Lab 4

Lab 4 Double Replacement Reactions

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

Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product In general: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

Synthesis reactions Synthesis reactions occur when two substances (generally elements ) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product Basically: A + B  AB Example: 2H 2 + O 2  2H 2 O Example: C + O 2  CO 2

Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 )

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

Procedures Various combinations of ionic compounds in solution were mixed Some of these combinations formed cloudy precipitates One of the products of these reactions was an ionic compound that was less soluble. It must have a lower Ksp.

Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  product + product AB + CD  AD + CB

A Precipitation Reaction NaI(aq) + Pb(NO 3 ) 2 (aq) NaNO 3 (aq) + PbI 2 (s)

NaI(aq) + Pb(NO 3 ) 2 (aq) NaNO 3 (aq) + PbI 2 (s)

NaI(aq) + Pb(NO 3 ) 2 (aq) NaNO 3 (aq) + PbI 2 (s) Balance the molecular equation above. Write the total ionic equation. Write the net ionic equation.

A demonstration Pb(NO 3 ) 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(NO 3 ) 2 (aq) + 2 KI(aq)  2 KNO 3 (aq) + PbI 2 (s)

Visualizing the Double Replacement Reaction Ionic equations show the ions in solution AgNO 3 (aq) + NaCl(aq)  NaNO 3 (aq) + AgCl(s) Ions in solution are actually dissociated or separated. In the solid the ions are together Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq)  Na + (aq) + NO 3 - (aq) + AgCl(s) Notice Na + and NO 3 - 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 Equations Write the balanced molecular equation. Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions. Cancel the spectator ions on both sides of the ionic equation AgNO 3 ( aq ) + NaCl ( aq ) AgCl ( s ) + NaNO 3 ( aq ) Ag + + NO 3 - + Na + + Cl - AgCl ( s ) + Na + + NO 3 - 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?

Forming the green nickel (II) hydroxide precipitate Write a balanced equation that would lead to the formation of the green precipitate. What does the insolubility of nickel (II) hydroxide suggest about the 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. How does filtering separate? What goes through the filter? What remains in the filter? Why must the filter and solid be rinsed with water? What is removed in this process? Why must the filter and solid be heated to dryness? What is removed in this process?

Another double replacement reaction Mixing an acid and base

And yet another double replacement reaction Ba(OH) 2 (aq) + H 2 SO 4 (aq) 

Net Ionic Equations These are the same as total ionic equations, but you should cancel out ions that appear on BOTH sides of the equation Total Ionic Equation: 2 K + + CrO 4 -2 + Pb +2 + 2 NO 3 -  PbCrO 4 (s) + 2 K + + 2 NO 3 - Net Ionic Equation: CrO 4 -2 + Pb +2  PbCrO 4 (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.

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     H 2 O

Precipitation Reactions Precipitate – insoluble solid that separates from solution net ionic equation Na + and NO 3 - are spectator ions “ If you’re not a part of the solution, then you’re a part of the precipitate!” Pb 2+ + 2NO 3 - + 2Na + + 2I - PbI 2 ( s ) + 2Na + + 2NO 3 - Pb(NO 3 ) 2 ( aq ) + 2NaI ( aq ) PbI 2 ( s ) + 2NaNO 3 ( aq ) precipitate Pb 2+ + 2I - PbI 2 ( s )

Chemistry In Action: An Undesirable Precipitation Reaction CO 2 ( aq ) CO 2 ( g ) Ca 2+ ( aq ) + 2HCO 3 ( aq ) CaCO 3 ( s ) + CO 2 ( aq ) + H 2 O ( l ) -

Try this one! Write the molecular, total ionic, and net ionic equations for this reaction: Silver nitrate reacts with Lead (II) Chloride in hot water. Molecular: Total Ionic: Net Ionic:

Total Ionic Equations Molecular Equation: K 2 CrO 4 + Pb(NO 3 ) 2  PbCrO 4 + 2 KNO 3 Soluble Soluble Insoluble Soluble Total Ionic Equation: 2 K + + CrO 4 -2 + Pb +2 + 2 NO 3 -  PbCrO 4 (s) + 2 K + + 2 NO 3 -

Lab 4

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Lab 4