Acids and Bases

Acids

• from the Latin word acere “sharp” or “sour”• taste sour (but you wouldn’t taste an acid to see)• change litmus paper red• corrosive to some metals (reacts to create hydrogen gas –

H2)• a substance that can donate a hydrogen ion (H+) to another

substance• create a hydrogen ion (H+) or hydronium ion (H3O+) when

dissolved in water

HCl H+ + Cl-

HydrochloricAcid

Hydrogenion

Chlorideion

Examples: hydrochloric acid, vinegar, lemon juice, rainwater

H2O Notice howthe hydrogenion is releasedwhen the acid

is in water

Bases

• taste bitter (but you wouldn’t taste a base to see)• feel slippery or soapy• change litmus paper blue• react with oils and grease• a substance that can accept a hydrogen ion (H+) from

another substance• create a hydroxide ion (OH-) when dissolved in water

Examples: sodium hydroxide, Drano, Tums, baking soda

NaOH Na+ + OH-

SodiumHydroxide

Sodiumion

Hydroxideion

H2O

Notice howthe hydroxideion is releasedwhen the baseis in water; this

ion can accept a hydrogen ion

(H+)

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

Arrhenius base is a substance that produces OH- in water

4.3

Acid/Base definitionsDefinition 1: Arrhenius

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.

A Brønsted-Lowry acid is a proton donor.A Brønsted-Lowry base is a proton acceptor.

acidconjugate

basebaseconjugate

acid

ACID-BASE THEORIES

The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

Conjugate Pairs

Learning Check!

Label the acid, base, conjugate acid, and conjugate base in each reaction:

HCl + OH-   Cl- + H2O

H2O + H2SO4   HSO4- + H3O

+

Acid

Acid

Base

Base

Conj.Base

Conj.Base

Conj.Acid

Conj.Acid

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

Under 7 = acid7 = neutral

Over 7 = base

Neutralization Reaction

• occurs when acids and bases react with each other to produce water and salt– acids release a hydrogen ion (H+) and bases

release a hydroxide ion (OH-) water (H2O)– the negative ion from the acid joins with the

positive ion of a base salt

HCl + NaOH H2O + NaClHydrochloric

Acid(acid)

Sodium Hydroxide

(base)

WaterSodium Chloride(salt)

Both the salt and water are neutral substances; therefore, that is why this is referred to as a neutralization reaction.