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ACIDS & BASESPresentation by ANISH SHARMAAcidsBasesStrong and weak acids and bases .IndicatorsPh scaleIonisation in waterNeutralisation reactionsEnvironmental hazard - acid rain

CONTENTSAcidsProduce H+ (as H3O+) ions in waterProduce a negative ion (-) tooTaste sour React with several metals releasing H2(g) corrosionReact with carbonates releasing CO2(g) Turn blue litmus (vegetable dye) redReact with bases to form salts and waterDestroy body tissue , corrosion of metals

BasesProduce OH- ions in waterTaste bitter, chalkyare electrolytesFeel soapy, slipperyReact with acids to form salts and water

Strengths of Acids and BasesStrong 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)2a.Strong acid (hydrochloric acid) b. weak acid (carbonic acid)

INDICATORSTo 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.

9Lesson 4How do we test?Demo invisible writing use phenol pthaelin spray with alkali create a colour PH scaleIndicators are extracted from plants (lichen) Ph is a measure of the conc of H+ in solutionChemicals which change colour in the presence of acids or basesEXPT universal indicator create rainbow in teams of 3 (H/O) colour ph scale naoh strong alkali, nh3 may need to dilute with waterHomework bring in flower to make indicator

pHpH 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 valueThe 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 basicAcid Base ConcentrationspH = 3pH = 7pH = 11OH-H3O+OH-OH-H3O+H3O+[H3O+] = [OH-] [H3O+] > [OH-] [H3O+] < [OH-] acidicsolutionneutralsolutionbasicsolutionconcentration (moles/L)10-1410-710-113

pH scaleThis scale is used to tell the concentration of H+ ions versus OH- ionsThings that are neutral are a 7 acids are below 7 and bases are above

Ionization of WaterOccasionally, 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 KwKw 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

pOHpOH 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 ReactionsWhen 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 + H2Obase acid salt water H3O+ and OH- combine to produce water

H3O+ + OH- 2 H2O from acid from base neutralNet ionic equation: H+ + OH- H2OKey Concepts:Acids and BasesAcid BaseproduceproduceH + ionsOH- ions100%Small %Strong acidWeak acid100%Small %

Strong base

Weak baseIonization in watergivesH+OH-product[H+] x [OH-]ispHundergoNeutralizationto formSalt &WaterSome Practical applications of pHAntacidsMedicines are based on the principle of acid-base neutralisation r*ns Used to neutralize stomach acid (HCl)Many contain one or more weak basesAlka-Seltzer: NaHCO3, citric acid, and aspirinDi-gel: CaCO3 and Mg(OH)2Gelusil: Al(OH)3 and Mg(OH)2Maalox: Al(OH)3 and Mg(OH)2 Mylanta: Al(OH)3 and Mg(OH)2

ACID RAINUnpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is acid rainCO2 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 NO222 million tons in 1980Acidic rain reactions Reactions with oxygen in air form SO32SO2 + 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 Corrodes sculpture and monuments . The Taj is the best example

Sculpture affected by acid rain Taj mahal 1958 and now 2009THANKYOU.