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6.1 Theories of Acids and Bases• Acids and Bases at home:
Acids
Product Acid(s) contained in the product
vinegar ethanoic (acetic) acid CH3COOH(aq)
wart remover salicylic acid, C6H4(OH)CO2H(aq)
soft drinks carbonic acid, H2CO3(aq) phosphoric acid, H3PO4(aq)
rust remover glycolic acid, CH2(OH)COOH(aq) phosphoric acid, H3PO4(aq)
lemon juice citric acid, C6H8O7(aq) ascorbic acid, C6H8O6(aq)
Bases
Product Base(s) contained in the product
oven cleaner aqueous sodium hydroxide, NaOH(aq)
drain cleaner aqueous sodium hydroxide, NaOH(aq)
antacids (some brands) magnesium hydroxide, Mg(OH)2(s)
glass cleaner (some brands) aqueous ammonia, NH3(aq)
chart page 208
6.1 Theories of Acids and Bases• Nomenclature
• Bases have no special nomenclature
• Acid nomenclature:
New IUPAC nomenclature – name the compound as if it was ionic adding the word “aqueous” in front
examples: HCl(aq) H2SO4(aq)
aqueous hydrogen chloride
aqueous hydrogen sulfate
this method is relatively new and still not commonly used by chemists
6.1 Theories of Acids and Bases• Classical acid nomenclature• Start by naming the compound as it was
ionic• Look at ending and apply following
rules
__________ide hydro_______ic acid
__________ate __________ic acid
__________ite __________ous acid
6.1 Theories of Acids and Bases• Example: Consider the following group
of acids:
rule 1
rule 2
rule 2
rule 3
rule 3
Formula Name (if it was ionic) Classical Acid Name
HCl(aq) hydrogenchloride hydrochloric acid
HClO4(aq) hydrogen perchlorate perchloric acid
HClO3(aq) hydrogen chlorate chloric acid
HClO2(aq) hydrogenchlorite chlorous acid
HClO(aq) hydrogen hypochlorite hypochlorous acid
put the word “aqueous” in front and you’ve got the IUPAC name
6.1 Theories of Acids and Bases• 2 elements to be careful about: S and P• both keep the middle syllable in classical acid
nomenclatureH2SO4(aq) “sulfuric acid”, not “sulfic acid”H3PO4(aq) “phosphoric acid”, not “phosphic acid”
• Quiz next day – same format as practice quiz you’ll do now
• After quiz you won’t need to know classical acid nomenclature by memory as the names and formulae of many acids are in your Data Booklet, pages 8 and 9
6.1 Theories of Acids and Bases• acids and bases can be defined
empirically (in terms of properties) or theoretically (in terms of theories that explain their properties)
Test Acids Bases
litmus paper turn blue litmus red turn red litmus blue
pH paper pH less than 7 pH greater than 7
electrical conductivity in solution
conduct electric current (electrolyte)
conduct electric current (electrolyte)
reaction with active metals, such as Mg(s) and Zn(s)
react to produce H2(g) do not react with active metals to produce H2(g)
taste Caution: Never taste anything in the lab.
taste sour taste bitter
feel Caution: Never deliberately
touch chemicals. Many acids and bases can burn
your skin.
have no characteristic feel feel slippery
chart page 210
6.1 Theories of Acids and Bases• Explaining (theories)• Arrhenius acid: ionizes in water to
produce H+(aq)base: dissociates in water to
produce OHˉ(aq)
• according to Arrhenius’ theory, acid formulas must contain H and base formulas must contain OH
• do Investigation 6.B to test this out
6.1 Theories of Acids and Bases• problems from lab: NH3(aq) was basic,
NaHCO3(aq) was basic, others??
• Arrhenius’ theory worked well for many, but not all acids and bases
• Slight modifications provide great improvement
6.1 Theories of Acids and Bases• revised or modified Arrhenius theory:• acid: reacts with water to produce
hydronium ion, H3O+(aq)
before: HCl(aq) H+(aq) + Clˉ(aq)now: HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq)
• base: dissociates or reacts with water to produce OHˉ(aq)
before: NaOH(s) Na+(aq) + OHˉ(aq)
now: exactly the same
6.1 Theories of Acids and Bases• Here’s where the benefit comes:
• NH3(aq):
before: NH3(aq) ???????
now: NH3(aq) + H2O(l) NH4+(aq) + OHˉ(aq)
now NH3’s basic behaviour is explained
NaHCO3(aq):
NaHCO3(s) Na+(aq) + HCO3ˉ(aq), then,
HCO3ˉ(aq) + H2O(l) H2CO3(aq) + OHˉ(aq)
now NaHCO3’s basic behaviour is explained
6.1 Theories of Acids and Bases• Try a weird acid like CO2(aq) (soda water)
• standard Arrhenius theory doesn`t explain• Revised:
CO2(g) + H2O(l) H2CO3(aq), then,
H2CO3(aq) + H2O(l) HCO3ˉ(aq) + H3O+(aq)
oxides will always be 2 steps – metal oxides to produce bases; non-metal oxides to produce acids
Worksheet BLM 6.1.0
6.2 Strong and Weak Acids and Bases
• terms: “strong acid” and “weak acid” have technical meaning – they are based on identity, not acidic behaviour
• note that at both 1.0 mol/L and 0.10 mol/L HCl(aq) is more reactive than CH3COOH(aq)
fig 6.7 page 218
6.2 Strong and Weak Acids and Bases
• Strong acid: reacts 100% with water or 100% ionized in water
HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq)
fig 6.8, page 219strong acids are the 1st 6 acids listed in your chart, page 8-9 of the Data Booklet
6.2 Strong and Weak Acids and Bases
• Weak Acid: reacts only partially (usually very weakly) with water or ionizes only partially
CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COOˉ(aq)
fig 6.9 page 220
do worksheet BLM 6.2.4
weak acids are all the others
6.2 Strong and Weak Acids and Bases
• Is it possible for a strong acid to be less acidic in behaviour than a weak acid?
• strong bases and weak bases:
aqueous ionic hydroxides and ionic oxides are strong bases
all other bases (from Data Booklet page 8-9 “Conjugate Base” column) are weak
yes, if its concentration is very low and the weak acid’s concentration is very high
read about “weak acids and bases” page 221 bottom and page 223 bottom
discuss questions 5-7, page 222
6.2 Strong and Weak Acids and Bases
• Mono and polyprotic acids
• monoprotic acids: have only 1 hydrogen atom that reacts to produce H3O+(aq), e.g. HCl(aq), HBr(aq), HNO3(aq)
• polyprotic acids: have 2 or more hydrogen atoms that react to produce H3O+(aq), e.g. H2SO4(aq) (diprotic), H3PO4(aq) (triprotic)
6.2 Strong and Weak Acids and Bases• in a series of acids, one with most H’s is
strongest
• e.g. H3PO4(aq)
• H3PO4(aq) + H2O(l) H3O+(aq) + H2PO4ˉ(aq)
H2PO4ˉ(aq) + H2O(l) H3O+(aq) + HPO42ˉ(aq)
HPO42ˉ(aq) + H2O(l) H3O+(aq) + PO4
3ˉ(aq)
H3PO4(aq) > H2PO4ˉ(aq) > HPO42ˉ(aq)
strongest weakest
6.2 Strong and Weak Acids and Bases• mono and polyprotic bases• monoprotic base: reacts with water or ionizes to
produce 1 OHˉ(aq)e.g. NaOH(aq), NH3(aq)
• polyprotic base: reacts with water or ionizes to produce 2 or more OHˉ(aq)
e.g. CO32ˉ(aq), HPO4
2ˉ(aq)
in a series of bases, one with the least H’s is most basic:
PO43ˉ(aq) > HPO4
2ˉ(aq) > H2PO4ˉ(aq)
strongest weakest
6.2 Strong and Weak Acids and Bases
• Read pages 224-225
• neutralization reaction:
acid + base water + a salt
neutral ionic compound
e.g. NaOH(aq) + HNO3(aq) H2O(l) + NaNO3(aq)
H3O+(aq) + OHˉ(aq) 2 H2O(l)
net ionic equation for all strong acid/strong base neutralizations:
6.3 Acids, Bases and pH• all aqueous solutions contain both H3O+(aq)
and OHˉ(aq) ionsIf [H3O+] is high, [OHˉ] is low
• following slide illustrates their relationship in aqueous solutions
• note: to fit this comfortably on 1 page, I have used H+(aq) instead of H3O+(aq), recognizing that they both represent same chemical entity
6.3 Acids, Bases and pH
neutral
acidic basic
example [H+]:10-7 mol/L
10-7 mol/L
10-1 mol/L
10-3 mol/L
10-5 mol/L
10-9 mol/L
10-11
mol/L10-13 mol/L
corresponding [OHˉ]:10-13 mol/L
10-11 mol/L
10-9 mol/L
10-5 mol/L
10-3 mol/L
10-1 mol/L
pH= 1 3 5 9 11 137
6.3 Acids, Bases and pH
fig 6.17, page 230
6.3 Acids, Bases and pH• H2O(l) + H2O(l) H3O+(aq) + OHˉ(aq)
• water is an extremely weak acid;[H3O+]=[OHˉ]=1.0 x 10-7 mol/L
• also, [H3O+]=[OHˉ]=1.0 x 10-7 mol/L in any neutral solution
• In previous slide if [H3O+] = 10ˉ9 mol/L, pH equaled 9
• formula: pH = -log [H3O+] or pH = -log [H+]
6.3 Acids, Bases and pH• log is a function on your calculator
• log of a # is the power of 10 you’d need to get the #
• based on this, what is log 100 (no calculator)?
• log 1000?• log 0.1?
?if log # ?, then 10 #
23-1
6.3 Acids, Bases and pH• log (10ˉ7 mol/L)=-7 (try it on your
calculator)
• Why do you think pH = - log [H3O+]?
• Discuss
should look like this
or you could enter like this
6.3 Acids, Bases and pH• Try the following exercise (write your
answers):• -log (1.89x10ˉ9) (enter as 1.89E-9)
• -log(1.89x10ˉ8)• -log(1.89x10ˉ7)• -log(1.89x10ˉ6)
8.723538
5.723538
6.723538
7.723538this part is related to the 1.89
this part is related to the power of 10
significant digitsnot significant
if [H3O+] = 1.89 x 10-6 mol/L, pH = 5.724 !
6.3 Acids, Bases and pH• General rule: when finding pH from
concentration, number of significant digits in concentration is same as the number of decimal places in pH! (this is rule 4 on significant digits handout!)
• When finding concentration from pH, number of decimal places in pH is same as significant digits in concentration
6.3 Acids, Bases and pH• What is meaning of pH increase by 2 units?
• Examples: Practice Problems 1a, 1c page 230
• 1a)
• 1c)
• Do worksheet BLM 6.3.4 questions 1, 2, 5, 6, 9, 10a
log 0.0027 2.57molLpH
12log 8.27 10 11.082molLpH
[H3O+] has decreased by 100 times 1( . . its original value!)100i e
6.3 Acids, Bases and pH• Measuring pH – indicators and pH
meters• Indicators: substances whose colour
changes with pH
here’s a few; fig 6.18, page 231
page 10, Data Booklet:shorthand formulas
HMr(aq)/Mrˉ(aq)
HBb(aq)/Bbˉ(aq)
HIc(aq)/Icˉ(aq)
4.8-6.0
6.0-7.6
11.4-13.0
6.3 Acids, Bases and pH• Examples: following indicators are
added to fresh samples of a solution. Results given. Estimate pH.
indicator colour
methyl violet blue
methyl orange yellow
methyl red red
phenolphthalein colourless
pH > 1.6
pH > 4.4
pH < 4.8
pH < 8.2
conclusion: pH 4.4 – 4.8
6.3 Acids, Bases and pH• Try this one:
indicator colour
indigo carmine blue
phenol red yellow
bromocresol green yellow
methyl orange orange
pH < 11.4
pH < 6.6
pH < 3.8
pH 3.2 – 4.4
conclusion: pH 3.2 – 3.8
do worksheet BLM 6.3.6
Investigation 6.D, page 232
6.3 Acids, Bases and pH• Demonstration: Investigation 6.E, page
234
6.3 Acids, Bases and pH• pH after dilution – note can’t raise pH of
an acid to > 7 by dilution (since water already has [H3O+] = 10ˉ7 mol/L)
• can’t lower pH of a base to < 7 by dilution
(since water already has [OHˉ] = 10ˉ7 mol/L)
6.3 Acids, Bases and pH• Example: A 35.0 mL sample of
0.489 mol/L HCl(aq) is diluted to 300 mL• What is pH of the concentrated solution?
• What is concentration of diluted solution?
• pH of diluted solution?
log 0.489 0.311molLpH
0.489 35.00.0571
300
i i f f
molLi i mol
Lff
c v c v
c v mLc
v mL
log 0.0571 1.244molLpH
do worksheet BLM 6.3.8 #2, 3, 4
6.3 Acids, Bases and pH• pOH = -log [OHˉ] (like pH, but for OHˉ)
• you haven’t heard of pOH because it’s never measured or reported – it’s calculated and used as a calculation tool because ………..
• pOH is opposite to pH – it’s low for bases and high for acids (see table 6.8, page 237)
pH + pOH = 14.00
6.3 Acids, Bases and pH• Further formulas:
• [H3O+] = 10ˉpH [OHˉ] = 10ˉpOH
• Examples:• Practice Problem 13a, page 241
• 2 ways to enter:
3.9 43 10 1 10 acidicmol
LH O 1 significant digit
a) type “10^-3.9”
b) Do “2nd log” then enter -3.9
6.3 Acids, Bases and pH• Practice Problem 13d, page 241
• What is the pOH of a 5.467 mol/L solution of barium hydroxide, Ba(OH)2?
Ba(OH)2(s) Ba(OH)2(aq) Ba2+(aq) + 2 OHˉ(aq)
11.35 12
14.00 2.65 11.35
10 4.5 10 acidicmolL
pOH
OH
21 5.467 10.934
log 10.934 1.039
mol molL L
molL
OH
pOH
6.3 Acids, Bases and pH• What is the concentration of sodium
hydroxide, NaOH(aq), that gives a solution with a pH of 10.32?
• since it’s a base start by finding pOH
• Since NaOH dissociates as • NaOH(s) Na+(aq) + OHˉ(aq),• [NaOH]=2.1x10-4 mol/L
pOH=14.00-10.32=3.683.68 410 2.1 10 mol
LOH
6.3 Acids, Bases and pH• Example: What mass of rubidium hydroxide,
RbOH(s), needs to be dissolved in 1.50 L of water to create a solution with a pH of 9.35?
• Do worksheet BLM 6.3.12 questions 1a, 2a, 3, 4, 6, 7, 8
14.00 9.35 4.65pOH 4.65 510 2.2 10 mol
LOH
5 512.2 10 1.50 3.4 10
1mol
LRbOHn L mol
5 33.4 10 102.48 3.4 10gmolRbOHm mol g
RbOH(s) → RbOH(aq) → Rb+(aq) + OH‾(aq)
6.3 Acids, Bases and pH• Putting it all together:• Worksheet BLM 6.3.13 question 1, 3, 4,
6, 7
6.3 Acids, Bases and pH• Chapter Review:
• Worksheet BLM 6.3.14
6.3 Acids, Bases and pH
