<!--<!-- The Rubber Chicken

 

Concepts

            Structural proteins

            Ions in the body

            Scientific Method

 

Overview

            One function of proteins is maintaining cell and organ structure, as in bone.  In this inquiry-based activity, students observe that a chicken leg bone that has been stored in vinegar is soft and rubbery.  During discussion of their observations they learn that much of bone is a matrix or meshwork of structural proteins that holds salt crystals.  They learn that a mild acid, vinegar, is sufficient to dissolve these salts, and the protein left maintains the bone’s shape but not its rigidity.  The students are led to ask, “What ions made up the salt crystals that gave the bone its strength?”  and perform experiments to answer this question.

 

Safety

Flame test: Students must wear goggles during this activity.  Loose hair must be tied back..  

 

Materials

<!--Jar containing chicken bone and enough vinegar to cover the bone (if using a leg bone, prepare this a week before the experiment; wing and other thin bones will need a few days)

<!--Portable bunsen burners

<!--Nichrome loops

<!--Small screw-cap bottles of concentrated hydrochloric acid and three 0.5 M solutions, each containing one of the following (anion identity doesn’t matter): calcium, potassium, and lithium

<!--Small (25- 100 mL) beaker

<!--Test tubes and test tube racks

<!--Labels for test tubes, markers

<!--Dropper bottles containing the following solutions: 0.5 M ammonium oxalate, magnesia mix (see recipe), vinegar, 0.5 M potassium phosphate (pH to mild acidity), 0.5 M copper sulfate (or nitrate),     0.5 M calcium nitrate, 0.5 M potassium nitrate

 

Methods

Introduction

<!--Pass around the chicken bones for the students to twist and bend.

 

Flame test 

<!--Turn on the portable Bunsen burner by turning the red knob on the top of the burner counterclockwise 2/3 of the way around (listen for a hissing sound) then pressing the red knob on the side of the burner.   

 

<!--Demonstrate dipping a nichrome loop into one of the ion solutions and holding it in the flame to see its characteristic color.

<!--Students can take turns seeing the color produced by each solution (be sure that each nichrome loop is dipped into only one type of solution) and noting their observations on the handout.  Flame colors: calcium- orange;  potassium- violet;  lithium- crimson

<!--Pour some of the vinegar from the jar containing the bone into a small beaker.  Once the students have tested all of the known solutions, they can test this solution to determine the identity of one of the “bone salt” ions (calcium, which will yield an orange flame). 

<!--After the students have finished, clean the loops by dipping them into hydrochloric acid and flaming them.

 

Precipitate test

<!--Divide the students into groups and give each group a set of ten test tubes in a rack. Demonstrate labeling one of the tubes with what solution is being tested and whether oxalate or magnesia mix is being added.  Allow the students to label the rest of the tubes, one for each condition in the table in the handout.

<!--Pour some of the vinegar from the jar containing the bone into pre-labeled dropper bottles.  Add about 1 mL of water to a test tube to show how much of each test solution students should add to their tubes.  Direct the students to add the test solutions to their tubes and test for precipitates by adding 10-15 drops ammonium oxalate or magnesia mix.  Instruct them to note in their handouts whether a precipitate forms and what color the precipitate is.

<!--Encourage the students to identify the ions (calcium and phosphate) that make up the “bone salt” based on their observations of the known solutions.

<!--Discard solutions from test tubes and reserve the tubes for reuse.

 

Expected results:

 

solution

Result after adding

oxalate

Result after adding

 magnesia mix

plain vinegar

(negative control)

-

-

vinegar containing

bone salts

White ppt

White ppt

potassium phosphate:

K3PO4

-

White ppt

copper sulfate:

CuSO4

Light blue ppt

Light blue ppt

calcium nitrate:

Ca(NO3)2

White ppt

-

potassium nitrate:

KNO3

-

-

Note:  Potassium phosphate will not form a precipitate with magnesia mix unless it is neutral or acidic.  When prepared with only water it is quite basic.

 

 

Discussion Questions

 

<!--Bone cells surround themselves with a matrix of protein that holds salt crystals.  These crystals make bone strong and rigid.

<!--Salts are molecules made up of positive and negative ions.

<!--Salts in our bodies are made from minerals we obtain from our diet.

 

How is the chicken bone that was kept in vinegar different from a normal chicken bone? 

          It is flexible and one can bend it!

 

 

What did the vinegar (acetic acid in water) do to the bone?  What was left of the bone after it was soaked in the vinegar?

 

          The vinegar extracted the bone salts  (calcium and phosphate)

          The proteins are left after vinegar extraction

 

Additional Discussion Questions and Points

 

What are some foods that are high in calcium?

          Dairy, soybeans and other legumes; green vegetables such as broccoli, collard and turnip greens, Chinese cabbage, and kale (spinach is high in calcium but also contains oxalate which bind calcium and keeps it from being absorbed by the body), molasses.

What are some foods that are high in phosphate/phosphorous?

          Meats (especially, liver, chicken and fish such as tuna), dairy (especially yogurt), soybeans and other legumes, peanut butter, sunflower seeds, and eggs.  Excess phosphorous is actually bad for bones because a proper balance among phosphorous, calcium, and magnesium is needed.  Eating too much meat or drinking too many soft drinks can lead to excessive phosphorous intake.

 

Why is it useful to have a negative control?

 

Ensure no contamination and that your reagents are behaving properly

 

Why is it called a negative control?      Because it does not produce a reaction

 

 

The Rubber Chicken

 

 

We can perform a flame test and a precipitate test to see what minerals came out of the bone.

 

Flame test

 

Metal                                        Flame color

lithium (Li)                               

calcium (Ca)                            

potassium (K)                          

 

“Unknown”                     Flame color                     Mineral from bone in vinegar

vinegar that

dissolved

minerals from

bone


 

Precipitate test

 

Does a precipitate (solid) come out of solution when you add oxalate or magnesia mix?  If so, what color is it?

 

Solution

Result after adding oxalate

Result after adding magnesia mix

plain vinegar (negative control)

 

 

vinegar containing bone salts

 

 

potassium phosphate: K3PO4

 

 

copper sulfate: CuSO4

 

 

calcium nitrate: Ca(NO3)2

 

 

potassium nitrate:

KNO3

 

 

 

What ions came out of the bone? 

 

 

 

What foods are good sources for these minerals that give bone its strength?

 

 

 

The plain vinegar was called a “negative control” because

<!--it would show how a solution that did not have any bone salt ions would behave in the precipitate test.

<!--it was crabby and never saw the positive side of things.

<!--it would show how a solution that did have bone salt ions would behave in the precipitate test.

<!--it had calcium in it.

 

What are two or three of the main things that make up bone?

 

 

المصدر: Akrum Hamdy
AkrumHamdy

Akrum Hamdy [email protected] 01006376836

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نشرت فى 19 سبتمبر 2010 بواسطة AkrumHamdy

أ.د/ أكـــرم زيـن العــابديــن محـــمود محمـــد حمــدى - جامعــة المنــيا

AkrumHamdy
[email protected] [01006376836] Minia University, Egypt »

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