Date […]
Chemistry Lab
Identifying Chemical Elements by Flame Test
Introduction
Have you ever wondered why a candle flame is yellow? 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 are
excited to higher energy levels. When these excited electrons fall back to
lower energy levels, they release excess energy in packages of light
called photons, or light quanta. The color of the emitted light depends on
its energy. Blue light is more energetic (shorter wavelength) than red
light (longer wavelength), for example. When heated, each element emits
a characteristic pattern of light energies, which is useful for identifying
the element. The characteristic colors of light produced when substances
are heated in the flame of a gas burner are the basis of flame tests for
several elements.
Purpose Perform the flame tests to identify several metallic elements.
Material
Safety goggles, big beaker with water to extinguish Q-tips, 1 gas burner, paper towel
One cotton swab for each metallic salt, small beaker with distilled water, samples of metallic salts
Safety
 Wear your safety goggles. (All steps.), be careful when working with an open flame.
 Some metallic salts are poisonous; avoid skin contact and do not taste any of them.
 Place a 250 mL beaker filled with tap water to extinguish the flame on your cotton swab if necessary.
Procedure
1)Take only five clean cotton swabs at one time and keep them away from any contamination by
placing only these unused swabs on a clean paper towel.
2) Moisten one cotton swab in distilled water. Then dip the moistened swab into the first metallic
salt (e.g. lithium chloride, sodium chloride, strontium chloride. barium chloride, potassium
chloride, calcium chloride, or copper chloride, or corresponding nitrate salts).
3) Insert the swab, now containing a few metal salt crystals, into a burner flame. The water on the
swab will help prevent it from catching on fire. Observe the color of the flame and record it in
your data table. Close vial before you open the next, so no lids get switched (contamination).
4) Repeat steps 2) and 3) with a new, clean swab and the next metallic salt (and so on). To avoid
contamination, which will yield in misleading results, do not dip any used or dirty swabs into
the distilled water or a different metallic salt.
5) After you tested all known metallic salts, repeat the procedure of steps 2) and 3) with the three
unknowns. Each unknown metallic salt will be one of the previously tested salts.
Observations
Table : Flame Test Colors
Ion
sodium, Na+
potassium, K+
calcium, Ca2+
barium, Ba2+
strontium, Sr2+
lithium, Li+
copper, Cu2+
unknown A
UA
unknown B
UB
unknown C
UC
Flame Color
Interpretations and Conclusions
1. What were your unknown metal ions in UA, UB and UC? How do you know?
UA_______________________ UB______________________ UC___________________
Because […]
Answer is complete sentences:
2. In your opinion, which elements produced the most easily identified color? […]
3. In your opinion, which elements are least easily identified? […]
4. In your opinion, which element produces the most intense color? […]
5. Would flame tests be useful for detecting metal ions present in a mixture of metal ions? Explain the
problems that could occur. […]
6. When a glass rod is heated, a yellow (or light orange) flame is observed around the point of heating.
Looking at the colors of your metals you tested, what does this yellow flame indicate? Why is it observed
when glass in heated? […]
7. Why do you think metallic salts, like the ones you tested in this experiment, are used in fireworks?
[…]
8. Explain why an element produces a characteristic color in a flame (see introduction) […]
9. List the colors of the visible spectrum in the order of increasing energy. (ROYGBIV) […]
10. What color has the shortest wavelength? [… has the shortest wavelength.]
11. What color has the longest wavelength? ? [… has the shortest wavelength.]