Lab 4 Procedure

CHM 100 LAB 4 CHEMICAL BONDING

The three parts of the lab are:

  1. Classify chemical substances as ionic or molecular based upon electronegativity differences (using the EMD PTE periodic table iPad app)
  2. Identify metal ions based upon flame test.
  3. Combine ions to write the formulas of chemical compounds that are produced by mixings.

Safety for this lab:

  • Wear safety glasses at all times.
  • ALWAYS clean up your entire station and any spills made at shared stations.
  • DO NOT deposit broken glassware in trash, place into broken glassware container located near paper towels.

Part 1: Classify chemical substances as ionic or molecular based upon electronegativity differences.

01Determine whether the compounds on the data table are molecular (covalent) or ionic bonded based on the Pauling Electronegativity Numbers (look up on EMD PTE Periodic Table Mobile App on Android or iPad).

With each element in the bond, look up their electronegativity value and subtract the two numbers (larger number – smaller number).

The range is as follows:

If the electronegativity difference between the two numbers is:

4.0 <—->2.0 IONIC

2.0 <—-> 1.6 IONIC, if one element is metal

2.0 <—-> 1.6 MOLECULAR (COVALENT), if both elements are nonmetals

1.6 <—-> 0.0 MOLECULAR (COVALENT)

Part 2: Identify metal ions (and boron) based upon flame tests.

l03_07Setting up the Bunsen Burners, burn the five unknown metal ions.  Identify on the DATA.

On the data sheet list the following:

  • The flame color
  • The metal cation of the unknown sample
  • The nonmetal anion for each unknown sample
  • The chemical formula
  • The chemical name

Below is a list of the possible unknown metal cations and nonmetal anions (all the anions are the chloride ion):

 Metal Cation Nonmetal Anion flame color
Li+ Cl red
Na+ Cl strong persistent orange
K+ Cl lilac (purple)
Ba2+ Cl pale greenish yellow
Cu2+ Cl blue-green

 

Burning boric acid

l0401Using a disposable pipet, fill an evaporating dish no more than 1/4 full with ethanol.l0402

Using a disposable pipet, place drop by drop very small amounts of saturated calcium acetate.  Stir after each drop and allow a few seconds to check for gel forming.  When a gel forms stop the addition of the calcium acetate.

If needed, pour off excess liquid, leaving in the evaporating dish the gel substance.

Using a match, ignite the gel substance IN THE FUME HOOD!

While this is burning, test boric acid by sprinkling a small amount onto the ignited flame.  Record your observations on the DATA SHEET.

l0403Using crucible tongs, carefully place a watch glass over the evaporating dish to put out the flame.

Warning: Evaporating Dish and Watch Glass is extremely hot, allow to cool before cleaning.

 

Part 3: Combine ions to write the formulas of chemical compounds that are produced by the mixing.

l0404You will be using dropper amounts of the ionic compound solutions provided.

 

l0405Obtain a GLOSSY EXPERIMENT l0406PAGE for combining ions and the different solutions containing the ions.

According to the EXPERIMENT PAGE add a few drops of the solutions (ALL LIQUIDS SOLUTIONS FOR THIS PART) containing the ions into the correct square.

Using the iPad, take a photo of this EXPERIMENT PAGE with all the combined drops.

On the Data Sheet record the following in each box:

  • chemical formula of the new ionic solid compound created
  • chemical name of the new ionic solid compound created

 

EXAMPLE:

CuSO4

Cu2+

NaOH

OH

write the color: observe

write formula: Cu(OH)2

write name: copper (II) hydroxide

or cupric hydroxide

l0407 For clean up, use a paper towel and wipe off the EXPERIMENT PAGE.

FINAL STEP: CLEAN YOUR STATION 

Use the sinks and soap to wash your glassware. 

PUT AWAY ALL EQUIPMENT AND CHEMICALS AND WIPE DOWN YOUR STATION.

Do not leave the lab until the instructor has inspected your clean station.

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