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Acids and BasesAcids and Bases

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Common Acids & Common Acids & BasesBases

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ExamplesAcids Bases

Lemon Juice Ammonia

Vinegar Baking Soda

Muriatic Acid Chocolate

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Examples

Acids Bases

SulfuricLye

LacticWashing Soda

Boric Milk of Magnesia

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Examples

Acids Bases

CokeLimestone

Vitamin CFireplace ashes

Aspirin Detergents

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Acid Properties• sour taste• change the color of litmus from blue to

red.• react with

– metals such as zinc and magnesium to produce hydrogen gas

– hydroxide bases to produce water and an ionic compound (salt)

– carbonates to produce carbon dioxide.

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Base Properties• bitter or caustic taste• a slippery, soapy feeling• the ability to change litmus red to blue• changes phenolphthalein to red• the ability to interact with acids• react with ammonium salts to produce ammonia gas

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Ashes and water make a slippery alkaline solution once used to clean hands.

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The Six Strong Acids

HCl(aq)

HBr(aq)

HI(aq)

H2SO4(aq)

HNO3(aq)

HClO4(aq)

Hydrochloric acid

Hydrobromic acid

Hydroiodic acid

Sulfuric acid

Nitric acid

Perchloric acid

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The Strong Bases

Group 1AMetal Hydroxides: Ba(OH)2(aq)

Sr(OH)2(aq)

LiOH(aq)

NaOH(aq)

KOH(aq)

CsOH(aq)

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• Svante Arrhenius was a Swedish scientist who lived from 1859-1927.

• In 1884 he advanced a theory of acids and bases.

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An Arrhenius acid “is a hydrogen-containing substance that dissociates to produce hydrogen ions.”

HA → H+ + A-

acid

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An Arrhenius base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution.

MOH → M+(aq) + OH-(aq)base

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An Arrhenius acid solution contains an excess of H+ ions.

An Arrhenius base solution contains an excess of OH- ions.

• If an acid is neutralized by adding base:

– the equiv of the acid = the equiv of the base.

H+ = OH–

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• J.N. Brönsted (1897-1947) was a Danish chemist and T. M. Lowry (1847-1936) was an English chemist.

• In 1923 they advanced their theory of acids and bases.

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A Brönsted acid is a proton (H+) passer.

A Brönsted base is a proton (H+) receiver.

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proton passerproton receiver

HCl (aq) + H2O (l) → H3O+ (aq) + Cl– (aq)

Brönsted AcidBrönsted Base

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hydrogen ion does not exist

in water

hydrogen ion combines with water

a hydronium ion is formed

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HCl(g) → Cl-(aq)baseacid

Conjugate acid-base pairs differ by a proton (H+).

When an acid passes a proton it becomes the conjugate base.

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Conjugate acid-base pairs differ by a proton (H+).

When a base accepts a proton it becomes the conjugate acid.

H3O+(aq)H2O (l) →acidbase

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Conjugate acid-base pairs differ by a proton (H+).

baseacid

HCl(g) + → Cl-(aq) + H3O+(aq)H2O (l)

acidbase

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• In 1923 G. N. Lewis developed a more comprehensive theory of acids and bases.

• The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

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1875-1946

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A Lewis acid is an electron-pair acceptor.

A Lewis base is an electron-pair donor.

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Lewis AcidElectron Pair Acceptor

Lewis BaseElectron Pair Donor

Electron pair donated to H+

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Lewis AcidElectron Pair Acceptor

Lewis BaseElectron Pair Donor

Electron pair donated to B

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Acid–Base Definitions

Theory Acid Base

Arrhenius

A hydrogen-containing substance that produces hydrogen ions in water

A hydroxide-containing substance that produces hydroxide ions in water

Brönsted A proton (H+) passer A proton (H+) receiver

LewisAny species that will accept an electron pair

Any species that donates an electron pair

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Reactions of AcidsReactions of Acids

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In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids.

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Reaction with Metals Acids react with metals that lie above hydrogen in the activity series of elements to produce hydrogen and an ionic compound (salt):

2HCl(aq) + Ca(s) → H2(g) + CaCl2(aq)

acid + metal → hydrogen + ionic compound

2H2SO4(aq) + Mg(s) → H2(g) + MgSO4(aq)

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3Zn(s) + 8HNO3(dilute) → 3Zn(NO3)2 (aq) + 2NO(g) + 4H2O(l)

Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen:

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HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)

Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water:

2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

acid base salt

acid base salt

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2HBr(aq) + K2O(s) → 2KBr(aq) + H2O(l)

Reaction with Metal Oxides In an aqueous solution the products are a salt and water. This type of reaction is closely related to that of an acid with a base:

2H2SO4(aq) + MgO(s) → MgSO4(aq) + H2O(l)

acid metal oxide salt

acid saltmetal oxide

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Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound:

2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)acid carbonate salt

H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)acid carbonate salt

HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2O(l) + CO2(g)acid carbonate salt

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H2CO3(aq) → CO2(g) + H2O(l)

Carbonic acid (H2CO3) is not the product when an acid reacts with a carbonate because carbonate spontaneously decomposes into carbon dioxide and water.

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Reactions of BasesReactions of Bases

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HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)

Reaction with Acids The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water:

2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

acid base salt

acid base salt

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Amphoteric Hydroxides Hydroxides of certain metals are amphoteric, meaning they are capable of reacting as either an acid or a base:

Zn(OH)2 + 2KOH(aq) → K2Zn(OH)4(aq) + H2O(l)Lewis acid base

Zn(OH)2 + 2HCl(aq) → ZnCl2(aq) + 2H2O(l)base acid salt

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Reaction of NaOH and KOH with Certain Metals Some amphoteric metals react directly with the strong bases sodium hydroxide and potassium hydroxide to produce hydrogen:

2NaOH(aq) + Zn(s) + 2H2O(l) → Na2Zn(OH)4(aq) + 3H2(g)

base + metal + water → salt + hydrogen

2KOH(aq) + 2Al(s) + 6H2O(l) → 2KAl(OH)4(aq) + 3H2(g)Lewis acid

Lewis acid

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SaltsSalts

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Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded).

Chemists use the terms ionic compound and salt interchangeably.Salts are usually crystalline and have high melting and boiling points.

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NaOH HCl

NaCl

base acid

salt

The positive ion of the salt is derived from the base.

The negative ion of the salt is derived from the acid.

Salt Formation

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Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

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Electrolytes are substances whose aqueous solutions conduct electricity.

Nonelectrolytes are substances whose aqueous solutions do not conduct electricity.

Electrolytes are capable of producing ions in solution.

Nonelectrolytes are not capable of producing ions in solution.

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Classes of compounds that are

electrolytes are:– acids

– bases

– salts

– solutions of oxides that form an acid or a base

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Dissociation andDissociation andIonization of ElectrolytesIonization of Electrolytes

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Dissociation is the process by which the ions of a salt separate as the salt dissolves.

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In a crystal of sodium chloride, positive sodium ions are bonded to negative chloride ions.

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In aqueous solution the sodium and chloride ions dissociate from each other.

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In aqueous solution the sodium and chloride ions dissociate from each other.

55Na+ and Cl- ions hydrate with H2O molecules.

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The equation representing the dissociation of NaCl is:

NaCl(s) + (x+y)H2O → Na+(H2O)x + Cl-(H2O)y

The equation can be written more simply as:

NaCl(s) → Na+(aq) + Cl-(aq)

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Ionization is the formation of ions.Ionization occurs as the result of a chemical reaction of certain substances with water.

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Acetic acid ionizes in water to form acetate ion and hydronium ion.

HC3H3O2 + H2O H3O+ + C2H3O2-→→

acid base acid base

HC3H3O2 H+ + C2H3O2-→→

The equation can be written more simply as:

In the absence of water ionization reactions do not occur.

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Strong and Strong and Weak ElectrolytesWeak Electrolytes

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Strong Electrolyte An electrolyte that is essentially 100% ionized in aqueous solution.Weak Electrolyte An electrolyte that is ionized to a small extent in aqueous solution.

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• Most salts are strong electrolytes.

• Strong acids and bases (highly ionized) are strong electrolytes.

• Weak acids and bases (slightly ionized) are weak electrolytes.

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HCl Solution

HC2H3O2 Solution

Strong Acid Weak Acid1% ionized100%

ionized

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HC2H3O2(aq) → H+ (aq) + C2H3O2(aq) -2 3 2C H O ( )aq→→

Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution.

ionizedunionized

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HNO3(aq) → H+(aq) + NO3(aq)-3NO ( )aq

HNO3, a strong acid, is 100 % dissociated.

HNO2(aq) → H+(aq) + NO2(aq)-2NO ( )aq→→

HNO2, a weak acid, is only slightly ionized.

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Electrolytes yield two or more ions per formula unit upon dissociation.

NaOH → Na+(aq) + OH-(aq)

Na2SO4 → 2Na+(aq) + SO4-(aq) 2-

4SO ( )aq

two ions in solution per formula unit

Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 2-43SO ( )aq

three ions in solution per formula unit

five ions in solution per formula unit

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Electrolytes yield two or more moles per mole of electrolyte upon dissociation.

NaOH → Na+(aq) + OH-(aq)

1 mole 1 mole 1 mole

Na2SO4 → 2Na+(aq) + SO4-(aq) 2-

4SO ( )aq1 mole 2 moles 1 mole

Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 2-43SO ( )aq

1 mole 2 moles 3 moles

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Colligative Properties ofElectrolyte Solutions

Colligative Properties ofElectrolyte Solutions

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Substances that form ions in aqueous solutions change the colligative properties of water in proportion to the number of ions formed.

NaOH → Na+(aq) + OH-(aq)

1 mole 1 mole 1 mole

Two moles of ions will depress the freezing point of water twice that of one mole of a nonelectrolyte.

Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 2-43SO ( )aq

1 mole 2 moles 3 moles

Five moles of ions will depress the freezing point of water five times that of one mole of a nonelectrolyte.

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Formulas for Calculations

Δtf = i m Kf

Δtb = i m Kb

i = ion multiplier

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Calculate kilograms of H2O

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1 mol NH Cl 6.57 g NH Cl = 0.123 mol NH Cl

53.5 g NH Cl

A solution is made by dissolving 6.57 g of ammonium chloride (NH4Cl) in 50.0 g H2O. What is the boiling point of the solution?

Calculate moles of NH4Cl:

2 2

1 kg50.0 g H O = 0.050 kg H O

1000 g

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A solution is made by dissolving 6.57 g of ammonium chloride (NH4Cl) in 50.0 g H2O. What is the boiling point of the solution?

Calculate the unionized boiling point elevation.

Calculate the ion multiplier.

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2

0.123 mol NH Cl0.050 kg H O

o1.25 CbΔt =o

2

4

0.51 C kg H O =

1 mol NH Cl

NH4Cl → NH4+(aq) + Cl–(aq)

i = 2

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A solution is made by dissolving 6.57 g of ammonium chloride (NH4Cl) in 50.0 g H2O. What is the boiling point of the solution?

Calculate the ionized boiling point elevation.

boiling point solution = boiling point solvent + Δtb.

= 100oC + 2.5oC = 102.5oC

bΔt = 1.25C 2 = 2.5C

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Go Back To Chapter 14 Go Back To Chapter 14 Slide 105Slide 105

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Ionization of WaterIonization of Water

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Water ionizes slightly.

acid base acid baseH2O + H2O → H3O+ + OH– →→

hydronium ion

hydroxide ion

H2O → H+ + OH– →→Water ionization can be expressed more simply as:

[H3O+] or [H+] = 1.0 x 10-7 mol/L

[OH–] = 1.0 x 10-7 mol/L

Two out of every 1 billion water molecules are ionized.

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• Since both H+ and OH– are produced in equal amounts,

[H+] [OH–] = 1.0 x 10-14 mol/L

• A special constant is applied to this product called the water constant, Kw

• Variations include:

Kw = [H+] [OH–]

+ -w w- +

K K[H ] = and [OH ] =

[OH ] [H ]

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Find the [OH–] in 0.0050 M H2SO4. Assume that H2SO4 is 100% ionized.

Since this is an acid solution, we must first find [H+].

+ +2 4

2 4

0.0050 mole H SO 2 moles H 0.010 moles H× =

liter solution 1 mole H S liter solutionO

= 0.01 MSince 1 mole H+ = 1 equiv, [H+] = Nacid

- w+

K[OH ] =

[H ]

-1412

-2

1.0 10= 1.0 10

1.0 10

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Introduction to pHIntroduction to pH

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Math MagicMath Magic

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The [H+] in orange juice is 2.0 10–4 . Change the [H+] to a more comprehensible number.

[H+] in orange juice is 2.0 10–4.

Change 2.0 into an exponent of base 10 by finding the logarithm:

Log 2.0 by calculator is 0.3010This means that 2.0 = 100.3010

2.0 10–4 = 100.3010 10–4 = 100.3010+ –4 = 10–3.699

Use the exponent with the sign reversed as ourmeasure of the acidity. Let’s call it pH. So pH = 3.7

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Typical [H+] in common substances

substance log pH

Lemon juice – 2.3 2.3

Vinegar – 2.8 2.8

Orange juice – 3.7 3.7

Coffee – 5.0 5.0

Rain – 5.6 5.6

Milk – 6.6 6.6

Blood – 7.4 7.4

H

35.0×10 31.6×10

42.0×10

51.0×10 62.5×10

72.7×10 84.0×10

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pH is the negative logarithm of the hydrogen ion concentration.

pH = -log[H+]

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Calculation of pHCalculation of pH

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pH = -log[H+]

[H+] = 1 x 10-5

when this number is exactly 1

pH = this number without the minus sign.

pH = 5

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pH = -log[H+]

[H+] = 2 x 10-5

when this number is between 1 and 10

The number of decimal places of a logarithm is equal to the number of significant figures in the original number.

pH is between this number and the next lower number (between 4 and 5).

one significant figure

pH = 4.7

one decimal place

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The pH scale of Acidity and Basicity

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pH LooppH Loop

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pH pOH

[H+] [OH–]

pH + pOH = 14

[H+] [OH–] = 10–14

pH = – log [H+]

[H+] =10– pH

pOH = – log [OH–]

[OH–] = 10– pOH

Note: [H+] = normality of the acid [OH–] = normality of the base

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pH Loop CalculationspH Loop Calculations

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Fill-in the BlankspH pOH [ H+] [ OH– ]

4 10–3

6.1

3 10–4

8

5.4

8.7 10–6

2

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Fill-in the Blanks AnswerspH pOH [ H+] [ OH– ]

2.4 11.6 4 10–3 2.5 10–12

6.1 7.9 7.9 10–7 1.2 10–8

10.5 3.5 3.3 10–11 3 10–4

8 6 1 10–8 1 10–6

8.6 5.4 2.5 10–9 4.0 10–6

5.1 8.9 8.7 10–6 1.1 10–9

12 2 1 10–12 1 10–2

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Acid RainAcid Rain

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Acid rain: any atmospheric precipitation that is more acidic than usual.

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• pH of rain is lower in the eastern US and higher in the western US.

• Unpolluted rain has a pH of 5.6 because of carbonic acid formation in the atmosphere.

CO2(g) + H2O(l) H2CO3(aq) H+ + HCO3–→← →←

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2. transportation of these oxides into the atmosphere

3. chemical reactions between the oxides and water forming sulfuric acid (H2SO4) and nitric acid (HNO3)

4. rain or snow, which carries the acids to the ground

Process of Acid Rain Formation

1. emission of nitrogen and sulfur oxides into the air

From the burning of fossil fuels.

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2. aluminum is leached from the soil into lakes and adversely affects fish gills.

3. the waxy protective coat on plants is dissolved making them vulnerable to bacteria and fungal attack

Effects of Acid Rain

1. freshwater plants and animals decline significantly when rain is acidic

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Effects of Acid Rain

4. it is responsible for extensive and continuing damage to buildings, monuments and statues

1908 1969

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Effects of Acid Rain

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Effects of Acid Rain

Smoky Mountains

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Cleopatra's Needle in New York City Central Park (originally erected in the Egyptian city of Heliopolis on the orders of Thutmose III, around 1450 B.C.). Erected in New York in 1881.

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