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Double Replacement Reactions (Khuong Mai)

Title:

Formula Writing and Chemical Naming via Double Replacements Reactions


Principle(s) Investigated: List all principles that apply to this activity.

1. Chemical reactions

2. Double Replacement Reaction (one of the five types of chemical reactions: synthesis, combustion, decomposition, single replacement, double replacement)

3. Evidence of chemical reactions (gas, odor, color, precipitation, heat exchange)

4· Writing and balancing chemical formula

5· Naming ionic compounds

6· Calculation of molecular mass


Standards: Paste in the appropriate California content standards.

1. Atomic and Molecular Structure

a. Students know how to relate the position of an element in the periodic table to its atomic number and atomic mass.

b. Students know how to use the periodic table to identify metals, semimetals, nonmetals, and halogens.

c. Students know how to use the periodic table to identify 1a, 2a, transition metals, ionization energy, electronegativities, and sizes of ions atoms.

d. Students know how to use the periodic table to determine the number of electrons available for bonding.

2. Chemical Bonds

a. Students know atoms combine to form molecules via covalent, ionic, or metallic bonds.

c. Students know salt crystals, such as NaCl, are repeating patterns of (+) & (-) ions held together by electrostatic attraction.
3. Conservation of Matter and Stoichiometry

a. Students know how to describe chemical reactions by writing balanced equations

c. Students know how to calculate the masses of reactants and products in a chemical reaction.

Materials: Include a list of materials and sources from which they may be obtained.

1. Holder tray with wells or beakers (for holding pipettes)

2. Eight 2-mL plastic pipettes (for each group of four)

3. One 250-mL beaker for waste disposal

4. Work sheet covered with a clear plastic sheet (for the 16 reactions)

5. Procedure hand-out

6. Anion solutions:

#1: Sodium Chloride, 10%, 100 mL
#2: Sodium oxalate, 10%, 100 mL
#3: Sodium carbonate, 10%, 100mL
#4: Sodium Hydroxide, 5%, 100 mL·        
7. Cation solutions:
#A: Silver nitrate, 2%, 100 mL
#B: Cobalt (II) sulfate, 5%, 100 mL
#C: Potassium ferricyanide, 5%, 100 mL
#D: Copper (II) sulfate, 5%, 100 mL

 

Procedure: Give a detailed explanation of the procedure and include diagrams if possible.

 

Part 1: Experimental: Double Replacement Reactions

Students will perform a series of 16 reactions on a plastic covered work sheet as seen below.

 

 

 

1

2

3

4

 

 

Cl-

(Chloride)

C2O42-

(Oxalate)

CO32-

(Carbonate)

OH-

(Hydroxide)

A

Ag+

1

2

3

4

B

Co2+

5

6

7

8

C

Fe3+

9

10

11

12

D

Cu2+

13

14

15

16

 

1. Pipette about 1 mL of each solution. Separate the anions and the cations in two separate holders.

Be careful not to mix up the order of the pipettes.

2. Add two drops of each of the anion solutions on the work sheet (above). Hint: It’s best to add in series.

For example, add the Cl- solution to boxes 1, 5, 9, &13.

3. Add two drops of each of the cation solutions on top of the anions.

4. Observe and record for sign of reactions (or none thereof) as color change and/or precipitation. 

5. Discard any residual from the pipettes to the waste-labeled beaker.

6. Return pipettes to holder.

                       

Part 2: Analysis of data – Writing and naming chemical formulas

1. Identify the cation and the anion that react together, and the precipitated product

2. Write the balanced chemical formula of the product (precipitate)

3. Calculate the molecular mass of the product

4. Figure out the formal name of the product  

 

An example is provided below: AgNO3 + NaCl --> AgCl + NaNO3

 

Rx #

Cation

Anion

Formula

M. Mass

Compound Name

Box #1

Ag+

Cl-

AgCl

133.32

Silver Chloride

…..

…..

…..

…..

…..

…..

 


Student prior knowledge: What prior concepts do students need to understand this activity?
Students must know what an ion is and that the ions are charged atoms, which may be either positive or negative. Furthermore they should be able to identify the number of charges by referring the atoms to the periodic table or the data sheet (for polyatomic ions).

 


Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent. 

 

Part 1: Experimental: Double Replacement Reactions:

1. Teacher: will explain the procedure and demonstrate a representative reaction (AgNO3 + NaCl --> AgCl + NaNO3) in box #1 using an overhead projector and a plastic-covered work sheet as shown above. In this reaction AgCl separates as a white precipitate and the name of the product is Silver Chloride.


Explanation: The ions that will be reacted together to form a precipitate will come from the dissociation of different compounds in an aqueous solution. For example:   

Solution #1:      NaCl(s)        -->     Na+(aq)   +   Cl-(aq)
Solution #A:     AgNO3(s)     -->     Ag+(aq)   +   NO3-(aq

Reaction:     AgNO3  +  NaCl   -->   AgCl   +  NaNO3

     Soln 1  +  Soln A  -->  White precipitate of AgCl


2. Students: will perform a series of 16 reactions on a plastic-covered sheet and record their observation on a data sheet.

 


Part 2: Analysis of data – Writing and naming chemical formulas

Students will analyze data, then write the formula of the products, and name them accordingly. To be able to analyze the data, the students were taught with the background information below.


Background: A chemical formula is a combination of symbols and numerical subscripts that represents the composition of a compound. The symbols indicate which elements are present and the numerical subscripts indicate the relative proportion of each element in the compound. These proportions can be predicted using the oxidation number or charges of the elements. When the atoms acquire a charge they are called ions.

It is important that all scientists use the same system for writing chemical formulas. This helps to ensure clear and consistent transmission of information. Therefore, the following rules should be used for writing chemical formulas:

1. In neutral compounds the sum of the charges of the elements (ions) must equal zero. One positive (+) will neutralize one negative (-) charge.

2. Elements (ions) with positive charges are written first.

3. When the relative proportions of the polyatomic ion in a ternary compound is greater than one, the symbol for that ion must be enclosed in parenthesis and then followed by a numeral subscript indicating its relative proportion, as in the ternary compound of aluminum sulfate whose formula would be Al2(SO4)3.

 

 

Questions & Answers: Give three thought-provoking questions and provide detailed answers.

Q1. What is a chemical formula?

A1: An expression revealing the number of atoms that constitute a particular chemical compound. 

 

Q2. What information does a subscript in a chemical formula provide?

A2: The subscript indicates the number of the preceding atoms present in the chemical symbol

 

Q3. When is parenthesis to be used in writing a chemical formula?

A3: Parenthesis is used when a subscript is required in the case of a polyatomic ion.

 

Q4. When is a roman numeral to be used in the name of a compound?

A4: A roman numeral is used in naming transition metal salts to indicate its oxidation state (charge). There are three exceptions: Ag+, Zn2+, and Sc3+, however. The roman numeral is not applicable because these three metals have each only one oxidation state (Ag+, Zn2+, and Sc3+).

 

Q5. It appears as if all transition metals have a roman numerals in their name (Copper (I) Chloride for CuCl). But why is the Silver Chloride (AgCl) does not a roman numeral? 

A5: As explained in A4, Ag, though listed as one of the transition metal, has only one oxidation number. The ion is listed as Ag+.

 

Q6. What is the meaning of “transition” in transition metals?

A6: To indicate multiple (transient) oxidation states of the metals.

 

 

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

 

1. Rust is actually Iron (III) Oxide or Fe2O3.

2. The tough stain found in bathroom floor or sink is actually Iron (III) Carbonate (box #11). Heavy metals react with carbonic acid in water to give trace of carbonates, which precipitate and build up with time.

3. The black taint on silverware is actually Silver Oxide or Ag2O. In one of the above reactions (box #4), the initial product was silver hydroxide (white), which decomposes instantaneously to black silver oxide.  

 

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

 

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made. 

 

 

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Khuong Mai,
Sep 29, 2011, 11:33 AM
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Sep 29, 2011, 9:52 AM
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Khuong Mai,
Sep 29, 2011, 9:52 AM
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Sep 29, 2011, 1:14 PM
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Sep 29, 2011, 9:43 AM
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