11The Chemistry The Chemistry of Acids and of Acids and BasesBases

The Chemistry The Chemistry of Acids and of Acids and BasesBases

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The information in this PowerPoint came from

Neil Rappat Bloomington High School

SouthBloomington, Indiana

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Acid and BasesAcid and Bases

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Acid and BasesAcid and Bases

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Acid and BasesAcid and Bases

66Acids

Have a sour taste. Vinegar is a solution of acetic acid. CitrusHave a sour taste. Vinegar is a solution of acetic acid. Citrusfruits contain citric acid.fruits contain citric acid.

React with certain metals to produce hydrogen gasReact with certain metals to produce hydrogen gas..

React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gasdioxide gas

Have a bitter taste.Have a bitter taste.

Feel slippery. Many soaps contain bases.Feel slippery. Many soaps contain bases.

Bases

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Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a

hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

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Anion Ending Acid Name

-ide hydro-(stem)-ic acid

-ate (stem)-ic acid

-ite (stem)-ous acid

Acid Nomenclature Review

No OxygenNo Oxygen

w/Oxygen w/Oxygen

An easy way to remember which goes with which…An easy way to remember which goes with which…

““In the cafeteria, you In the cafeteria, you ATEATE something something ICICky”ky”

99Acid Nomenclature Flowchart

hydro- prefix-ic ending

2 elements

-ate endingbecomes-ic ending

-ite endingbecomes

-ous ending

no hydro- prefix

3 elements

ACIDSstart with 'H'

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• HBr HBr (aq)(aq)

• HH22COCO33

• HH22SOSO33

hydrohydrobromicbromic acidacid

carboncarbonicic acidacid

sulfursulfurousous acidacid

Acid Nomenclature Review

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Name ‘Em!

• HI HI (aq)(aq)

• HCl HCl (aq)(aq)

• HH22SOSO33

• HNOHNO33

• HIOHIO44

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Some Properties of Bases

Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Are electrolytesAre electrolytes

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

pH greater than 7pH greater than 7

Turns red litmus paper to blue “Turns red litmus paper to blue “BBasic asic BBlue”lue”

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Some Common Bases

NaOHNaOH sodium hydroxidesodium hydroxide lyelye

KOHKOH potassium hydroxidepotassium hydroxide liquid soapliquid soap

Ba(OH)Ba(OH)22 barium hydroxidebarium hydroxide stabilizer for plasticsstabilizer for plastics

Mg(OH)Mg(OH)22 magnesium hydroxidemagnesium hydroxide “MOM” Milk of magnesia“MOM” Milk of magnesia

Al(OH)Al(OH)33 aluminum hydroxidealuminum hydroxide Maalox (antacid)Maalox (antacid)

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Acid/Base definitions

• Definition #1: Arrhenius (traditional)

Acids – produce H+ ions (or hydronium ions H3O+)

Bases – produce OH- ions

(problem: some bases don’t have hydroxide ions!)

1515Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

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Acid/Base Definitions

• Definition #2: Brønsted – Lowry

Acids – proton donor

Bases – proton acceptor

A “proton” is really just a hydrogen atom that has lost it’s electron!

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A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor

acidconjugate

basebase conjugate

acid

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ACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIES

The Brønsted definition means NHThe Brønsted definition means NH33 is is aa BASEBASE in water — and water is in water — and water is itself anitself an ACIDACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H 2OBaseAcidAcidBase

NH4+ + OH-NH3 + H 2O

1919Acids & Base Acids & Base DefinitionsDefinitions

Lewis acid - a Lewis acid - a substance that substance that accepts an electron accepts an electron pairpair

Lewis base - a Lewis base - a substance that substance that donates an electron donates an electron pairpair

Definition #3 – Lewis Definition #3 – Lewis

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Lewis Acid/Base ReactionLewis Acid/Base Reaction

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Lewis Acid-Base Lewis Acid-Base Interactions in BiologyInteractions in Biology

• The heme group The heme group in hemoglobin in hemoglobin can interact with can interact with OO22 and CO. and CO.

• The Fe ion in The Fe ion in hemoglobin is a hemoglobin is a Lewis acidLewis acid

• OO22 and CO can act and CO can act as Lewis basesas Lewis bases

Heme group

2222The The pH scalepH scale is a way of is a way of expressing the strength expressing the strength of acids and bases. of acids and bases. Instead of using very Instead of using very small numbers, we just small numbers, we just use the NEGATIVE use the NEGATIVE power of 10 on the power of 10 on the Molarity of the HMolarity of the H++ (or (or OHOH--) ion.) ion.

Under 7 = acidUnder 7 = acid 7 = neutral 7 = neutral

Over 7 = baseOver 7 = base

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pH of Common pH of Common SubstancesSubstances

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More About WaterMore About Water

HH22O can function as both an ACID and a BASE.O can function as both an ACID and a BASE.

In pure water there can beIn pure water there can be AUTOIONIZATIONAUTOIONIZATION

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HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION.

The strength of an acid (or base) is determined by the amount of IONIZATION.

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Strong and Weak Strong and Weak Acids/BasesAcids/Bases

• Generally divide acids and bases into STRONG or Generally divide acids and bases into STRONG or WEAK ones.WEAK ones.

STRONG ACID:STRONG ACID: HNOHNO3 3 (aq) + H(aq) + H22O (l) --->O (l) --->

HH33OO+ + (aq) + NO(aq) + NO33- - (aq)(aq)

HNOHNO33 is about 100% dissociated in water. is about 100% dissociated in water.

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• Weak acidsWeak acids are much less than 100% ionized in are much less than 100% ionized in

water.water.

One of the best known is acetic acid = CHOne of the best known is acetic acid = CH33COCO22HH

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

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• Strong Base:Strong Base: 100% dissociated in 100% dissociated in water.water.

NaOH (aq) ---> NaNaOH (aq) ---> Na+ + (aq) + OH(aq) + OH- - (aq)(aq)

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Other common strong Other common strong bases include KOH andbases include KOH and Ca(OH)Ca(OH)22..

CaO (lime) + HCaO (lime) + H22O -->O -->

Ca(OH)Ca(OH)22 (slaked lime) (slaked lime)CaOCaO

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• Weak base:Weak base: less than 100% ionized less than 100% ionized in waterin water

One of the best known weak bases is One of the best known weak bases is ammoniaammonia

NHNH3 3 (aq) + H(aq) + H22O (l) O (l) NH NH44+ + (aq) + OH(aq) + OH- - (aq)(aq)

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

3030pH testing

• There are several ways to test pHThere are several ways to test pH

–Blue litmus paper (red = acid)Blue litmus paper (red = acid)

–Red litmus paper (blue = basic)Red litmus paper (blue = basic)

–pH paper (multi-colored)pH paper (multi-colored)

–pH meter (7 is neutral, <7 acid, >7 pH meter (7 is neutral, <7 acid, >7 base)base)

–Universal indicator (multi-colored)Universal indicator (multi-colored)

– Indicators like phenolphthaleinIndicators like phenolphthalein

–Natural indicators like red cabbage, Natural indicators like red cabbage, radishesradishes

3131Paper testing

• Paper tests like litmus paper and pH Paper tests like litmus paper and pH paperpaper

– Put a stirring rod into the solution Put a stirring rod into the solution and stir.and stir.

– Take the stirring rod out, and Take the stirring rod out, and place a drop of the solution from place a drop of the solution from the end of the stirring rod onto a the end of the stirring rod onto a piece of the paperpiece of the paper

– Read and record the color change. Read and record the color change. Note what the color indicates. Note what the color indicates.

– You should only use a small You should only use a small portion of the paper. You can use portion of the paper. You can use one piece of paper for several one piece of paper for several tests.tests.

3232pH paperpH paper

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pH meter

• Tests the voltage of the Tests the voltage of the electrolyteelectrolyte

• Converts the voltage to Converts the voltage to pHpH

• Very cheap, accurateVery cheap, accurate

• Must be calibrated with Must be calibrated with a buffer solutiona buffer solution

3434pH indicators

• Indicators are dyes that can be added that will change color in the presence of an acid or base.

• Some indicators only work in a specific range of pH

• Once the drops are added, the sample is ruined

• Some dyes are natural, like radish skin or red cabbage

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ACID-BASE REACTIONSACID-BASE REACTIONSTitrationsTitrations

ACID-BASE REACTIONSACID-BASE REACTIONSTitrationsTitrations

HH22CC22OO44(aq) + 2 NaOH(aq) --->(aq) + 2 NaOH(aq) --->

acidacid basebase

NaNa22CC22OO44(aq) + 2 H(aq) + 2 H22O(liq)O(liq)

Carry out this reaction using aCarry out this reaction using a TITRATIONTITRATION..

Oxalic acid,Oxalic acid,

HH22CC22OO44

3636Setup for titrating an acid with a baseSetup for titrating an acid with a base

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TitrationTitrationTitrationTitration

1. Add solution from the buret.1. Add solution from the buret.2. Reagent (base) reacts with 2. Reagent (base) reacts with

compound (acid) in solution compound (acid) in solution in the flask.in the flask.

3.3. Indicator shows when exact Indicator shows when exact stoichiometric reaction has stoichiometric reaction has occurred. (Acid = Base)occurred. (Acid = Base)

This is called This is called NEUTRALIZATION.NEUTRALIZATION.