Chapter 6Acids and

Bases

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Stomach Acid & Heartburn• the cells that line your stomach produce

hydrochloric acid to kill unwanted bacteria to help break down food to activate enzymes that break down food

• if the stomach acid backs up into your esophagus, it irritates those tissues, resulting in heartburnacid refluxGERD = gastroesophageal reflux disease = chronic

leaking of stomach acid into the esophagus

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Curing Heartburn

• mild cases of heartburn can be cured by neutralizing the acid in the esophagusswallowing saliva which contains bicarbonate iontaking antacids that contain hydroxide ions and/or

carbonate ions

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Properties of Acids• sour taste

• react with “active” metals i.e., Al, Zn, Fe, but not Cu, Ag, or Au

2 Al + 6 HCl AlCl3 + 3 H2

corrosive

• react with carbonates, producing CO2

marble, baking soda, chalk, limestone

CaCO3 + 2 HCl CaCl2 + CO2 + H2O

• change color of vegetable dyesblue litmus turns red

• react with bases to form ionic salts

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Common AcidsChemical Name Formula Uses Strength

Nitric Acid HNO3 explosive, fertilizer, dye, glue Strong

Sulfuric Acid H2SO4 explosive, fertilizer, dye, glue,

batteries Strong

Hydrochloric Acid HCl metal cleaning, food prep, ore

refining, stomach acid Strong

Phosphoric Acid H3PO4 fertilizer, plastics & rubber,

food preservation Moderate

Acetic Acid HC2H3O2 plastics & rubber, food preservation, Vinegar

Weak

Hydrofluoric Acid HF metal cleaning, glass etching Weak

Carbonic Acid H2CO3 soda water Weak

Boric Acid H3BO3 eye wash Weak

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Structures of Acids

• binary acids have acid hydrogens attached to a nonmetal atomHCl, HF

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Structure of Acids• oxy acids have acid hydrogens attached to

an oxygen atomH2SO4, HNO3

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Structure of Acids• carboxylic acids have

COOH groupHC2H3O2, H3C6H5O7

• only the first H in the formula is acidic the H is on the COOH

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Properties of Bases• also known as alkalis

• taste bitteralkaloids = plant product that is alkaline

often poisonous

• solutions feel slippery

• change color of vegetable dyesdifferent color than acid red litmus turns blue

• react with acids to form ionic saltsneutralization

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Common BasesChemical

Name Formula

Common Name

Uses Strength

sodium hydroxide

NaOH lye,

caustic soda soap, plastic,

petrol refining Strong

potassium hydroxide

KOH caustic potash soap, cotton, electroplating

Strong

calcium hydroxide

Ca(OH)2 slaked lime cement Strong

sodium bicarbonate

NaHCO3 baking soda cooking, antacid Weak

magnesium hydroxide

Mg(OH)2 milk of

magnesia antacid Weak

ammonium hydroxide

NH4OH, {NH3(aq)}

ammonia water

detergent, fertilizer,

explosives, fibers Weak

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Structure of Bases

• most ionic bases contain OH ionsNaOH, Ca(OH)2

• some contain CO32- ions

CaCO3 NaHCO3

• molecular bases contain structures that react with H+

mostly amine groups

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Indicators• chemicals which change color depending on

the acidity/basicity• many vegetable dyes are indicators

anthocyanins

• litmus from Spanish mossred in acid, blue in base

• phenolphthaleinfound in laxativesred in base, colorless in acid

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Arrhenius Theory• bases dissociate in water to produce OH- ions and

cationsionic substances dissociate in water

NaOH(aq) → Na+(aq) + OH–(aq)

• acids ionize in water to produce H+ ions and anionsbecause molecular acids are not made of ions, they cannot

dissociate they must be pulled apart, or ionized, by the water

HCl(aq) → H+(aq) + Cl–(aq)in formula, ionizable H written in front

HC2H3O2(aq) → H+(aq) + C2H3O2–(aq)

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Arrhenius Theory

HCl ionizes in water,producing H+ and Cl– ions

NaOH dissociates in water,producing Na+ and OH– ions

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Hydronium Ion• the H+ ions produced by the acid are so reactive they

cannot exist in waterH+ ions are protons!!

• instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O+

H+ + H2O H3O+

there are also minor amounts of H+ with multiple water molecules, H(H2O)n+

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Arrhenius Acid-Base Reactions

• the H+ from the acid combines with the OH- from the base to make a molecule of H2O

it is often helpful to think of H2O as H-OH

• the cation from the base combines with the anion from the acid to make a salt

acid + base → salt + water

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

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Problems with Arrhenius Theory• does not explain why molecular substances, like NH3,

dissolve in water to form basic solutions – even though they do not contain OH– ions

• does not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions

• does not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions

• does not explain acid-base reactions that take place outside aqueous solution

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Brønsted-Lowry Theory• in a Brønsted-Lowry Acid-Base reaction, an

H+ is transferred does not have to take place in aqueous solution broader definition than Arrhenius

• acid is H donor, base is H acceptor base structure must contain an atom with an

unshared pair of electrons• in an acid-base reaction, the acid molecule

gives an H+ to the base molecule H–A + :B :A– + H–B+

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Brønsted-Lowry Acids• Brønsted-Lowry acids are H+ donors

any material that has H can potentially be a Brønsted-Lowry acid

because of the molecular structure, often one H in the molecule is easier to transfer than others

• HCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O+ ionswater acts as base, accepting H+

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

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Brønsted-Lowry Bases• Brønsted-Lowry bases are H+ acceptors

any material that has atoms with lone pairs can potentially be a Brønsted-Lowry base

because of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than others

• NH3(aq) is basic because NH3 accepts an H+ from H2O, forming OH–(aq)water acts as acid, donating H+

NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)

base acid