Precipitation Reactions

Precipitation Reactions

Example: Write the complete balanced molecular equation for the reaction between Na3PO4 (aq) and CaCl2 (aq). Write the complete ionic equation and the net ionic equation for the reaction.

Ions: Na+ PO43-

Ca2+ Cl-

Possible Products:

NaCl

Ca3(PO4)2


Solubilities:

NaCl

Ca3(PO4)2

soluble

insoluble

(aq)

(s)


Unbalanced Molecular Eq’n:

Na3PO4 (aq) + CaCl2 (aq) Ca3(PO4)2 (s) +NaCl (aq)

Balanced Molecular Eq’n:

2 Na3PO4 (aq) + 3 CaCl2 (aq) Ca3(PO4)2 (s) +6 NaCl (aq)


Complete Ionic Equation:

6 Na+ (aq) + 2PO43- (aq) + 3 Ca2+ (aq) + 6 Cl- (aq)

Ca3(PO4)2 (s) + 6 Na+ (aq) + 6 Cl- (aq)

Net Ionic Equation:

3 Ca2+ (aq) + 2 PO43- (aq) Ca3(PO4)2 (s)


Example: Write the equation for the reaction between NH4Cl (aq) and CaSO4 (aq).

Ions: NH4+ Cl-,

Ca2+ SO42-

Possible Products: (NH4)2SO4

CaCl2


Solubility of Products:

(NH4)2SO4

CaCl2

soluble

soluble

(aq)

(aq)


NH4Cl (aq) + CaSO4 (aq) No Reaction

If both products are soluble (aq), then NO REACTION is presumed to occur between the ionic compounds involved. The reaction mixture simple contains a

mixture of soluble ions.

On your exam, you should be able to indicate whether a reaction occurs or not. •If it occurs, write the formulas for the products and balance.•If no reaction occurs, write the words, “No Reaction”

Acids & Bases Acids:

substances that ionize in aqueous solution to form one or more hydrogen ions (H+)

increase the concentration of H+ ions in solution

Acids are sometimes called proton donors. H+ is often called a proton

Acids & Bases Examples of Acids:

HCl hydrochloric acid HNO3 nitric acid HC2H3O2 acetic acid H2SO4 sulfuric acid H3PO4 phosphoric acid

Note: Acids can form different numbers of H+ ions!

Acids & Bases Monoprotic acids

have one H in the formula form a single H+ ion when they ionize

HNO3 (aq) H+ (aq) + NO3- (aq)

Acids & Bases Diprotic acids

have two H’s in the formula can form two H+ ion when they ionize

completely

H2SO4 (aq) 2H+ (aq) + SO42- (aq)

Polyprotic acids: Have two or more H’s in the formula Form two or more H+ ions when they ionize

completely

Acids & Bases Bases:

substances that accept (react with) H+ ions. any substance that increases the OH-

concentration when added to water

Examples:

Hydroxide ion (OH-) OH- (aq) + H+ (aq) H2O (l)

Acids & Bases Examples (cont)

Common hydroxide containing bases: NaOH, KOH, Ca(OH)2

Note: These are strong electrolytes!

NaOH (aq) Na+ (aq) + OH- (aq)

Acids & Bases Examples (cont):

Ammonia (NH3) Does not contain OH-

Accepts H+ ion from water and increases the OH- concentration in the water

NH3(aq) + H2O (l) NH4+ (aq) + OH- (aq)

NH3 is a weak electrolyte!!

Acids & Bases Strong Acid:

an acid that is a strong electrolyte ionizes completely in solution

Weak Acid: an acid that is a weak electrolyte

an acid that does not ionize completely

Acids & Bases Strong acids:

Know the names and formulas of the 7 common strong acids:

HCl (aq) hydrochloric acid HBr (aq) hydrobromic acid HI (aq) hydroiodic acid HClO3 chloric acid HClO4 perchloric acid HNO3 nitric acid H2SO4 sulfuric acid

Acids & Bases Examples of Weak Acids

HF (aq) hydrofluoric acid H3PO4 phosphoric acid HC2H3O2 acetic acid

Acids & Bases Strong Base:

a base that is a strong electrolyte ionizes completely in solution

Weak Base: a base that is a weak electrolyte does not ionize completely in solution

Acids & Bases Strong Bases: Know the names and formulas

of the strong bases

Alkali metal (1A) hydroxides LiOH lithium hydroxide NaOH sodium hydroxide KOH potassium hydroxide RbOH rubidium hydroxide CsOH cesium hydroxide

Acids & Bases Strong bases to know (con’t):

Heavy alkaline earth metal (2A) hydroxides Ca(OH)2 calcium hydroxide Sr(OH)2 strontium hydroxide Ba(OH)2 barium hydroxide

Acids & Bases Examples of Weak Bases:

ammonia (NH3) sodium bicarbonate (NaHCO3)

baking soda a component of Alka-Seltzer

Acid-Base Reactions Reactions between acids and bases are called

neutralization reactions. The products of these reactions have very

different properties than the reactants.

HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq)

Sharpsour

bitterslippery

salt

Acid-Base Reactions Salt:

any ionic compound whose cation comes from a base and whose anion comes from an acid

An ionic compound that is neither an acid nor a base

In general,

acid + metal hydroxide a salt + water

Acid-Base Reactions Neutralization reactions are a type of

metathesis reaction.

To predict the products: identify the ions present exchange anions write the correct formulas for the products write a balanced equation

Acid-Base Reactions

Example: Write the balanced equation for the reaction between HBr (aq) and Ca(OH)2 (aq).

Ions: H+ Br-

Ca2+ OH-

Possible Products:H-OH = H2O

CaBr2

2HBr (aq) + Ca(OH)2 (aq) CaBr2 (aq) + 2H2O (l)

Acid-Base Reactions Notice that you can also write complete and

net ionic equations for acid-base reactions:

Complete ionic equation:

2 H+ (aq) + 2Br- (aq) + Ca2+ (aq) + 2 OH- (aq) Ca2+ (aq) + 2 Br- (aq) + 2 H20 (l)

Molecular equation:

2HBr (aq) + Ca(OH)2 (aq) CaBr2 (aq) + 2H2O (l)

Acid-Base Reactions

Net ionic equation:

H+ (aq) + OH- (aq) H2O (l)

Note: This is the net ionic equation between any strong acid and strong base.

Complete ionic equation:

2 H+ (aq) + 2Br- (aq) + Ca2+ (aq) + 2 OH- (aq) Ca2+ (aq) + 2 Br- (aq) + 2 H20 (l)

Acid-Base Reactions

Example: Write the balanced equation for the reaction between Mg(OH)2 (s) and HCl (aq).

Ions: Mg2+ OH-

H+ Cl-

Products: MgCl2 (aq)

H-OH = H2O (l)

Acid-Base Reactions

Molecular Equation:Mg(OH)2 (s) + 2 HCl (aq) MgCl2 (aq) + 2 H2O (l)

Net ionic equation:Mg(OH)2 (s) + 2 H+ (aq) Mg2+ (aq) + 2 H2O (l)

Complete Ionic Equation:Mg(OH)2 (s) + 2 H+ (aq) + 2 Cl- (aq) Mg2+ (aq) +

2 Cl- (aq) + 2 H2O (l)

Acid-Base Reactions There are many bases that do not contain OH-

Na2S NaCN NaHCO3

These bases react with acids to form gaseous products.

Acid-Base Reactions

Examples:

Na2S (aq) + 2 HCl (aq) H2S (g) + 2 NaCl (aq)

HCl (aq) + NaHCO3 (aq) NaCl (aq) + H2CO3 (aq)

but:H2CO3 (aq) H2O (l) + CO2 (g)

so:

HCl (aq) + NaHCO3 (aq) NaCl (aq) + H2O (l) + CO2 (g)

Oxidation-Reduction Reactions Precipitation Reactions:

ions combine to form insoluble products

Neutralization Reactions: H+ ions and OH- ions combine to form H2O

Oxidation-Reduction (Redox) Reactions: Atoms or ions give or accept electrons

Redox Reactions Corrosion of your car

battery terminal is caused by a reaction between the metal terminal, oxygen, and the battery acid, H2SO4.

This reaction is a redox reaction.

Redox Reactions Oxidation-Reduction Reactions (Redox

Reactions) reactions that involve the transfer of

electrons between two reactants an element in one reactant is oxidized while

an element in another reactant is reduced

Mg (s) + 2 H+ (aq) Mg2+ (aq) + H2 (g)

oxidized reduced

Redox Reactions Oxidation:

the loss of electrons chemical species becomes more

positively charged

the gain of oxygen

the loss of hydrogen

Redox Reactions Reduction:

the gain of electrons the chemical species becomes more

negatively charged

the gain of hydrogen

the loss of oxygen

Redox Reactions LEO:

Lose Electrons Oxidation

GER:

Gain Electrons Reduction

GER

LEO

LEO says GER

Redox Reactions

Oil Rig

Oil : Oxidation Involves

Loss of e-

Rig : Reduction Involves

Gain of e-

Redox Reactions Electrons are not explicitly shown in

chemical equations.

Oxidation Numbers are used to keep track of electrons gained and lost during redox reactions.

Oxidation number a hypothetical number assigned to an

individual atom present in a compound using a set of rules.

May be positive, negative, or zero

Rules for Oxidation Numbers

Oxidation numbers are always reported for individual atoms or ions not groups of atoms or ions!!!!!!!!!!!

For an atom in its elemental form, the oxidation number is always zero.

H2: oxidation # = 0 for each H atom Cu: oxidation number = 0 Cl2: oxidation # = 0 for each Cl atom


For any monoatomic ion, oxidation # = charge on ion

K+ oxidation # = +1 Cl- oxidation # = -1 S2- oxidation # = -2


Group 1A Metal Cations: Always +1

Group 2A Metal Cations: Always +2

Hydrogen (H) +1 when bonded to nonmetals -1 when bonded to metals


Oxygen (O) -1 in peroxides (O2

2-) -2 in all other compounds

Fluorine (F) always -1


The sum of the oxidation numbers of all atoms in any chemical species (ion or neutral compound) is equal to the charge on that chemical species

H2O: 1 + 1 + -2 = 0

MgCl2: 2 + -1 + -1 = 0

MnO4- : 7 + -2 + -2 + -2 + -2 = -1

Oxidation Numbers For many compounds, you will be able to

directly apply the rules to determine the oxidation number of all atoms except for one. Use the last two rules to determine the

oxidation number of that last element.

Oxidation Numbers

Example: Determine the oxidation state of all elements in SO3.

Is it elemental?

Are any monoatomic ions present?

Which elements have rules?

Set up an equation to find the remaining oxidation number.

No

No

O = -2

S + 3(-2) = 0 S = +6

Oxidation Numbers

Example: Determine the oxidation number of Mn and O in MnO4

-.

Mn + 4(-2) = -1 so Mn = +7

Is it elemental?




No

No

O = -2

Oxidation Numbers

Example: Determine the oxidation state of all elements in NaNO3

Is it elemental?




No

Na+

Na = +1, O = -2

1 + N + 3(-2) = 0 N = +5

Oxidation Numbers

Example: Determine the oxidation number of P in HPO4

2-

Oxidation Numbers

Example: Determine the oxidation state of all elements in Cr2O7

2-.

Precipitation Reactions

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