C-1.2, C-1.5-6, C-1.8, C2.2-3
Following completion of this lesson, students will be able to:
C-1.2 Use appropriate laboratory apparatuses, technology, and techniques safely and accurately when conducting a scientific investigation.
C-1.5 Organize and interpret the data from a controlled scientific investigation by using mathematics (including formulas, scientific notation, and dimensional analysis), graphs, models, and/or technology.
C-1.6 Evaluate the results of a scientific investigation in terms of whether they verify or refute the hypothesis and what the possible sources of error are.
C-1.8Use appropriate safety procedures when conducting investigations.
C-2.2Summarize atomic properties (including electron configuration, ionization energy, electron affinity, atomic size, and ionic size).
C-2.3 Summarize the periodic table’s property trends (including electron configuration, ionization energy, electron affinity, atomic size, ionic size, and reactivity).
1. Concept Exploration (~10 min)
Begin by having the students gather around a Bunsen burner. Ask the students to carefully watch and mentally record there observations. Start by taking a pair of tongs and hold them over the blue cone in the flame. They should heat up and glow red, and produce a typical orange flame. Explain to the students that a blue flame is hotter than a orange flame, which is why it changed color. Now repeat this with a pre-1982 penny (it must be pre 1982 otherwise the copper will not show the green flame). The penny will also turn red hot, but will produce a green flame. Ask the student to hypothesize why this happened.
2. Concept Introduction (~20 min)
This lab should be started after an explaination of the atomic emission spectra. The atomic emission spectrum is characteristic of the element being examined and can be used to identify an element. The fact that only certain colors appear in the elements atomic emission spectrum means that only specific frequencies of light are emitted. Because those emitted frequencies are related to energy by the formula Ephoton = hv, only photons with specific energies are emitted. In this way unknown compounds can sometimes be identified by the color flame they produce. Include in
your discussion the atomic properties of the chloride elements involved in the lab, and how they represent trends in the periodic table.
Concept Application (30 min)
6, 50-mL beakers
(Note: these solutions can be made from a solid anhydrous compound, just crush and saturate in water)
Place 1-2 cm of each chloride solution into a 50mL beaker, labeling each. The 6 th
beaker will contain the ‘unknown’ which can be any solution. Divide students into lab groups
Have students dip one of six cotton swabs into the lithium chloride solution. Put the swab into the flame of a Bunsen burner. Observe the color of the flame and record it in your data table.
Repeat step 2 for each of the metallic chloride solutions: sodium chloride, potassium chloride, calcium chloride, and strontium chloride. Record the color of each flame in your data table.
Repeat step 2 using a sample of unknown solution obtained from your instructor.
Record the color of the flame produced.
Flame Test Data Sheet
Answer the following questions in complete sentences:
1. Suggest a reason why each compound produced a flame of a different dolor even though they all contain chlorine
2. Explain how an elements flame test might be related to its atomic emission spectrum
3. Infer the identity of the unknown and explain your reasoning