AP ChemistryChemical Reactions

Practice for Question #4

AP ChemistryGranada Hills Charter High School ~ 2007

Complex Ion Formation

• a concentrated solution of ammonia is added to a solution of zinc iodide to form a complex ion.

• 4 NH3 + Zn2+ Zn(NH3)42+

• What precipitate could have been formed had the reactant been a dilute solution of ammonia?

• Zinc hydroxide

REDOX

• sodium metal is added to water. • Na + H2O Na+ + H2 + OH- • Is the resulting solution acidic, basic or

neutral? EXPLAIN and give an example of how you could prove your response.

• The resulting solution would be basic. This could be observed through the addition of phenolphthalein indicator which would turn pink in base.

Organic

• Chlorine gas is bubbled into to octane

• Cl2 + C10H22 C10H21Cl + H+ + Cl-

• Describe the relative pH of the resulting solution as acidic, neutral or basic.

• The solution would be acidic as the substitution reaction replaces a hydrogen with chloride releasing H+.

Double Replacement

• dilute acetic acid solution is added to solid magnesium carbonate.

• 2 HC2H3O2 + MgCO3 2 C2H3O2

- + H2O + CO2 + Mg2+

• Would the resulting solution be acidic, basic or neutral? EXPLAIN. (This would be too difficult to answer - especially without Ka values however…)

• The resulting solution would likely be close to or slightly lower than neutral because acetate is a conjugate base (from a weak conjugate acid) and the CO2 in water would be acidic as a non-metal oxide in water produces an acidic solution.

• Solid ammonium chloride is added to water

• NH4Cl + H2O NH3 (aq) + H3O+ (aq) + Cl-(aq)

• Is the resulting solution acidic, basic or neutral? EXPLAIN

• The ammonium ion is the conjugate acid of a weak base and it therefore creates an acidic solution in water.

General Acid/Base, Hydrolysis

REDOX

• a solution of tin(II) chloride is added to a solution of iron(III) sulfate.

• Sn2+ + 2 Fe3+ Sn4+ + 2 Fe2+

• Write and balance the oxidation half-reaction for mass and charge

• Sn2+ Sn4+ + 2 e-

Complex Ion Formation

• an excess of nitric acid solution is added to a solution of tetraamminecopper(II) sulfate.

• 4H+ + Cu(NH3)42+ 4 NH4

+ + Cu2+

• List the spectator ions in this reaction.

• NO3- and SO4

2- nitrate and sulfate ions

REDOX

• a piece of lithium metal is dropped into a container of nitrogen gas.

• 6Li + N2 2Li3N

• Besides a redox reaction, how else might this reaction be classified.

• Synthesis Reaction: a more complex product made from simple reactants

Lewis Acids and Bases

• the gases boron trifluoride and ammonia are mixed.

• BF3 + NH3 BF3NH3

• Based on behavior, what type of species is boron trifluoride in this reaction? EXPLAIN.

• BF3 is behaving as a Lewis acid as it is accepting the electron pair provided by nitrogen in a coordinate covalent bond.

REDOX

• a piece of iron is added to a solution of iron(III) sulfate.

• Fe + 2 Fe3+ 3 Fe2+

• Write the valence electron orbital notation of the resulting product illustrating and specifying diamagnetic or paramagnetic.

• [Ar]3d __ __ __ __ __ paramagnetic

Complex Ion Formation

• excess concentrated potassium hydroxide solution is added to a precipitate of zinc hydroxide to form a complex ion.

• 2 OH- + Zn(OH)2 Zn(OH)42-

• What would be observed in this reaction?

• A white solid would dissolve into a clear, colorless solution.

Precipitation and Qualitative Analysis

• A solution of silver nitrate, iron (III) nitrate, copper (II) nitrate and zinc nitrate are treated with 6 M hydrochloric acid

• Ag+ + Cl- AgCl

• What would be observed in this reaction?

• A white solid would form from a clear and colorless solution mixture.

Double Replacement

• hydrogen sulfide is bubbled through a solution of silver nitrate.

• H2S + 2 Ag+ Ag2S + 2H+

• Describe what change would be observed as the reaction proceeded.

• Gas would be observed bubbling through a clear and colorless solution forming a black precipitate.

Lewis Acids and Bases

• solid sodium oxide is added to water.

• Na2O + H2O 2 Na+ + 2 OH-

• Is the resulting solution acidic, basic or neutral? EXPLAIN

• Basic. Metal oxides form basic compounds in water.

Combustion

• 1-Propene ignites in air

• 2 C3H6 + 9 O2 6 CO2 + 6 H2O

• Describe the hybridization and molecular geometry change about carbon-1 in the reactant to the carbon in the product.

• sp2 hybridized in a trigonal planar geometry to sp hybridized in a linear geometry.

Precipitation and Qualitative Analysis

• Carbon dioxide gas is bubbled through a solution of barium hydroxide.

• CO2 + Ba2+ + 2OH- BaCO3 + H2O

• What would be observed in this reaction?

• The initial clear solution would turn milky-white as the barium carbonate was formed.

Lewis Acids and Bases

• powdered magnesium oxide is added to a container of carbon dioxide gas.

• MgO + CO2 MgCO3

• If the product were dissolved in water, predict the acidity, basicity or neutrality of the resulting solution.

• The dissociated carbonate ion would produce a basic solution in water as it is a conjugate base of a weak acid.

Double Replacement

• dilute nitric acid is added to crystals of pure calcium oxide.

• H+ + CaO Ca2+ + H2O

• What would you observe as this reaction took place?

• The solid, CaO would disappear.

Complex Ion Formation

• excess concentrated sodium hydroxide solution is added to solid aluminum hydroxide to form a complex ion.

• Al(OH)3 + 3 OH- Al(OH)63-

[or Al(OH)4-]

• Name the complex formed in this reaction.

• hexahydroxoaluminate or tetrahydroxoaluminate

Decomposition

• A small amount of manganese dioxide is added to hydrogen peroxide

• 2H2O2 2H2O + O2

• What would be observed as this reaction proceeded

• A great amount of heat and water vapor (steam) is released (exothermic). The manganese dioxide is not consumed in the reaction as it serves as the catalyst.

Double Replacement (Metathesis)

• Concentrated hydrochloric acid is added to aqueous sodium sulfite

• 2 H+ + SO32- SO2 + H2O

• What bond angle changes take place from the S-O bond of the reactant to the S-O bond of the product.

• The sulfite is trigonal pyramidal (approx. 107 while the sulfur dioxide is bent (less than 120).

Redox

• Solid gold is added to a mixture of concentrated nitric acid and HCl to form a complex ion.

• 4 H+ + 4 Cl- + NO3- + Ag

AgCl4- + NO + 2 H2O

• What is the acid mixture called?

• Aqua regia

Lewis Acids and Bases

• solid calcium oxide is heated in the presence of sulfur trioxide gas.

• CaO + SO3 CaSO4

• Classify this type of reaction

• This is a Lewis Acid/Base reaction with CaO behaving as a Lewis Base and SO3 as the Lewis Acid. It is also a synthesis reaction.

Double Replacement

• a saturated solution of calcium hydroxide is added to a solution of magnesium chloride.

• 2 OH- + Mg2+ Mg(OH)2

• List all spectator ions:

• Ca2+ and Cl-

Lewis Acids and Bases

• solid ammonium carbonate is heated.

• (NH4)2CO3 2NH3 + CO2 + H2O

• How would an observer confirm the presence of the products of this reaction.EXPLAIN.

• Detection of an ammonia odor and possible formation of water vapor or droplets could be detected. It would be difficult to determine the presence of CO2 without further tests.

Complex Ion Formation

• a concentrated solution of ammonia is added to a solution of copper(II) chloride to form a complex ion.

• 4 NH3 + Cu2+ Cu(NH3)42+

• Describe the color change that is observed

• The pale blue solution turns a deep blue color.

• sulfuric acid is added to barium hydroxide in equimolar volumes

• 2 H+ + SO42- + Ba2+ + 2 OH-

H2O + BaSO4 • What would you observe in conductivity as the

reaction progressed?• If a conductivity apparatus was utilized, the

indicator bulb would initially burn brightly then dim to off as the non-conductive solid product was formed. The dissociation of pure water is so minimal it likely wouldn’t even be detected by the apparatus though it is a weak electrolyte.

Acid/Base, Precipitation

• Chlorine gas reacts with sodium bromide solution

• Cl2 (g) + 2 Br - (aq) Br2 + 2 Cl -

(aq)

• Which species is the oxidizing agent• Chlorine is the oxidizing agent• What would you see as the reaction proceeds?• The solution would turn brown from the

presence of bromine.

REDOX

• Sulfur dioxide gas is bubbled through water

• SO2(g) + H2O (l) H2SO3(aq)

• What other major species would be in solution once equilibrium was established?

• H+ and HSO3-

(and in small quantity SO32- )

General Acid/Base, Hydrolysis

Double Replacement

• equal volumes of dilute equimolar solutions of sodium carbonate and hydrochloric acid are mixed.

• CO32- + H+ HCO3

-

• What would occur if the hydrochloric acid was increased?

• Carbon dioxide and water would be formed as products.

Precipitation

• A solution of silver nitrate and sodium chromate are mixed

• 2 Ag+ + CrO42- Ag2CrO4

• What would be observed as the reaction proceeded?

• A clear and colorless solution is mixed with a clear yellow solution and a red precipitate is formed.

Precipitation

• Solutions of zinc sulfate and potassium phosphate are mixed.

• 3 Zn2+ + 2 PO43- Zn3(PO4)2

• When a flame test of the resulting solution is done what would be observed?

• A lavender or lilac flame color would be observed

Complex Ion Formation

• a solution of potassium thiocyanate is added to a solution of iron(III) chloride.

• SCN- + Fe3+ FeSCN2+

• Describe any observation that would occur in this reaction.

• A colorless and yellow solution would turn a dark blood red.

REDOX

• an acidified solution of potassium permanganate is added to a solution of sodium sulfite.

• 6H++ 2MnO4- +5SO3

2- 2Mn2++ 3 H2O +5 SO42-

• Write the reduction half-reaction for mass and charge

• 5 e- + 8 H+ + MnO4- Mn2+ + 4H2O

• (unlikely candidate for the test as too much time needed to balancing the redox rxn)

Lewis Acids and Basesodd reactions

• phosphorus(V) oxytrichloride is added to water [You shouldn’t have this - too hard with no

choices this year.] • POCl3 + H2O H3PO4 + Cl- + H+

• Note that molecular phosphorus compounds form acids with water.

• PCl5 + H2O H3PO4 + H2O + Cl- + H+ • PCl3 + H2O H3PO3 + Cl- + H+

STUDY

Special thanks to Edye Eudell of Westridge Girls’ Academy in Pasadena and Paul Groves, of South Pasadena High School for Content Contributions, Editing for Assistance in the

development of this PowerPoint