Acids and Bases Chapter 19 DHS Chemistry. Definitions Bronsted – Lowry Arrhenius.
The Nature of Acids and Bases Arrhenius Definition Bronsted-Lowry Definition HA + B A - + HB +...
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Transcript of The Nature of Acids and Bases Arrhenius Definition Bronsted-Lowry Definition HA + B A - + HB +...
The Nature of Acids and Bases
• Arrhenius Definition• Bronsted-Lowry Definition
HA + B A- + HB+
Conjugate acid-base pair
Equilibrium Expressions
• Acid dissociation constant is for the equilibrium that exists as an acid spontaneously dissociates.
• Works the same as the other equilibrium expressions we’ve been writing.
Acid Strength
Types of acids
• Diprotic Acids- two hydrogen atoms, dissociate with different strengths.
• Oxyacids- H is attached to an oxygen.• Organic Acids- contain a carboxyl group.
• Hydrohalic Acids- H attached to a halogen.
R OH
O
Write the equilibrium expression for the autoionization of water.
Autoionization of Water
• Water is amphoteric (properties of acid and base)
Do Now
The pH Scale
• pH = -log[H+]• Related by exponents of 10. As [H+]
increases, the pH will decreases.
log Kw = log [H+] + log [OH-]pKw = pH + pOH14 = pH + pOH
The number of
S.F. in the concentration
value equals the
number of decimal
places in the pH value.
Try Me Problems!!
• Calculate the pH or pOH as required for each of the following solutions at 25oC, and state whether the solution is neutral, acidic, or basic.a) 1.0 x 10-5 M OH-
b) 1.0 x 10-7 M OH-
c) 1.0 M H+
More Try Me!
• Calcualte pH and pOH for each of the solutions from the problem before.
Even More Try Me!
• The pH of a sample of human blood was measured to be 7.41 at 25oC. Calculate the pOH, [H+], and [OH-] for the sample.
Acid Strength Matters
• Identify the MAJOR SPECIES present in your sample.
• Determine if the autoionization of water will impact the concentration of [H+] or not (compare concentrations)
Strong Acid Example
Lets pretend I have 1.0 M HCl.major species: H+ , Cl-, H2O
H+ from HCl will be 1.0 M H+ from H2O will be 1.0 x 10-7
M H+ from H2O is negligible.
We can now base our calculations on the H+ values from our major species.
In the Event of a Weak Acid…
1. Write out major species.2. Determine if H20’s H+ are
significant.3. Write Ka for dominating species
4. Use an ICE chart
Weak Acid Example
Lets pretend I have 1.0 M HF, solve for [H+]
major species: HF, H2O
HF H+ + F- Ka = 7.2 x 10-4
H2O H+ + OH- Kw= 1.0 x 10-
14
Dominating source of H+: HF
ICE it up!
HF H+ + F-I 1.0 0 0C -x +x +xE 1-x x x
Plug into Ka expression, BUT DO NOT SOLVE YET
5% rule
• If x is small, cross out subtracted/added x’s• How small? 5% of original concentration.
• Similarly, percent dissociation/ionization has formula:
100xionizationpercent ionconcentratinitialddissociateamount 100xionizationpercent ionconcentratinitialddissociateamount
%5100][ xoHA
x %5100][ xoHA
x
Try Me!
• Calculate the pH of a solution that contains 1.0 M HCN (Ka = 6.2 x 10-
10) and 5.0 M HNO2 (Ka = 4.0 x 10-
4). Also calculate the concentration of cyanide ion (CN-) in this solution at equilibrium.
Try Me Trickier!
Lactic acid (HC3H5O3) is a waste product that accumulates in muscle tissue during exertion, leading to pain and fatigue.
In a 0.10 M aqueous solution, lactic acid is 3.7 % dissociated. Calculate Ka for the acid.
Bases
• Strong bases have/cause complete ionization, just like acids.
• KOH and NaOH are the most common group I soluble strong bases
• Group II hydroxides are insoluble strong bases
• Not all bases need to have OH- (Brønsted Lowry)
H3CNH2(aq) + H2O(l) H3CNH3+
(aq) + OH-(aq)
Common Base Structures
AmmoniaAmmonia MethylamineMethylamine DimethylamineDimethylamine
PyridinePyridine EthylamineEthylamine EphedrineEphedrine
Useful Application
• Amines can form soluble acid salts
Pseudoephedrine + HCl ↔ pseudophedrineHCl
Strong Base Try Me
Calculate the pH of a 5.0 x 10-2 M NaOH solution.
Weak Base Try Me
Calculate the pH of a 15 M solution of ammonia (Kb = 1.8 x 10-5)
Polyprotic Acids
• Dissociate stepwise
• For weak acids, Ka1 > Ka2 > Ka3
• Sulfuric acid is a freak because it is strong for hydrogen 1 and a weak acid for hydrogen 2. Only impacts normal process if we are using dilute solutions.
Try ME! Concentrated H2SO4
Calculate the pH of a 1.0 M solution of H2SO4.
Try Me 2! Dilute H2SO4
• Calculate the pH of 1.0 x 10-2 M H2SO4
Regular Type Polyprotics
Calculate the pH, and the concentration of each ion formed by the complete dissociation of hydrogen in a 5.0 M solution of phosphoric acid.
Once upon a time there was a salt…
• What is a salt?
• What power does it have in solution?
Solution is Basic Solution is Acidic
salt of astrong acid
and astrongbase
Solution is Neutral
salt of a
weak acid
and a
strong
base
salt of astrong acid
and the C.A.
of a weakbase
salt
of th
e C
.B.
of a
wea
k ac
idan
d th
e C
.A.
of a
wea
kba
se
salt with a
highly charged
metal cation
varies
Try This On!
Calculate the pH of a 0.10 M NH4Cl solution, given that Kb for NH3 is 1.8 x 10-5
Structural Effects
• Hydrohalic Acids• Bond Strength• Bond Polarity
• Oxyacids• Number of Oxygen atoms
H-F H-Cl H-IH-Br
OXIDES
Covalent oxides in water form acids• CO2 + H2O H2CO3
• Ionic oxides in water form bases• K2O + H2O 2KOH
If X has high EN,the oxide will act as acid
If X has low EN,OH stays together
and oxide actsas a base.
Lewis Definition
• Lewis Acids• Accepts e- pair
• Lewis Bases• Dontates e- pair