Upload
leslie-copeland
View
220
Download
0
Embed Size (px)
Citation preview
Acids and Bases
Acids Taste sour Begin with H Found in many foods and drinks Turn blue litmus paper red pH 0-6.9 Corrosive Forms H+ (or H30+)ions in solutions
Hydrogen Hydronium
Bases Bitter End in OH Turn red litmus paper blue pH 7.1-14 Found in many cleaning products Slippery Corrosive Forms OH- ions in solution
Hydroxide
Acids and Bases
Neutral: H+ = OH-
Acidic: H+ > OH-
Basic: H+ < OH-
↑H+ = ↓OH- = more acidic = ↓ pH acidic ↓H+ = ↑OH- = more basic = ↑ pH
Water = Neutral
H2O = HOH
HOH → H+ + OH-
Free Hydrogen ion bonds with water molecule toform Hydronium ion
H+ and H3O+ used interchangeably
Hydronium Ion = Hydrogen Ion
Self ionization - two water molecules react to form a hydronium ion (H3O+) and hydroxide ion.
H20 → H+ + OH-
pH scale Shows the strength of acid or base on
a scale of 0-14. Numbers below 7 = acids…the lower
the number, the more acidic Numbers above 7 – bases…the higher
the number the more basic.
pH and pOH pH + pOH = 14
If the pH = 2, what is pOH
If the pH = 4, what is the pH
If the pOH = 7, what is the pH
Calculating pH Formula: pH = -log [ H+ ]
You can calculate pH by finding the negative logarithm of the concentration of hydrogen ions.
Calculating pH A solution contains 1.0 x 10-8 mol/L of
H+ ions, what is the pH of this solution?Formula: pH= -log [H+]
pH = -log (1.0 x 10-8)
pH = 8 = Base
Calculating pH A solution contains 3.5 x 10-5 M of H+
ions, what is the pH of the solution?Formula: pH= -log [H+]
pH= -log ( 3.5 x 10-5)
pH = 4.5 = acid
pH and Water Water is amphoteric; it can act as both
an acid and a base in an aqueous solution.
Water contains an equal number of H+ and OH- ions.
H2O H+ + OH-
Ion Product Constant of Water Kw is the ion product constant for water.
Represents the equilibrium for the self ionization of water.
Formula:
Kw = [H+][ OH-]
[H+] = 1.0 x 10-7
[ OH-]= 1.0 x 10-7
What is the Kw?
Kw= (1.0 x 10-7) x (1.0 x 10-7)
Kw= 1.0 x 10-14
This is a constant on your STAAR Chart
The H- concentration of an aqueous solution is 1.0 x 10-5M. What is the OH- ion concentration?
Kw= [H+][OH-]
Kw= 1.00x10-14 List the Knowns
H+ = 1.0 x 10-5
1.00 x 10-14 = 1.0 x 10-5 [OH-] plug into
formula
[OH-] = 1.00 x 10-14/ 1.0 x 10-
5 = 1.0 x 10 -
9mol/L M
The OH- concentration of an unknown solution is 2.4 x 10-4. What is the H+
concentration of the solution? Is the unknown solution acidic, basic, or neutral?
Kw= [H+][OH-]
1.0 x 10-14 = [H+][ 2.4 x 10-4] [H+] = 1.0 x 10-14/ 2.4 x 10-4
[H+] = 4.16x 10-11
-log(4.16 x 10-11)= pH= 10.4 = Basic solution
Acid Base Reactions
Acid + Base = neutralization reaction
Acid + Base → water + salt (always)
Salt = (+) ion from base & (-) ion from acid Positive ions are always listed first
HA + BOH → HOH + B+A-
Arrhenius Swedish Chemist Svante Arrhenius
created a model for acids and bases in 1883.
Arrhenius Model- AcidHCl (g) H+ (aq) + Cl-
(aq)Acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution.
Arrhenius Model- Base• Base is a substance that contains a
hydroxide group and dissociates to produce a hydroxide ion in aqueous solution.
NaOH (s) Na+(aq) + OH- (aq)
Bronsted- Lowry Model Danish chemist Bronsted and English
chemist Lowry proposed a model that focuses on the Hydrogen Ion
An Acid is a hydrogen-ion donor A Base is a hydrogen-ion acceptor
Ionization The Bronsted-Lowry Model also shows if
and acid or base is strong based on ionization. Strong acid- completely ionized Weak acid- partial ionization
Strength and Concentration Strength – how completely it ionizes
Strong – ionizes completely or almost completely
Weak – ionizes partly Concentration
Concentrated - a lot of acid/base in water.
Dilute – a little acid/base in water.
12 M HCl is a strong acid with a high concentration
Adding 6L of water to this solution would do what to the solution: strong acid, dilute solution
Vinegar has acetic acid, which is weak, in low concentration = dilute
12 M acetic acid would still be weak, because it only partially ionizes, but it would be a concentrated solution, because there is a lot of acid dissolved in a little water.
Strong Acids Since strong acids are completely
ionized they produce the maximum number of ions. Strong acids are good conductors Reaction only moves in one direction,
represented with an arrow in one direction.
HCl H+ + Cl-
HBr H+ + Br –
H2SO4 H+ + HSO4 _
Weak Acids An acid that ionizes partially in dilute
aqueous solutions Produce fewer ions, so they are poor
conductors Reactions move both directions until
equilibrium is reached, represented by an arrow in both directions
HF H+ + F-
H2S H+ + HS-
H2CO3 H+ +HCO3
-
Conjugate Acid The species produced when a base
accepts a hydrogen ion to form an acid
Conjugate BaseThe species that results when an acid donates a hydrogen ion to form a base.
Conjugate acid – base pairs
2 compounds with the same chemical formula, but the acid of the pair will have 1 more H
NH3 & NH4-
H2SO4 & HSO4-
H2O & H3O+
Bronsted-Lowry Model
NH3 + H2O → NH4+
+ OH-
BASE
ACIDCONJUGATE
ACID
CONJUGATEBASE
Precipitate Reactions When two compounds come together to
form an aqueous compound and a solid compound. 2NaOH(aq)+CuCl2(aq) 2NaCl(aq)+Cu(OH)2(s)
KI(aq) + AgNO3(aq)KNO3(aq) + AgI(s)
Use your STAAR chart to check solubility If insoluble – compound will precipitate or
settle out of solution as a solid
Oxidation-Reduction Reaction A reaction in which electrons are
transferred from one atom to another
2KBr(aq) + Cl2(aq) 2KCl(aq) + Br2(aq)
The chlorine on the left steals electrons from the bromine in KBr to become KCl and Br2 on the right.
Oxidation- Reductions Reaction
Remember Acid-Base Reaction
Form SALT + WATER
Mg(OH)2 + 2HCl MgCl2 + H20
base + acid salt + water
Salt = any ionic compound made up of a cation (+) from a base and an anion (-) from an acid
Identify the following reaction: as 1) precipitation, 2) oxidation-reduction, or 3)acid-base
2K + Br2 2KBr
H3N + CsOH Cs3N + H2O
MgCl2 + Li2CO3 MgCO3 + LiCl
Look on STAAR chart to see if either compound Is insoluble
Titration Use known solution (standard solution) to find
the concentration of an unknown solution Drop by drop process Endpoint – point of color change of indicator
When neutralized
Buffers Resist changes or swings in pH Blood pH approx 7.4
Fatal if fall or rise more than 0.3 pH units Buffers in your blood prevent big changes
when, for example, you eat an orange (citric acid)