Acids and Bases Notes

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Acids and Bases Notes

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I. Strength of Acids and Bases

• A. Bases
• Strong Bases metal hydroxides of Group I and II
  metals (except Be) that are soluble in water and
  dissociate (separates into ions) completely in
  dilute aqueous solutions
• Weak Bases a molecular substance that ionizes
  only slightly in water to produce an alkaline
  (basic) solution (ex. NH3)

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Johnny was a chemist, a chemist he's no more for
what he thought was H2O was H2SO4.

• B. Acids
• Strong Acids an acid that ionizes (separates
  into ions) completely or very nearly completely
  in aqueous solutions (will not be on Ka chart).
• Weak Acids an acid that ionizes only slightly
  in dilute aqueous solutions (will be on the Ka
  chart).
•  

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Why do white bears dissolve in water? Because
they're polar.

• 1. Binary or hydrohalic acids HF, HCl, HBr,
  HI, etc. hydro____ic acid are usually strong
  acids
• HF and H2S are weak hydrohalic acid. Although
  the H-F bond is very polar, the bond is so strong
  (due to the small F atom) that the acid does not
  completely ionize.

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• 2. Oxyacids contain a polyatomic ion
• a. Most common form (MCF) ic ending strong
  acids (contain 2 oxygen per hydrogen)
• HNO3 nitric from nitrate
• H3PO4 - phosphoric from phosphate
• H2SO4 - sulfuric from sulfate
• HClO3 - chloric from chlorate

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• b. Acids with l less oxygen than the MCF ous
  ending- weaker acids
• HNO2 nitrous from nitrite
• H3PO3 - phosphorous from phosphite
• H2SO3 - sulfurous from sulfite
• HClO2 - chlorous from chlorite
•  
• c. Acids with 2 less oxygen than the MCF
  hypo___ous very weak acids
• HNO - hyponitrous
• H3PO2 - hypophosphorus
• HClO - hypochorous
•  

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• d. Acids with 1 more oxygen than the MCF
  per______ic very strong acids
• HClO4 perchloric acid
• HNO4 - pernitric acid
• e. Organic acids have carboxyl group -COOH -
  usually weak acids
• HC2H3O2 - acetic acid
• C7H5COOH - benzoic acid

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Q What's the most important thing to learn in
chemistry?A Never lick the spoon

• II. Characteristics of Acids and Bases (page
  453-458)
• There are 3 different definitions for acids and
  bases and I have summarized them all here. Keep
  in mind that there are some exceptions and this
  is just a guide to follow when trying to
  determine if a substance is an acid or a base.

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Acids Bases

• Usually contain OH
• Bitter taste
• Litmus paper turns blue
• pH paper 8-14 or pH meter
• Phenolphthalein pink
• Feels slippery
• Electrolyte
• pHgt7

• Usually begin with H
• Sour taste
• Litmus paper turns red
• pH paper 1-6 or pH meter
• Phenolphthalein - colorless
• Feels like water
• React with metals to produce H2
• Electrolyte
• pHlt7

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Acids Bases

• Arrhenius Acid donates (or produces) hydronium
  ions (H3O) in water or hydrogen ions (H) in
  water
• Bronsted-Lowry Acid donates a proton (H) in
  water, H3O has an extra H, if it donated it to
  another molecule it would be H2O (page 467)
• HNO3 H2O ? H NO3- 
• HNO3 H2O ? H3O NO3-  
• HCl H2O ? H Cl-
• HCl H2O ? H3O Cl-
•  

• Arrhenius Base donates (or produces) hydroxide
  ions (OH-) in water
• Bronsted Lowry Base accepts a proton in water,
  OH- needs an extra H if it accepts one from
  another molecule it would be H2O (page 468)
• KOH H2O ? K OH-
• NH3 H2O ? NH4 OH-

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Acids Bases

• Lewis Base Not all bases contain OH, any atom,
  ion, or molecule that donates an electron pair to
  form a covalent bond it a base

• Lewis Acid Not all acids contain H, any atom,
  ion, or molecule that accepts an electron pair
  from a covalent bond is an acid

Q. What do you do when you find a dead chemist?
A. Barium.

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HF H2O ? F -
H3O Acid Base Conjugate
Conjugate Base Acid
Conjugates

• Here HF donated a proton (H) to the water and
  the water accepted the proton (H).
• HF is referred to as the acid and water is
  referred to as the base.
• The fluoride ion, F- is referred to as the
  conjugate base of HF. F- can accept a proton
  (H) to be stable.
• The hydronium ion, H3O is referred to as the
  conjugate acid of water. H3O can donate a
  proton (H) to be stable.

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Example Determine the acid, base, conjugate
acid, and conjugate base in each of the following
equations

• HCl H2O ? Cl- H3O
  
• Acid Base Conjugate
  Conjugate
•   Base Acid
•  H2SO4 H2O ? HSO4- H3O
• Acid Base Conjugate
  Conjugate
•   Base Acid
•  NH3 H2O ? OH- NH4
• Base Acid Conjugate Base
  Conjugate Acid

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• 2. What is the conjugate base of the following
  substances?
• H2O ________________
• NH4________________
• HNO2_______________
• HC2H3O2_________________
•  
• 3. What is the conjugate acid of the following
  substances?
• HCO3-__________________
• H2O____________
• HPO42-____________
• NH3___________

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III. pH Scale brackets mean concentration

• The pH scale indicates the hydronium ion
  concentration, H3O or molarity, of a solution.
  (In other words how many H3O ions are in a
  solution. If there are a lot we assume it is an
  acid, if there are very few it is a base.)
• Q How do you make a
• 24-molar solution?
• A Put your artificial teeth
• in water.

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Where does the pH scale come from?
H
1 X 100 1 X 10-1 1 X 10-2 1 X 10-3 1 X 10-4 1 X 10-5 1 X 10-6 1 X 10-7 1 X 10-8 1 X 10-9 1 X 10-10 1 X 10-11 1 X 10-12 1 X 10-13 1 X 10-14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH
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pOH Scale

• The pOH scale indicates the hydroxide ion
  concentration, OH- or molarity, of a solution.
  (In other words how many OH- ions are in the
  solution. If there are a lot we assume it is a
  base, if there are very few it is an acid.)

Two chemists meet for the first time at a
symposium. One is American, one is British. The
British chemist asks the American chemist, "So
what do you do for research?" The American
responds, "Oh, I work with aerosols." The British
chemist responds, "Yes, sometimes my colleagues
get on my nerves also."
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• OH-

1 X 100 1 X 10-1 1 X 10-2 1 X 10-3 1 X 10-4 1 X 10-5 1 X 10-6 1 X 10-7 1 X 10-8 1 X 10-9 1 X 10-10 1 X 10-11 1 X 10-12 1 X 10-13 1 X 10-14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pOH
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Example

• Lemon juice (citric acid) pH 2, pOH 12
• Pure water pH 7, pOH 7
• Milk of magnesia pH 10, pOH 4

• The last words of a chemist
• And now for the taste test.
• 2. I wonder if this is hot?
• 3. And now a little bit of this...
• 4. And now shake it a bit.

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4. Calculations Involving pH, pOH, H3O, and
OH- of strong Acids and Bases
1st determine which ion will be produced, either
OH or H3O (Acids produce H3O and bases produce
OH-). 2nd use formula to determine pH or pOH.
3rd check to see if answer is reasonable. pH
-log H3O pOH -log OH- pOH pH
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Example Problems

• 1.      What is the pH of a 0.001M NaOH solution?
• 1st step Hydroxide will be produced and the
  OH- 0.001M
• 2nd step pOH -log 0.001
• pOH 3
• pH 14-3 11

The answer to the problem was "log(1x)". A
student copied the answer from the good student
next to him, but didn't want to make it obvious
that he was cheating, so he changed the answer
slightly, to "timber(1x)."
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• 2. What is the pH of a 3.4X10-5M HCl solution?
• 3. What is the pH of a solution if the pOH 5?
• 4. What is the pH of a 10 liter KOH solution if
  5.611 grams of KOH were used to prepare the
  solution?
• 5. What is the pOH of a 1.1X10-5M HNO3 solution?
• 6. If the pH of a KOH solution is 10.75, what is
  the molar concentration of the solution? What is
  the pOH? What is the H?

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• The pH of a strong acid cannot be greater than 7.
  If the acid concentration H3O is less than
  1.0X10-7, the water becomes the important source
  of H3O or H and the pH is 7.00. Just
  remember to check if you answer is reasonable!
• 7.      What is the pH of a 2.5X10-10M HCl
  solution?
•  
•  
• 8.      What is the pH of a 1.0X10-11M HNO3
  solution?

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• 3. Amphoterism and WaterWater is an amphoteric
  substance - a substance that can act as an acid
  or as a base. Autoionization of water
• H2O H2O ? H3O OH-

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• Ion product constant for water (Kw)
  Kw H30OH- or Kw HOH-
• Because at 25C H l.0 X l0-7 M and OH-
  l.0 X l0-7 M the Kw 1.0 X l0-14 mol2/L2
  
• No matter what an aqueous solution contains, at
  25C H OH- l.0 x l0-14
• Kw varies with temperature.
• Neutral solution H OH- Acidic
  solution H gt OH- Basic solution
  H lt OH-

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Calculations Involving Weak Acids

• Weak acid strength is compared by the Ka values
  of the acids. The smaller the Ka, the weaker the
  acid. Strong acids do not have Ka values because
  strong acids completely ionize in water so there
  would be almost no unionized acid

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Calculations Involving Weak Bases

• Weak base strength is compared by the Kb values
  of the bases. The smaller the Kb, the weaker the
  base. Strong bases do not have Kb values because
  strong bases completely ionize in water so there
  would be almost no unionized base

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C. Calculations Involving pH of Weak Acids - RICE

• Calculating the pH of weak acids involves setting
  up an equation. Always start by writing the
  equation, setting up the acid equilibrium
  expression (Ka), defining initial concentrations,
  changes, and final concentrations in terms of x,
  substituting values and variables into the Ka
  expression and solving for x. The RICE method
  will be used.

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C. Calculations Involving pH of Weak Acids - RICE
R Reaction
I Initial concentration
C Change
E Equilibrium concentration
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Example Calculate the pH of a 3.5 M solution of
acetic acid.
R Reaction HC2H302 H20 H30 C2H302-
I Initial concentration 3.5 --- 0 0
C Change -x x x
E Equilibrium concentration 3.5 x x x
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• K productscoef
• reactantscoef
• So K H30 C2H302-
• HC2H302
• K for acteic acid is 1.8 X 10-5. Substituting we
  get
• 1.8 X 10-5 xx
• 3.5 x
• Because of sig figs we can neglect the -x

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Practice problem 2

• Find the pH of a l.50 M solution benzoic acid
  (C6H5COOH) solution. Ka 6.4 X 10-5

R Reaction
I Initial concentration
C Change
E Equilibrium concentration
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Practice problem 3

• Find the pH of a l5.0 M ammonia solution.

R Reaction
I Initial concentration
C Change
E Equilibrium concentration
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IV. Acid Rain

• Many industrial processes produce gases such as
  NO, NO2, CO2, SO2, and SO3. These compounds can
  dissolve in atmospheric water to produce acidic
  solutions that fall to the ground in the form of
  rain or snow. Marble found in many buildings and
  statues is composed of calcium carbonate, when
  acid snow or rain falls on these structures a
  great deal of damage is caused. (page 475)

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V. Neutralization Reactions

• Neutralization Reaction the reaction of an acid
  with a base to produce water and a salt. (This
  occurs when H3O and OH- ions are supplied in
  equal numbers by the reactants.)
• Salt - an ionic compound composed of a cation
  from a base and an anion from an acid.
• Example HCl NaOH ? HOH NaCl

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Practice

• H2SO4 KOH ? K2SO4 H2O
• HCl NaOH ? NaCl
  H2O
• 3. phosphoric acid and ammonium hydroxide

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VI. Titrations

• Titration A neutralization reaction of an acid
  by a base or vice versa it is usually used to
  find the concentration, molarity, of an unknown
  acid or base. The concentration of the other is
  known.
• Standard solution solution of known
  concentration (in buret). The titrant is added
  to a solution of unknown concentration until the
  substance being analyzed is just consumed
  (stoichiometric point or equivalence point).
• _____________- change color at the end point of a
  titration. Examples phenolphthalein and methyl
  orange
• ____________________ point-the point at which the
  two solutions used in a titration are present in
  chemically equivalent amounts.