Student Worksheet for the Demonstration
Dancing Flames

Aluminum.with.Oxide.Layer (189K)
Aluminum is very reactive and when exposed to air is quickly coated with a hard, nearly impervious layer of aluminum oxide (Al2O3).

Aluminum is one of the more active metals in the activity series. It is so active that it can replace hydrogen in water. And yet, we never see aluminum dissolve in water. The reason is that the surface of aluminum is coated with a thin layer of aluminum oxide which protects the metal from contacting air or water. This oxide is very unreactive and even protects aluminum from dissolving in some acids. However, in the presence of certain ions, such as the chloride ion (Cl), aluminum will suddenly react vigorously with water and the ions of less active metals.

In this demonstration aluminum foil is submerged in a mixture of hydrochloric acid (HCl) and copper(II) chloride (CuCl2) solution. A 20 cm by 5 cm piece of aluminum foil is pushed into a 250 mL flask containing 50 mL of 1 M hydrochloric acid and 3.5 g of copper(II) chloride dihydrate (CuCl2·2H2O). To demonstrate the presence of one of the chemical products, a flame is brought to the mouth of the flask. The demonstration is best enjoyed in a darkened room.


Questions
  1. In this demonstration one chemical reaction that occurs involves aluminum (Al) and copper(II) chloride (CuCl2). Predict the products of this reaction and write a balanced chemical equation.
  2. What physical evidence do you have for the reaction between Al and CuCl2? Describe the observations that show this reaction is taking place. Note that solutions of copper ions are blue but many other ionic compounds make colorless solutions.
  3. There is another chemical reaction occuring in this demonstration. Predict the products of the reaction between hydrochloric acid (HCl) and aluminum and write a balanced chemical equation.
  4. What observations of the demonstration support the fact that the reaction between Al and HCl has taken place?
  5. Once the protective layer of aluminum oxide is broken down the aluminum is free to react directly with the water. Write and balance a chemical equation describing this reaction.
  6. The amount of copper(II) chloride dihydrate (CuCl2·2H2O) used in this demonstration is 3.5 g. If the aluminum was only reacting with copper(II) chloride (and not the hydrochloric acid) then how many grams of aluminum are consumed by reacting with all of the copper(II) chloride?
    Also, how many grams of copper form?
  7. All of the hydrochloric acid present in the flask is used up and some aluminum remains at the end of the demonstration. What is the limiting reactant for this reaction?
  8. The hydrochloric acid solution has a concentration of 1.0 M (1.0 moles per liter). A volume of 50 mL of the solution is used in the demonstration. How many grams of hydrogen gas are formed when this amount of acid reacts with aluminum?

Given the data in the questions, 0.369 g of aluminum are consumed by reaction with the 3.5 g of copper(II) chloride dihydrate; 1.305 g of copper form, and 0.050 g of hydrogen form.

This demonstration is based on a demonstration by by Declan Fleming, published on the Royal Society of Chemistry (RSC) web site. In case you missed the classroom demonstration there is a video which you can watch at the RSC site: https://eic.rsc.org/exhibition-chemistry/dancing-flames/2000045.article.

Last Updated: Oct 01, 2019
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