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)