Acids and Bases

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Chapter 18

• Acids and Bases
• Rainbow Connection
• 2

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Ch. 18- Acids and Bases

• Acids and bases have a central role in chemistry
• They affect our daily life
• Uses manufacturing processes, environmental
  issues, functioning of our bodies
• Acid/ Base Video

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Properties of Acids

• Have pH ? 0-6
• Tart or sour taste
• Will conduct electricity
• Cause indicators to change color (turns blue
  litmus red)
• Reacts w/ metals (Mg,Zn) to form H2 gas
• Neutralize w/ a base? forms a salt and H20
• Ex. Citrus foods, tomatoes, vinegar

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Acid Formulas (memorize)

• HCl ( Hydrochloric Acid)
• HNO3 (nitric acid)
• H2SO4 (sulfuric acid)
• H2CO3 (carbonic acid)
• HC2H3O2 (acetic acid)
• H3PO4 (phosphoric acid)

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Properties of Bases

• Also known as alkaline
• pH ? 8-14
• Have a bitter taste, slippery feel
• Causes indicators to change color (turns red
  litmus blue)
• Conducts electricity
• Reacts w/ acid to neutralize ? form a salt and
  H2O
• Ex. Cleaning products, soap, baking soda

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Acid/ Base Theories

• Definitions have changed over the years as new
  information has been found
• Arrhenius Theory video

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Arrhenius Theory (1887)

• Applies to a H2O solution
• Svante Arrhenius (Swedish) saw that not only do
  acids/ bases conduct electricity, they ionize (or
  release charged particles) when dissolved in
  water
• Theory
• Acids- substance that ionize produced (H)
  hydrogen ions in H2O
• Bases- ionize to produce (OH-) hydroxide ions in
  H2O

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• Ex. HCl ? H(aq) Cl-(aq)
• ACID
• NaOH ? Na(aq) OH-(aq)
• BASE

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Brønsted- Lowry Theory (1923) (video)

• Working independently of each other, Johannes
  Brønsted (Danish) and Thomas Lowry (English)
  defined a theory that can be used w/ all solvents
  not just H2O (they found that substance lost or
  gained protons)
• Acid- in a chemical reaction, this is the
  substance that loses or donates a proton (H ion)
• Base- substance that accepts or gains a proton
  (H ion proton)

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• HCl H2O ? H3O Cl-

Accepts proton (base)
Donates (loses) proton (acid)
H3O ? hydronium ion (formed when H2O gains
H ion)
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• NH3 H2O ? NH4 OH-

Accepts proton (base)
Donates (loses) proton (acid)
Amphoteric (H2O) acts as an acid or a base
(depending on the situation)
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Conjugates

• The particles that are formed as products can
  react again (reversible reaction), they behave
  like acids and bases (we call these conjugates)
• Conjugate video

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• Conjugate Acid - Particle that forms after the
  base accepts a proton (H) from the acid
• Conjugate Base particle that remains after a
  proton (H) has been released by the acid

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• Ex.
• HNO3 NaOH ? H2O NaNO3
• (H-OH)

Acid
Conjugate Base
Base
Conjugate acid
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Disappearing ink
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• Ex.
• KOH HBr ? KBr H2O

Base
Conjugate Acid
Acid
Conjugate Base
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Neutralization Reaction

• Occurs when an acid and a base react and there is
  a complete removal of all of the H and OH- ions
• Water will be formed w/ a salt in this double
  displacement reaction
• The solution will be neutral in pH
• Important in neutralization of soil, antacids

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Salt

• Crystalline compound composed of the negative
  (non-metal) ion of the acid and the positive
  (metallic ) ion of the base
• Salt examples CaSO4 (plaster board), NaCl, KCl,
  (NH4)2SO4 (fertilizer)

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Examples of Neutralization Reactions

• Sodium hydroxide hydrochloric acid ? sodium
  chloride water
• NaOH HCl ? NaCl H2O (H-OH)

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• Potassium hydroxide sulfuric acid ? water
  potassium sulfate
• KOH H2SO4 ?

H- OH K2SO4
2 KOH H2SO4 ? 2 H-OH K2SO4
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• Aluminum hydroxide acetic acid ?

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Titration
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Titration

• Used for a convenient method to determine the
  concentration or molarity of an acid or base
• Uses 2 burets (long glass tubes used to measure
  volume)- Buret .05 ml

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Definition

• Analytical method in which a standard solution is
  used to determine the concentration of another
  solution
• Standard solution- one in which the
  concentration is known

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Process

• Using a given amount of acid in a flask, add
  phenolphthalein and titrate to the end point with
  the base (making sure to mark down all the
  volumes)
• The whole reaction is a neutralization reaction
• Use an indicator to see the endpoint in which
  complete neutralization occurs (wait for
  phenolphthalein stays light pink for 30 sec)

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Past endpoint
Endpoint
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Titration Process
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Calculations

• Reminder M moles
• liters
• So Base (titrated soln) ?
• Moles (base) volume (base) x Molarity
  (base)
• Acid (standard soln) ?
• Moles (acid) volume (acid) x Molarity
  (acid)

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• Look at balanced equation and find the moles of
  the standard and the moles of the titrated
  unknown (look at coefficients)
• Most times it is a 11 ratio
• 1 NaOH 1 HCl ? NaCl H2O (H-OH)
• So 1 mole (base) 1 mole (acid)
• Therefore MA VA MBVB

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Problem

• A titration of 15.00 ml of HCl, required 38.57 ml
  of a 0.152 M base NaOH. Calculate the molarity
  of the HCl (acid).
• MA ?

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• MA VA MBVB
• MA M BVB
• VA
• MA (.152M) (38.57 ml)
• (15.00ml)
• MA .391 M

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Titration Calculation
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ID- A, B, CA, CB

• CaCO3 HCl ? CaCl2 H2CO3
• KOH H3PO4 ? K3PO4 H2O

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• phosphoric acid calcium hydroxide ?calcium
  phosphate water
• HBr Al(OH)3?
• Sulfuric acid potassium hydroxide ?

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Indicators

• Used to find out if things are acidic or basic
• Def weak organic acids or bases whose colors
  differ from the colors of their conjugate acids
  or bases

base
acid
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Needs of Indicators

• Solution being tested needs to be colorless
• You need to be able to distinguish the color
  change
• Need several indicators to cover entire pH range
  (0-14)
• Liquid solution

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Indicator Examples

• Litmus ? red turns blue base, blue turns red
  acid
• Phenolphthalein? hot pink gt pH 10
• Bromothymol blue ? blue base (8), Green
  neutral, yellow acid (6)
• Universal Indicator ? Rainbow (all pHs 4-10)
• (bromothymol blues)

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How Chemists use Indicators
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Ionization of H2O

• Pure water can self ionize, it also acts as an
  acid or a base (amphoteric)
• So H2O(aq) ? H(aq) OH- (aq)
• Experiments have shown that the concentration of
  H 1 X 10 7M and OH- 1 x 10 7 M in pure
  water
• means concentration

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Ion Product Constant for water

• Equilibrium expression from the multiplication of
  the concentrations of the products
• H OH- ?
• (1 x 10 7)(1 x 10 7) 1.0 x 10 -14
• H OH- 1.0 x 10 -14

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• If H 1.5 x 10 -6 M, what is the OH- ?
• H OH- 1.0 x 10 -14
• (1.5 x 10 -6) OH- 1.0 x 10 -14
• OH- 1.0 x 10 -14
• 1.5 x 10 -6
• OH- 6.7 x 10-9 M

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pH Concept (video)

• Acidity scale developed by Soren Sorenson base on
  the power of the hydrogen
• pH measure of the hydrogen ion concentration of
  the solution
• Equal to the negative logarithm of the hydrogen
  ion concentration
• 2. pH - log H

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• Ex. H 1.5 x 10-8
• pH ?
• Graphing Calc.
• (-) log 1.5 (2nd) EE -8
• Regular calc.
• 1.5 EE -8 log /-
  pH 7.8

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To go from pH to Hconcentration

• 3. H antilog (-pH)

Antilog 10x key
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• pH 3.5
• H ?
• H antilog (-pH)
• H antilog (-3.5)
• Graphing 2nd log -3.5
• Regular 3.5 /- 2nd log
• (to put in sci.not. Use 2nd 5)
• H 3.2 x 10 -4 M

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pOH (hydroxide power)

• pH pOH 14
• pH 8
• pOH ?
• 8 ? 14 pOH 6
• pOH - log OH-
• OH- antilog (-pOH)

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• H 3.5 x 10 -7 M, OH- ?
• pH 8.95 , H ?
• OH- 5.65 x 10 -2 M, pOH ?
• pOH 11.9, H ??

• Formula 1
• Formula 3
• Formula 5
• Formula 4, then 3 or
• Formula 6, then 1

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Rosengarten acid and base video