Acids and BasesWhat are Acids and Bases???

Acids • Acids have a very tart, sour taste to them.

• Many acids are highly caustic and should not be put to a taste test.

• Acids are electrolytes (they dissociate in water)• They break down into H3O+ ions which have a positive charge and

is just passed from water molecule to water molecule.

• Electricity can be passed through an acidic solution and is able to light a light bulb.

Acids and Metals• Acids react with many metals

• In these reactions, the hydronium reacts with the metal to produce hydrogen gas as one of the products.

2 H3O+(aq) + Zn(s) 2 H2O(l) + H2(g) + Zn2+

(aq)

• Notice that the HCl have been replaced with _____________.• HCl will break down into _________ ions and _________ ions.• The chlorine ions cancel out and do not appear in the net ionic

equation. Why is this??

Strong Vs. Weak• Some electrolytes are strong and others are weak, depending

on whether they dissociate completely or partially.

• Acids are electrolytes and therefore can be classified as strong or weak acids.

• Strong acid will dissociate COMPLETELY in water.

HNO3(l) + H2O(l) H3O+(aq) + NO3

-(aq)

• The strong acids are:

Weak Acids• When a weak acid is dissolved in water, only a small fraction of

its molecules are ionized at any given time.

• These reactions are usually reversible

• Example:

HOCl(l) + H2O H3O+(aq) + ClO-

(aq)

• Which acids are weak acids?

Polyprotic Acids• What do you think the term “polyprotic” means?

• A single molecule can react to form more than one hydronium ion. This occurs with stronger acids containing more than one hydrogen atom (hydronium ion).

• Consider sulfuric acid:

H2SO4(l) + H2O(l) H3O+(aq) + HSO4

-(aq)

Now, it can go one more step (it has one more H):

HSO4-(aq) + H2O(l) H3O+

(aq) + SO42-

(aq)

Bases• Solutions of bases are slippery to the touch. • If you are working with a strong base and your fingers feel

slippery like soap, wash them immediately!• This slippery feeling comes from the base reacting with the oils in

your skin, converting them to soaps.• This property is why bases are often used as cleaning agents

(ammonia)

• Alkali metals react with water VIOLENTLY to produce bases.They are very reactive and will actually react with the

water in the air to form hydroxides.

• These solutions are said to be basic or alkaline.

Strong Vs. Weak Bases• Acids generate the ___________ ion, bases generate the

hydroxide, or OH- ion.

• A strong base is a base that ionizes completely in a solvent. This solvent can be water or, if the base is insoluble in water, a ____________ solvent may be used.

• A weak base is a base that releases few hydroxide ions in aqueous solution.

• Example: Ammonia

Weak Bases• Weak bases, like ammonia, also DO NOT completely

dissociate:

NH3(aq) + H2O(l) NH4+

(aq) + OH-(aq)

• A few of the ammonia molecules react with water to reach equilibrium.

• The vast majority of ammonia molecules, however, remain un-ionized at any given time.

BrØnsted-Lowry Classification

• BrØnsted-Lowry acids donate protons

• Any species that donates a proton can be called an acid by this definition.

HCl + H2O H3O+ + Cl-

• This can also be thought of as:

HCl H+ + Cl-

Followed by H+ + H2O H3O+

BrØnsted-Lowry Classification

• BrØnsted-Lowry bases accept protons

• Any species that accepts a proton can be called a base by this definition.

• Ammonia serves as the proton acceptor and is therefore the BrØnsted-Lowry base.

NH3(aq) + H2O(l) NH4+

(aq) + OH-(aq)

Conjugate Acids and Bases

• When considering BrØnsted-Lowry acids and bases, an acid-base reaction is very simple:

One molecule or ion passes a proton to another molecule or ion.

• Whatever loses the proton in the ____________ and whatever gains the proton is the ____________ .

NH3(aq) + H2O(l) NH4+

(aq) + OH-(aq)

• The water donates the proton to ammonia so it is an acid. The ammonia then is going to be the ___________ because it _____________ the proton.

Conjugate Acids and Bases

• The conjugate acid is the acid that forms when a base gains a proton.

• The conjugate base is the base that is formed when an acid loses a proton.

NH3(aq) + H2O(l) NH4+

(aq) + OH-(aq)

• The ammonia is the base, the water is the acid.• The Ammonium ion is the __________________ and the

hydroxide ion is the __________________ .

Conj AcidConj Base

AcidBase

Amphoteric Substances

• The term amphoteric describes a substance, such as water, that has the properties of an acid and the properties of a base.• Usually just depends on who it is with and what role

needs to be played.

• These species can donate AND accept a proton when needed.

• The hydrogen carbonate ion, HCO3-, is amphoteric in

aqueous solution.

Amphoteric Substances

HCO3-(aq) + NH3(aq) CO3

2-(aq) + NH4

+(aq)

• Hydrogen carbonate acts as an acid here with ammonia (a base). Donates a proton to the NH3

HCO3-(aq) + H3O+

(aq) H2CO3(aq) + H2O(l)

• Hydrogen carbonate acts as a base here with hydronium (an acid). Accepts a proton to the H3O+ ion

Base

Base

Acid

Acid Conjugate Base

Conjugate Acid

Conjugate Acid

Conjugate Base

Water• Water itself is amphoteric.

• A water molecule can donate a proton and become a hydroxide ion in the process.

• It can also accept a proton to become a hydronium ion.

• This is why water is the product of the N.I.E. of an acid-base neutralization reactions (DBL displacements with an acid and a base).

• Continue looking over the notes and tests for the EXAM coming up.

• Vocab sheet due Monday!!