Families of elements - experiment 7

Families of elements - experiment 7

E EM EL F 7 O T S N E E

I IL IM R M E FA XP E S

T N PERFORMANCE OBJECTIVES OBJECTIVES To study similar chemical properties for groups of elements in the periodic table.

To observe flame tests and reactions for barium, calcium, lithium, potassium, sodium, and strontium solutions. To observe halide tests for bromide, chloride, and iodide solutions. To identify the alkali or alkaline earth element and the halide in an unknown solution. DISCUSSION The elements in the periodic table are found in rows and columns.

Elements in horizontal rows are called periods. The elements in vertical columns are called groups, or families. In this experiment, we will study three families of elements a) Alkali metals b) alkaline earth metals c) halides

Identification will be based on reactions in the above families DISCUSSION Flame Test a) Observation of flame test and solutions reactions for selected alkali and alkaline earth elements. b) A flame test is performed by placing a small amount of solution on the end of a coiled wire.

DISCUSSION Colors are specific for each element. Yet flame tests can be misleading. Example is sodium is often present as an impurity giving most flame test a weak yellow flame. http://www.youtube.com/watch?v=NEUbBAGw14k EQUIPMENT 13 x 100 mm test tubes (6) and test tube rack

test brush flame-test wire (nichrome or platinum wire) CHEMICALS Ammonium carbonate solution 0.5 M (NH4)2CO3 Ammonium phosphate solution 0.5 M(NH4)3PO4 Ammonium sulfate solution 0.5 M (NH4)2SO4 Barium solution, 0.5 M BaCl2

Calcium solution, 0.5 M CaCl2 Lithium solution, 0.5 M LiCl Potassium solution, 0.5 M KCl Sodium solution, 0.5 M NaCl Strontium solution, 0.5 M SrCl2 CHEMICALS Bromide solution, 0.5 M NaBr Chloride solution, 0.5 M NaCl

Iodine solution, 0.1 M NaI Hexane, C6H14 Dilute nitric acid, 6 M HNO3 Chlorine water (bleach) Unknown solutions LAB PROCEDURE A. Analysis of Known Solutions 1. Flame Tests of Known Solutions

(a) Place six test tubes in a rack. Add 10 drops of barium, calcium, lithium, potassium, sodium, and strontium solutions into separate test tubes (Figure 2). LAB PROCEDURE (b) Obtain a flame-test wire and make a small loop in the end. Remove contamination by placing the wire loop at the tip of a burner flame. Continue to heat

the wire until there is no longer any color produced in the flame. Note: If a flame-test wire continues to produce a colored flame, dip the wire into dilute hydrochloric acid and heat the wire to red heat. LAB PROCEDURE Dip the clean wire into the test tube containing the barium solution. Place the loop

at the tip of the flame. Record your observation. Clean the wire and repeat the flame test for calcium, lithium, potassium, sodium, and strontium solutions. LAB PROCEDURE 2. Reactions of Known Solutions (a) Add a few drops of ammonium carbonate, (NH4)2CO3, solution in each test tube

that was used for the flame test. If a precipitate forms, record ppt in the Data Table. If there is no reaction, record NR. LAB PROCEDURE (b) Clean the test tubes and rinse with distilled water. Put 10 drops of the barium, calcium, lithium, potassium, sodium, strontium solutions into separate test tubes. Add a few drops of ammonium phosphate, (NH4)3PO4, solution in each

test tube. Record your observations in the Data Table. LAB PROCEDURE Clean the test tubes and put 10 drops of barium, calcium, lithium, potassium, sodium, and strontium solutions in separate test tube. Add a few drops of ammonium sulfate, (NH4)2SO4, in each test tube and record your observations.

LAB PROCEDURE 3. Halide Tests of Known Solutions (a) Place three test tubes in a test tube rack. Add 10 drops of the following in separate test tubes: bromide solution, chloride solution, iodide solution. (b) Add 10 drops of hexane, C6H14, 1 drop of nitric acid, HNO3, and a few drops of chlorine water to each test tube (Figure 3). Shake each test tube and observe the color of the upper hexane layer.

Note: Dispose of the hexane layer in a waste container for organic chemicals. LAB PROCEDURE B. Analysis of an Unknown Solution 1. Flame Test Record the unknown number or a solution assigned by the Instructor. Perform a flame test on the solution, and record your observation in the Data Table.

LAB PROCEDURE 2. Solution Reactions Put 10 drops of unknown solution into three test tubes. Add a few drops of ammonium carbonate, (NH4)2CO3, to the first test tube; a few drops of ammonium phosphate, (NH4)3PO4, to the second; and a few drops of ammonium sulfate, (NH4)2SO4, to the third. Record your observations in the Data Table. LAB PROCEDURE

3. Halide Test Put 10 drops of unknown solution into a test tube. Add 10 drops of hexane, C6H14, 1 drop of nitric acid, HNO3, and a few drops of chlorine water. Shake the test tube and record the color of the upper hexane layer. LAB PROCEDURE http://www.youtube.com/watch?v=NEUbBAGw14k

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