CHM 1025C/CHM 1032C

Chemical Reactions Experiment:

 

GOALS:

 

1.         To observe chemical reactions going to completion through precipitation and neutralization.

 

2.         To familiarize the student with laboratory reagents, reading and writing chemical formulas.

 

3.         To notice various solubility characteristics of various solids with various solvents.

 

4.         To manipulate a reagent bottle or dropper bottle  so that the student may pour dangerous chemicals without spilling a drop.

 

5.         To scrub glassware so as to remove chemicals and oils from the surface.

 

EQUIPMENT:

tube rack with 12 test tubes

Test tube holder

50 or 125 mL Erlenmeyer Flask

Eye dropper - long stem pipette

Plastic Wash bottle with DI Water

Burner and Tubing

Test tube brush on wash sink

 

 

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CHEMICALS:

Magnesium Ribbon (small pieces)

Copper wire (small sections)

 

Calcium metal (small piece)

 

Copper Sulfate pentahydrate (small vial)

CuSO4 5H2O

 

Cobalt Chloride dihydrate (small vial)

CoCl22H2O

 

Nickel Chloride hexahydrate (small vial)

NiCl26H2O

 

Sodium hydrogen carbonate (baking soda)

NaHCO3

Concentrated HCl (small via)

Concentrated NH3 or NH4OH (small vial)

 

Aluminum Nitrate - Al(NO3)3

 

Copper (II) Nitrate – Cu(NO3)2

 

Silver Nitrate - AgNO3

 

Potassium Carbonate – K2CO3

(or Sodium Carbonate - Na2CO3)

 

Sodium Phosphate – Na3PO4

(or Potassium Phosphate – K3PO4)

 

Phenolphthalein Indicator

Nitric Acid – HNO3 (aq)

Sulfuric Acid – H2SO4 (aq)

Phosphoric Acid – H3PO4 (aq)

Vocabulary or Background:

 

QUALITATIVE ANALYSIS:                      Laboratory Techniques which identify the presence or absence of various anions and cations.

 

QUANTITATIVE ANALYSIS:        Laboratory techniques used to identify HOW MUCH

                                                      OF a substance is present in a mixture

 

CATION:        Any metallic (or positive) ion, including the ammonium polyatomic ion

 

ANION:          Any non-metallic (or negative) ion, including all negative polyatomic ions

 

AQUEOUS SOLUTION, (aq):        A water solution of a compound, usually ionic

 

PRECIPITATE:        Solid formation in an aqueous solution upon the addition of a precipitating agent

 

FILTRATE:   Liquid portion of a solution which comes through the filter paper

 

CENTRIFUGATE:   Clear liquid portion above the residue that separates from a mixture after centrifuging the mixture

 

SOLUTION:  Homogeneous mixture of solute and solvent which passes through filter paper.  Also cannot be separated by centrifuging.  Solute and solvent are ionic or molecular in size.  Always clear (never cloudy).

 

                     WASHING GLASSWARE:

                          After washing test tubes and other glassware with soap and tap water, they have to be rinsed again using deionized water.  This removes any ions left on the glassware by tap water.  It is not necessary to dry glassware used in this lab because deionized water will not affect any of the reactions.  You should use a plastic squeeze  wash bottle.  Keep it filled with deionized water.  Use it to rinse glassware, to add deionized water to reactions and to wash precipitates.  Remember to wash and rinse graduated cylinders and pipets and stirring rods between uses.

 

Discussion:

Chemists write Chemical Reactions using formulas and symbols to describe a chemical change. These are the symbolic representation of a chemical sentence, Consider substance A and substances B undergoing a chemical change to produce substances C and D, we write:

The physical states of the chemicals are noted in the chemical equation by writing the abbreviations (s), (l), (g), or (aq) for solid, pure liquid, gas, or aqueous (water) solution.

 

Substances A and B are called Reactants or the subject of the sentence.

The horizontal arrow reads “yields” or “produces” and is the verb of the sentence.

Substances C and D are called Products or the predicate of the sentence.

 

In Chapter 8 of the Hein CHM 1025C book, Chapter 7 of the Corwin 1025 book, and/or Chapter 5 of the CHM 1032C chemical reactions are introduced.  CHM 1025C students should read carefully about how to write and balance chemical reactions from your Hein textbook, sections 8.1 The Chemical Reaction and Section 8.2 Writing and Balancing chemical reactions.. In the Corwin book: read section 7.1(Evidence for Chemical Reactions); Section 7.2( Writing Chemical Equations); and Section 7.3 (Balancing Chemical Equations). In McMurry read Section 5.1 ( chemical reactions) and section 5.2 (balancing chemical reactions). 

 

 

Most of the reactions in this experiment are the type of ION EXCHANGE or Double Replacement.  That is, two ionic compounds exchange their ions to form two or more compounds. 

 

Ion exchange reactions (precipitation and neutralization) are discussed in section 8.3 in the Hein text. Likewise in Corwin’s section 7.9 Solubility Rules; section 7.1 Double-Replacement Reactions; and section 7.11 Neutralization Reactions are discussed. McCurry text has Section 5.4 (Precipitation reactions and solubility guideline) and section 5.5 (Acids, Bases, and neutralization).

 

                                                                      

Most textbooks introduce the main types of simple inorganic chemical reactions:

 

Types of Chemical Reactions             Hein  Corwin      McMurry

Combination

A + B à AB

8.3

7.5

Not introduced

Decomposition

AB à  A + B

8.3

7.6

Not introduced

Single Replacement

A + BC è B + AC

8.3

7.8

Not introduced

Double Replacement

AB + CD à  AD + CB

8.3

7.10

5.3, 5.4

 

 

 

 

 

 

 Rewrite Chemical Reactions into Net Ionic Reactions

 

In Chapter 15, Section 14.11 of the Corwin CHM 1025C textbook there is a four page discussion on re-writing equations into net ionic form. Corwin discusses four guidelines for writing these net ionic reactions. Below is a brief summary of these rules:

 

In aqueous solutions rewrite as ions: electrolytes such as

  1. soluble salts,
  2. strong acids*,
  3. strong bases**.

*The common strong acids are hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, hydrobromic acid and hydroiodic acid. Assume they are 100% ionized in the aqueous solution.

 

**Strong bases include KOH, LiOH, NaOH, Ca(OH)2 , Sr(OH)2, and Ba(OH)2 which are actually soluble salts.

 

Assume all other acids and bases are weak and you do not re-write them as ions..

 

In aqueous solutions leave in molecular form compounds which are nonelectrolytes:

  1. Insoluble salts,
  2. weak acids and bases,
  3. covalent molecules.

 

Below are examples of chemical equations which are also rewritten in net ionic form

 

A chemical reaction has taken place if:

 

1. An insoluble solid is produced as a product. This called a precipitate. Above C (s) would be a precipitate. Sometimes a precipitate is shown as an arrow down C ¯.

 

Barium Nitrate (aq) + Sodium Sulfate (aq)

 

          Ba(NO3)2 (aq)  +  Na2SO4 (aq)  BaSO4 ¯  + 2 NaNO3 (aq) 

                Soluble salt                       soluble salt                    insoluble                soluble salt

 

Total Ionic with Spectators Cancelled:

Ba2+(aq) + 2NO31-(aq) + 2Na1+(aq) + SO42-(aq)  BaSO4¯ + 2Na1+(aq) + 2NO31-(aq)   

 

Net Ionic:

          Ba2+(aq)   +   SO42-(aq)      BaSO4 ¯ 

 

2. A gas is released as a product. When CO2 is formed from an acid reacting with an ionic carbonate or bicarbonate compound, the gas bubbles from the solution. When Ammonia gas, NH3 is formed it doesn’t bubble, but oozes from the solution and you can smell it. Many times a gas evolves which is odorless, but a reaction has taken place. Sometimes when a gas is formed as a product D (g), an arrow pointing up is written after the compound: D.

 

Sodium Hydrogen Carbonate + Acetic Acid

 

          NaHCO3  (aq)  +  HC2H3O2 (aq) CO2   + H2O(l)  +  NaC2H3O2 (aq)

               Soluble salt                         weak acid                        molecular      molecular           Soluble salt

 

Total Ionic with Spectators Cancelled:

Na1+(aq) + HCO31-(aq) + HC2H3O2 (aq) CO2   + H2O(l)  +  Na1+(aq) + C2H3O21-(aq)

 

Net Ionic:

          HCO31-(aq) + HC2H3O2 (aq) CO2   + H2O(l)  +  + C2H3O21-(aq)

 

 

3. If water is formed from the neutralization reaction of an acid with a base. Heat Energy Change is noted by the test tube becoming warm (Exothermic).

 

Hydrochloric Acid (aq) + Sodium Hydroxide (aq)

 

         HCl (aq)    +    NaOH (aq)       NaCl (aq)    +  HOH (l)

             Strong Acid                  Strong Base                       soluble salt                  molecular

 

Total Ionic with Spectators Cancelled:

H1+(aq) + Cl1-(aq)   +  Na1+(aq) + OH1-(aq)   Na1+(aq) +  Cl1-(aq)      +  HOH (l)

 

Net Ionic:

          H1+(aq)   +   OH1-(aq)      HOH (l) 

 

 

4. A permanent color change is observed.

 

Hein has a similar discussion in Section 15.7 beginning on page 354. McMurry devotes section 5.8 to Net Ionic Reactions.

 

 

Suggestion:

When adding drops from a dropper bottle or washing test tubes, you should wear disposable gloves.

 

 

 

PROCEDURES:

 

A.    Combination Reactions (Instructor Demonstration)

 

1.            The instructor will hold a 2 cm strip of Magnesium ribbon with crucible tongs into a hot burner flame. Describe the flame when the ribbon ignites and observe the product residue. Record your observation on the data sheet and write/balance the chemical reaction

 

2.            The instructor will place a moisten cotton ball with concentrated hydrochloric acid in one end of a long glass tube and a moisten cotton ball with concentrated ammonium hydroxide in the other, then quickly insert a rubber stopper in both ends. One student will keep time until they see the reaction appear. This procedure will be repeated with a second stoppered tube. When the reaction is first noticed another student will record the position of the reaction. All students will record the time and measurement on their data page and write the chemical reaction.

 

 

 

3.            Review on the website the reaction of sulfur burning:

http://www.lsua.us/chem1001/Chap8Movies/aabtpxt0.html

Record your observation on the data sheet and write/balance the chemical reaction

 

4.            Review on the web site the reaction of sodium with chlorine:

http://www.lsua.us/chem1001/Chap8Movies/aabtpxi0.html

Record your observation on the data sheet and write/balance the chemical reaction

 

B.  Decomposition Reactions

1.  Obtain a test tube rack and 12 test tubes. Number the tubes (#1- #12)

Image result for images for test tube rack

 

2.  Put a small piece of Copper Sulfate pentahydrate in a test tube and with test tube holder heat the test tube gently with a burner.

 

Note the color change and see if you see moisture near the top of the test tube.

 

                                          

Write the chemical reaction in your data table.

 

Repeat the experiment with Cobalt chloride dihydrate (Red) and Nickel chloride hexa hydrate (green).

 

Record your results in the data table. Save the three tubes for Part D: double replacement reactions below.

 

3.  Add sodium hydrogen carbonate (baking soda) to the bottom of a 50 or
125 mL Erylenmeyer flask. Thinly cover the bottom of the flask. Using a ring stand and wire gauze support the flash with a safety ring.

Image result for images for erlenmeyer flask attached to ring stand

 

             Insert a faming splint into the top of the flask (Wood popsicle stick) into
             the flask before heating. Note how long it burns. 

 

             Heat the flask strongly (fisher burner) until you see moisture collecting
             near the top, then insert another flaming stick into the mouth of the flask.

             What happens?

             Record your results on the data page and write the chemical reaction.

 

B.  Single Replacement Reactions (Module 5i Part G):

1.          Place 20 drops of distilled water in a test tube. Carefully add a very small piece of calcium to the test tube and record the results.

 

2.          Place 20 drops of distilled water in a test tube. Add a small piece of magnesium metal to the test tube, Record the results. Then add one drop of concentrated hydrochloric acid to the tube at the instructor’s desk. Record the results on your data page and write the reaction.

 

3.           Place 20 drops of silver nitrate in a test tube and place a small piece of copper wire in the test tube. After 5 to 10 minutes record the results on your data page and write the reaction.

 

 

 

D. Double Replacement Reactions

 

  1. Place 10 drops of Aluminum nitrate, Copper (II) Nitrate, and Silver nitrate into test tubes #4, #5, and #6 in your test tube rack. (Module 5i Part H)

 

Add a few drops of potassium carbonate or sodium carbonate to each test tube. Record the results on your data page and write the reactions

 

  1. Place 10 drops of Aluminum nitrate, Copper (II) Nitrate, and Silver nitrate into test tubes #7, #8, and #9 in your test tube rack.

 

Add a few drops of Sodium phosphate or Potassium phosphate to each test tube. Record the results on your data page and write the reactions

 

  1. Add 40 drops of water (2 mL) to test tubes #1, #2, #3.

Separate half the solutions (1 mL) into test tubes #10, #11, #12.

 

Add a few drops of potassium carbonate or sodium carbonate to each test tube (#1, #2, #3). Record the results on your data page and write the reactions

 

Add a few drops of Sodium phosphate or Potassium phosphate to each test tube (#10, #11, #12). Record the results on your data page and write the reactions

 

 

 

E. Double Replacement Neutralization Reactions

 

1.  Clean all of the test tubes using soap solution and a test tube brush in the wash sink, but first dump the contents in the waste jars in the hood.

 

2.  Place 10 drops of nitric acid, sulfuric acid, and phosphoric acid separately into test tubes #1, #2, #3. Note the concentration of the acids (.1M), 0.5M, or 1.0 M.

 

3. Add two drops of phenolphthalein (acid - base indicator) to each test tube. In an acidic solution the solution is colorless. When the solution becomes basic it turns to pink.

 

4. One at a time, add dilute sodium hydroxide (same concentration) drop by drop into each of test tubes #1, #2, #3 until you note a color change.

 

5. Record your results and write the reactions.

(M-5i Part H1).

Dispose the contents into the waste jars in the hood and scrub the test tubes

 

F.  Turn in your data page before you check out.

 

G. As a post lab report, rewrite the balanced equation into
    net ionic form and submit when signing into Lab the
    following week.

 

 

 

 

Supplemental Online Single Replacement Reactions:

 

  1. View Online: http://www.lsua.us/chem1001/Chap8Movies/aabtpxx0.html

 

In this video, Sodium reacts with water (Sodium is an Active Metal).

The demonstration used an acid base indicator Bromothymol Blue to show DI water is yellow color when acid.

 

(Water is supposed to be neutral, neither acidic nor basic, but water has amounts of carbon dioxide dissolved which makes it mildly acidic.)

 

As the reaction proceeds the solution changes color to blue indicating that the solution is now basic. Record your observations and write the reaction in your data table.

 

 

The second part of this video shows the violent reaction of potassium with water. Again Bromothymol Blue indicator is present. Record your observations and write the reaction in your data table under supplemental reaction #5.

 

  1. View Online: http://www.lsua.us/chem1001/Chap8Movies/aabtpxv0.html

 

In this video, Zinc Reacts with Tin(II) Nitrate.

 

Record your observations and write the reaction in your data table under supplemental reaction #6.