ACIDS AND BASES

ACID, BASE, OR NEUTRAL? Bitter taste Doesn’t conduct electricity Feels slippery Dissolves metals Has no odor Has a strong, acrid odor Turns litmus blue Is unreactive Feels sticky Feels greasy Turns phenolphthalein solution red Dissolves grease Bubbles when baking soda is added Is oily

acid

base neutra

lbase

acidbase

or neutral

baseneutra

lneutra

l

acid

neutral

acidbase

acid

ARRHENIUS DEFINITION OF ACID AND BASE

ACID – hydrogen containing compound that ionizes to yield hydrogen ions (H+) in aqueous solution

BASE – compound that ionizes to yield hydroxide ions (OH-) in aqueous solution

IONIZABLE HYDROGENS Only hydrogens in very polar bonds

ionize.

Some acids have more than one ionizable hydrogen

DIPROTIC ACIDS 2 ionizable hydrogens (H2SO4 )TRIPROTIC ACIDS 3 ionizable hydrogens (H3PO4 )

This is the hydrogen that ionizes in acetic

acid

Carboxyl group

ARRHENIUS BASE OR ACID? Ca(OH)2

HNO3

KOH

C2H5COOH

HBr

H2SO4

Base Acid Base Acid Acid Acid

BRONSTED-LOWRY DEFINITION OF ACID AND BASE

ACID – hydrogen ion (H+) donor

BASE – hydrogen ion (H+) acceptor

IDENTIFY EACH REACTANT AS A HYDROGEN DONOR (ACID) OR HYDROGEN ACCEPTOR (BASE) HNO3 + H2O H3O+ + NO3

-

CH3COOH + H2O H3O+ + CH3COO-

NH3 + H2O NH4+ + OH-

H2O + CH3COO- CH3COOH + OH-

Acid

(donor)

Base

(acceptor)

Acid

(donor)

Acid

(donor)

Acid(donor)

Base

(acceptor)

Base

(acceptor)

Base(acceptor

)

Water acts as both a

hydrogen donor and hydrogen acceptor – it

acts as both an acid and a base.

It is AMPHOTERIC

CONJUGATE ACIDS & BASESCONJUGATE ACID – formed when a base

gains a hydrogen ionCONJUGATE BASE – formed when an

acid donates a hydrogen ion

NH3 and NH4+ are a

conjugate acid base pair

LABEL THE CONJUGATE ACID-BASE PAIRS HNO3 + H2O H3O+ + NO3

-

CH3COOH + H2O H3O+ + CH3COO-

NH3 + H2O NH4+ + OH-

H2O + CH3COO- CH3COOH + OH-

CBCA

CBCA

CACB

CBCA

LEWIS ACIDS AND BASES ACID – a substance

than can accept a pair of electrons to form a covalent bond

BASE – a substance than can donate a pair of electrons to form a covalent bond

SELF-IONIZATION OF WATER

2H2O (L) ⇆ H3O+(aq) + OH-(aq)

At any given time, there are only VERY small amounts of [H3O+] and [OH-] ions in water (1 molecule out of 550,000,000

dissociates) Water dissociates to form equal concentrations of

H3O+ and OH- making water neutralAt 25◦C, Kw = [H+] [OH-] = [1 x 10-7 ] [1 x 10-7 ] = 1 x 10-14

ION-PRODUCT CONSTANT OF WATER

ACIDIC SOLUTIONS VS. BASIC SOLUTIONS

[H+] is greater than [OH-]

[OH-] comes from self-ionization of water

Extra [H+] comes from substances that dissolve in water to create [H+]

[H+] is greater than 1x10-7

Acidic Solution Basic Solution

[H+] is less than [OH-] [H+] comes from self-

ionization of water Extra [OH-] comes from

substances that dissolve in water to create [H+]

[H+] is less than 1x10-7 Also known as alkaline

solution

ION CONCENTRATIONS IN ACIDIC, NEUTRAL AND BASIC SOLUTIONS

ACIDIC, BASIC OR NEUTRAL? [H+] = 6.0 x 10-10 M

[OH-] = 3.0 x 10-2 M

[H+] = 2.0 x 10-7 M

[OH-] = 1.0 x 10-7 M

[OH-][H+]= 1.0 x 10-

14

[H+]= 1.0 x 10-

14

3.0 x 10-

2 [H+] = 3.3 x 10-

13

Basic

Basic (hydrogen ion concentration is less than 1.0 x 10-7

Acidic (hydrogen ion concentration is greater than 1.0 x 10-7

Neutral

ACIDIC SOLUTIONS VS. BASIC SOLUTIONS

[H+] is greater than [OH-]

[OH-] comes from self-ionization of water

Extra [H+] comes from substances that dissolve in water to create [H+]

[H+] is greater than 1x10-7

pH < 7.0 pOH > 7.0

Acidic Solution Basic Solution

[H+] is less than [OH-] [H+] comes from self-

ionization of water Extra [OH-] comes from

substances that dissolve in water to create [H+]

[H+] is less than 1x10-7 Also known as alkaline

solution pH > 7.0 pOH < 7.0

MEASURING PH Acid-Base

Indicators – an acid or a base that: Dissociates in known

pH range Acid and base forms

are different colors in solution

Accuracy challenged by changes in temp & human error

pH meter Quick Accurate within .01

pH units

ACID RAIN

PH & POH

pH = –log[H+] pOH = –log[OH-] pH + pOH = 14

Use LOG key on calculator not LN to calculate pH!

Use antilog (10x) key on calculator to calculate M from pH

SAMPLE PROBLEMS

pH = -log[H+] pH = -log[8 x 10-11] pH = 10.10

Some calculators require that you push LOG key first while some require that you put in the # first then press LOG

pOH = -log[OH-] pOH = -log[2 x 10-3 ] pOH = 2.70

Some calculators may keep giving you errors if you try converting into – log. Just calculate using positive and switch the answer sign

What is the pH of a solution if the [H+] is 8 x 10-11 M?

What is the pOH of a solution if the [OH-] is 2 x 10-3 M?

SAMPLE PROBLEMS

pOH = -log[OH-] pOH = -log[3.5 x 10-

2 ] pOH = 1.46

pH + pOH = 14 14 – 1.46 = pH 12.54 = pH

M = mol solute / L solution35 g HNO3 / 63 g = .56 mol

M = .56 mol / 5.8 L = .097 M pH = -log[H+] pH = -log[.097 ] pH = 1.01

pH + pOH = 14 14 – 1.01 = 12.99 = pOH

What is the pH of a solution if the [OH-] is 3.5 x 10-2 M?

What is the pH & pOH of a solution made by adding water to 35 grams of nitric acid until the volume of the solution is 5800 mL?

PLACE THE FOLLOWING COMPOUNDS IN ORDER OF INCREASING [H+]

1M weak acid 1M strong acid 1M strong base 1M weak base

1M strong base 1M weak base 1M weak acid 1M strong acid

WRITE THE EXPRESSION FOR THE ACID DISSOCIATION CONSTANT OF THE STRONG ACID HF:

Ka = [H+ ][A- ]

[HA]

Ka = [H+ ][F- ]

[HF]

HF(aq) H+(aq) + F-

(aq)

WRITE THE EXPRESSION FOR THE BASE DISSOCIATION CONSTANT FOR THE WEAK BASE HYDRAZINE. HYDRAZINE REACTS WITH WATER TO FORM N2H5

+ ION

Kb = [OH- ][N2H5+ ]

[N2H4]

N2H4(aq) + H2O(l) N2H5+

(aq) + OH-(aq)

PLACE THE FOLLOWING ACIDS IN ORDER FROM WEAKEST TO STRONGEST (USE TABLE ON P.607)

HOOCCOOH HCO3

-

H2PO4-

HCOOH

HCO3-

H2PO4-

HCOOH HOOCCOOH

A .10M SOLUTION OF FORMIC ACID HAS AN EQUILIBRIUM [H+] = 4.2 X 10-3M. WHAT IS THE KA OF FORMIC ACID?

HCOOH(aq) H+(aq) + HCOO-

(aq)

(4.2 x 10-3 ) (4.2 x 10-3 ) (.10 – 4.2x10-3 )

Ka = 1.8 x 10-4