ACIDS & BASES

Presentation by JANAT PREET

Submitted to Mr.VINAY SHARMA

• Acids• Bases• Strong and weak acids and bases .• Indicators• Ph scale• Ionisation in water• Neutralisation reactions• Environmental hazard - acid rain

CONTENTS

Acids

þ Produce H+ (as H3O+) ions in water

þ Produce a negative ion (-) too

þ Taste sour

þ React with several metals releasing H2(g) corrosion

þ React with carbonates releasing CO2(g)

þ Turn blue litmus (vegetable dye) red

þ React with bases to form salts and water

þ Destroy body tissue , corrosion of metals

Bases

Produce OH- ions in water

Taste bitter, chalky

are electrolytes

Feel soapy, slippery

React with acids to form salts and water

Strengths of Acids and Bases

Strong acids completely ionize (100%) in aqueous solutions

HCl + H2O H3O+ + Cl- (100 %

ions)Strong bases completely (100%) dissociate into ions in aqueous solutions. NaOH Na+ (aq) + OH-(aq)

(100 % ions)

• Weak acids do not dissociate into H+ completely in water .eg H2CO3 (l)

CH3COOH (l) +H2O H+ (aq) + CH3COO- (aq)

• Weak bases similarly do not completely ionise in water eg.

NH3(g) + H2O NH4 + (aq) + OH – (aq)

HCO3

– (aq) + H2O H2CO3

(aq) + OH-

(aq)

Strengths of acids and bases.• Strong acids and strong bases are

good electrolytes due to 100% ionisation into H+

and OH- ions respectively in water. good conductors

Severe burns to body tissue Strong acids H2SO4(l); HNO3(l) strong bases NaOH ;KOH; also k/a

alkalis. • Weak acids and weak bases are weak

electrolytes (lesser concentration of ions) Most acids in nature are weak

eg.acetic acid citrus acid etc.

Weak bases eg Al(OH)3 Mg(OH)2

a.Strong acid (hydrochloric acid) b. weak acid (carbonic acid)

INDICATORS• To decide if something is an acid or

a base we can use an indicator.• Litmus and Universal Indicator are

examples of indicators.• They change colour depending on if

they are in an acid or a base.

pH• pH stands for power of hydrogen From the French

pouvoir hydrogene • First given by Soren Sorenson

• It is measured on a scale of 0 to 14.

• The formal definition of pH is the negative logarithm of the hydrogen ion activity.

pH = -log[H+] or ph = -log [H3O+] also [H3O+] = 1 x 10-exponent

the exponent = pH

[H3O+] = 1 x 10-pH M

pH value• The pH value of a substance is

directly related to the ratio of the hydrogen ion and hydroxyl ion concentrations.

• If the H+ concentration is higher than OH- the material is acidic.

• If the OH- concentration is higher than H+ the material is basic.

• 7 is neutral, < is acidic, >7 is basic

Acid – Base Concentrations

pH = 3

pH = 7

pH = 11OH-

H3O+OH-

OH-H3O+

H3O+

[H3O+] = [OH-] [H3O+] > [OH-] [H3O+] < [OH-] acidic

solutionneutralsolution

basicsolution

conc

entr

atio

n (m

oles

/L)

10-14

10-7

10-1

pH scale• This scale is used

to tell the concentration of H+ ions versus OH- ions

• Things that are neutral are a 7 acids are below 7 and bases are above

Ionization of Water

• Occasionally, in water, a H+ is transferred between H2O molecules. Important equilibrium is set up .

. . . . . . . .H:O: + :O:H H:O:H + + :O:H-

. . . . . . . . H H H

water molecules hydronium hydroxide ion +

ion (-)

Ion Product of Water Kw

Kw Is the water constant .It is the product of molar concentrations of H+ and OH- ions in the above equilibrium reaction

[ ] = Molar concentration

Kw = [ H3O+ ] [ OH- ]

= [ 1 x 10-7 ][ 1 x 10-7 ]

= 1 x 10-14

also p Kw = -log Kw

pOH• pOH is sometimes used as a measure of

the concentration of hydroxide ions, OH−, or alkalinity .

• pOH is not measured independently, but is derived from pH. pOH =

• The concentration of hydroxide ions in water is related to the concentration of hydrogen ions by

[OH−] = KW /[H+] • where KW is the self ionisation constant of

water.• pOH= -log [OH −]

Acid –Base Neutralization Reactions

When acid and bases with equal amounts of hydrogen ion H+ and hydroxide ions OH- are mixed, the resulting solution is neutral( salt and water ).NaOH (aq) + HCl(aq) NaCl + H2O

base acid salt water H3O+ and OH- combine to produce water

H3O+ + OH- 2 H2O from acid from base neutral

Net ionic equation: H+ + OH- H2O

Key Concepts: Acids and Bases

Acid Base

produce produce

H + ions OH- ions

100% Small %

Strong acid

Weak acid

100% Small %

Strong base

Weak base

Ionization in water

gives

H+ OH-

product

[H+] x [OH-]

is

pH

undergo

Neutralization

to form

Salt & Water

Some Practical applications of pH

pH measureme

nts are important

in medicine, biology,

chemistry, agriculture, forestry,food science,

environment science

oceanography,civil

engineering and many

others

For agricult

ure.

Knowing the pH of the soil can help in better

and effective production . The pH can

be manipula

ted by adding lime or

fertilisers

. For effective water

and food

treatment for safe

consumption and

healthy living.

. Prevent

ing environmental hazards

like acid rain

AntacidsMedicines are based on the principle of acid-

base neutralisation r*ns Used to neutralize stomach acid (HCl)Many contain one or more weak bases

Alka-Seltzer: NaHCO3, citric acid, and aspirin

Di-gel: CaCO3 and Mg(OH)2

Gelusil: Al(OH)3 and Mg(OH)2

Maalox: Al(OH)3 and Mg(OH)2

Mylanta: Al(OH)3 and Mg(OH)2

ACID RAIN

Unpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is “acid rain“CO2 in the air forms carbonic acid

CO2 + H2O H2CO3 Adds to H+ of rain

H2CO3 H+ (aq) + HCO3-(aq)

Other acidic gases that cause acid rain SO2 26 million tons in

1980NO and NO2 22 million tons in 1980Acidic rain reactions

Reactions with oxygen in air form SO3

2SO2 + O2 2 SO3

Reactions with water in air form acidsSO3 + H2O H2SO4 sulphuric

acidNO + H2O HNO2 nitrous

acid HNO2 + H2O HNO3 nitric acid

Sources of Acid Rain

Power stationsOil refineriesCoal with high S contentCar and truck emissionsBacterial decomposition, and

lighting hitting N2

Effects of acid rain Respiratory problems in humans

Leaches Al from soil, which kills fish and other marine organisms

Corrodes sculpture and monuments . The Taj is the best example

Sculpture affected by acid rain

Taj mahal 1958 and now 2009

THANKYOU.