Acids and Bases

Acids and Bases

Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water

acid

base
acid
base
acid
conjugate base
base
conjugate acid


O
H
H
+
O
H
H
O
H
H
H
O
H
-
+
[
]
+
Acid-Base Properties of Water
H2O (l) H+ (aq) + OH- (aq)
H2O + H2O H3O+ + OH-
acid
conjugate base
base
conjugate acid
autoionization of water

Molecular Structure and Acid Strength

H X
H+ + X-
The stronger the bond
The weaker the acid
HF << HCl < HBr < HI

Molecular Structure and Acid Strength

Z
O
H
Z
ნѿtྟྨⵏྡ,ྪЉЉྦрǔːϰԐĕಢ㐍ਂУfǯЂ诨ᔫ…їƁࠀƿǀࠀǿȁࠀȿ̿쎀οText Box 22Ⴐ͠ዔҀwྟྨ‫䠠+ꄀⰏ؀਀܀ЀȀ᠀Ā਀᠀ḀĀȀ᠀ꨀฏ؀܀ऀऄꘀఏ퐀퀁ဃ༅̀쓰ༀЀ胰Āऀჰ 瀀찀뜀Ȁ਀ࣰ܀4̀䌀଀⫰Ѐ缀老ዃ뼀Ȁ䜀爀漀甀瀀 ㈀㌀牟汥⽳爮汥汳쇏썪ర惻惯彴왐펈ꅛ틗耾閱Ⳅ貶뉤穧읪銎㿸썉⟡暭턣�껂쇫戜⶞⽜럇』嵚渎䳥渖炤弘號괳뚮⺐ꢱ䩩ୖ굋퀊甩橑ᢲ빇霣莻ᘏ蹓쌹쭭ꋋ贖࿋㬚홺뼤䝷ꀫ�鎔浥溌븿ꯖ徴郎䛻纫ӱ儬ﺟ⿇ꡲﲯ굅肔ӣ�ꌇᢶԓ夁쬯兦돠￿䭐ȁ-!쯶оƅ଀ἀ开敲獬ⸯ敲獬䭐ȁ-!ف텻Ыьȇ牤⽳潤湷敲⹶浸偬Ջ̀̀뜀ༀကࣰ耀倄、刕༈ᄀ⳰ༀ᐀␐ĀᰏDȀĀȀༀഀ鼀ЏЀꠀ猏吀敨传䠭戠湯⁤楷汬戠⁥潭敲瀠汯牡愠摮攠獡敩⁲潴戠敲歡椠㩦娍椠⁳敶祲攠敬瑣潲敮慧楴敶漠൲⁚獩椠⁡楨桧漠楸慤楴湯猠慴整ྡ48 2< 28<ྪtЉЉྦшĠɀ͠Ҁ֠ћҲ㐅਀ЈvЂǻ䄄섅Ŀƿǿ̿쎀쎁οCHA56015Picture 27CHA56015ࡊǫᒫႊ O-
+ H+
d-
d+
The O-H bond will be more polar and easier to break if: Z is very electronegative or Z is in a high oxidation state



Molecular Structure and Acid Strength
1. Oxoacids having different central atoms (Z) that are from the same group and that have the same oxidation number.
Acid strength increases with increasing electronegativity of Z
H O Cl O
O
•
• •
• •
• •
• •
• •
• •
• •
• •
• H O Br O
O
•
• •
• •
• •
• •
• •
• •
• •
• •
• Cl is more electronegative than Br
HClO3 > HBrO3

Molecular Structure and Acid Strength

2. Oxoacids having the same central atom (Z) but different numbers of attached groups.
Acid strength increases as the oxidation number of Z increases.
HClO4 > HClO3 > HClO2 > HClO

Arrhenius acid is a substance that produces H+ (H3O+) in water

A Lewis acid is a substance that can accept a pair of electrons
A Lewis base is a substance that can donate a pair of electrons
Definition of An Acid
H+
H O H
•
• •
• + OH-
•
• •
• •
• acid
base
N H
•
• H
H
H+
+
N H
H
H
H
acid
base

Lewis Acids and Bases

N H
•
• H
H
acid (electrophile)
base (nucleophile)
F B
F
F
+
F B
F
F
N H
H
H
No protons donated or accepted!
Let’s look at this reaction, and others like it more closely. To see what’s really going on we need to look at the MOs.


According to Arrhenius, an acid is any substance that produce H+ ions in a solution HCl → H+ + Cl-It is the Hydrogen ion (H +) that is produced that makes HCl an acid.Some other common acids include:HNO3 nitric acidH2SO4 sulphuric acidHC2H5O2 acetic acid H3C6H5O7 citric acidNote the H+ at the beginning of each formula These are the acidic Hydrogen. The ones that separate in solution

A base is any substance that produce hydroxide ion (OH-) when it dissolved in water. For example :NaOH → Na + + OH-Is produced that makes NaOH a base .Some common base include:KOH potassium hydroxideCa(OH)2 calcium hydroxideNH3 amoniaQ- How can NH3 be abase when it does not contain a hydroxide/

Remember, the definition of abase says that it must produce OH- ions when it dissolves in water. It does not necessary have to contain the OH- ion.NH3 react with water molecules to produce NH4 ions and OH- ions, so it is considered a base NH3 + H2O → NH4++ OH-

Buffers solutionWhen a week acid is dissolved in water the acid partially dissociates into a hydrogen ion and a conjugate base. The molecular acid, hydrogen ion and base in equilibrium:CH3COOH H++CHOO-

When an acid is added to the buffers the H+ combine with the conjugate base. CH3COO-. Since the excess H+ is neutralized the pH remains constant.CH3COOH H++CH3COO-CH3COO- +H + H+ CH3COOH

When a base is added to the buffer, the OH- combine with the H+ in solution , forming water. The acid molecular dissociates releasing more H +and CH3COO-. The pH remains constant. CH3COOH H++CH3COO-  H++CH3COO- + OH- CH3COOH +H2O