Acids and Bases

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Acids and Bases

• An Introduction

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Introduction

• Inorganic and organic acids are important
  industrial chemicals in 2002, H2SO4 was the
  number 1 chemical produced in the U.S.
• 36,000,000 metric tons (80,000,000,000 lbs)
• 1metric ton 1000Kg 2204.6lbs

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Common Household Acids

• Some common household acids
• Vinegar CH3COOH
• Citric acid
• Ascorbic acid

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Common Household Acids and Bases
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Common Household Bases

• Some common household bases
• Ammonia - NH3 (cleaners)
• Sodium hydroxide NaOH (oven cleaner and drain
  cleaner)
• Calcium oxide CaO (cement)

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Physical Properties

• Physical properties of acids
• Sour/tart taste
• Pricking/stinging sensation on the skin
• blue to red litmus paper
• Physical properties of bases
• Bitter taste
• Slippery to touch
• red to blue litmus paper

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Acid Base Theories

• The great theorists

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Definitions of Acids and Bases

• Arrhenius
• Acid produce H in water
• Ex. HCl hydrochloric acid
• Base produce OH- in water
• Ex. NaOH sodium hydroxide

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Definition of Acids and Bases

• Brondsted-Lowry
• Acid donates a proton
• Base accepts a proton
• H, H has no neutrons so this is a proton

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Definition of Acids and Bases

• Lewis
• Acid electron pair acceptor
• Base electron pair donor
• BF3 F NH3 H
• F B H N
• F H
• Can accept e- Can donate e-

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Ammonia NH3
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Strong Acids
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• For the equation
• HX (aq) ? H (aq) X- (aq)
• HX is the acid
• For example
• HCl (aq) ? H (aq) Cl (aq)
• In strong acids, this reaction goes to
  completion (only products are left, none of the
  reactants remain)

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Strong Acids

• The Big 6 Acids
• HCl hydrochloric acid
• H2SO4 sulfuric acid
• HNO3 nitric acid
• H3PO4 phosphoric acid
• HF hydrofluoric acid
• HClO4 Perchloric acid

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Weak Acids, ex. CH3COOH
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Equilibrium

• Ka HCl-
• HCl
• Ka is the equilibrium constant for acids (a
  measure of the relative strength of an acid)
• means concentration in moles/liter or
  Molarity
• For strong acids, the Ka is so large that is
  cannot be measured, because the acids completely,
  totally dissociates

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Weak Acids Have Ka lt 1

• HSO4- hydrogen sulfate ion 1.2 x 10 -2
• HClO2 chlorous acid 1.2 x 10 -2
• HNO2 nitrous acid 4.0 a 10 -4
• HCN hydrocynaic acid 6.2 x 10 -10
• NH4 ammonium ion 5.6 z 10 -10
• HOC6H5 phenol 1.6 x 10-10
• Note Bases are very weak acids

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Strong Bases

• Strong Bases are like strong acids they
  dissociate completely
• HB ? B OH-
• For example
• KOH ? K OH-

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Weak Bases, Ex. NH3

• The Kb is just like the Ka
• Kb BOH-
• BOH
• B is not Boron, but from HB ? B OH-
• Kb is the equilibrium constant of a base
• is concentration in Molarity (mole/liter)

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Molarity is moles per liter

• Convert given masses into moles (if in grams) and
  volume into liters (if given in something other
  than Liters)

Mole Stew- how many moles are in a liter of
water
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Measuring Concentration of Hydrogen

• pH -log H
• Find the pH if H 1.00 x 10-5
• How about the pH if the H 5.43 x 10-3
• pOH - log OH-
• Find the pOH if OH- 3.78 x 10 -8
• How about the pOH if OH- 8.99 x 10 -2
• What would the pH of each of these be?

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pH Scale
http//www.youtube.com/watch?v3otQdpMfiRg
http//www.youtube.com/watch?vYvnwiP1u8-A
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Stop notes here for now

• Well continue another day.
• Thanks!

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Acid-Base Indicators

• Common Indicators
• Phenolphtalein pink in base, clear in acid
• Litmus Paper red? blue blue?red
• Bromthymol blue pH 3 green pH 4.5 blue
• Methyl red pink in acid, yellow in base
• There is an indicator for every purpose
• http//www.youtube.com/watch?vvrOUdoS2BtQ

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pH Indicators
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pH Meter

• pH meters, unlike indicators, directly measure
  the concentration of H ions. They do this by
  measuring the electrical conduction of the
  solution.
• Why will the solution with more H conduct
  electricity better?

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Acid Nomenclature

• Binary Acids
• Prefix hydro- suffix -ic
• HCl hydrochloric
• HI hydroiodic
• HS hydrosulfuric

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Acid Nomenclature

• Ternary
• Common form --ic
• HSO4, HClO3, HNO3
• Sulfuric, chloric and nitric
• One fewer oxygen -ous
• Two fewer oxygen hypo-- and -ous
• One more oxygen per- and --ic

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Acid Base Reactions

• Salts are produced by an acid/base
  neutralization
• 2HCl Ca(OH)2 ? 2H2O CaCl2 ? salt
• H2SO4 2NaOH ? Na2SO4 2H2O
• salt
• What is a salt??
• pH -logH
• 10-H
• pH lt 7 acidic
• pH 7 gt basic
• pH 7 neutral http//www.youtube.com/watch?vP
  CM5IwJ8wcs

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Acid-Base Titrations

• Titrations are done to find the molarity of the
  acid or the base.
• A buret (a long graduated cylinder ) is
• attached to the ring stand with a
• buret clamp.
• Liquid can be delivered by turning
• the stopcock.
• http//www.youtube.com/watch?vsFpFCPTDv2wfeature
  related

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Setting up a titration

• Usually the acid is placed in the flask with an
  indicator that will change color at pH 7.
• Phenolphthalein is often used. Why is
  phenolphthalein a good choice?

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Filling the buret

• After rinsing with both
• deionized water and base, base is placed in the
  buret.
• Why is this done over the sink?

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Filling the buret

• Open the stopcock and let the base level drop to
  the top line (zero line) on the buret.

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Reading the buret

• The buret is graduated so that the amount of base
  delivered can be easily measured.
• Read it as you would a graduated cylinder (at eye
  level, from the bottom of the meniscus)

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Doing the titration

• The base is slowly added to the acid while
  mixing,

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Finding the endpoint

• until the solution hits the
• endpoint.
• Note that the solution is barely pink. A dark
  pink means that too much base has been added.

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What is an endpoint?
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Acid-Base Titration Calculations

• If we used 20 ml of 3.0 M HCl, how many ml of
• 3.0 M NaOH would we expect to need?
• HCl NaOH ? NaOH H2O
• 20 ml 3 mol 1 mol NaOH 1 L 20 ml
• 1 L 1 mol HCl 3 mol

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Acid-Base Titrations

• So, what if you use 24.5 ml of 0.15 M NaOH to
  neutralize 50.0 ml of 2.5 M H2SO4? What is the
  concentration of the NaOH?
• 2NaOH H2SO4 ? Na2SO4 2H2O
• 50.0 ml 2.5 mol 2 mol NaOH 1 L
• 1 L 1 mol H2SO4 24.5
  ml
• What unit will the answer be in?
• How many sig figs can we report?

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Acid Rain

• What is Acid Rain?
• http//www.youtube.com/watch?vHE6Y0iEuXMQ
• SO2 and NO2/NO3 from industry and cars
• Produce
• H2SO4 and HNO3 when combined with water
• Can fall as rain, snow and as solid deposition

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Where does Acid Rain Fall?
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What are the effects?

• Forrest depletion tree death
• Can be seen in NH in White Mountains

Clear lakes due to acid rain clear because No
plants or fish or other life is in the lake
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• Statues like this one, show corrosion due to acid
  rain.
• Copper and marble are both acted on by acid

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Effects of Acid Rain

• Maple sugar production in the Northeast may be
  down due to acid rain this is projected to
  continue
• Car paints have had to be reformulated and there
  are many products on the market to repair damage