Question

SCH3U U1 Experiment #10 DecompositionReactions

Purpose:

To observe four decompositionreactions.

Hypothesis:

Part A:

Lead (II) Nitrate > Lead +Nitrogen Gas + Oxygen Gas

Part B:

Hydrogen Peroxide > Water + OxygenGas

Part C:

Ammonium Carbonate > Ammonia +Carbon Dioxide

Part D:

Copper (II) Carbonate > CopperOxide + Carbon Dioxide

Materials:

See experiment handout. U1 Experiment#10 Decomposition Reactions

Procedure:

See experiment handout. U1 Experiment#10 Decomposition Reactions

Part D: (teacherdemonstration)

1)Heat a small amount of CopperCarbonate in a test tube over a Bunsen burner.

2)Collect the gas produced and bubblethrough lime water.

Observations:

PartA:

Lead (II) Nitrate --pale yellow finedull powder

Glowing splint test-- reignited

Burning splint test-- brightened

--brown gas was produced (NitrogenDioxide)

Part B:

Hydrogen Peroxide-- clear, colorlessliquid

Magnesium (IV) Oxide-- fine blackpowder

Flaming splint test-- wasextinguished

Glowing splint test-- reignitessplint

Reaction: reacts vigorouslyproducing a gas, dark powder mixed throughout. Reaction continuedfor several minutes.

Part C:

Ammonium Carbonate-- fine dull whitepowder

Red litmus-- turned blue

Blue litmus-- stayed blue

Dried cobalt paper-- turned pink

Glowing splint test--extinguished

Burning splint test--extinguished

Part D:

Copper Carbonate-- dull green-bluefine powder

Lime water-- clear liquid

Results of lime water test: Limewater turned cloudy and milky, and a precipitate formed in limewater.

CuCO₃ turns black as thereaction occurs.

Conclusion:

Four decompositions reactions wereobserved. In all of the experiments gases were produced.

Discussion:

1)The balanced equations are:

Part A:

2Pb(NO₃)₂ >4NO₂ + 2PbO + O₂

Part B:

H₂O₂ >H₂ + O₂

Part C:

(NH₄)₂CO₃ > 2NH₃ +CO₂ + H₂O

Part D:

CuCO₃ > CO₂+ CuO

2) The gas produced though thedecomposition of compounds containing the carbonate ion is carbondioxide (CO₂).

3) There are many tests to confirmthe presence of different gases. To test for CO₂ you canbubble the gas through lime water and it should turn cloudy ormilky. To test for O₂ you can place a glowing splint inthe gas and it should ignite. The presence of NH₃ can beconfirmed by it's ability to extinguish a glowing or flamingsplint, also it turns red litmus paper blue, and has a distinctivepungent odor. The presence of water vapor can be confirmed withcobalt paper, which turns pink when contacted by water vapor.Hydrogen gas (H₂) is tested for by placing a flamingsplint in the unknown gas, and a popping sound will be heard, thesplint will also be extinguished.

4) A balanced chemical equation forammonium gas and water is:

NH₃ + H₂O >NH₄⁺_(aq) +OH^-_(aq)

This explains why NH₃causes red litmus paper to turn blue, as the products areNH₄⁺ + OH^- , and OH^- isan indicator of a base, and bases turn red litmus paper blue. Thishappens because as the ammonium gas contacts the moist litmus paperit reacts with the water that has moistened the paper beforeeffecting the litmus paper.

5) A balanced chemical equation forcarbon dioxide and water is:

CO₂ + H₂O >H₂CO_3(aq)

The product is carbonic acid, andacids turn moist litmus paper red. The carbon dioxide reacts withthe water held by the litmus paper before reacting with the litmuspaper so is acidic when affecting the paper.