Acids, Bases,

1
Unit 8

• Acids, Bases, Salts

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Electrolytes

• Acids, Bases, and Salts are all classified as
  electrolytes
• An electrolyte is a compound that dissociates
  (ionizes) when it dissolves in water AND conduct
  electricity
• To dissociate means to split bonds and turn from
  ONE neutral compound into MULTIPLE ions
• Remember, salt ionic compound
• The dissociation of dissolved salts explains why
  dissolved salts conduct electricity (mobile,
  charged ions are present)
• A nonelectrolyte is any compound that does NOT
  dissociate when dissolved in water
• Any covalent compound (a molecule) that is NOT an
  acid or base example C6H12O6

3
Arrhenius Theory

• Arrhenius theory is one definition of what acids
  and bases could be.
• Arrhenius acids are molecules that dissociate and
  result in H as one of the ions
• More H makes a solution more acidic
• H may attach to a water molecule to produce
  hydronium ions H H2O ? H3O
• See Table K
• Most acid formulas are written with the H as the
  first ion
• 3 Examples from Table K _____, _____, _____
• Exception COOH groups indicate that you have
  an organic acid the last H is the one that
  dissociates into an H ion example from Table K
  __________
• Acids tend to taste sour ex) acetic acid in
  vinegar, citric acid in citrus fruit, Ascorbic
  acid (vitamin C)

4

• Arrhenius Bases are molecules that dissociate and
  result in hydroxide, OH-, as one of the ions
• Having more OH- makes the solution more basic (
  therefore, less acidic)
• Exception When Carbon is the main element in the
  compound, the OH will NOT dissociate
• So, if carbon is present the molecule is NOT a
  base
• These molecules are organic alcohols, not bases
• Example C2H5OH is an alcohol, NOT a BASE
• Arrhenius Bases tend to be metals with OH- ions
• 3 examples from Table L _____, _____, _____
• Bases tend to taste bitter (and feel slippery)
• Ex) Cabbage, black coffee, unsweetened chocolate

5

• Other Acid-Base Theories
• Bronsted-Lowry is another major acid-base theory
• Acids are molecules that donate H ions (a proton
  donator) to other molecules (This is similar to
  Arrhenius theory)
• Bases are molecules that accept H ions (a proton
  acceptor) from other molecules (This is NOT
  similar to Arrhenius theory)
• Find the Bronsted-Lowry base on Table L _______.
• It acts as an H acceptor
• Salts You already know what these molecules are
• So why are you writing notes on this?
• Ok fine, salts are compounds that contain ionic
  bonds
• Metals bonded to Nonmetals
• These compounds do not contain H or OH- but they
  do dissociate into ions
• Ex) MgCl2 dissociates into Mg2 and 2 Cl- ions

6
Measuring Acidity

• The pH scale
• A scale that measures the acidity/basicity of a
  solution
• A logarithmic scale of the H
• The higher the H , the lower the pH value
• The lower the H , the higher the pH value
• Ranges from 0 14
• 0 EXTREMELY acidic
• 14 EXTREMELY basic
• 7 neutral, the H OH-
• Acids Any pH lt 7 is acidic, the H gt OH-
  
• Bases Any pH gt 7 is basic, the H lt OH-

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The pH Scale

• Each pH value is a factor of 10 away from the
  next pH value
• When you change the pH value up or down by 1, the
  solution became either 10x more acidic or 10x
  less acidic
• Examples)
• pH 4 is 10x more acidic than pH 5
• pH 4 is ___ more acidic than pH 6
• pH 9 is ___ less acidic than pH 5

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Acid Base Indicators

• Indicators are molecules that change color as the
  acidity of a solution changes.
• They indicate that a pH change has occurred
• See Table M
• 6 common indicators are listed
• Each has a pH range where they change color
• Each changes between specific colors
• If the solution is at a lower pH than the first
  pH listed, the indicator stays the first color
  listed
• If the solution is at a higher pH than the second
  pH listed, the indicator stays the second color
  listed
• The color change only occurs when the pH is
  between the values listed on Table M
• Ex) Methyl orange is red at pH 3, orange at pH 4,
  and yellow at pH 5

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Acid Base Indicators

• Examples What color is the indicator bromcresol
  green if it is used in a solution at
• pH 2.0
• pH 3.8
• pH 4.5
• pH 5.4
• pH 6.7
• pH 9.0
• pH 11.5

Yellow Yellow Green Blue Blue Blue Blue
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Neutralization Rxns

• A very specific chemical reaction where an Acid
  reacts with a Base to produce a Salt and Water
• The SAME products are always made
• The actual salt may differ, but there will always
  be a salt made
• General Rxn Acid Base ? Salt Water
• Example
• HCl NaOH ? NaCl H(OH)
• Try to predict the products in example 2
• HNO3 KOH ?
• KNO3 H2O

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Neutralization Rxns

• Try example 3
• Ca(OH)2 H2SO4 ?
• CaSO4 2 H(OH)
• Example 4
• HBr Ca(OH)2 ?
• 2 HBr Ca(OH)2 ? CaBr2 2 H2O
• Example 5
• H2SO4 KOH ?
• H2SO4 2 KOH ? K2SO4 2 H2O
• Example 6
• H3PO4 NaOH ?
• H3PO4 3 NaOH ? Na3PO4 3 H2O

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Neutralization Rxns

• After a neutralization occurs, will the leftover
  salt solution still conduct electricity?
• It depends on whether the salt is soluble or not
• Look the salt up on Table F
• Soluble salt mobile ions conducts electricity
• Insoluble salt ions are stuck in crystal
  lattice nonconductor
• Ex) The products of a neutralization rxn between
  H3PO4 and Mg(OH)2 are water and Mg3(PO4)2
• Mg3(PO4)2 is insoluble on Table F, therefore, the
  resulting solution will NOT conduct electricity

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Neutralization Practice

• Complete the following neutralization reactions
  AND predict whether the resulting salt solution
  will conduct electricity
• H2SO4 Mg(OH)2 ?
• H(C2H3O2) KOH ?
• H3PO4 Al(OH)3 ?
• H3PO4 Ca(OH)2 ?

• MgSO4 2 H2O Yes
• K(C2H3O2) H2O Yes
• AlPO4 3 H2O No
• Ca3(PO4)2 6 H2O No

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Titrations

• You titrate in order to determine the molarity of
  an acid or base that has an unknown concentration
  
• You do this by neutralizing it with an acid or
  base that has a known concentration
• Equivalence Point When equal amounts of acid and
  base have been reacted together
• The resulting solution is neutral (pH 7)
• Moles of acid ions moles of base ions
• End Point When an indicator changes color
• When titrating, the goal is pH 7. You must use
  an indicator with an end point that includes pH
  7.
• Use Bromthymol Blue or Litmus (sometimes
  phenolphthalein is used)

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Titrations

• Since you need the of moles of H to equal the
  of moles of OH-, use the formula
• MAVA MBVB
• How many mL of 0.4M HCl are needed to neutralize
  40.0 mL of 0.1M KOH?
• 10mL of HCl
• How much 5M Mg(OH)2 can be neutralized using 30
  mL of 3M H2SO4?
• 18 mL of Mg(OH)2

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What if

• the number of H ions in an acid is DIFFERENT
  from the number of OH- ions in a base?
• MAVA MBVB wont work if you dont know the
  special rules to set it up
• Multiply the acid side of the formula by the
  number of H ions in the formula
• Multiply the base side of the formula by the
  number of (OH)- ions
• Do your calculations

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Examples

• What volume of 0.2M NaOH is needed to neutralize
  50ml of a 0.2M H2SO4 solution?
• 2(0.2M)(50ml) (0.2M)(VB)
• VB 100ml of NaOH
• What volume of 0.6M Ca(OH)2 is needed to
  neutralize 125ml of a 0.25M HCl solution?
• (0.25M)(125ml) 2(0.6M)(VB)
• VB 26ml of Ca(OH)2
• What volume of 0.4M H3PO4 is needed to neutralize
  25ml of a 0.7M solution of Ca(OH)2?
• 3(0.4M)(VA) 2(0.7M)(25ml)
• VB 29.2ml of H3PO4