Name Date Class

Kitchen Chemicals

The chemical and physical properties of a substance make up a sort of fingerprint that characterizes the substance. In this ChemLab, you will test four unknown solids using three different liquids. The unknowns are common materials that you'd probably find in your kitchen. The results of your tests will give you the information you need to unravel the compositions of mixtures of two solids and three solids.

PROBLEM

How can you identify a material by comparing its properties with those of known materials?

OBJECTIVES

  1. Observe the chemical and physical reactions of four common kitchen materials with three test reagents.
  2. Compare and interpret the reactions of the test reagents with five two-solid and three-solid mixtures of the common kitchen materials.
  3. Infer the composition of each of five unknown mixtures by comparing their reactions with those of the known materials.

MATERIALS

96-well microplate

9 test tubes

spatulas

3 thin-stemmed pipets

masking tape

marking pen

SAFETY PRECAUTIONS

Inline Figure

Wear an apron and goggles. Do not touch or taste any of the solids or liquids, even though you may believe you know their identities.

PROCEDURE

  1. Label four test tubes A, B, C, and D . Label five test tubes 1 through 5.
  2. In the four lettered test tubes, place about 1 g of each of the labeled samples supplied by your teacher. These are the common kitchen materials.
  3. In the numbered test tubes, place about 1 g of each of the numbered samples supplied by your teacher. These are the unknown mixtures. If you use the same spatula for each material, rinse and dry it before dipping into the next solid to avoid contaminating one material with another.
  4. Label three long columns of wells on the microplate I, II, and III . Label nine rows of wells on the microplate A, B, C, and D, and 1 through 5.
  5. Place the microplate on a sheet of white paper.
  6. Add a small amount of each material to the row of three wells that has the appropriate letter or number.
  7. Observe and record the texture of each of the nine materials in the data table.
  8. Label the three pipets I, II, and III . From the containers of reagent liquids supplied by your teacher, draw into the bulb of each pipet the liquid corresponding to the label number on that pipet.
  9. Add 3 drops of liquid I to each of the nine materials in column I .
  10. Observe any changes that take place, and record them in the data table.
  11. Repeat steps 9 and 10 using liquid II and then liquid III.

DATA AND OBSERVATIONS

Solid Color Texture Reaction with liquid 1 Reaction with liquid 2 Reaction with liquid 3
Pure solids

A

(salt)
  white, clear  crystals or powder  dissolves dissolves  dissolves 

B

(baking soda)
  white  powder dissolves  fizzes    dissolves

C

(baking powder)
  white   powder fizzes  fizzes    fizzes 

D

(starch)
  white  powder   dissolves  dissolves  dissolves and produces dark blue color
Two-solid mixtures

1

      fizzes   fizzes   fizzes 


2

      dissolves  fizzes   blue


3

      fizzes   fizzes   fizzes and blue
Three-solid mixtures

4

     dissolves   fizzes   blue


5

      fizzes   fizzes   fizzes and blue

ANALYZE AND CONCLUDE

  1. Interpreting Data What properties and reactions characterize each of the four kitchen solids?

    Solid A dissolves in all three reagents, but it does not fizz or turn blue. Solid B dissolves in reagents I and III, and fizzes with reagent II. Solid C fizzes with all three reagents. SOlid D dissolves with all three reagents and produces a blue color with reagent III.


  2. Drawing Conclusions Can you positively identify the solids that are contained in any of the five mixtures? If so, identify the solids and explain your conclusions.

    Mixture 2 contains solids B and D because it fizzes with reagent II only and turns blue with reagent III. Mixture 3 contains solids C and D because it fizzes with all three reagents adn turns blue with reagent III. Mixture 4 contains solids A, B, and D because it does not fizz with reagents I and III.


  3. Making Inferences If you are unable to conclusively identify the solids in any of the mixtures, what are their likely identities? Explain.

    Mixture I contains soldis C and A or B because it fizzes with all three reagents but does not turn blue with reagent III. Mixture5 contains solids C, D, and A or B because it fizzes with all three reagents and turns blue with reagent III.


APPLY AND ASSESS

  1. Two of the four original solids, baking powder and baking soda, are often used in making baked goods. What characteristic probably makes them useful in baking? Which solids display this characteristic?
    Solids B and C react to produce a gas or gases that could enable baked goods to rise.

  2. Baking powder is a mixture of two or more compounds, and it reacts with water or any other liquid that contains water. Baking soda is a single compound that reacts with acidic solutions but not with water. Which of the solids do you think is baking powder? Explain.
    Solid C is probably baking powder because it fizzes with all three liquid reagents.

  3. One of the solids is an organic compound you may have learned about in a biology course. It produces a characteristic color when combined with iodine. Which solid gave this reaction? What is the identity of this compound?
    Solid D produces the dark blue color reaction with reagent III. It is starch.