CHM 1020

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CHM 1020

• Lecture 8
• Acids Bases

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Properties

• Acids
• Strong weak electrolytes
• Sour/tart
• Sting
• Reacts with metals to forms H2
• Turns blue litmus paper red
• Neutralizes basic solutions

• Bases
• Strong weak electrolytes
• Bitter
• Slippery
• No reaction with metals
• Turns red litmus paper blue
• Neutralizes acidic solutions

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• Identify each as a characteristic of an
• A) acid or B) base.
• ____1. has a sour taste
• ____2. produces OH- in aqueous solutions
• ____3. has a chalky taste
• ____4. is an electrolyte
• ____5. produces H in aqueous solutions

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Definitions of Acids Bases

• Arrehenius
• Acid substance that separates in water to
  produce hydrogen ions
• Base substance that separates in water to
  produce hydroxide ions
• Acids can be monoprotic, diprotic or triprotic

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• According to the BrØnsted-Lowry theory,
• acids donate a proton (H).
• bases accept a proton (H).

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• Conjugate Acid particle formed when bases gains
  a proton
• Conjugate base particle formed when an acid has
  donated a proton
• Conjugate acid-base pair 2 substances related
  by the loss or gain of a single proton
• Amphoteric substance that can act as both an
  acid and a base

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• A. Write the conjugate base of the following.
• 1. HBr
• 2. H2S
• 3. H2CO3
• B. Write the conjugate acid of the following.
• 1. NO2-
• 2. NH3
• 3. OH-

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• Identify the sets that contain acid-base
  conjugate pairs.
• 1. HNO2, NO2-
• 2. H2CO3, CO32-
• 3. HCl, ClO4-
• 4. HS-, H2S
• 5. NH3, NH4

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• Determine the acid, base, conjugate acid-base
  pair for the following
• HNO3 H2O ? H3O NO3
• Na2CO3 H2O ? H2CO3 OH -

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• Lewis
• Acid electron-pair acceptor
• Base electron-pair donor

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• A strong acid completely ionizes (100) in
  aqueous solutions.
• HCl(g) H2O(l) H3O (aq) Cl- (aq)
  
• A weak acid dissociates only slightly in water to
  form a few ions in aqueous solutions.
• H2CO3(aq) H2O(l) H3O(aq) HCO3-
  (aq)

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• In water, the dissolved
• molecules of a strong
• acid
• dissociate into ions.
• give large concentrations of H3O and the anion
  (A-).

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• In weak acids,
• only a few molecules dissociate.
• most of the weak acid remains as the
  undissociated (molecular) form of the acid.
• the concentrations of the H3O
• and the anion (A-) are small.

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• Strong acids
• make up six of all the acids.
• have weak conjugate bases.

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• Weak acids
• make up most of the acids.
• have strong conjugate bases.

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• Strong bases
• are formed from metals of Groups 1A (1) and 2A
  (2).
• include LiOH, NaOH, KOH, and Ca(OH)2.
• dissociate completely in water.
• KOH(s) ? K(aq) OH-(aq)

• Weak bases
• are most other bases.
• dissociate only slightly in water.
• form only a few ions in water.
• NH3(g) H2O(l) NH4(aq) OH-(aq)

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• Identify each of the following as a strong or
  weak acid or base.
• A. HBr
• B. HNO2
• C. NaOH
• D. H2SO4
• E. Cu(OH)2

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Ionization of Water

• In water,
• H is transferred from one H2O molecule to
  another.
• one water molecule acts as an acid, while another
  acts as a base.
• H2O H2O H3O OH-
  
• .. .. ..
  ..
• O H HO HOH OH-
• .. .. ..
  ..
• H H H
• water water hydronium
  hydroxide ion ()
  ion (-)

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• In pure water,
• H3O 1.0 x 10-7 M
• OH- 1.0 x 10-7 M
• In acidic solution,
• increases the H3O.
• cause the H3O to exceed 1.0 x 10-7 M.
• decreases the OH-.

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• In basic solutions,
• increases the OH-.
• causes the OH- to exceed 1.0 x 10- 7M.
• decreases the H3O.

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• The ion product constant, Kw, for water
• is the product of the concentrations of the
  hydronium and hydroxide ions.
• Kw H3O OH-
• can be obtained from the concentrations in pure
  water.
• Kw H3O OH-
• Kw 1.0 x 10- 7 M x 1.0 x 10- 7 M
  
• 1.0 x 10- 14
• In neutral, acidic, or basic solutions,
• the Kw is always 1.0 x 10-14.

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Examples

• What is the H3O of a solution if OH- is 5.0
  x 10-8 M?
• If lemon juice has H3O of 2 x 10-3 M, what is
  the OH- of the solution?
• 1) 2 x 10-11 M
• 2) 5 x 10-11 M
• 3) 5 x 10-12 M

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• The OH- of an ammonia solution is 4.0 x 10-2 M.
  What is the H3O of the solution?
• 1) 2.5 x 10- 11 M
• 2) 2.5 x 10-12 M
• 3) 2.5 x 10-13 M

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pH Scale

• is used to indicate the acidity of a solution.
• has values that usually range from 0 to 14.
• is acidic when the values are less than 7.
• is neutral with a pH of 7.
• is basic when the values are greater than 7.

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• The pH of solutions can be determined using
• a) pH meter
• b) pH paper
• c) indicators that have specific colors at
  different pH values.

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• Determine the pH of the following solutions
• H 1 X 10 -6 M
• OH 1 X 10 -2 M
• OH 4.0 X 10 -11 M
• H 5.0 X 10 -6 M
• What if the H given the following pHs
• 6
• 12.2
• 2.64
• What is the OH given the following pHs
• 9
• 4.5
• 7.6

• pH - log H
• pOH - log OH
• pH pOH 14
• kw HOH

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• Titration
• is a laboratory procedure used to determine the
  molarity of an acid.
• uses a base such as NaOH to neutralize a measured
  volume of an acid.

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• An indicator
• is added to the acid in the flask.
• causes the solution to change color when the acid
  is neutralized.

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• At the end point,
• the indicator gives the solution a permanent pink
  color.
• the volume of the base used to reach the end
  point is measured.
• the molarity of the acid is calculated using the
  neutralization equation for the reaction.

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Buffers

• When an acid or base is added
• to water, the pH changes drastically.
• to a buffer solution, the pH is maintained pH
  does not change.

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• Buffers
• resist changes in pH from the addition of acid or
  base.
• in the body, absorb H3O or OH- from foods and
  cellular processes to maintain pH.
• are important in the proper functioning of cells
  and blood.
• in blood maintain a pH close to 7.4. A change in
  the pH of the blood affects the uptake of oxygen
  and cellular processes.

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• A buffer solution
• contains a combination of acid-base conjugate
  pairs.
• may contain a weak acid and a salt of its
  conjugate base.
• typically has equal concentrations of a weak acid
  and its salt.
• may also contain a weak base and a salt of the
  conjugate acid.

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• The function of the weak acid in a buffer is to
  neutralize a base. The acetate ion produced adds
  to the available acetate.
• CH3COOH OH- CH3COO- H2O
• acetic acid base
  acetate ion water

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Function of Conjugate Base

• The function of the acetate ion CH3COO- is to
  neutralize H3O from acids. The acetic acid
  produced contributes to the available weak acid.
• CH3COO- H3O CH3COOH H2O
• acetate ion acid
  acetic acid water

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Summary of Buffer Action

• Buffer action occurs as
• the weak acid in a buffer neutralizes base.
• the conjugate base in the buffer neutralizes
  acid.
• the pH of the solution is maintained.

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• Identify each solution as
• 1) acidic 2) basic 3) neutral
• A. ___ HCl with a pH 1.5
• B. ___ pancreatic fluid H3O 1 x 10-8 M
• C. ___ Sprite soft drink pH 3.0
• D. ___ pH 7.0
• E. ___ OH- 3 x 10-10 M
• F. ___ H3O 5 x 10-12

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Neutralization reactions

• Write the products of the following reactions of
  acids.
• A. MgCO3(s) 2HCl(aq)
• B. HCl NaOH
• C. 2HCl Ca(OH)2