1 1 6 Living Thi?igs Are Basically Alike unit ii 



milky.) Can you put these same elements together without having them 

 combine? How? 



1 1 . Try the test which has been discovered for detecting starch. Ob- 

 tain a water solution of iodine crystals and potassium iodide (Lugol's 

 solution). Add a few drops to a small amount of starch in water. Mix 

 the iodine solution with sugar, protein (white of an egg), fats (butter or 

 lard), table salt, and water. What is your result in each case? Why do 

 you add iodine to these other substances? Note that you have not re- 

 peated the chemist's experiment since you have not tried iodine with a 

 vast number of other compounds. Why can iodine be used as a test for 

 starch? 



12. Trv the test which has been discovered for detecting simple sugars. 

 Dissolve some grape sugar (corn syrup will do) in water. Add either 

 Fehling's solution or Benedict's solution. Heat the mixture until it boils. 

 What is the final color of the substance? Do you get the color change 

 with any substance other than simple sugar? Why do you test these 

 other substances? Do your classmates get the same results? 



13. Trv the test that has been discovered for detecting proteins. Mix 

 some of the white of an egg with dilute nitric acid. Boil the mixture for 

 a few seconds. (Careful!) What color change do you notice? Now add 

 ammonium hydroxide. What is the second color change? What else must 

 you do? Why? 



14. Try the test for detecting fats. Rub a bit of butter on a piece of 

 unglazed paper. Hold the paper to the light. The spot that appears on 

 the paper is called a transhicein spot. Why? All fats leave a translucent 

 spot on paper. Do substances other than fats produce this kind of spot? 



15. Try the test that has been discovered for detecting water. Boil 

 some water in an open dish. Hold a dry, cold glass tumbler over the 

 boiling water. What forms on the sides of the glass? Heated water vapor 

 condenses when it strikes a cold object. If you try this test on the other 

 substances you may get the same results. Explain. 



16. Try the test for detecting mineral compounds. Trv to burn table 

 salt. Since minerals do not burn, at least not at the low temperature at 

 which other substances burn, they will remain as a white ash. What be- 

 comes of starch, sugar, fat, and protein when they are burned? 



17. The difference between a mixture and a compound. Examine iron 

 filings and powdered sulfur. They are examples of elements. Describe 

 them. One property of iron is that magnets attract it. Siiow that this is 

 so. Now stir together some iron filings and sulfur powder until they are 

 thoroughly mixed. Apply the magnet. What happens? In stirring the two 

 elements together did a compound form or did you form a mixture? 

 Explain your answer. Next, heat in a crucible a small amount of iron 

 filings and powdered sulfur. After thorough heating apply the mac^net. 

 What happens? I'"xplain. This is a compound. Put into words what you 

 understand to be the difference between a mixture and a compound. 



