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Acid-Base ReactionsAcid-Base Reactions

If an acid reacts with a metal, a salt of that acid and hydrogen is produced.

aluminum + sulfuric acid → aluminum sulfate + hydrogen

2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g)

2Al(s) + 6H+(aq) → 2Al3+(aq) + 3H2(g)

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In the case of this single replacement reaction, the metal must be more

active than the hydrogen it is trying to

replace.

If the metal is not more reactive, there will be no reaction.

When an acid reacts with a salt, a new saltand a new acid is produced.

silver nitrate + hydrochloric acid → silver chloride +

nitric acid

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AgNO3(aq) + HCl(aq) → AgCl(s) +

HNO3(aq)

Ag+(aq) + Cl-(aq) → AgCl(s)

All double replacement (metathesis) reactions must produce a phase change for the reaction to occur. The phase change may result from:

Formation of a precipitate: A precipitate forms when the inter-ionic attractions are greater than the attraction between the ions and the water.

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Formation of a gas: Gases may form directly from the reaction itself or from the decomposition of one of the products.

Formation of a molecular species: The formation of unionized molecules in a solution removes the ions from the solution. An example of this is water formed when an acid and a base neutralize each other.

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Common Gases FormedCommon Gases Formed

Some common gases formed in doublereplacement reactions are given below.

any acid + any sulfide → salt + hydrogen

sulfide

HNO3(aq) + K2S(aq) → H2S(g) +

KNO3(aq)

H+(aq) + S2-(aq) → H2S(g)

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any carbonate + any acid → carbon dioxide + water

+ salt

Ba(HCO3)2(aq) + H2SO4(aq) → BaSO4(s)

+ 2H2O(l) + CO2(g)

Ba2+(aq) + 2HCO3

-(aq) + H+(aq) + HSO4

-(aq) → BaSO4(s) + 2H2O(l) + 2CO2(g)

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any sulfite + any acid → sulfur dioxide +

water + salt

MgSO3(aq) + 2HClO4(aq) → Mg(ClO4)2(aq) +

H2SO3(aq)

SO32-(aq) + 2H+ → H2O(l) + SO2(g)

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any ammonium salt + strong base → salt + water +

ammonia

NH4Br(aq) + LiOH(aq) → LiBr(aq) +

NH4OH(aq)

NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)

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More Acid-Base ReactionsMore Acid-Base Reactions

When writing acid-base reactions, be sure toaccount for states.

Co(OH)2(s) + HNO3(aq) →

Co(OH)2(s) + H+(aq) → Co2+(aq) + H2O(l)

Mn(OH)2(s) + HIO4(aq) →

Mn(OH)2(s) + 2H+(aq) → Mn2+(aq) + 2H2O(l)

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LiNO2(aq) + H2O(l)

NO2-(aq) + H2O(l) HNO2(aq) + OH-

(aq)

CsF(aq) + HBr(aq) →

F-(aq) + H+(aq) → HF(aq)

Al(OH)3(s) + HI(aq) →

Al(OH)3(s) + 3H+(aq) → Al3+(aq) + 3H2O(l)

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NH3(aq) + HBrO4 →

NH3(aq) + H+(aq) → NH4+(aq)

HCN(aq) + KOH(aq) →

H+(aq) + OH-(aq) → H2O(l)

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Net Ionic Equation WrapUpNet Ionic Equation WrapUp

Formulas for reactants and products arewritten to show the predominant form of

eachsubstance as its exists in an aqueoussolution.

Strong acids, strong bases, and soluble salts are written in ionized or dissociative form.

Weak acids, weak bases, gases, water, organic compounds, and insoluble salts are always written molecular form.

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Questions that determine how a species is to

be written.

Does the solute dissolve in water?

If no, write the molecular formula. If yes,

continue.

i.e. I2, AgCl, C6H12O6

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Does the solute dissociate or ionize?

If yes, write the ionic form. If no, write the molecular formula.

i.e. HCl, NaOH

The only substances that should be written in

ionic form are:

Soluble salts, strong acids, and strong bases.

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Important Reactants and Products Important Reactants and Products

H2SO4 written as a reactant or product mustbe written:

H2SO4(aq) → H+(aq) + HSO4-(aq)

When the following gases are formed asproducts, they decompose and must bewritten as:

H2SO3(aq) → SO2(g) + H2O(l)

H2CO3(aq) → CO2(g) + H2O(l)

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NH4OH(aq) → NH3(g) + H2O(l)

The only exception to this rule is whenH2SO3, H2CO3, or NH4OH are formed fromhydrolysis.

In the case of hydrolysis, the concentrations that result are so small that their decomposition does not take place.

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Selective SolubilitySelective Solubility

Which of the following will be more soluble inan acidic solution than in a basic solution?

CaCO3

CaCO3 would be more soluble in an

acidic solution because CO32- is a

relatively strong conjugate base of H2CO3.

CaCO3(s) + 2H+(aq) → Ca2+(aq) + CO2(g) + H2O(l)

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BaF2

BaF2 would be more soluble in an acidic solution because F- is a strong conjugate base of HF.

BaF2(aq) + 2H+(aq) → 2HF(aq) + Ba2+(aq)

AgCl

Cl- is an extremely weak conjugate base which results in no HCl being formed. However, AgOH is insoluble which would make AgCl more soluble in an acidic solution.

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Acidic and Basic AnhydridesAcidic and Basic Anhydrides

Anhydride means without water.

When a nonmetallic oxide hydrolyzes, it forms

an acid.

SO2 is an acidic anhydride because when it reacts with water, sulfurous

acid is formed.

SO2(g) + H2O(l) → H2SO3(aq)

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Cl2O is the acidic anhydride of HClO.

2HClO(aq) → Cl2O(aq) + H2O(l)

When a metallic oxide hydrolyzes, it forms abase.

Na2O is a basic anhydride because when it reacts with water, sodium hydroxide is

formed.

Na2O(s) + H2O(l) → 2NaOH(aq)

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CuO is the basic anhydride of Cu(OH)2.

CuO(s) + H2O(l) → Cu(OH)2(s)

Remember that in the case of hydrolysis, the

concentrations of H2SO3, H2CO3, and NH4OHare so small that their decomposition doesnot take place.