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ACID & BASEAnnisa HayatunnufusBachelor of Pharmacy

For Subject Physical Chemistry

CONTENTA. Acid & Base (Introduction)

GENERAL DEFINITI

ON THEORIES

CHARACTERISTICS

CLASSIFICATION

DEFINITIONINDICATOR &

MEASURING TOOLS

DISSOCIATION CONSTANT

ACID & BASE EQUILIBRIUM

CONSTANT pH CALCULATION

B. pH Measure of

Acidity

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A. Acid & Base (Introduction)

?ACIDS

BASE Ionic compounds (a compound with a positive/negative charge) that break apart in water to form a hydrogen ion (H+).

Strength proportional to concentration of H+ ions in the solution. 

Ionic compounds that break apart to form a negatively charged hydroxide ion (OH-) in water.

Strength proportional to concentration of Hydroxide ions (OH-).

Solutions containing bases are often called alkaline.

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A. Acid & Base (Introduction)

THEORIES

Brønsted-lowry

LewisArrhenius

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A. Acid & Base (Introduction)

CHAR

ACTE

RIST

ICS ACIDS BASES

Sour Bitter

Change color of litmus paper to red

Change color of litmus paper to blue

One of composer of many food and beverages (ie. vinegar, cheese, fruits)

In normal state present in a form of solid crystal and the strong ones are caustic

React with certain metals to produce gaseous H2

Feel slippery

React with bases to form salt & water

React with acids to form salt & water

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CLASSIFICATION

A. Acid & Base (Introduction)

ACIDS BASESFrom its origin

Organic Acid

Generally weak acids,

corrosive, and abundant in

nature

Anorganic Acid

Generally strong acids,

corrosive, and human-made

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CLASSIFICATION

A. Acid & Base (Introduction)

ACIDS BASESFrom amount of

proton given

Monoprotic

Donates only one proton or hydrogen

atom per molecule: HCl,

HNO3

Polyprotic

Donates more than

one proton or hydrogen

atom per molecule: H2S, H2SO4, H3PO4

• H2S HS- S2-

• H3PO4 H2PO4- HPO4

2- PO43-

Example:

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CLASSIFICATION

A. Acid & Base (Introduction)

ACIDS BASESFrom its strength

From its strength

Strong Acid

Completely ionized in

solution. There are only 7

strong acids: HCl, HBr, HI, H2SO4, HNO3, HClO3, HClO4

Strong Base

Completely ionized too with

only 8 members:

LiOH, NaOH, KOH, RbOH,

CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

Weak Acid

Not completely ionized in solution.

Examples are all acids aside from the ones

mentioned before.

Weak Base

Also not completely

ionized. Examples are all acids aside from the ones

mentioned before.

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CLASSIFICATION

A. Acid & Base (Introduction)

ACIDS BASESFrom its origin

Organic Acid

Generally weak acids,

corrosive, and abundant in

nature

Anorganic Acid

Generally strong acids,

corrosive, and human-made

From its strength

From its strength

Strong Acid

Completely ionized in

solution. There are only 7

strong acids: HCl, HBr, HI, H2SO4, HNO3, HClO3, HClO4

Strong Base

Completely ionized too with

only 8 members:

LiOH, NaOH, KOH, RbOH,

CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

Weak Acid

Not completely ionized in solution.

Examples are all acids aside from the ones

mentioned before.

Weak Base

Also not completely

ionized. Examples are all acids aside from the ones

mentioned before.

! Example:

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B. pH Measure of Acidity

The strength of an acid or base in an aqueous solution is measured on a scale called a pH scale.

The pH scale is a measure of the hydrogen ion concentration. It spans from 0 to 14 with the middle point (pH 7) being neutral (neither acidic or basic). Any pH number greater than 7 is considered

a base and any pH number less than 7 is considered an acid.

0 is the strongest acid and 14 is the strongest base.

pH?

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B. pH Measure of Acidity

INDICATOR & MEASURING TOOLS

Litmus Paper

Indicator Low pH color

High pH color

Hydrangeaflowers blue pink to

purpleAnthocyanins red blue

Litmus red blue

Hydrangea flower

DigitalElectronic

Universal Indicator Solution Low pH color pH range High pH color

Thymol blue (first transition) Red 1.2 – 2.8 Yellow

Methyl red Red 4.4 – 6.2 Yellow

Bromothymol blue Yellow 6.0 – 7.6 Blue

Phenolphthalein Colorless 8.3 – 10.0 Fuchsia

pH Meter

Universal Indicator

Paper

Red Cabbage

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B. pH Measure of Acidity

Dissociation Constant (Kw)Can also be known as ion product of water. Water dissociation is one of the most fundamental acid-base reaction In this reaction, water breaks apart to form a hydrogen ion (H+) and a hydroxide ion (OH-). In pure water, we can define a special equilibrium constant (Kw) as follows:

H2O H+ + OH-

KW = [H+][OH-] = 1.00x10-14

• Kw value of 1.00 x 10-14 is only applied at 25° C (unitless) and 1 atm pressure

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B. pH Measure of Acidity

The equilibrium constants (Ka & Kb)

HA + H2O → H3O+ + A– A− + H2O → HA + OH–

• The strength of an acid HA in water can be defined by the equilibrium:

• Similarly, the strength of the base A– in water is defined by the equilibrium:

How are Ka and Kb related? The answer can found by multiplying the above two

expressions for Ka and Kb:

∴ Ka Kb = Kw

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B. pH Measure of Acidity

The equilibrium constants (Ka & Kb)

HA + H2O → H3O+ + A– A− + H2O → HA + OH–

• The strength of an acid HA in water can be defined by the equilibrium:

• Similarly, the strength of the base A– in water is defined by the equilibrium:

How are Ka and Kb related? The answer can found by multiplying the above two

expressions for Ka and Kb:

∴ Ka Kb = Kw

As the strength of a series of

acids increases, the strengths of their conjugate

bases will decrease!

• Kw, Ka, & Kb are needed in calculating reactions that involve weak acid/base

(ex: buffer solutions & hydrolisis of salt)

• Buffer solutions:

• contains a weak acid (ex: CH₃COOH) together with a salt of the acid

(ex: CH₃COONa)

• used to resists a change in its pH when H+ or OH– ions are added or

removed.

• usage ex.: Blood is strongly buffered (mainly by bicarbonate) to

maintain its pH at 7.4±0.3; pH values below 7.0 or above 7.8 cause

death within minutes.

• Hydrolisis of Salt:

• dissolved salts that derives from weak acid & weak base may cause an

increase or decrease of pH according to the Ka & Kb value of the salt.

• when Ka > Kb, solution will be more acidic. When Ka < Kb, solution will

be more alkaline.

CUKSTAW (CUKUP TAU/ADDITIONAL) INFORMATION

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B. pH Measure of Acidity

Calculating pH

• pKb = - log (Kb)• Kb = 10-pKb

• Kb = antilog ( - pKb)

• pKa = - log (Ka)• Ka = 10-pKa • Ka = antilog ( - pKa)

• pOH = - log [OH-]• [OH-] = 10-pOH

• [OH-] = antilog ( - pOH)

• -log [H+]• [H+] = 10-pH • [H+] = antilog ( - pH)

[H+] [OH-]

KbKa

pH + pOH = 14

Content References

• Lower, Stephen. Introduction to Acid-base Chemistry. Chem1 General Chemistry Reference Text [Online] 1999. Available from: http://www3.imperial.ac.uk/library/subjectsandsupport/referencemanagement/vancouver/references [Accessed 10th November 2014]

• Bogren, Sue & Urbana Middle School Teachers. Acid, Base, and pH Tutorial. [Online]. Available from: http://lrs.ed.uiuc.edu/students/erlinger/water/background/ph.html [Accessed 10th November 2014]

• Gunawan, Ary. BAB 2. ASAM, BASA, DAN GARAM. United Science. Weblog. [Online] Available from: http://unitedscience.wordpress.com/ipa-1/bab-2-asam-basa-dan-garam/ [Accessed 10th November 2014]

• UNKOWN. Pengertian Asam Basa. Alfikimia. Weblog. [Online] Available from: http://alfikimia.wordpress.com/kelas-xi/larutan-asam-basa/a-pengertian-asam-basa/ [Accessed 10th November 2014]

• Shodor Organization. Acid-Base Chemistry. [Online]. Available from: http://www.shodor.org/unchem/basic/ab/ [Accessed 10th November 2014].

• http://depts.washington.edu/chemcrs/bulkdisk/chem142A_win07/notes_Solutions_Chapter_07.pdf [Accessed 15th November 2014]

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