chapter 6 acids and bases. 2 stomach acid & heartburn the cells that line your stomach produce...
TRANSCRIPT
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