UNIVERSIDAD AUTÓNOMA DE NUEVO LEON

CIDEB

STAGE III: ACIDS AND BASES,

OPPOSITES THAT NEUTRALIZE

Formative Objective: The student solvestheoretical and experimental problemsrelated to acidic and basic solutions in dailylife. Thinks about the negative effects of acidrain in the surroundings and proposepossible solutions to this environmentalphenomenon

ACIDS

•Taste sour

•In aqueous solution, conduct electricity

•React with bases to form salt and water

•React with metals to form hydrogen gas

•React with carbonates to form carbon

dioxide, water and a salt

•Corrosive

•Contain hydrogen ions (H+)

•Have a pH lower than 7

•Turn blue litmus paper to a red colour

BASES

•Taste bitter

•Feel slippery or soapy

•In aqueous solution, conduct

electricity

•React with acids to form salts and

water

•Corrosive

•Contain hydroxyl ions (OH-)

•Have a pH higher than 7

•Turn red litmus paper to a blue colour

Magnesium and zinc react with aqueous solutions of acids to produce hydrogen gas.

Metal carbonates and hydrogen carbonates also react with aqueous solutions of acids to produce carbon dioxide (CO2) gas.

All water solutions contain hydrogen ions (H+) and hydroxide ions (OH-).

An acidic solution contains more hydrogen ions than hydroxide ions.

A basic solution contains more hydroxide ions than hydrogen ions.

A neutral solution contains equal concentrations of hydrogen ions and hydroxide ions

Pure water produces equal numbers of H + ions and OH- ions in a process called self-ionization, in which water molecules react to form a hydronium ion and a hydroxide ion.

Bases release

hydroxide

ions in water

Acids release

hydrogen

ions in water

States that an acid is a substancethat contains hydrogen and ionizes to produce hydrogen ions in aqueous solution.

A base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solution.

BUT, Ammonia (NH3) and sodium carbonate (Na2CO3) do not contain a hydroxide group, yet both substances produce hydroxide ions in solution and are well-known bases.

Base is a proton

acceptor; it

accepts a

hydrogen ion, H+

Acid is a proton

donor; it donates

a hydrogen ion,

H+

When a molecule of acid HX dissolves in water, it donates a H + ion to a water molecule. The water molecule acts as a base and accepts the H + ion.

◦ The hydronium ion is an acid because it has an extra H + ion that it can donate.

◦ X - is a base because it has a negative charge and can readily accept a positive hydrogen ion.

Conjugate acid: is produced when a base accepts a hydrogen ion.

Conjugate base: is produced when an aciddonates a hydrogen ion.

Conjugate acid-base pair consists of twosubstances related to each other by the donating

and accepting of a single hydrogen ion.

Hydrogen fluoride: A Brønsted-Lowry acid

Ammonia: A Brønsted-Lowry base

Water: a Brønsted-Lowry acid and base; wateris AMPHOTERIC because can act as both acidand base

To write the conjugate base of an acid:◦ A H+ is lost

◦ The compound becomes more negative.

To write the conjugate acid of a base:◦ A H+ is added

◦ The compound becomes more positive.

H2O OH-

HNO3 NO3-

ACIDS CONJUGATE BASES

SO4-2

HSO4-

C2H3O2- HC2H3O2

BASES CONJUGATE ACIDS

Ionization of sulfuric acid in two steps

• Can donate only one hydrogen ion

(proton) per formula unit.

• Ex: HCl, HNO3, HC2H3O2

Monoprotic

acids

• Contain two ionizable hydrogen atoms per

molecule.

• Ex: H2SO4

Diprotic acids

• Contain three hydrogen ions to donate

• Ex: H3PO4Triprotic acids

• Any acid that has more than one ionizable

hydrogen atom.Polyprotic acids

The difference between acetic acid’s ionizablehydrogen atom and the other three hydrogen atoms is that the ionizable atom is bonded to the element oxygen, which is more electronegative than hydrogen. The difference in electronegativity makes the bond between oxygen and hydrogen polar

Observe the following reaction:

H2O + CH3NH2 → OH- + CH3NH3+

Is an acid-base reaction according toArrhenius model? If so, identify the acid and the base.

Is an acid-base reaction according toBronsted-Lowry model? If so, identify the acidand the base.

Electrolyte: an ionic compound whoseaqueous solution conducts an electriccurrent.◦ ACIDS

◦ BASES

◦ SALTS

Strong acids: Acids that ionize completely. Because strong acids produce the maximum number of ions, they are good conductors of electricity.

Weak acids: An acid that ionizes only partially in dilute aqueous solution; produce fewer ions and thus cannot conduct electricity as well as strong acids.

“The conjugate base of a strong acid is veryweak”

“The conjugate base of a weak acid is strong”

Strong bases: A base that dissociates entirely into metal ions and hydroxide ions.

Weak bases: ionize only partially in dilute aqueous solution.

Pure water contains equal concentrations of H+ and OH- ionsproduced by self-ionization.

The ion product constant for water is the value of the equilibrium constant expression for the self-ionization of water.

In pure water at 25º C: [H3O

+] = 1.0 x 10-7 M[OH-] = 1.0 x 10-7 M

In pure water, the concentration of hydronium ions equals the concentration of hydroxide ions. This product is called the ion product constant of water Kw

• The [H+] is greater than 1.0 x 10-7 M Acidic solutions

• The [H+] is lower than 1.0 x 10-7 M Basic solutions

• The [H+] is equal to 1.0 x 10-7 M Neutral

solutions

Substances that change color depending onthe concentration of hydrogen ions in a solution.

The reaction of an acid with a base in aqueous solution to produce a salt and water.

The salt is an ionic compound made up of a cation from a base and an anion from an acid.

Buffers are solutions that resist changes in pHwhen limited amounts of acid or base areadded.

Is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

The mixture of ions and molecules in a buffer solution resists changes in pH by reacting with any hydrogen ions or hydroxide ions added to the buffered solution.

A buffer solution’s capacity to resist pH change can be exceeded by the addition of too much acid or base. The amount of acid or base a buffer solution can absorb without a significant change in pH is called the buffer capacity of the solution.

The greater the concentrations of the buffering molecules and ions in the solution, the greater the solution’s buffer capacity.