Acids & Bases

Acids• Arrhenius Model• Produce hydrogen ions aqueous solution.• HCl H+ (aq) + Cl- (aq)

• Acids you SHOULD know:• Strong Acids

• Hydrochloric acid, HCl• Nitric acid, HNO3

• Sulfuric acid, H2SO4

• Weak Acids• Phosphoric acid, H3PO4

• Acetic acid, HC2H3O2

Properties of Acids• Acids taste sour • Acids affect indicators

• Blue litmus turns red • Methyl orange turns red • Acids have a pH lower than 7 • Acids are proton (hydrogen ion, H+) donors • Acids react with active metals, produce H2 • Acids react with carbonates • Acids neutralize bases

Bases• Arrhenius Model • Produce Hydroxide ions.• NaOH Na+ (aq) + OH- (aq)

• Examples of Bases• Sodium hydroxide (lye), NaOH • Potassium hydroxide, KOH

• Magnesium hydroxide, Mg(OH)2

• Calcium hydroxide (lime), Ca(OH)2

Properties of Bases• Bases taste bitter • Bases affect indicators

• Red litmus turns blue

• Phenolphthalein turns purple • Bases have a pH greater than 7 • Bases are proton (hydrogen ion, H+)

acceptors • Solutions of bases feel slippery• Bases neutralize acids

Bronsted – Lowery Model•ACID:  Substance that can donate

proton (H+1).

•BASE:  Substance that can accept proton (must contain lone pair of electrons).

The pH Scale•The pH scale measures how acidic or

basic a substance is. • The pH scale ranges from 0 to 14. A pH of 7

is neutral. • A pH less than 7 is acidic. A pH greater than

7 is basic. • The pH scale is logarithmic and as a result, each whole

pH value below 7 is ten times more acidic than the next higher value. • For example, pH 4 is ten times more acidic than pH 5 and 100

times (10 times 10) more acidic than pH 6. • The same holds true for pH values above 7, each of which is

ten times more alkaline (another way to say basic) than the next lower whole value.

The pH Scale•The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value.

• For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. • The same holds true for pH values above 7, each of

which is ten times more alkaline (another way to say basic) than the next lower whole value.

Calculating pH or pOH• pH = -log[H+]

• Example [H+] = 1.0 x 10-9

•Answer pH=9.0

• pOH = -log[OH+]• Example [OH+] = 1.0 x 10-6

•Answer pOH = 6

•pOH + pH = 14.0

Acids Neutralize Bases• HCl + NaOH NaCl + H2O

•Neutralization reactions ALWAYS produce a salt and water.• H2SO4 + 2NaOH Na2SO4 + 2H2O

• 2HNO3 + Mg(OH)2 Mg(NO3)2 + 2H2O

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

2 HCl + Mg(OH)2 MgCl2 + 2 H2O

Acid Base Titration•Titration • a method for determining the

concentration of a solution by reacting a known volume of that solution with a solution of known concentration.

• In a titration procedure, a measured volume of an acid or base of unknown concentration is placed in a beaker or flask, and initial pH recorded.

Titration with an Indicator

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