In this lab you are identifying an unknown household chemical given
to you. The unknown substance is one of the eight common household chemicals. In the actual experiment that you would do, all those eight substances would be supplied to you, and then you to carry out physical and chemical tests for each of those known substance. You then do the same tests for the given unknown substance and then compare your test results to the known substances to see which one matches most to identify your unknown. The known substances are table salt, sugar, vinegar (acetic acid), baking soda, baking powder, citric acid, Vitamin C (ascorbic acid), and starch. You are identifying the unknown substance from its physical and chemical properties along with the unknown. The physical properties include color, odor, texture, solubility, and the conductivity measurement where you don't carry out a chemical reaction to identify what your unknown is. Texture means if the substance is crystalline or a powdery material. For example, table salt is crystalline while starch is a powdery substance. You are not forming any new substance in physical test. The chemical properties on the other hand involve chemical reactions, forming new substances to enable its identification. The chemical tests are acid - base reaction, heating the substance at high temperature where it decomposes. For example, when sugar is heated to high temperature, it chars to a black solid which is carbon. Similarly, starch reacts with iodine solution forming a blue-black color, which is a confirmative chemical test for starch.
In this lab you are measuring the conductivity using a conductivity meter. Greater the conductivity of a solution, greater is the number of ions in the solution, that is greater its dissociation into its ions when dissolved in water. You are measuring the pH to determine if the substance is an acid or a base. You are recording your observations for all the eight known household chemicals and doing the same tests for the given unknown, which is one of these eight substances. As I have said earlier the tests you are doing include color, texture, acid reaction, starch test, solubility, conductivity, pH,
1. A professor asks the class to carry out two more additional physical tests other than the ones listed above. What would be your choice? Which two physical tests you would do - along with the ones mentioned above to confirm the identity of the unknown.
2. What two things are unaffected in a physical change?
3. When dilute HCl was added to your unknown there was a brisk evolution of gas bubbles. Which one of the eight known substances would produce such gas? Write the chemical reaction and identify the gas.
4. Jane came to the lab very late. She had no time to complete the experiment. However, her lab partner gave her the following information about the unknown:
The substance is: white in color, crystalline, no odor, soluble in water, pH in neutral range, conductivity is very low (non electrolyte). Which of the household chemical her unknown is?
5. If Jane is given some extra time to carry out only one test (physical or chemical) which one should she do to confirm her answer from the above data? What would be your suggestion to her?
6. Which of the tests that you are doing in this lab may relate to a chemical reaction? Indicate two such tests.
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