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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.