| GOALS: In this laboratory you will observe the physical and chemical properties of several elements. By the end of the laboratory you should know characteristic properties of some families of elements and be able to distinguish between the properties of a metal and a nonmetal. |
| INTRODUCTION: The elements are the most basic materials found on earth. Each element is made up of only one type of atom and this does not change during a chemical reaction. The periodic table contains all of the elements and organizes them into columns and rows. The rows in the periodic table are also known as periods and as you go across a period from left to right the number of protons and electrons increases for the atoms of each succeeding element. Also very important are the columns in the periodic table, also known as groups or families. The chemical and physical properties of an element are usually similar to other members of its family. The periodic table was originally organized around the similarities of groups before anything was known about the details of atomic structure. In this laboratory you will explore the properties of some of the groups in the periodic table. |
Instructions
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For each of the elements in this experiment
record as many observations of the following properties as you can.
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| 1) Physical state - Is the element a solid, liquid or gas? |
| 2) Appearance, Luster, Color - Is the element
shiny or dull? Does the element have a distinctive
color? |
| 3) Hardness, Malleability - For solid elements
are they soft or hard? Are they brittle or pliable
when pressed with a spatula? |
| 4) Electrical conductivity (maybe) - Use a conductivity tester to determine if the element conducts. |
| 5) In your conclusions, group together elements
with similar physical properties and discuss their
relative position on the periodic table. Can you develop a list of properties that are characteristic of elements in a particular area of the table? |
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These tests will use elements that are representative of the main groups in the periodic table. Keep in mind that chemical reactivity can vary widely up and down a group. However, you will not be able to test the properties of more than one or two elements of each group due to cost, toxicity and radioactivity. In general these reactions should be carried out IN THE HOOD WITH THE SASH DOWN. |
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| Reactivity with air: If you look at the bottles of sodium and potassium in the hood, you will notice that they are stored under a liquid, mineral oil. The reason for this is that these elements react with oxygen in the air. Observe this reaction by first cleaning off a pea sized piece of sodium IN THE HOOD using a dry paper towel. Do not touch the metals with your fingers. Then cut the sodium with a spatula and watch the freshly cut surface. Record observations in your notebook. |
| Reactivity with water: IN THE HOOD, clean off a BB sized piece of sodium with dry paper towel. Drop the sodium in a half full beaker of water and record your observations. Test the reacted water with litmus paper (red means acidic, blue means basic). Repeat the procedure with a BB sized piece of potassium. USE A SAMPLE OF POTASSIUM WHICH IS ONE QUARTER TO ONE THIRD THE SIZE OF THE SODIUM. Explain in your conclusions why this group is called the alkali metals. What would you predict to happen with cesium? Does reactivity with water increase or decrease as you go down this group? |
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| Reactivity with air: Clean off a short piece (about 1 inch) of magnesium ribbon using sandpaper. Watch the freshly cleaned surface and record in your notebook any observations. IN THE HOOD, light a Bunsen burner. Without looking directly at the burner, use tongs to hold the magnesium ribbon in the flame. Write down what you observe. This is the reaction of magnesium with oxygen in the air. |
| Reactivity with water: IN THE HOOD, repeat the water reactivity test with magnesium and calcium. Record your observations. Does reactivity of this group with water increase decrease as you go down the periodic table? Are alkali earth metals more or less reactive than alkali metals in the same row? |
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| Repeat the air and water reactivity tests with a small piece of aluminum. Is there a trend in air and water reactivity as you go across a row in the table? Predict the reactivity of Gallium with air and water based on the trends you've observed. |
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| Reactivity with air: Before you begin, put about one inch of water in a wide mouth bottle and cover it with a watch glass. Put a pea sized piece of phosphorus in a long handled metal spoon and IN THE HOOD heat the phosphorus using a Bunsen burner until it ignites. Trap some of the smoke in the wide mouth bottle of water and put the watch glass back on top. When the phosphorus has burnt out, gently shake the bottle of smoke to dissolve it in the water. Then test the water using litmus paper. Record all of your observations in your notebook. |
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| Reactivity with air: Repeat the ignition experiment you just performed on phosphorus with sulfur. Be sure to keep everything IN THE HOOD and use a fresh spoon and bottle of water. |
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| In this part of the laboratory you will be mixing each halogens with solutions of the potassium halide salts KCI, KBr and KI to determine which halogen is most reactive. You will know a reaction is occurring when the color of the final solution is different than the color of either starting solution. In pure form chlorine (Cl2) is a toxic pale green gas bromine (Br2) is a dangerous red liquid and iodine (I2) is a purple solid. You will be working with the halogens dissolved in water to make chlorine water, bromine water and iodine water. In solution the halogens are much less dangerous. |
| Begin by mixing several milliliters of chlorine water with several milliliters of KCI solution. Do you see a color change? Do you think a reaction occurred? Repeat this procedure with chlorine water and KBr solution. Any color change? Any reaction? Repeat the procedure with chlorine water and KI and answer the same questions. How many reactions did you observe with chlorine water? |
| Repeat the procedure and observations with bromine water + KCI, bromine water + KBr, and bromine water + KI. How many reactions did you notice? |
| Repeat the procedure again with iodine water + KCI, iodine water + KBr and iodine water + KI. How many reactions did you notice. Which halogen is most reactive? least reactive? What is the trend in reactivity as you go down the periodic table? Is this the same or different than the trend for the alkali metals? Discuss all of these questions. in your conclusions. |
1) What does alkali mean?
2) Who first proposed a periodic table of the elements?
3) What is the difference between a physical property and a chemical property?
4) How many groups are shown in the periodic table?
5) What are the atomic symbols of sodium, potassium,
magnesium, calcium, aluminum, gallium, phosphorus, sulfur, chlorine, bromine
and iodine?