Binary acids – use the prefix “hydro” + the name of the negative (second ion), changing the ending to “-ic acid”.Oxy-acids – Name the polyatomic ion, change the ending to either “-ic acid” or “-ous acid” according to the “ate = ic, ite = ous” rule.
HCl (aq) hydrochloric acid HBr (aq) hydrobromic acid HI (aq) hydroiodic acid HF (aq) hydrofluoric acid H2S (aq) hydrosulfuric acid
H2SO4 sulfuric acid
H2SO3 sulfurous acid
H3PO4 phosphoric acid
H3PO3 phosphorous acid
HNO3 nitric acid
Acids and Bases
What is an Acid? Base?
What do you think and acid is?
What do you think a base is?
Properties of Acids and Bases! Acids have specific properties
Sour taste pH beow 7.00 S.U. Turn litmus paper red Dissolve metals
Bases have similar properties Bitter taste pH above 7.00 S.U. Feel slippery Turn litmus paper blue
What else can they do?
Acids and bases neutralize each other In other words, they raise/lower the pH to a
non-acid/non-base
Acids and Bases can both destroy human tissue
How do they do that?
Acids and bases are electrolytes The ions that they produce give them their
properties
Strength of Acids
A strong acid is one that dissolves completely in solution. A weak acid is one that does not dissolve
completely.
Why would an acid not dissolve completely?
Do you know any acids or bases?
List some common acids and bases Vinegar is Acetic Acid Ammonia is a Base Sodium Bicarbonate (Baking soda) is a Base Batteries contain Sulfuric Acid Your stomach contains Hydrochloric Acid!
There are more than one
There are 3 different types of acids and bases Arrhenius Brönsted-Lowry Lewis
Arrhenius Acids and Bases
An Arrhenius Acid is a substance that releases H3O+ ions in an aqueous solution HCl H2O H3O+ + Cl-
An Arrhenius Base is a substance that releases –OH in an aqueous solution NaOH H2O Na+ + OH-
Brönsted-Lowry Acids and Bases
A Brönsted-Lowry acid is any species that can donate a proton (H+ ion) to another species; a proton donor
A Brönsted-Lowry base is any speices that can accept a proton (H+ ion) from another species; a proton acceptor
HCl + H2O H3O+ + Cl-
Which is the Brönsted-Lowry acid/base? Acid is the proton donator Base is the proton acceptor
HCl is the acid H2O is the base
Water: Acid or Base?
Take a look at these two reactions
1. NH3 + H2O NH4+
+ OH-
2. HCl + H2O H3O+ + Cl-
In reaction #1, which is the B-L acid? Base? Water is the acid and ammonia is the base
In reaction #2? HCl is the acid and water is the base
Amphiprotic
A compound that can be both a proton donor OR a proton acceptor in separate reactions is called amphiprotic or amphoteric
Lewis Acids and Bases
A Lewis Acid is any species that can accept a pair of electrons from another species; electron pair acceptor
A Lewis Base is any species that can donate a pair of electrons from another species; electron pair donor
Remember Lewis Structures!
Let’s look at a few examples
H+ H+ is an electron pair acceptor
:Ö-H- OH- is an electron pair donor
:Ö-H Lewis acid-base product
..
H
..
Compare the Definitions
Acid Base Acid Base Acid BaseReleases H
+
Releases O
H-
Proton donor
Proton acceptor
Electron pair acceptor
Electron pair donor
LewisBrönsted-LowryArrhenius
Acid-Base Equilibria
In a chemical reaction involving both acids and bases, dynamic equilibrium can still be achieved
A species that is an acid in the forward direction, can become the base in the reverse direction
HNO2 + H2O H3O+ + NO2-
acid base acid base
Let’s take a look at this reaction HNO2 donates a proton in the forward reaction
and is therefore a B-L acid H2O accepts a proton in the forward reaction
and is the B-L base In the reverse direction, H3O+ donates a
proton; B-L acid And NO2
- accepts a proton; B-L base
Conjugate Pairs
When an acid donates a proton, it becomes a conjugate base
When a base accepts a proton, it becomes a conjugate acid
Why? The acid-base reaction can be a reversible
reaction and so when you move in the opposite direction, the compounds are redefined as acids and/or bases
Conjugates
For example, look at the following reaction
HCl + H2O H3O+ + Cl-
Which reactant is the acid? The base? Now, in the reverse direction, which product
is the acid? The base? Now, what are the conjugate pairs?
Conjugates, some more
Look at this reaction:NH3 + H2O NH4
+ + OH-
Which reactant is the acid? The base? Now, in the reverse direction, which product
is the acid? The base? Now, what are the conjugate pairs?
Conjugate Practice
What are the conjugate pairs for the following reactions?
HNO3 + OH- H2O + NO3-
HNO3 is the acid and NO3- is the conjugate base
OH- is the base and H2O is the conjugate acid
H2SO4(aq) + SO32-(aq) HSO4
-(aq) + HSO3-(aq)
Sulfuric acid is the acid and HSO4- is the conjugate
base Sulfite ion is the base and HSO3
- is the conjugate acid
Strength
If a acid is strong, then the conjugate base is weak and vice-versa
Strong/Weak Electrolytes
An electrolyte is a solution that will conduct an electrical current.
Any ionic compound that dissociates in solution will conduct electricity.
If a substance dissociates 100%, it is called a strong electrolyte.
A weak electrolyte dissociates < 100% (usually < 5%)
Strong Acids
Binary acids: HCl, HBr, and HI are strong acids. All other
binary acids are weak.
Oxy acids: If the number of oxygen atoms exceed the
number of hydrogen atoms by 2 or more, the acid is strong.
Strong Bases
Hydroxides made from metals in group 1 or group 2 are strong bases.
All other hydroxides are weak bases.
Molecular Structure and the Strength of Acids The strength of an acid depends on a number
of factors, such as the properties of the solvent, the temperature, and the molecular structure of the acid.
We compare the strengths of two acids, in the same solvent and at the same temperature. That way we can focus on the structure of the acid.
Binary Hydrides
HA ---> H+ + A- Two factors influence the extent to which the
acid undergoes ionization. One is the strength of the H-A bond
the stronger the bond, the more difficult it is for the HA molecule to break up and hence the weaker the acid.
Polarity versus Strength
The other factor is the polarity of the H-A bond. The difference in electronegativities between
H and A results in a polar bond. If the bond is highly polarized, it is a stronger
acid.
Hydrohalic Acids
The halogens form a series of binary acids called the hydrohalic acids.
The strengths of the hydrohalic acids increase in the following order: HF<<HCl<HBr<HI
Other Non-metallic Acid Strengths
In any vertical column (Group) of nonmetallic elements, there is a tendency toward increasing acidity of the hydride with increasing atomic number (as you go down the group).
For example, among the group VIA elements the acid strength increases in the order: H2O< H2S<H2Se<H2Te
Oxyacids
Many common acids contain one or more O-H bonds.
Practice Problems
1. HF
weak
2. H2S
weak
3. H2SO4
strong
4. H2CO3
weak
5. Fe(OH)3
weak
6. Barium hydroxide
strong
7. Chloric acid
strong
8. Sulfurous acid
weak
9. Hypochlorous acid
weak
10. Tin(IV) hydroxide
weak
Ba(OH)2
HClO3
H2SO3
HClO
Sn(OH)4
Review
In the following equations, name the acid and base. What was your justification? NH3 + H2O NH4
+ + OH-
2NaBr + H2SO4 Br2 + SO2 + 2NaOH
Review
What is the difference between a strong acid and a weak acid?
A buffer is a solution made from a weak acid and it’s conjugate base that neutralizes a small amount of acids or bases added to it
Calculating pH
pH
pH is a measure of how acidic, neutral or basic a solution is
The scale for pH is 0-14 7 is neutral 0-7 is acidic 7-14 is basic
The Numbers mean . . .
pH + pOH = 14 S.U.
pH = -log10[H3O+]
pOH = -log10[OH-]
What is pH?
The term pH refers to a scale that describes how strongly acidic or basic a solution is pH + pOH = 14 Acidic = 0-7 Neutral = 7 Basic = 7-14
The Kw Constant
Kw = 1.0 x 10-14
at standard thermodynamic temperature (25oC or 298 K)
Ionization Constants of Acids and Bases HA(aq) + H2O(l) ↔ H3O+(aq) + A-(aq)
Keq= [H3O+][A-] / [HA][H2O]
In a dilute solution, the concentration of water is constant, so
Keq= [H3O+][A-] / [HA]
Ionization Constants
The Ionization Constant for water; Kw is derived as follows:
First: for the acids
HA(aq) + H2O(l) H3O+(aq) + A-(aq)
Keq = Ka = [H3O+][A-] / [HA]
Now the bases . . .
B(aq) + H2O(l) BH+(aq) + OH-(aq)
Keq = Kb = [BH+][OH-] / [B]
Combine the two
HA(aq) + H2O(l) H3O+(aq) + A-(aq)
Keq = Ka = [H3O+][A-] / [HA]
&
B(aq) + H2O(l) BH+(aq) + OH-(aq)
Keq = Kb = [BH+][OH-] / [B]
=
Kw= [H3O+][OH-]
Calculations
Problem:What are the hydronium and hydroxide ion
concentrations in a 0.10M HCl?
HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
Kw = [H3O+][OH-]
1.0 x 10-14 = (0.1M) x [OH-]
[OH-] = 1.0 x 10-13
Calculating pH
A pH is equal to the -log10 of the Hydronium ion concentration
pH = -log10[H3O+]
If an acid has a [H3O+] of 1.0 x 10-2M; then the pH is 2 S.U.
S.U. = standard unit
Calculating [H3O+]
The concentration of Hydronium ions can be determined by the reverse calculation, sort of If the pH of a solution is 5.05 S.U., then the
concentration of [H3O+] is 10-pH. 5.05 S.U. = 10-5.05 = 8.9 x 10-6 M
Tricks
If your concentration is 1.0 x 10-10 M, then your pH will be 10 S.U.! The negative exponent becomes the pH
If your concentration is greater than 1.0, then the pH will be less than the negative exponent. 2.5 x 10-10 M = >10 S.U. = 9.6
This comes in handy when you are answering multiple choice questions about the pH of a solution.
Practice Problems
What is the pH of a solution if the [H3O+] is 5.0 x 10-3M?
What is the pH of a solution if the [OH-] is 2.0 x 10-3M?
What is the [H3O+] of a solution whose pH is 3.3?
What is the [OH-] of a solution whose pH is 8.1?
Arrhenius Neutralization Reaction
An Arrhenius acid-base reaction looks something like this (does it kind-a look familiar?
HCl + NaOH
HCl + NaOH H2O + NaCl
Neutralization Reactions
Any acid-base reaction is called a neutralization reaction. By products are always a salt, water (or a
gas). Heat is also generated These reactions can be violent
Predict the Products
HNO3 + KOH KNO3 + HOH
HBr + NH4OH NH4Br + HOH
H3PO4 + Ca(OH)2 Ca3(PO4)2 + HOH
H2SO3 + LiOH Li2SO3 + HOH
How do you measure pH?
Litmus Paper Color change indicator pH meter
Compare the Scale
pH [H3O+] [OH-] pOH 0 1 x 10-0 M 1 x 10-14 M 14 1 1 x 10-1 M 1 x 10-13 M 13 2 1 x 10-2 M 1 x 10-12 M 12
Acid & Base Indicators
Acid and Base indicators are substances that change color in response to a specific pH
Different indicators are used depending on the range of the sample
Comparison Chart
Indicator Color at pH 4.6 Color at pH 7.9 Methyl orange Yellow Yellow Bromothymol blue Yellow Blue Thymol blue Yellow Yellow
Which of these indicators can be used to distinguish between a solution whose pH is 4.6 S.U. and one that is 7.9 S.U.?
Look at the chart. Only Bromothymol blue can distinguish between the two solutions.
Comparison Chart
Indicator Transition Range of pH
Color Change
Methyl orange 3.2 – 4.4 Red to Yellow Bromothymol blue 6.0 – 7.6 Yellow to Blue Thymol blue 8.0 – 9.6 Yellow to Blue Phenolphthalein 8.2 – 10 Colorless to Pink Bromocresol green 3.8 – 5.4 Yellow to Blue Litmus 5.5 – 8.2 Red to Blue
Which indicators can be used to distinguish between Soln. A: pH = 2.0 and Soln. B pH = 5.0?
Methyl orange
Comparison Chart
Indicator Transition Range of pH
Color Change
Methyl orange 3.2 – 4.4 Red to Yellow Bromothymol blue 6.0 – 7.6 Yellow to Blue Thymol blue 8.0 – 9.6 Yellow to Blue Phenolphthalein 8.2 – 10 Colorless to Pink Bromocresol green 3.8 – 5.4 Yellow to Blue Litmus 5.5 – 8.2 Red to Blue
Which indicators can be used to distinguish between Soln. A: pH = 5.0 and Soln. B pH = 9.0?
Bromothymol blue or litmus
Titrations
Titration The process, operation, or method of determining the concentration of a substance in a solution to which the addition of a reagent having a known concentration is made in carefully measured amounts until a reaction of definite and known proportion is completed, as shown by a color change or by electrical measurement, and then calculating the unknown concentration.
The equivalence point (end point) is reached when a titrant is added and is stoichiometrically equal to the amount of moles of substance (known as analyte) present in the sample; or, the smallest amount of titrant that is sufficient to fully neutralize or react with the analyte
Titrations
NaVa = NbVb
(look familiar?) N is normality N = M x n (the number of moles of H+ or OH- ions
released into solution)
The titrant is usually the solution of known concentration that is delivered by a burette into a known quantity of the solution of unknown concentration
The titraver is the indicating solution
Naming Acids
Acids are formed when a Hydrogen is added to an anion
Take the anion root, 1. Add a hydro- in front2. Change the ending from –ide or -ate to –ic;
or from –ite to -ous3. Put them all together and add the word
“acid”
HCl
Take the anion root, 1. Add a hydro- in front
Hydro
2. Change the ending from –ide or –ate to –ic; or from –ite to -ous
chloride chloric
3. Put them all together and add the word “acid” Hydrochloric Acid
Acid/Base Nomenclature
Arrhenius Theory Binary Acids:
Prefix = hydro--hydro-- Suffix = --ic--ic
Examples:
HClHydroHydrochloricic acid
HBrHydroHydrobromicic acid
Acid/Base Nomenclature
Arrhenius Theory Oxy acids:
H+ combined with a polyatomic anion containing oxygen (P.178)
No prefix If the name of the anion ends –ate, the
acid ends –ic If the name of the anion ends –ite, the
acid ends -ous
Oxy Acid Examples
Ion Acid
SO4-2 H2SO4
Sulfate Sulfuric acid
NO3- HNO3
Nitrate Nitric acid
NO2- HNO2
Nitrite Nitrous acid
CO3-2 H2CO3
Carbonate Carbonic acid
Acid/Base Nomenclature
Arrhenius Theory Bases:
Name the hydroxide base.
Naming Bases
Bases are MUCH easier to name
Simply name the cation and anion NaOH Sodium hydroxide
Practice Problems
1. HF
hydrofluoric acid
2. H2S
hydrosulfuric acid
3. H2SO3
sulfurous acid
4. NaOH
Sodium hydroxide
5. Fe(OH)3
Iron (III) hydroxide
6. Calcium hydroxide
Ca(OH)2
7. Chromic acid
H2CrO4
8. Phosphorous acid
H3PO3
9. Acetic acid
HC2H3O2
10. Hydroselenic acid
H2Se
Homework Quiz: p. 538 #1-13
1. What are the observable properties of an acid?
2. What is an Arrhenius definition of a base?
3. How does a strong acid differ from a weak acid?
4. How does the definition of a Bronsted-Lowry definition of an acid differ from that of the Arrhenius definition?
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