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Acids and Bases

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Acids and Bases An Introduction – PowerPoint PPT presentation

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Title: Acids and Bases


1
Acids and Bases
  • An Introduction

2
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

3
Common Household Acids
  • Some common household acids
  • Vinegar CH3COOH
  • Citric acid
  • Ascorbic acid

4
Common Household Acids and Bases
5
Common Household Bases
  • Some common household bases
  • Ammonia - NH3 (cleaners)
  • Sodium hydroxide NaOH (oven cleaner and drain
    cleaner)
  • Calcium oxide CaO (cement)

6
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

7
Acid Base Theories
  • The great theorists

8
Definitions of Acids and Bases
  • Arrhenius
  • Acid produce H in water
  • Ex. HCl hydrochloric acid
  • Base produce OH- in water
  • Ex. NaOH sodium hydroxide

9
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

10
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-

11
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12
Ammonia NH3
13
Strong Acids
14
  • 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)

15
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16
Strong Acids
  • The Big 6 Acids
  • HCl hydrochloric acid
  • H2SO4 sulfuric acid
  • HNO3 nitric acid
  • H3PO4 phosphoric acid
  • HF hydrofluoric acid
  • HClO4 Perchloric acid

17
Weak Acids, ex. CH3COOH
18
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

19
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

20
Strong Bases
  • Strong Bases are like strong acids they
    dissociate completely
  • HB ? B OH-
  • For example
  • KOH ? K OH-

21
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)

22
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
23
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?

24
pH Scale
http//www.youtube.com/watch?v3otQdpMfiRg
http//www.youtube.com/watch?vYvnwiP1u8-A
25
Stop notes here for now
  • Well continue another day.
  • Thanks!

26
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

27
pH Indicators
28
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?

29
Acid Nomenclature
  • Binary Acids
  • Prefix hydro- suffix -ic
  • HCl hydrochloric
  • HI hydroiodic
  • HS hydrosulfuric

30
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

31
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

32
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

33
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?

34
Filling the buret
  • After rinsing with both
  • deionized water and base, base is placed in the
    buret.
  • Why is this done over the sink?

35
Filling the buret
  • Open the stopcock and let the base level drop to
    the top line (zero line) on the buret.

36
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)

37
Doing the titration
  • The base is slowly added to the acid while
    mixing,

38
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.

39
What is an endpoint?
40
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

41
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?

42
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

43
Where does Acid Rain Fall?
44
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45
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
46
  • Statues like this one, show corrosion due to acid
    rain.
  • Copper and marble are both acted on by acid

47
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
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