Lab 4

Lab 4Lab 4

Double Replacement Double Replacement ReactionsReactions

Reaction TypesReaction Types

DECOMPOSITION (Lab 1)DECOMPOSITION (Lab 1) SYNTHESIS (Lab 1)SYNTHESIS (Lab 1) COMBUSTION (Lab 1)COMBUSTION (Lab 1) DOUBLE REPLEACMENT (Lab 4)DOUBLE REPLEACMENT (Lab 4) SINGLE REPLACEMENT (Lab 5)SINGLE REPLACEMENT (Lab 5)

Decomposition ReactionsDecomposition Reactions

• Decomposition reactionsDecomposition reactions occur occur when a compound breaks up into the when a compound breaks up into the elements or in a few to simpler elements or in a few to simpler compoundscompounds

• 1 Reactant 1 Reactant Product + Product Product + Product • In general: AB In general: AB A + B A + B• Example: 2 HExample: 2 H22O O 2H 2H22 + O + O22

• Example: 2 HgO Example: 2 HgO 2Hg + O 2Hg + O22

Decomposition ReactionsDecomposition Reactions

Synthesis reactionsSynthesis reactions• Synthesis reactionsSynthesis reactions occur when two occur when two

substances (generallysubstances (generally elementselements) combine ) combine and form a compound. (Sometimes these and form a compound. (Sometimes these are called combination or addition are called combination or addition reactions.)reactions.)

reactant + reactant reactant + reactant 1 product 1 product• Basically: A + B Basically: A + B AB AB

• Example: 2HExample: 2H2 2 + O+ O2 2 2H 2H22OO

• Example: CExample: C + O+ O2 2 CO CO22

Synthesis ReactionsSynthesis Reactions

Combustion ReactionsCombustion Reactions• Combustion reactions Combustion reactions

occur when a occur when a hydrocarbon reacts with hydrocarbon reacts with oxygen gas.oxygen gas.

• This is also called This is also called burning!!! In order to burning!!! In order to burn something you burn something you need the 3 things in the need the 3 things in the “fire triangle”:“fire triangle”:1) A Fuel (hydrocarbon)1) A Fuel (hydrocarbon)2) Oxygen to burn it with2) Oxygen to burn it with3) Something to ignite 3) Something to ignite the reaction (spark)the reaction (spark)

Combustion ReactionsCombustion Reactions• In general: In general:

CCxxHHy y + O+ O2 2 CO CO2 2 + H+ H22OO• Products in combustion are Products in combustion are

ALWAYS carbon dioxide and ALWAYS carbon dioxide and water. (although incomplete water. (although incomplete burning does cause some by-burning does cause some by-products like carbon products like carbon monoxide)monoxide)

• Combustion is used to heat Combustion is used to heat homes and run automobiles homes and run automobiles (octane, as in gasoline, is (octane, as in gasoline, is CC88HH1818) )

Combustion Combustion ReactionsReactions

Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

ProceduresProcedures

Various combinations of ionic Various combinations of ionic compounds in solution were mixedcompounds in solution were mixed

Some of these combinations formed Some of these combinations formed cloudy precipitatescloudy precipitates

One of the products of these One of the products of these reactions was an ionic compound reactions was an ionic compound that was less soluble. It must have a that was less soluble. It must have a lower Ksp.lower Ksp.

Double Replacement Double Replacement ReactionsReactions

• Double Replacement Reactions Double Replacement Reactions occur occur when a metal replaces a metal in a when a metal replaces a metal in a compound and a nonmetal replaces a compound and a nonmetal replaces a nonmetal in a compoundnonmetal in a compound

• Compound + compound Compound + compound product + product + productproduct

• AB + CD AB + CD AD + CB AD + CB

A Precipitation ReactionA Precipitation Reaction

NaI(aq) + Pb(NO3)2(aq) NaNO3(aq) + PbI2(s)

NaI(aq) + Pb(NO3)2(aq) NaNO3(aq) + PbI2(s)

NaI(aq) + Pb(NO3)2(aq) NaNO3(aq) + PbI2(s)

Balance the molecular equation above.

Write the total ionic equation.

Write the net ionic equation.

A demonstration

Pb(NO3)2 (aq) + KI(aq) There are four different ions in the mix.

Visualize the collisions.

Which collisions will result in a weak ionic bond easily broken by another collision?

Which collisions will not even occur due to repulsions between the ions?

Which collisions will form strong ionic bonds and clumps of ions visible as a cloudy precipitate?

Pb(NO3)2 (aq) + 2 KI(aq) 2 KNO3(aq) + PbI2(s)

Visualizing the Double Replacement Reaction

Ionic equations show the ions in solution

AgNO3(aq) + NaCl(aq) NaNO3(aq) + AgCl(s)

Ions in solution are actually dissociated or separated. In the solid the ions are together

Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) Na+(aq) + NO3

-(aq) + AgCl(s)

Notice Na+ and NO3- ions have not changed. They are spectator ions.

Net ionic equation leaves out the spectator ions. Ag+(aq) + Cl-(aq) AgCl(s)

Writing Net Ionic EquationsWriting Net Ionic Equations1. Write the balanced molecular equation.

2. Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions.

3. Cancel the spectator ions on both sides of the ionic equation

AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3

-

Ag+ + Cl- AgCl (s)

Write the net ionic equation for the reaction of silver nitrate with sodium chloride.

Write the balanced equation for this double replacement reaction.

Which collisions will result in a weak ionic bond easily broken by another collision?

Which collisions will not even occur due to repulsions between the ions?

Which collisions will form strong ionic bonds and clumps of ions visible as a cloudy precipitate?

Write the net ionic equation for the reaction.

Write the balanced equation for this double replacement reaction.

Which collisions will result in a weak ionic bond easily broken by another collision?

Which collisions will not even occur due to repulsions between the ions?

Which collisions will form strong ionic bonds and clumps of ions visible as a cloudy precipitate?

Write the balanced equation for this double replacement reaction.

Which collisions will result in a weak ionic bond easily broken by another collision?

Which collisions will not even occur due to repulsions between the ions?

Which collisions will form strong ionic bonds and clumps of ions visible as a cloudy precipitate?

How is this solution at equilibrium and saturated?

Solubility Rules

Forming the green nickel Forming the green nickel (II) hydroxide precipitate(II) hydroxide precipitate

Write a balanced equation that Write a balanced equation that would lead to the formation of the would lead to the formation of the green precipitate.green precipitate.

What does the insolubility of nickel What does the insolubility of nickel (II) hydroxide suggest about the (II) hydroxide suggest about the value of its Ksp?value of its Ksp?

Gravimetric Analysis-

A quantitative analysis of a double replacement reaction

The solid produced in the reaction is isolated by filtering and rinsing. After the filter and solid are dried, the mass of the barium sulfate is measured.

Procedural questions.Procedural questions.

How does filtering separate? What How does filtering separate? What goes through the filter? What goes through the filter? What remains in the filter?remains in the filter?

Why must the filter and solid be Why must the filter and solid be rinsed with water? What is removed rinsed with water? What is removed in this process?in this process?

Why must the filter and solid be Why must the filter and solid be heated to dryness? What is removed heated to dryness? What is removed in this process?in this process?

Another double Another double replacement reactionreplacement reaction

Mixing an acid and baseMixing an acid and base

And yet another double And yet another double replacement reactionreplacement reaction

Ba(OH)Ba(OH)22(aq) + H(aq) + H22SOSO44(aq) (aq)

Net Ionic EquationsNet Ionic Equations

These are the same as total ionic These are the same as total ionic equations, but you should cancel out equations, but you should cancel out ions that appear on BOTH sides of the ions that appear on BOTH sides of the equationequation

Total Ionic Equation:Total Ionic Equation:

2 K2 K++ + CrO + CrO44 -2-2 + Pb + Pb+2+2 + 2 NO + 2 NO33--

PbCrOPbCrO44 (s) + 2 K (s) + 2 K++ + 2 NO + 2 NO33--

Net Ionic Equation:Net Ionic Equation:

CrOCrO44 -2-2 + Pb + Pb+2+2 PbCrO PbCrO44 (s) (s)

Write equations (molecular, total and net ionic) for the reaction shown above. Explain the formation of the precipitate and the ions remaining in solutions by describing the collisions and attractions.

H2O

Ions in solution are dissociated attracted to the water by ion-dipole attractions. While ions in the precipitate held in fixed positions by ionic bonds between the ions

Precipitation ReactionsPrecipitation Reactions

Precipitate – insoluble solid that separates from solution

net ionic equation

Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3

-

Na+ and NO3- are spectator ions

Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)

precipitate

Pb2+ + 2I- PbI2 (s)“If you’re not a part of

the solution, then you’re a part of the precipitate!”

Chemistry In Action:

CO2 (aq) CO2 (g)

Ca2+ (aq) + 2HCO3 (aq) CaCO3 (s) + CO2 (aq) + H2O (l)-

An Undesirable Precipitation Reaction

Try this one!Try this one!

Write the molecular, total ionic, and net ionic Write the molecular, total ionic, and net ionic equations for this reaction: Silver nitrate equations for this reaction: Silver nitrate reacts with Lead (II) Chloride in hot water.reacts with Lead (II) Chloride in hot water.

Molecular: Molecular:

Total Ionic:Total Ionic:

Net Ionic:Net Ionic:

Total Ionic EquationsTotal Ionic Equations

Molecular Equation:Molecular Equation:

KK22CrOCrO44 + Pb(NO + Pb(NO33))22 PbCrOPbCrO44 + 2 + 2 KNOKNO33

SolubleSoluble SolubleSoluble Insoluble Insoluble Soluble Soluble

Total Ionic Equation:Total Ionic Equation:

2 K2 K++ + CrO + CrO44 -2-2 + Pb + Pb+2+2 + 2 NO + 2 NO33--

PbCrOPbCrO44 (s) + 2 K (s) + 2 K++ + 2 NO + 2 NO33--

Solubility TableSolubility Table