Unit 11: Reactivity

Acid-Base, Precipitation, Oxidation-Reduction(Redox)These are the 3 categories of reactions

Properties of AcidsTart or _Sour___________React with certain_metals_____ to produce

hydrogen gasReact with bases to produce water and a saltTurns blue litmus to the color __RED_____Electrolytes = __conduct_______ electricity

Acids – vinegar, carbonated drinks, citrus fruit

Properties of Bases__Bitter_______ tasteFeel _slippery______React with acids to form water and a saltTurns red litmus to the color _blue_______Electrolytes = __conduct___ electricity

Bases – antacid tablets, household cleaning agents

Ions in Solution

___Acidic_______– contain more H+ than OH-

_Basic_________– contain more OH- than H+

_Neutral____– contain equal amounts of H+ and OH-

Naming Acids - reminderI ate something icky.I bite something delicious.

(binary acids)

HX

“X” ends in -ide

Hydro _____ic acid

“X” ends in -ate

_______ic acid“X” ends in -ite

_______ous acid

HCl: hydrochloric acid

HF: hydrofluoric acid

H2SO3: sulfurous acid

HNO2: nitrous acid

H2SO4: sulfuric acid

HNO3: nitric acid

Naming Bases - reminderA base is a compound that produces

hydroxide ions, (OH-), when dissolved in water.

Bases are named the same way any other ionic compound is named.

NaOH – sodium hydroxideCa(OH)2 – calcium hydroxide

Arrhenius Acids and BasesSvante Arrhenius (Swedish chemist)

(1859-1927)1890’s – formulated firstuseful theory of acids and bases.

Acid: contain H+ ; the dissolved compound pr0duces a hydrated hydrogen ion (H3O+

(aq) , hydronium) and an anion.

Base(alkali): contains at least one OH- ion that dissociates when dissolved in water. Dissolved compound produces hydroxide ion and a cation.

Reaction produces H2O and a dissolved salt. This process is known as Neutralization.

Bronsted-Lowry 1920’s – definitions of acids andbases expanded independently by – Danish chemist Johannes Bronsted and English chemist Thomas Martin LowryMore broad definition of acids/bases

Acids- hydrogen ion, or proton, donorsBases- hydrogen ion, or proton, acceptors

Bronsted-Lowry (cont.)A conjugate acid and conjugate base are formed.Base gains hydrogen ion; particle formed is

conjugate acid.The particle that remains when an acid has

donated a hydrogen ion is the conjugate base.Example: when HCl gas dissolves and ionizes in water,

HCl is the proton donor (acid), water is the proton acceptor (base), the hydronium ion is the conjugate acid, and the chloride ion is the conjugate base.

HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)

acid base conjugate acid conjugate base

Neutralization Reactionsacid + base a salt + water

HCl + NaOH NaCl + H2O

Neutralization reactions are a type of double replacement reactions.

WaterWater can act as an acid or a base

H2O as an acid donates one H+ to become OH-

H2O as a base accepts one H+ to become H3O+

This is called the Hydronium ion (H3O+)

Neutral Solution[H+] = hydrogen ion concentration[OH-] = hydroxide ion concentration

Neutral Solution—Any aqueous solution in which the concentration of H+, [H+], and the concentration of OH-, [OH-], are equal.

In pure water at 25 oC, [H+] = [OH-] = 1.0 x 10-7 M.

In any aqueous solution, [H+] and [OH-] are interdependent. That is,When [H+] increases, [OH-] must decrease,

and vice versa.

Ion-product Constant for Water (Kw)

The product of the concentrations of the hydrogen ions and hydroxide ions in water is called the ion-product constant for water (Kw).

Kw = [H+] x [OH-] = 1.0 x 10-14 M

Kw = (1.0 x 10-7M) x (1.0 x 10-7M) = 1.0 x 10-14 M

If you know one, you can calculate the other.pH scale is derived from the value of Kw.Brackets, [ ], denote “concentration of”

The pH concept pH is the French abbreviation for “pouvier d’hydrogen.” In English, this translates to the “power of hydrogen.”

The pH of a solution is the negative logarithm of the hydrogen-ion concentration.

Pure water, pH = 7, is said to be neutral.

The formula is: pH = -log[H+] pH = -log (1 x 10 -7) = 7

Likewise…………. pOH = -log[OH-]Since Kw = 1 x 10-14, for any solution: pH + pOH = 14

pOH = 14 – pH pH = 14 - pOH

pH (cont.)Each unit of pH represents a power of 10.

Example: Baking soda has pH of 8.4 Milk has pH of 6.4This difference is 2 pH units.Since each unit represents a power of 10, the

[H+] in milk is 102 (or 100) times the [H+] in baking soda.

The pH Scale

Strength and DissociationStrong & weak acids are determined by how

much they dissolve into ions in water.Strong acids – completely ionize

higher conductivity lower pH than same concentration of

weak acidexamples: HCl and H2SO4

Weak acids - only partially ionize lower conductivity examples: carbonic acid, acetic acid

Strength and Dissociation (cont.)Strong base - higher conductivity higher pH than same concentration of a

weak base example: NaOH

Weak base - lower conductivity examples: ammonia & sodium

bicarbonate

Acid-Base IndicatorsAn _indicator__ is an acid or a base that

undergoes dissociation in a known pH range.

An indicator is useful for measure of pH because its acid form and base form have different colors in solution.

Ex: litmus paper, pH paper, phenolphthalein

Acid-Base Indicator Table (See pg. 590)

pH MetersA __pH Meter__ is used to make rapid,

accurate pH measurements.

If a pH meter is connected to a computer or chart recorder, it can be used to make a continuous recording of pH changes.

Most pH meters are accurate to within 0.01 pH unit of the true pH.

Acid StrengthThe _strength______ of an acid or a base tells you

the degree of ionization

Strong acids & bases break down into __all__________ ions. (Completely ionized, or dissociated)Ex: Strong acid – hydrochloric acid, sulfuric acid Strong base – Sodium hydroxide

Weak acids & bases break down into just a few ions(Partially ionized, or dissociated)

Ex: Weak acid – acetic acid, carbonic acid Weak base – Sodium bicarbonate (baking

soda)

TitrationLab technique used to experimentally determine

the molarity of a solution.A titration is a carefully monitored addition of one

solution into another solution.Often done by the use of a burette, which allows

for accurate measurement needed to neutralize the other solution.

An indicator or pH meter is needed to identify at what point the neutralization process is complete.

(ex: Phenolphthalein - colorless to pink around pH=9)

Oxidation-ReductionAlso known as redox reactionsVery common in nature – rusting and other types of

corrosion are typical examplesA chemical reaction in which one reactant loses

electrons and another gains electrons.Example: Fe Fe+2 + 2e- (Iron loses e-s.) O2 + 4e- 2O-2 (Oxygen gains e-

s.)

Put together: 2Fe + O2 2FeONote: In order to be balanced, have total of 4 electrons lost by iron and 4 gained

by oxygen.

Redox (cont.)The reactant being oxidized (losing electrons) is

called the reducing agent.The reactant that is reduced (gaining electrons)

is called the oxidizing agent.Typically, redox reactions happen in water or

moist surroundings.Note: ALL batteries produce electricity via

redox reactions. Regular batteries eventually consume the reactants. Rechargable batteries reverse the redox reaction by adding electricity (electrons), so they last longer.

Remember to use Activity Series of Metals for info, too!

PrecipitationPrecipitation reaction may occur when two

solutions of IONIC substances are mixed.If one or both pairs of ions in the combined

solutions form ionic compounds with very little to no solubility in water (unable to dissolve or very little), then a new, insoluble ionic solid will precipitate out.

Note: this is NOT the same as the physical change of crystallization seen in some solutions due to temperature changes.