
  mol.
• A mole has two definitions
• Definition 1 6.02x1023 number of that object
• 1.00 mole 6.02x1023
• Definition 2 The formula weight (FW) in grams
• 1.00 mole FW in g (from periodic chart)
• The above two definitions work because 6.02x1023
  protons or neutrons weights 1.00 gram.
• From the two definitions obtain 6.02x1023
  FW in g

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II. Mole A. Review
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II. Mole A. Review

• Mole Conversion Factors to know
• 1.00 mole Formula Weight in Grams
• 1.00 mole 6.02x1023
• Example Typical conversion factors for H2O
• 1.00 mole 18.0 g H2O 1.00 mole H2O
• 18.0 g H2O 1.00 mole 6.02x1023 molecules

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II. Mole B. Calculations

• 1. How many grams are in 1.0 mole of H2SO4.
• 2x1 (H) 32 (S) 4x16 (O) 98 g H2SO4
• 2. How many grams are in 1.00 mole of Ca(NO2)2.
  
• 40 (Ca) 2x14 (N) 4x16 (O) 132 g
  Ca(NO2)2
• 3. How many moles are in 0.36 g Be.
• 0.36g Be x 1.0 mole Be 0.040 mole Be
• 9.0g Be
• 4. How many moles are in 36 g of H2O.
• 36g H2O x 1.0 mole H2O 2.0 moles H2O
• 18 g H2O

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II. Mole B. Calculations continued

• 5. How many g present in 1.5x10-3 moles CaCO3?
• 1.5x10-3 moles CaCO3 x 100. g CaCO3
  0.15 g CaCO3
• 1.00 mole CaCO3
• 6. How many molecules (mc) are in 0.20 moles (m)
  H20
• 0.20 m H2O x 6.0x1023 molec 1.2x1023
  molecules H2O
• 1 m H2O
• 7. How many moles (m) of O atoms are in 2.0 moles
  of H3PO4?
• 2.0 m H3PO4 x 4 m O 8.0
  moles of O atoms
• 1 m H3PO4

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II. Mole C. Chemical Formulas

• composition (g element) x 100 .
• total g compound
• Example (Note pick 1 mole of compound for
  total g)
• Calculate composition of C and of H in C4H10
• - Total g of compound (4 x 12 g C) (10 x 1 g
  H) 58 g
• C (48 g C / 58 g) x 100 83 C
• H (10 g H / 58 g) x 100 17 H

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III. Stoichiometry A. Introduction

• 4 Fe 3 O2 -----------) 2 Fe2O3
• Balancing coefficients in a RXN can be used as
  molecules or moles. So, 4 moles of Fe reacts
  with
• 3 moles of O2 to yield 2 moles of Fe2O3
• - The coefficients in a balanced chemical
  reaction can be used as conversion factors in
  calculating the amount of product produced or the
  amount of reactant used.
• - Example How many moles of Fe2O3 will be
  produced from
• 4 moles of Fe? 2 moles? 8 moles?
  1 mole?
• 2 1 4 0.5

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III. Stoichiometry B. Problems

• - The previous problem could be easily solved
  however, more difficult problems can be solved
  using the conversion factor method and the
  following logic
• a b
  c
• g known -----) moles known -----)
  moles unknown -----) g unknown
• Periodic Chart Balanced
  Chemical Eqn Periodic Chart
• - Note that you may be required to enter to
  exit the problem with either grams or moles.

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III. Stoichiometry B. Problems Continued

• - You are given only one amount of reactant and
  you assume that there is enough of the other
  reactants to completely react.
• - You are given 1 CH4 2 O2 ----) 1 CO2
  2 H2O
• How many moles of H2O can be produced from 109
  moles of CH4?
• 109 m CH4 x 2 m H2O 218 mole H2O
• 1 m CH4

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III. Stoichiometry B. Problems Continued

• -You are given 1 C 1 O2 --------)
  1 CO2
• - How many g of O2 will react with 10.0 g of C?

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III. Stoichiometry B. Problems Continued

• Given 2 Al(OH)3 3 H2SO4
  -----) 6 H2O 1 Al2(SO4)3
• 1. How many moles of H2SO4 are needed to produce
  8.0 moles of Al2(SO4)3
• 8.0 moles Al2(SO4)3 x 3.0 moles H2SO4 / 1.0
  mole Al2(SO4)3 24 moles H2SO4
• 2. How many moles of H2O will be produced from
  156 g of Al(OH)3 ?
• 156 g Al(OH)3 x 1 mole Al(OH)3 x
  6 mole H2O
• 
  
  6.00 mole H2O
• 78.0 g Al(OH)3
  2 mole Al(OH)3

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III. Stoichiometry B. Problems Continued

• Given 4 Al 3 O2 -------) 2
  Al2O3
• 3. How many g of Al are needed to react with 64
  g of O2?
• 1 mole O2 4 mole Al
  27 g Al
• 64 g O2 x x
  x 72 g Al
  
• 32 g O2 3 mole O2
  1 mole Al
• Periodic Chart
  
  Periodic Chart
• (1 mole FW in g) Balanced
  Chemical Eqn (1 mole FW in g)

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IV. Solutions A. Introduction

• Definitions
• Solution homogeneous mixture of two or more
  substances.
• Solvent Single component of a solution which is
  present in greatest amount.
• Solute(s) Component(s) of a solution which are
  present in smaller amounts.
• Concentration Measure of amount of solute in a
  given volume of solution.

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IV. Solutions B. Concentration

• Concentration Units There are several ways that
  we use to quantitatively indicate amounts of
  solute in a solution.
• 1. W/V g solute / mL solution x 100
  
• Example 18 g of NaCl is in 200. mL of solution.
  What is NaCl?
• 18 g / 200. mL x 100 9.0
• 2. Parts per Billion (ppb) ng solute / g
  solution (mL if aqueous)
• Example 520 ng of benzene are found in 1.0 L of
  water. What is the ppb?
• ppb 520 ng benzene / 1000 mL 0.52 ng/mL
• 3. Molarity moles solute / L solution M
  m/L
• - May have to calculate M, L or moles (m). Use
  the equations
• M m/L m MxL L m/M

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IV. Solutions B. Concentration
Examples

• a) What is the M if dissolve 4 moles in 0.5 L?
• M m/L 4 m / 0.5 L 8 m/L or 8 M
• b) 0.80 g of NaOH is dissolved in 200. mL.
  Calculate the M
• M m/L 0.80 g NaOH x 1 mol NaOH / 40. g
  0.020 mol
• M 0.020 mol / 0.200 L 0.10 m/L or 0.10 M
• c) How many moles of HI are in 3.0 L of 2.0 M HI?
• M m/L m M x L 2.0 m/L x 3.0 L 6.0
  m or mole s

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IV. Solutions C. Solubility

• Soluble Insoluble refer to how much solute
  dissolves in a given solvent with water being the
  most common solvent.
• Examples Group IA, nitrate, acetate and
  ammonium compounds are very soluble in water
  except for group IA ammonium, most Sulfides are
  not soluble.
• Water dissolves many ionic and less polar
  compounds.
• Non-polar compounds like organic compounds do not
  dissolve in water, but dissolve in organic
  solvents.
• The general rule on solubility is Like Dissolves
  Like.

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V. Review of Moles

• 1) Use moles to convert from g to moles or from
  moles to g. 1 mole FW in grams
• - How many moles are 32 g of Br2?
• 32 g Br2 x 1 mole Br2 0.20 mole
  Br2
• 160 g Br2
• 2) Use moles to convert to numbers of atoms or
  molecules. 1 mole 6.02x1023
• - How many molecules are in 76 g of F2?
• 76 g F2 x 1 mole F2 x 6.02x1023 molec F2
  1.2x1024 molec
• 38 g F2 1 mole F2

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V. Review of Moles

• 3) Use moles to calculate quantities in
  reactions.
• 2 Mg 1 O2 -----) 2 MgO
• - How many moles of MgO can be made from 2.0
  moles of O2?
• 2.0 moles O2 x 2 mole MgO 4.0 m
  MgO
• 1 mole O2
• -Note If start off with g of a chemical, then
  convert to moles first

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V. Review of Moles

• 4) Use moles to calculate M concentrations.
• M m / L
• - What is the M of a solution that contains 8.0
  moles of NaOH in 4.0 L water?
• M m 8.0 moles NaOH 2.0 moles/L of
  NaOH
• L 4.0 L