Properties of Acids and BasesTopic 8.2

But first, a review!

Acid Base

Arrhenius Definition

An acid is any chemical compound which when dissolved in water gives a solution with a hydrogen ion activity greater than in pure water.

A base is an aqueous substance that can accept hydrogen ions.

Bronstead Lowry Definition An acid is an substance which donates a proton.

A base is any substance which accepts a proton.

pH value Less than 7.0 Greater than 7.0Litmus paper Blue litmus paper turns red red litmus paper turns bluePhenolphthalein Remains colorless Makes the solution pink

Dissociation (in water) Acids free hydrogen ions (H+) when mixed with water.

Bases free hydroxide ions (OH-) when mixed with water.

Chemical Formula

An acid has a chemical formula with H at the beginning of it. For example, HCl (Hydrochloric Acid). There is one exception to his rule, CH3COOH = Acetic Acid (vinegar).

A base has a chemical formula with OH at the end of it. For example, NaOH (Sodium Hydroxide).

Practice problems

Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:

acid base conjugate acidconjugate baseHC2H3O2(aq) + H2O(l) C2H3O2

–(aq) + H3O+(aq)

conjugate acid-base pairs

acidbase conjugate acidconjugate baseOH

–(aq) + HCO3–(aq) CO3

2–(aq) + H2O(l)

conjugate acid-base pairs

acid base conjugate acidconjugate baseHF(aq) + SO3

2–(aq) F–(aq) + HSO3–(aq)

conjugate acid-base pairs

acidbase conjugate acidconjugate baseCO3

2–(aq) + HC2H3O2(aq) C2H3O2–(aq) + HCO3

–(aq)

conjugate acid-base pairs

acid base conjugate acidconjugate baseH3PO4(aq) + OCl

–(aq) H2PO4–(aq) + HOCl(aq)

conjugate acid-base pairs

(a)

(b)

(c)

acid base conjugate baseconjugate acidHCO3

–(aq) + S2–(aq) HS–(aq) + CO32–(aq)

conjugate acid-base pairs

baseacid conjugate acidconjugate baseH2CO3(aq) + OH

–(aq) HCO3–(aq) + H2O(l)

conjugate acid-base pairs

acid base conjugate acidconjugate baseH3O+(aq) + HSO3

–(aq) H2O(l) + H2SO3(aq)

conjugate acid-base pairs

8a)

8b)

11a)

base acid conjugate baseconjugate acidOH

–(aq) + HSO3–(aq) H2O(l) + SO3

2–(aq)

conjugate acid-base pairs

11b)

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Properties of Acids• taste sour• cool to use in movies• corrode metals (produce H2 gas)• react with bases to form salt and water• pH is less than 7• turns blue litmus paper to red

• strong acids are strong electrolytes, weak acids are weak electrolytes

Properties of Bases• produce OH- ions in solution (Arrhenius definition)• taste bitter

• feel soapy, slippery • dissolve oil and grease• react with acids to form salt and H2O• pH is greater than 7• turns red litmus paper to blue• strong bases are good electrolytes, weak bases weak

electrolytes

Bases in Solution• soluble bases are considered to be alkalis

– when added to water release an OH- ion• base(aq) = alkali

– K2O(s) + H2O(l) 2K+(aq) + 2OH-(aq)

– NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)

– CO32-(aq) + H2O(l) ⇌ HCO3

-(aq) + OH-(aq)

– HCO3-(aq) ⇌ CO2(g) + OH-(aq)

The 5 Reactions of Acids

“swap the hydrogen for the metal”

ACIDS

Salt + Water Salt +

Water + CO2

Salt + H2

Salt + Water

(NH4)Salt Water

METAL(if more reactive than

hydrogen)

METAL CARBONATE or HYDROGEN

CARBONATE(base)

METAL HYDROXIDE

(base)

BASES(without OH)

METAL OXIDE(base)

1. Acids reaction with metals

• most dilute acids react with metals above hydrogen in the reactivity series to produce H2 gas and a solution of a salt– in general:

• reactive metal + acid salt + hydrogen» Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

» Mg(s) + 2HNO3(aq) Mg(NO3)2(aq) + H2(g)

» Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g)

» Mg(s) + 2CH3COOH(aq) (CH3COO)2Mg(aq) + H2(g)

2. Acid reaction with metal hydroxides

• acids react to give salt and water when a metal hydroxide(OH) or aqueous ammonia is added

• in general:– metal hydroxide + acid salt + water

• NaOH(aq) + HNO3(aq) NaNO3(aq) + H2O(l)

3. Acid reaction with metal carbonates or hydrogen carbonates

• acids react to give CO2(g) when a metal carbonate or metal hydrogen carbonate is added

• in general– (metal)CO3 + acid salt + water + carbon dioxide– (metal)HCO3 + acid salt + water + carbon dioxide

• CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

• NaHCO3(s) + HCl NaCl(aq) + H2O(l) + CO2(g)

4. Acid Reaction with metal oxides

• acids react to give salt and water when a metal oxide is added:

• in general:– metal oxide + acid salt + water

• CuO(s) + H2SO4(aq) CuSO4(aq) + H2O(l)

• CuO(s) + 2HNO3(aq) Cu(NO3)2(aq) + H2O

• CuO(s) + 2HCl(aq) CuCl2(aq) + H2O(l)

• CuO(s) + 2CH3COOH(aq) Cu(CH3COO)2(aq) + H2O(l)

5. Acid reactions with bases without an OH

• a base is a substance that reacts with an acid to form water and a salt only, this is known as neutralization– most have an OH, however some do not

• in general:– base + acid salt + water

• NH3(aq) + HNO3(aq) NH4NO3

• NH3(aq) + H+(aq) NH4+(aq)

• H3PO4(aq) + 3NaHCO3(s) Na3PO4(aq) + 3H2O(l) + 3CO2(g) • CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

ACIDS

Salt + Water Salt +

Water + CO2

Salt + H2

Salt + Water

(NH4)Salt Water

METAL(if more reactive than

hydrogen)

METAL CARBONATE or HYDROGEN

CARBONATE(base)

METAL HYDROXIDE

(base)

BASES(without OH)

METAL OXIDE(base)

http://4.bp.blogspot.com/-86H134GI3Uw/URhvD-tpfDI/AAAAAAAAALI/blBbOligJOA/s1600/Acid+base+reactions.jpg

Acids and bases effects on indicators• indicators

– substances that change color in an acid or base (concentration of hydrogen ions changes)

http://www.google.com/url?sa=i&rct=j&q=acid+base+indicators&source=images&cd=&cad=rja&docid=2QYISJEjinLLHM&tbnid=VWAYZleKXN9HUM:&ved=&url=http%3A%2F%2Fcnmesm.wikispaces.com%2FRed%2BCabbage%2BJuice-%2BA%2BNatural%2BpH%2BIndicator&ei=GtlpUZ7XJ-jXiAKS7oHYDA&bvm=bv.45175338,d.cGE&psig=AFQjCNFQFNqWalVKutbki1MRgon8yW1n6w&ust=1365977755251354