Experiment 13: Classifying Elements

Purpose

To determine the characteristics that can be used to divide the chemical elements into groups with similar properties.

Introduction

Physicalproperties

Brittle or malleable? Brittle substances break easily. Malleable substances bend, but don’t break.

Appearance: Observe the color. Is it shiny or dull?

Does the element conduct electricity?

Chemical properties: Does the element react with CuCl2? With acid?

In this experiment, you will run five different tests on solid samples of eight separate elements, each of which will be identified only by code letters, a-h. Three of the tests will involve physical properties, while the other two will illustrate chemical behavior. Tests will be carried out test tubes, except as otherwise indicated. Element h will be distributed by your teacher, since it is unsafe to handle directly. The other seven elements are quite safe, although reasonable precautions (such as washing your hands thoroughly before leaving the laboratory) should always be taken.

Due to difficulties in handling element h, your teacher will demonstrate the tests for brittleness and for conductivity during the pre-lab discussion. You will do the other tests on h yourself.

Prelaboratory Assignment

  • Write the Title, purpose,procedurein your lab notebook before class.
  • Write a table for the data section

Element / Malleable or Brittle? / Conducts? / Shiny or Dull? / Color or Other Characteristics

Answer the Prelaboratory Questions.
1. Consult the periodic table on the inside back cover of your text. Based on the elements you are familiar with, where are most of the metals found?
2. Look at the numbering system for the groups as explained in Chapter 3 of your textbook (p68). Do the “A” groups contain mostly metals or mostly nonmetals? Do the groups in the middle of the table, (transition elements) contain mostly metals or mostly nonmetals?
3. What basis did Mendeleev use to divide the elements into groups?

Materials

  • 8 Test tubes
  • Test tube rack
  • Tweezers
  • Conductivity tester
  • Distilled water wash bottle

Reagents = chemicals

  • 0.5 M HCl(aq)
  • 0.5 M CuCl2(aq)
  • Samples of elements a-h

Safety

1. Handle hydrochloric acid with care; it is corrosive to skin and clothing.

2. At least one of the solid element samples is toxic, and will stain skin and clothing. Avoid touching the samples; wash your hands thoroughly with soap and water before leaving the laboratory.

3. Safety goggles and a lab apron must be worn at all times in the laboratory.

Procedure

Part 1 Tests of Physical Properties

1.Get a sample of each element, a-g. Is it dull or shiny? Note the color.

2. Using tweezers, try bending each sample. Will it bend (is it malleable), or does it snap or crumble into pieces, showing brittleness? If you can’t get it to break, it is malleable. If it is already a powder, then it is probably brittle.

3. Test the electrical conductivity of your sample by touching the two wire ends of your conductivity tester to each sample. Decide if the bulb lights or not. Record your results in the Data Table.

Part 2 Tests of Chemical Properties.

4.Put a small amount of each element in a test tube in the test tube rack.Keep track of what element is in what test tube:

A / B / C / D
E / F / G / H

5.Add a small amount of acid (HCl) to the test tube with element a. Record any signs of a chemical reaction (heat, bubbles, color change…).Repeat for each element.

6.Using a wash bottle, clean each test tube and pour the waste in the waste bucket.

7. Repeat 5 and 6 with CuCl2.

Cleaning Up

1. Pour test tubes out into the waste bucket. Use the wash bottle to rinse them.

2. Wash them and all other equipment in the sink, using the test tube brush. Show equipment at your station to the teacher for full points.

3. Wash your hands thoroughly before leaving the laboratory.

Prelaboratory Assignment

  • Write the Title, purpose, procedure in your lab notebook before class.
  • Write a table for the data section

Element / Malleable or Brittle? / Conducts? / Shiny or Dull? / Color or Other Characteristics
  • Answer the Prelaboratory Questions.
    1. Consult the periodic table on the inside back cover of your text. Based on the elements you are familiar with, where are most of the metals found?
    2. Look at the numbering system for the groups as explained in Chapter 3 of your textbook (p68). Do the “A” groups contain mostly metals or mostly nonmetals? Do the groups in the middle of the table, (transition elements) contain mostly metals or mostly nonmetals?
    3. What basis did Mendeleev use to divide the elements into groups?
  • Make a table with these headings in your data section

Analysis and Conclusions

Answer in your laboratory notebook.

1. For each of the five tests of physical and chemical properties, group the eight elements according to their behavior on that particular test.

  • Malleable or brittle?
  • Shiny or dull?
  • Conducts?
  • Reacts with HCl(aq)?
  • Reacts with CuCl2?

2. Combine your five lists from Question 1 into two groups of elements such that all the members of a given group are alike in at least most of the properties tested. You may find that you have one or two elements that don’t clearly belong to either of your two categories because some properties fit one group, while other properties fit the second group better. If that happens, make them a third category.

3. Describe briefly the criteria you used to make your groupings. Identify any difficulties you encountered in deciding where to place each element.

4. Using the definitions for metals, nonmetals and metalloids from your textbook, and your groupings, try to identify each of the elements a through h as being a metal, a nonmetal, or a metalloid.