1. On a separate sheet of paper o Write out and answer pre-lab Questions o Make a Data Table with the following headings and appropriate number of rows (read the lab!!!!):
Solid Color
Reaction with water
Reaction with vinegar
Reaction with iodine solution
We use chemicals everyday to cook, bake, and sometimes to feel better. The chemical and physical properties of a substance make up an identification tag for each substance. A chemist can use these properties to identify an unknown substance or to determine the contents of a mixture of substances.
When substances are mixed together two things can happen:


Nothing. The substances are mixed but no change occurs.
Formation of new substances. The substances interact to produce one or more different substances. This process is called a chemical reaction.
How do you know if a chemical reaction has occurred? Important clues that a chemical change has happened are: a color change, the production of a gas, the formation of a solid, or the production of heat.
In this experiment you will mix several pure substances commonly found in your kitchen with water, vinegar, and a methanol solution containing dissolved iodine and observe the interactions. Then you will use your results to identify several unknown mixtures and to determine the main ingredient in a product that is commonly used to relieve an upset stomach.

Apparatus
1.
2.
3.
4.
5.
6.
7.
8.
Safety goggles
Lab apron
3 thin-stemmed Beral pipets
Masking tape
Marking pen
7 small test tubes
Spatulas
2 24-well test plate
Reagents
 1% iodine solution in methanol


Vinegar
 Salt
 Baking soda
Baking powder
 Sugar (sucrose)
 Starch
 Mixture 1
 Mixture 2
None of the chemicals (known to chemists as reagents ) is hazardous, but commonsense procedures should be followed:
1.
Wear safety goggles and an apron at all times in the laboratory.
2.
Wipe up all spills with large amounts of water.
3.
Alcohol solutions can be flammable.
4.
Wash your hands thoroughly before you leave the laboratory.
1.
Label five test tubes: 1, 2, 3, 4, and 5. Label two more test tubes: Mix 1 and Mix 2.
2.
Label the three Beral pipets, water, vinegar, and iodine (alc) solution.

3.
From the stock bottles provided by your teacher, place a small amount (about the size of a large pea) of each pure substance into the labeled (1 – 5) test tubes that you just prepared. Be sure you put solid #1 in test tube #1, etc. Record the color of each substance in a data table.
4.
Place your 2 24-well test plates side by side and flat on the lab bench so that the long edge is horizontal. Place a small amount of pure substance 1 in the first three wells of the first row (across). Repeat this procedure with three samples of pure substance 2 in the second row. Continue with this process until you have placed three samples of each substance to be tested in the wells in the same order as shown in the data table.
5.
Note the color of each sample, recording your observations in your data table.
6.
Draw the correct liquid into each Beral pipet from the containers supplied by your teacher. Carefully place these with their tips up in an empty beaker to hold them until you are ready to use the liquids.
7.
Add four drops of water to each substance in the first column (vertical) of your test plate.
8.
Note any changes that occur and record your observations on your data table.
9.
Repeat steps 7 and 8, using the vinegar and alcohol solutions for columns 2 and 3.
When you are finished, rinse out your well plate and shake it to dry it.
1.
Rinse the well plate, shake it dry and put it away.
2.
Wash the test tubes and return them to their proper location.
3.
Wash your hands thoroughly with soap and water before leaving the lab.
Questions:
Pre-lab Questions:
1.
What is the difference between a physical and a chemical property?
2.
List three clues used to tell whether a chemical reaction has occurred?

Post-lab Questions:
1.
Two of the pure substances (baking powder and baking soda) are used to make baked products. What chemical property makes these substances useful in baking?
How is this property useful in baking? Which two of the five pure substances exhibit this property?
2.
Baking soda reacts with acidic solutions, but not with water. Identify which of the five pure compounds is baking soda, and which is baking powder. Explain.
3.
One of your pure substances produced a characteristic color (blue-black) when it reacted with the iodine-alcohol solution. Starch is an organic compound you have probably encountered in your biology course. Identify which of the pure substances is starch.
4.
Compare your data for the pure substances with the data for each of the two solid mixtures. Which of the pure substances shows behavior that is similar to what you saw with the two-solid mixtures (Mixture 1 and Mixture 2)? If you cannot positively identify your mixture, discuss the possibilities for the mixtures.
Mixture 1 is ___________________ and ___________________
Mixture 2 is ___________________ and ___________________
Conclusion
Write on paragraph (5 sentences minimum) restating the purpose and whether or not you have achieved the purpose of the lab

Intent
This exploratory experiment challenges students to identify unknown household chemicals by comparing their physical and chemical properties with those of known substances tested in the laboratory. It provides an excellent opportunity for students to practice their observation skills and use logic and reasoning skills to support their conclusions.
Objectives
1.
To determine the physical and chemical properties of salt, baking soda, baking powder, starch and sugar.
2. To identify several unknown mixtures of solid household chemicals by comparing the results of tests on these unknowns to tests of the samples from Objective 1.
(for each lab team of 2 students)
Apparatus
 Safety goggles (2)
 Lab apron (2)
 3 thin-stemmed Beral pipets


Masking tape
 Marking pen
8 test tubes (13 x 100)
 Spatulas
 24-well test plate
Reagents


1% iodine solution in methanol
 Vinegar
 Salt
Baking soda
 Baking powder
 Sugar (sucrose)



Starch
 Black paper
Crushed AlkaSeltzer™ (or generic brand)
1.
Place samples of each solid in laboratory containers, labeled 1 – 5. Use the following order: 1 = salt, 2 = baking soda, 3 = baking powder, 4 = starch, 5 = sugar. Do not place the name of the substance on the label. Do not use household containers to avoid confusion and ingestion of chemicals used in the laboratory by mistake.
2. Use commercial vinegar solutions for ease in preparation.
3. Prepare unknowns 1 and 2 by mixing equal parts of all possible pairs of the solids.
Distribution is simplest if you place the peasized samples into 18 × 150 test tubes or small vials which are numbered. Be sure to make at least 2.5 times as many unknowns as you have students. Some students will need an additional sample because of loss.
4.
For mix 3, use Alka-Se ltzer™ type product that has been crushed to a fine powder.
Distribute in the same manner as indicated in Hint 3.
Since this is an exploratory exercise it is best to keep the prelab to a minimum. Be sure to remind students to take careful observations, since many of the solids are the same color. You may also want to remind students of the iodine test for starch. You can easily illustrate this by using a piece of white bread or a potato and dropping some of the iodine solution on it.
1.
You may need to assist students in determining whether a gas has been produced. It can be difficult to observe the formation of a gas in the well plates.
2.
Remind students to use the black paper to assist them in the observation of white precipitates and the solubility of white solids.
All substances are household chemicals and can be disposed of in the same manner as you would at home.
The well plate should withstand the methanol with little difficulty, but students should remove the iodine from the wells thoroughly and as soon as the experiment is completed.

Name___________________________
Section___________ Date___________
1. What is the difference between a physical and a chemical property?
A chemical property is the ability of a given substance to change to a different substance. A physical property refers to all other characteristics of the substance, such as color and state.
2.
List three clues used to tell whether a chemical reaction has occurred.
1. Gas evolution
2. Color Change
3. Release of heat
Solid
3 baking powder
Color Reaction with water
Pure solids
1 (salt) White
2 baking soda White
White
Nr
Nr
Gas released
4 starch
5 sugar
Mixture 1 2/4
Mixture 2 1/5
Mixture 3
White
White
White
White
White
Nr
Nr
Nr
Nr gas
Reaction with vinegar
Nr
Gas released
Gas released
Nr
Nr gas
Nr gas
Reaction with iodine solution
Nr(stains yellow)
Nr(stains yellow)
Turns purple
Turns purple
Nr(stains yellow) purple
Nr
Nr

Analysis and Conclusions
1.
Compare your data for the pure substances with the data for each of the two solid mixtures.
Which of the pure substances shows behavior that is similar to what you saw with the two-solid mixtures, Mixture 1 and Mixture 2. If you cannot positively identify your mixture, discuss the possibilities for the mixtures.
Mix 1 = 2 + 4
Mix 2 = 1 + 5
2.
Compare your results for the unknown mixture (Mixture 3) to the observed characteristics of each pure substance. Can you identify any of the pure substances as a component of the unknown? Explain.
Substance 3
3.
Based on your answer to question 1, what is the identity for each of your two-solid mixtures?
There are many possible combinations; answers should match observations.
Mixture 1 is ___baking soda____ and ____starch______________.
Mixture 2 is ___sugar______ and _____salt______.
4.
What is the major component of the unknown (Mixture 3), commonly used as an upset stomach-and pain reliever)? Compare your results to the ingredients on the package.
Answers will vary, but students should at least identify baking soda.
5.
Two of the pure substances (baking powder and baking soda) are used to make baked products. What chemical property makes these substances useful in baking? How is this property useful in baking? Which two of the five pure substances exhibit this property?
Both substances release gas when combined with vinegar. This gas helps baked goods to
“rise”.
6.
Baking soda reacts with acidic solutions, but not with water. Identify which of the 5 pure compounds is baking soda and which is baking powder. Explain.
Number 2 is baking soda and number 3 is baking powder. Baking soda did not react with water and baking powder did.
7.
One of your pure substances produced a characteristic color (blue-black) when it reacted with the iodine-alcohol solution. Starch is an organic compound you probably encountered in your biology course. Identify which of the pure substances is starch.
Number 4 is starch. Number 3, baking powder often gives a purple-black color, too, but much less intense, since it contains only a small amount of starch.

What property do the upset-stomach reliever and the baking ingredients have in common? Give a hypothesis for how this property could possibly produce relief for an upset stomach.
Both release gas. Hypotheses will vary.