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Double-Replacement Reactions

Ions of two compounds exchange places to form two new compounds

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Sandwich Reactions

Credit: rick
License: CC BY-NC 3.0

A Roast Beef Sandwich [Figure1]

Double Replacement Reactions

How does a double replacement reaction differ from a single replacement action?

Double replacement reactions follow the form AB + CD → AD + BC. These reactions are important and can be used to do things like neutralize acids or bases. For instance, an antacid neutralizes stomach acid.

2HCl + Ca(OH)2 → CaCl2 + 2H2O

Both of the products are neutral, and the acid has been neutralized.

Sometimes it can be easy to just switch the components around - after all, it’s easy on paper to write AB + CD → AC + BD.  Is this possible?  We can understand double replacement reactions with sandwiches.

You are given two sandwiches, one with Italian bread and roast beef, and one with Dutch crunch and turkey. You are supposed to give one sandwich to your brother and keep one for yourself. However, you like roast beef and Dutch crunch, and don’t like turkey and Italian bread. You decide to perform a double replacement reaction, and you go from:

Turkey on Dutch crunch + roast beef on Italian bread


Roast beef on Dutch crunch + turkey on Italian bread

Creative Applications

1. While maintaining the integrity of the sandwich, could you have created Italian/Dutch crunch + roast beef/turkey?

2. In a double replacement reaction, could the cations combine with one another, and the anions combine with one another?

3. How does a double replacement reaction different from single replacement reactions? What would a single replacement reaction look like in our example?

4. What is another example of a double replacement reaction, chemically or real world?

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Image Attributions

  1. [1]^ Credit: rick; License: CC BY-NC 3.0

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