Video Transcript
Which of the following terms best describes the color of the flame produced by rubidium salts? (A) Blue, (B) yellow, (C) violet red, (D) orange red, (E) blue green.
Rubidium is an alkali metal. It’s located in group one of the periodic table, which is found on the left-hand side. The alkali metals that we commonly encounter are lithium, sodium, potassium, rubidium, and cesium. These have the symbols Li, Na, K, Rb, and Cs, respectively. All of these metals produce colored flames in a flame test, but the color produced does depend upon the metal concerned. A flame test is a simple qualitative test used in chemistry to identify a metal from its emission spectrum. In this respect, a qualitative test just tells us which metal is present in a sample from the flame color produced. It doesn’t tell us how much of the metal is present in the sample.
If small samples of alkali metal salts are introduced into a hot Bunsen burner flame on a clean platinum or nichrome wire, then colored flames will be observed. In the case of lithium salts, a red or crimson flame is observed. If sodium salts are used, a very strong yellow-to-orange flame is observed. If potassium salts are used, a pink or lilac flame is seen. With rubidium salts, a red-to-violet flame is seen. Cesium salts produce a blue-to-violet flame.
Since this question only concerns the color produced by rubidium salts in a flame test, we’d expect to observe a red-to-violet flame. The best match for this description is violet red. So, to answer the question “Which of the following terms best describes the color of the flame produced by rubidium salts?,” violet red is the correct answer.
