Reactions

Types of Reactions

Purpose:

The purpose of this experiment is to explore composition, decomposition, single replacement, and double replacement reactions, and to write a balanced equation for each reaction.

Materials:

Burner Test Tubes

Wood Splints Test Tube Holder

Safety Goggles Array of Chemicals

*To test for hydrogen, a flaming splint test was performed

*To test for oxygen, a glowing splint test was performed

I. Composition (Synthesis)

Magnesium ribbon burned in air.

BURN Light the tip of a piece of Mg in the hottest part of the burner flame.

OBSERVE CAUTION: Do not look directly at the burning Mg.

2 Mg + O2=> 2 MgO

Observations:

Gray/silver metal, small, clear gas, white powder residue. Very bright light and white smoke emitted.

II. Decomposition

a) Heating of lead dioxide

OBTAIN Obtain a test tube containing a small amount of lead dioxide.

HEAT Heat it "directly" over a burner flame.

TEST When a color change is observed, test the gas produced to

determine what it may be.

2 PbO2=> 2 PbO + O2

Observations:

brown powder, red hot, orange particles formed, creamy yellow colored solid formed on bottom, oxygen formed

b) Heating of lead nitrate

OBTAIN Obtain a test tube containing a small amount of lead nitrate.

HEAT Heat it strongly over a burner flame in the fume hood.

TEST When a brown gas is observed, test to determine what other gases may be present.

FUME When testing is completed, turn on the fume hood. (assume the products to be:

lead oxide, nitrogen dioxide, and oxygen)

2 Pb(NO3)2=> 2 PbO + 4 NO2 + O2

Observations:

White, salt-like crystal, brown gas formed, yellow on bottom, oxygen formed, brown toxic gas formed

c) Electrolysis of Water

OBSERVE Observe the electrolysis of water. The two gases produced will be tested later in front of the whole class.

2 H2O=> 2 H2 + O2

Observations:

Clear water, liquid, oxygen formed, hydrogen formed, bubbles

III. Single Replacement

a) Flat piece of zinc with copper nitrate soln.

Flat piece of copper with silver nitrate soln.

POUR Pour a few milliliters of the soln. into a test tube and add the piece of metal.

TIME Let this sit for a few minutes.

OBSERVE Record your observations.

Zn + Cu(NO3)2=> Zn(NO3)2 + Cu

Cu + 2 AgNO3=> Cu(NO3)2 + 2 Ag

Observations:

Zinc- silver, copper nitrate- blue, the zinc in the copper nitrate turned black, blue- green solution, copper- red/brown/orange, metal, silver nitrate- off white, the copper with silver nitrate turned black, bubbles

b) Aluminum with Hydrochloric acid (3 - 6M)

Copper with Hydrochloric acid

Zinc (mossy) with Hydrochloric acid

POUR Pour a few milliliters of acid into each of three test tubes.

ADD Add a piece of metal to each test tube and allow to sit.

TEST If a reaction is observed, test to identify the gas produced.

2 Al + 6 HCl=> 2 AlCl3 + 3 H2

Cu + 2 HCl => CuCl2 + H2

Zn + 2 HCl => ZnCl2 + H2

Observations:

Aluminum- very small, light, white; Hydrochloric acid- clear; Little bubbles formed, very white, completely broken down

Copper- small, gray, light; hydrochloric acid- clear; turned orange

Zinc- small, gray, light; hydrochloric acid- clear; bubbling reaction, hydrogen produced, zinc turned to particles, flame at top when tested for gas

c) Calcium in Water

ADD Add a piece of calcium metal to a few milliliters of water in a test tube.

TEST If reaction is observed. Test to identify the gas produced.

Ca + 2 H2O=> Ca(OH)2 + H2

Observations:

Calcium- white, bubbling reaction, hydrogen produced, loud popping sound when tested for gas, calcium dissolved- creamy white liquid formed

d) Halogen Replacement Demo

OBSERVE Chlorine or Bromine water will be added to sodium iodide and sodium bromide.

TTE (trichloro-trifluoro-ethane) will be used as a medium for the observation.

2 KBr + Cl2=> Br2 + 2 KCl

2 KI + Br2=> I2 + 2 KBr

KCl + I2=> No Reaction

Observations:

Bromine- yellow; bromine goes up into oil

Br2 by itself will be yellow- with oil yellow

Chlorine- clear; colorless with oil

Iodine- yellow brown; pink with oil

IV Double Replacement (Metathesis) (Ionic)

ADD Add a few drops of each together in a clean test tube and record your observations.

a) barium chloride and potassium chromate.

b) barium chloride and sodium sulfate.

c) ferric chloride and sodium hydroxide.

CLEAN UP Please clean your equipment and flush the sink at the end of the period .

BaCl2 + K2CrO4=> BaCrO4 + 2 KCl

BaCl2 + Na2SO4 => BaSO4 + 2 NaCl

FeCl3 + 3 NaOH=> Fe(OH)3 + 3 NaCl

Observations:

Barium chloride- clear, potassium chromate- yellow; turned creamy yellow

Barium chloride- clear, sodium sulfate- clear, turned milky white color

Ferric chloride- tinted yellow, sodium hydride- clear, turned brown with yellowish stuff on the bottom

Conclusion:

1. What observations confirmed that chemical reactions are taking place?

a. bubbles

b. smoke

c. light produced

d. color change

e. change in smell

f. phase change

2. Using the solubility rules in Table 8.3, page 227, and your balanced equations, identify which product is the precipitate formed in each of the Double Replacement reactions.

a. BaCrO4

b. BaSO4

c. Fe(OH)3

3. For the compound in Single Replacement reactions, explain how to predict which ion is replaced.

A single- replacement reaction occurs when atoms of one element replace the atoms of a second element in a compound. The relative reactivities of two metals determine if one metal can replace another in a compound. The activity series of metals lists metals in decreasing reactivity, to determine if they can be replaced.

4. Describe several benefits of completing this hands on lab.

During this lab, several reactions were observed. Composition, single replacement, decomposition, and double replacement reactions were completed. For each reaction, a balanced equation was derived.

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