Name:_______________________



Name:_______________________ Block:_____

Lab: Flame Tests for Metals

Instructions: You are going to complete a formal lab write-up for this lab. Lab reports are formal documents and should be typed. You will be given time in junior seminar to type your lab report. You should refer to your formal lab write-up rubric when writing your formal lab report.

Background: Have you ever wondered why a candle flame is yellow? Why are fireworks different colors? The characteristic yellow of a candle flame comes from the glow of burning carbon fragments. The carbon fragments are produced by the incomplete combustion reaction of the wick and candle wax. When elements, such as carbon, are heated to high temperatures, some of their electrons absorb energy and move to higher energy levels around the nucleus. When these excited electrons fall back to lower energy levels, they release excess energy in the form of light, which you can see. Since each atom has a unique arrangement of electrons, each gives a unique color. The color of the emitted light depends on its energy. Blue light is more energetic than red light, for example. When heated, each element emits a characteristic pattern of light energies, which is useful for identifying the element. In this experiment, you will perform the flame tests used to identify several metallic elements.

Materials (per lab group)

Safety goggles 8 small test tubes test-tube rack

Paper towel scoopulas 50-mL beaker

Cue tips gas burner

Potassium chloride, KCl calcium chloride CaCl2 strontium chloride (SrCl2)

Lithium chloride LiCl copper(II)nitrate Cu(NO3)2 sodium chloride (NaCl)

Barium chloride BaCl2 Beaker distilled H2O unknown salt

Safety

*In this lab, the solutions you will be using contain harmful materials. Avoid skin contact with these chemicals. Observe all precautions, especially the ones listed below.

← Wear your safety goggles

← Do NOT taste or touch any substances used

← Do not at any time touch the end of the cue tip after the flame test, it will be hot!

← Return and dispose of all materials in the appropriate waste bins.

Procedure

1. Obtain a beaker filled with water and cue tips from the front of the room.

2. Obtain a small sample of each of the metal salts from the front of the room.

3. Create a data table to record your observations. Dip the cue tip soaked in water into the sample of metal salt and heat the sample in the burner flame. Record the color of the flame into the data table you created. Dispose of cue tip into beaker at front of the room. Test the remaining samples, using a new cue tip each time. Record your observations for each metal into the data table.

4. Perform a flame test on your unknown salt. Record your observations.

5. Dispose of the unused portions of your samples as directed by your teacher.

Pre-lab Questions

1. Describe what happens to the electrons of an element when the element is heated to high temperatures.

2. What color of light is associated with the most energy? What color of light is associated with the least amount of energy?

3. Why should you wash your hands thoroughly at the conclusion of this experiment?

4. List 3 characteristics of metals, nonmetals, and metalloids.

Conclusions

1. Which elements produced the most easily identified colors?

2. Which elements are least easily identified? Explain.

3. Which element produces the most intense color?

4. Would flame tests be useful for detecting metal ions present in a mixture of metal ions? Explain.

5. The energy of colored light increases in the order red, orange, yellow, green, blue, violet. List the metallic elements used in the flame tests in increasing order of the energy of the light emitted.

6. Based on your observations, identify the unknown metal salt that you were given. How were you able to identify this particular metal?

7. Which of the following pairs of compounds would give the same flame test? Explain.

a) NiCl2 and CaCl2

b) CaCl2 and Ca(NO3)2

c) ZnCO3 and FeCl3

d) CaCl2 and CH2Cl

8. What are possible sources of error in this experiment?

Barium: light green

Calcium: brick red

Copper: blue/green

Lead: blue/white

Potassium: lilac

Sodium: bright orange

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