Double Replacement Reactions

Double Replacement Reaction

Background Information:

What Is a Double Replacement Reaction?

Imagine going to a dance and having a dance partner. Once you arrive to the dance, you interact with other people and you end up switching dance partners with another person. Now you end up with a new dance partner. The same kind of thing can be compared to what occurs in a double replacement reaction in chemistry.

A double replacement reaction is a type of chemical reaction where two compounds react, and the positive metal ions and the negative nonmetal ions of the two reactants switch places, forming two new compounds or products.

Double replacement reactions take the form:

A⁺B^- + C⁺D^- → A⁺D^- + C⁺B^-

Prelab Questions:

1.    What happens in a Double Replacement Reaction?  Write in your own words.

2.    When you mix chemicals together, how do you know that a chemical reaction has occurred? (Evidence of a chemical reaction.)

Reaction #1:

Procedures:

1.    Goggles On!  No Lab Stools.  Do not sit on lab tables.

2.    Get a test tube of Sodium carbonate solution and a test tube of Calcium chloride solution.  Record their physical properties on the data table.

3.    Pour the two chemicals into a clean beaker.  Stir with a glass stir stick or plastic spoon.

4.    Record what happens on your data table.  What proof of a chemical reaction do you see?

5.    Clean up:  Return test tubes to Mrs. Jenner.  Clean out beaker and clean stir stick or spoon.

6.    Answer questions

Data:

Physical Properties of Sodium carbonate
Physical Properties of Calcium chloride
Proof of a Chemical Reaction

Conclusion Questions:

1.    Optional:  Balance the chemical equation for this reaction.

Na₂CO₃    +   CaCl₂  ----------à     CaCO₃         +      NaCl

2.    Look at the two products of this reaction.  Sodium chloride is table salt.  Calcium carbonate is chalk.  What can you see forming in this reaction, table salt or chalk?  How do you know?  Use specific evidence from the lab.

3.    How is this reaction an example of a Double Replacement Reaction?  Be specific about reactants and products.

Reaction #2:

Procedures:

1.    Get a test tube of Copper sulfate and a beaker of Ammonia.  Record the physical properties of both. 

2.    Use a dropper to put drops of Ammonia into the Copper sulfate.  Record what happens with the first drops and what happens as you add more Ammonia.

3.    Clean up:  Return Ammonia beaker to the tray. DO NOT CLEAN.

                   Rinse out the Copper sulfate test tube very well.  Return to Mrs. Jenner.

Data:

Physical properties of Copper sulfate solution
Physical properties of Ammonia
Reaction adding small amount of Ammonia
Reaction adding lots of Ammonia

1.    Optional:  Balance the chemical equation for this reaction:

CuSO₄    +        NH₄OH     ------------à       Cu(OH)₂     +          (NH₄)₂SO₄

2.    What evidence do you have that a chemical reaction occurred? 

Name  _________________________________________

Decomposition Reaction:

Also Known As Elephant Toothpaste

Purpose:  To observe a decomposition reaction.  A decomposition reaction occurs when one compound breaks down into two or more molecules or elements.

AB --------à A + B

We are also using a catalyst in this reaction to encourage the reaction to happen quickly.  The reaction will happen slowly but it’s more fun for this reaction if it happens quickly.  We are using Potassium iodide and/or Manganese dioxide as catalysts in this reaction.  They DO NOT bond to any of the reactants.  They exit the reaction exactly the same so we do not write them into the reaction equation.

Procedure:

1.     Put on goggles. 

2.     Get one test tube with a small amount of  Potassium iodide (KI).

3.     Obtain a graduated cylinder with  15 ml of concentrated Hydrogen peroxide and soap.

BE CAREFUL WITH HYDROGEN PEROXIDE!  IT CAN CAUSE BURNS AT THIS CONCENTRATION!

4.  All together we are going to drop the Hydrogen peroxide INTO the Potassium iodide.  Watch and record the results.

THIS REACTION IS HIGHLY EXOTHERMIC!!!  DO NOT TOUCH THE ELEPHANT TOOTHPASTE!  IT WILL TAKE UP TO 5 MINUTES TO COOL ENOUGH TO MOVE.

5.     Wait until Mrs. Jenner says you can clean up your lab.  The contents of the test tube will not hurt you (it’s mostly water with soap). The temperature is a safety concern.

6.     Clean up by bringing the test tube, test tube rack and tray up to the front of the class.  Give Mrs. Jenner the rack and test tube.  Take the tray to clean and dry.

7.     If everything is cleaned up in time, Mrs. Jenner will do a large elephant toothpaste for the class.

Conclusions:

1.     This is the equation for the decomposition of Hydrogen peroxide.  Potassium iodide (or Manganese dioxide) is a catalyst and it is not involved with the chemical reaction.  This is not balanced.  As a challenge, see if you can balance the equation.

H₂O₂    ------à        O₂    +      H₂O

  

2.     Describe what happened when Hydrogen peroxide decomposed into water and oxygen (what did the reaction look like).

3.     Why is the catalyst important in this reaction?

4.     Why is this a decomposition reaction?

5.     Why did we add soap?  (Hint:  The reaction makes oxygen gas.  Why is having soap fun when a gas is produced?)

Elephant Toothpaste Reaction Video - Decomposition Reaction

Copper sulfate and Iron Reaction - Single Replacement Reaction

Name  ______________________________

Date    _________

Single Replacement Reaction

Purpose: 

To observe a single replacement reaction and balance the equation for the reaction.

Background:

A single replacement reaction occurs when a pure substance replaces another element in a compound.  One element kicks another element out.

                             A   +     BC   --------à     AC   +    B

There is one thing ALONE on both sides of the equation.

Procedures:

1.    Pour Copper II sulfate solution about 2/3 full in a test tube.

2.    Unbend one side of an IRON paperclip so that there is a “hook” in the paperclip.

3.    Hang the paperclip over the edge of the test tube so that the long end of the paperclip is in the CuSO₄ solution. 

4.    Observe what is happening to the paperclip.

5.    Follow clean-up directions and answer questions.

Conclusions:

1.    The formula for the reaction is below.  Is the equation balanced?  If not, balance it.

        Fe    +    CuSO₄  ----------à   Fe₂(SO₄)₃    +   Cu

           

2.    Why is this reaction considered a single replacement reaction? Compare the definition to the actual chemical reaction.

3.    Describe the reaction.  The Iron (Fe)  and the Copper (Cu)  switch

places in the reaction.  Did you see this?  Explain.

4.    Why do Iron and Copper switch places?  (Hint:  Why do chemical reactions occur?  Why do we fill party balloons with Helium and not Hydrogen?)

5.    In chemical reactions, compounds and elements rearrange to form new chemicals and compounds with new properties.  Is this true of the reaction you viewed today?  Explain.

Notes for Test on Friday

Click HERE for notes.