Chapter 15.2“Acids, Bases,

and Salts”

Properties of AcidsProperties of Acids They taste They taste soursour (don’t try this at home). (don’t try this at home). They can They can conduct electricityconduct electricity..

–Can be strong or weak electrolytes in aqueous solution

React with metalsReact with metals to form H to form H22 gas. gas. Change the colorChange the color of indicators of indicators

(for example: blue litmus turns to red).(for example: blue litmus turns to red). React with basesReact with bases (metallic hydroxides) (metallic hydroxides)

to form water and a salt.to form water and a salt.

Properties of AcidsProperties of Acids They have a They have a pH of less than 7pH of less than 7 (more (more

on this concept of pH in a later lesson)on this concept of pH in a later lesson) They They react with carbonates and react with carbonates and

bicarbonatesbicarbonates to produce a salt, water, to produce a salt, water, and carbon dioxide gasand carbon dioxide gas

How do you know if a chemical is an How do you know if a chemical is an acid?acid?– It usually starts with Hydrogen.

– HCl, H2SO4, HNO3, etc. (but not water!)

Acids Affect Indicators, by Acids Affect Indicators, by changing their colorchanging their color

Blue litmus paper turns red in contact with an acid (and red paper stays red).

Acids Acids have a have a

pH pH lessless

than 7than 7

Acids React with Active MetalsAcids React with Active Metals

Acids react with active metals to form salts and hydrogen gas:

HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

This is a single-replacement reaction

Effects of Effects of Acid RainAcid Rain on Marble on Marble(marble is calcium (marble is calcium carbonatecarbonate))

George Washington:BEFORE acid rain

George Washington:AFTER acid rain

Strong vs. WeakStrong vs. Weak When all the When all the

molecules of an molecules of an acid break apart acid break apart in water to in water to produce hydrogen produce hydrogen ionsions

When few When few molecules of an molecules of an acid break apart acid break apart in water to in water to produce hydrogen produce hydrogen ionsions

Sulfuric AcidSulfuric Acid = H = H22SOSO44 Highest volume Highest volume

production of production of anyany chemical in the U.S. chemical in the U.S. (approximately 60 billion pounds/year)(approximately 60 billion pounds/year)

Used in the production Used in the production of paperof paper

Used in production of Used in production of fertilizersfertilizers

Used in petroleum Used in petroleum refining; auto batteriesrefining; auto batteries

Nitric AcidNitric Acid = HNO = HNO33 Used in the production Used in the production

of fertilizersof fertilizers Used in the production Used in the production

of explosivesof explosives Nitric acid is a Nitric acid is a volatile volatile

acid – its reactive acid – its reactive components evaporate components evaporate easilyeasily

Stains proteins yellow Stains proteins yellow (including skin!)(including skin!)

Hydrochloric AcidHydrochloric Acid = HCl = HCl Used in the “pickling” Used in the “pickling”

of steelof steel Used to purify Used to purify

magnesium from sea magnesium from sea waterwater

Part of gastric juice, it Part of gastric juice, it aids in the digestion of aids in the digestion of proteinsproteins

Sold commercially as Sold commercially as Muriatic acidMuriatic acid

Phosphoric AcidPhosphoric Acid = H = H33POPO44 A flavoring agent in A flavoring agent in

sodas (adds “tart”)sodas (adds “tart”) Used in the Used in the

manufacture of manufacture of detergentsdetergents

Used in the Used in the manufacture of manufacture of fertilizersfertilizers

NotNot a common a common laboratory reagentlaboratory reagent

Acetic AcidAcetic Acid = HC = HC22HH33OO2 2 (also called Ethanoic Acid, CH(also called Ethanoic Acid, CH33COOH)COOH)

Used in the Used in the manufacture of plasticsmanufacture of plastics

Used in making Used in making pharmaceuticalspharmaceuticals

Acetic acid is the acid Acetic acid is the acid that is present in that is present in household household vinegarvinegar

Acids Acids NeutralizeNeutralize Bases BasesHCl + NaOH → NaCl + H2O

-Neutralization reactions ALWAYS produce a salt (which is an ionic compound) and water.

-Of course, it takes the right proportion of acid and base to produce a neutral salt

Acid and BasesAcid and Bases Can water dissociate(break apart)?Can water dissociate(break apart)?

H2O H+ + OH-

High concentration of HHigh concentration of H++ ions ions indicate an acidic solution.indicate an acidic solution.

High concentration of OHHigh concentration of OH-- ion ion indicate a basic solution (also indicate a basic solution (also called alkaline)called alkaline)

Properties of BasesProperties of Bases (metallic hydroxides)(metallic hydroxides)

React with acidsReact with acids to form water to form water and a salt.and a salt.

Taste Taste bitterbitter.. Feel slipperyFeel slippery (don’t try this either). (don’t try this either). Can be strong or weak Can be strong or weak

electrolyteselectrolytes in aqueous solution in aqueous solution Change the colorChange the color of indicators of indicators

(red litmus turns blue).(red litmus turns blue).

Examples of BasesExamples of Bases(metallic hydroxides)(metallic hydroxides)

Sodium hydroxide, Sodium hydroxide, NaOHNaOH ((lye for drain cleaner; soaplye for drain cleaner; soap))

Potassium hydroxide, Potassium hydroxide, KOH KOH ((alkaline batteriesalkaline batteries))

Calcium hydroxide, Calcium hydroxide, Ca(OH)Ca(OH)22 ((limelime; ; masonrymasonry))

Magnesium hydroxide, Magnesium hydroxide, Mg(OH)Mg(OH)22 ((Milk of MagnesiaMilk of Magnesia))

Bases Affect IndicatorsBases Affect Indicators

Red litmus paper turns blue in contact with a base (and blue paper stays blue).

Phenolphthalein turns purple in a base.

Bases Bases have a have a

pH pH greatergreater than 7than 7

Bases Neutralize AcidsBases Neutralize Acids

Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.

The pH concept – from 0 to 14The pH concept – from 0 to 14 pH = pH = pouvoir hydrogenepouvoir hydrogene (Fr.) (Fr.)

“hydrogen power” “hydrogen power”

definition: definition: pH = -log[HpH = -log[H++]] in in neutralneutral pH = pH = 77 in in acidicacidic solution=< solution=<7 7

pH pH < < -log(10-log(10-7-7))– pH < 7 (from 0 to 7 is the acid range)

– in base, pH > 7 (7 to 14 is base range)

Measuring pHMeasuring pH Why measure pH?Why measure pH?

Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.

Sometimes we can use Sometimes we can use indicatorsindicators, other times , other times we might need a we might need a pH pH metermeter

How to measure pH with wide-range paperHow to measure pH with wide-range paper

1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod.

2.Compare the color to the chart on the vial – then read the pH value.

Some of the Some of the many pH many pH

Indicators Indicators and theirand theirpH rangepH range

Acid-Base IndicatorsAcid-Base Indicators Although useful, there are Although useful, there are limitationslimitations

to indicators:to indicators:–usually given for a certain

temperature (25 oC), thus may change at different temperatures

–what if the solution already has a color, like paint?

– the ability of the human eye to distinguish colors is limited

Acid-Base IndicatorsAcid-Base Indicators A A pH meterpH meter may give more definitive may give more definitive

resultsresults–some are large, others portable–works by measuring the voltage

between two electrodes; typically accurate to within 0.01 pH unit of the true pH

–Instruments need to be calibrated

Acid-Base ReactionsAcid-Base Reactions

Acid + Base Acid + Base Water + Salt Water + Salt Properties related to every day:Properties related to every day:

–antacids depend on neutralization

–farmers adjust the soil pH

–human body kidney stones from insoluble salts

SaltSalt A A saltsalt is an ionic compound that: is an ionic compound that:

–comes from the anion of an acid

–comes from the cation of a base

–is formed from a neutralization reaction

–some neutral; others acidic or basic