Question

A solution contains cobalt(II) chloride. Identify three metals that could be placed in the solution to cause the cobalt to be plated out as a metal.

Short answer

Three metals that could be placed in the solution to cause the cobalt to be plated out as a metal are Magnesium (Mg), Aluminium (Al), and Zinc (Zn).

Step-by-step solution

Understand Reactivity Series

The reactivity series arranges metals from most to least reactive. In general, metals towards the top of the series can displace those below them from their salt solutions. However, this also means they are more likely to corrode or dissolve themselves.

Identify the Position of Cobalt in Reactivity Series

Cobalt is a moderately reactive metal. In the reactivity series, it is positioned below metals like potassium (K), sodium (Na), lithium (Li), calcium (Ca), magnesium (Mg), aluminium (Al), and zinc (Zn). This means any of these metals can displace cobalt from its salt solution.

Select Three Metals that are More Reactive than Cobalt

From the list of metals that are more reactive than cobalt, you can choose any three. An example selection could be Magnesium, Aluminium, and Zinc. Any of these metals placed in the cobalt chloride solution would cause cobalt metal to be plated out.

Key concepts

Metal Displacement

Metal displacement is a fascinating process explored through the reactivity series. This tool helps us understand which metals can replace others in compounds. The crux of metal displacement is that a more reactive metal will replace a less reactive metal in a solution of its salt.

The reactivity series is like a league table for metals. Typically, the more reactive a metal, the higher its position in the series. Metals at the top are powerful displacers, though they can also be more prone to corrosive behavior. For our purpose, magnesium (Mg), aluminum (Al), and zinc (Zn) are the stars. They are all more reactive than cobalt, enabling them to displace cobalt from its compound in solution.

In practical terms, as you add a more reactive metal into a solution containing cobalt ions, say cobalt(II) chloride, the stronger metal takes the place of cobalt. This leads to cobalt ions converting back into solid cobalt metal. The removed cobalt ions become visible as they deposit on the surface of the added metal, demonstrating a cool and clear chemical reaction.

Cobalt(II) Chloride

Cobalt(II) chloride is an interesting and vibrant chemical compound. Usually found in either its anhydrous form or hydrated form, the compound takes on different colors—starting pale blue when anhydrous and turning pink when hydrated. This color transformation is neat, often used to indicate moisture presence.

Chemically, cobalt(II) chloride consists of cobalt and chloride ions, with a chemical formula of \(\text{CoCl}_2\). In its aqueous form, these ions are free to move, making it a perfect participant in displacement reactions. When a more reactive metal enters the solution, cobalt ions get replaced as the metal ions move in.

Monitoring these reactions visually offers substantial learning. When magnesium, aluminum, or zinc is introduced to an aqueous cobalt(II) chloride solution, cobalt metal begins forming on the metal, leaving you with both a practical demonstration and a deeper understanding of metal displacement.

Plating Reactions

Plating, or electrodeposition, is a process where metal ions in a solution deposit onto a conductive surface. It's a common occurrence in electrochemistry, playing a vital role not only in science experiments but also in industrial applications like coating jewelry or circuit boards.

In a displacement-based plating reaction, like when placing magnesium into cobalt(II) chloride, the magnesium is more reactive and replaces the cobalt ions. These ions settle and plate onto the magnesium surface as a thin layer of metallic cobalt.

When trying such experiments, you observe firsthand the transformation as cobalt gets reduced and deposits. This not only enriches how reactions are perceived but illustrates distinct chemical principles. Seeing metal transform and deposit with your own eyes makes chemical concepts more tangible and exciting. The visibility of the process makes understanding these chemical changes less abstract and more approachable for learners.