Chemistry 11: Organic Chemistry Determination of Boiling Points of Organic Compounds—Ketones and Alcohols Name: _________________________________ April 21, 2016 Due Date: April 26, 2016 Safety Precautions (5)     

Always wear your lab coat and safety glasses while in the lab (lab coat is to be done up and safety goggles are to be on at ALL times) Only closed toed shoes can be worn (sandals are unacceptable) and no shorts or skirts will be permitted. Handle the capillary tubes with care, they break easily. Handle the thermometer with care, it breaks easily. Do not put your face too close to the test tube. These liquid give off fumes that can be harmful and cause headaches if you breathe them in for too long.

Introduction The boiling point of a compound is the temperature at which it changes from a liquid to a gas. This is a physical property often used to identify substances or to check the purity of the compound. It is difficult, though, to find a boiling point. Usually, chemists can only obtain a boiling range of a 2 - 3oC accuracy. This is usually sufficient for most uses of the boiling point. In this experiment, you will look at the boiling point range of acetone (a ketone, also known as propanone), methanol, ethanol, and propanol. Your goal is to look at the difference in the boiling point ranges and explain why they exist by identifying and deconstructing the functional groups that they contain. You will then have an unknown that you will have to identify based on its boiling point ranges and the ranges of your known compounds. Purpose The purpose of this experiment is to identify the boiling point range of ketones and alcohols and explain any variations that occur. It is also to identify and unknown compound based on its boiling point. Equipment    

Hot plate Thermometer Large test tube Clamp

   

250 mL beaker Capillary tube Ring stand 10 or 50 mL graduated cylinder

Materials   

Acetone (propanone) Methanol Isopropyl Alcohol (2-propanol)

  

Ethanol Propanol Unknown substance

Procedure 1. Fill the 250 mL beaker 3/4 of the way full with tap water and place it on the hot plate. Turn on the hot plate. 2. Place 5 mL of one of the organic compounds into a test tube. 3. Place a capillary tube into the test tube with the closed end upwards. 4. Clamp the test tube to the ring stand and place the thermometer into the test tube. 5. Carefully lower the test tube/thermometer combination into the beaker so that the test tube is halfway submersed in water. 6. As the liquid in the test tube approaches its boiling point, a few bubbles will be observed flowing out of the end of the capillary tube. When a steady stream of bubbles are observed, turn off the hot plate and allow the contents in the test tube to cool. 7. As the contents of the test tube cools, observe the capillary tube. When the liquid in the test tube begins to flow into the capillary tube, record the temperature of the liquid as the boiling point temperature. Watch closely, this part of the procedure happens quickly. 8. Pour the contents of your test tube into the waste station in the fume hood. Don’t let your capillary tube fall in! 9. Repeat steps 1—7 for your other four compounds as well as your one unknown compound. Be sure to rinse out your test tube and capillary tube after each substance and to rinse off your thermometer. 10. Clean up your lab station before heading back to the classroom to work on your lab write-up. Data (5) Compound

Boiling Point Range (⁰C)

Acetone Methanol Ethanol Propanol Isopropyl Alcohol Unknown Compound Analysis and Questions 1. What is the identity of your unknown substance? (1)

2. Write the molecular formula and draw the structure of acetone (propanone), methanol, ethanol, and propanol. (8)

3. Are any of the above compound structural isomers of one another? If so, which ones? (2)

4. According to the literature, what is the accepted boiling point range for acetone, methanol, ethanol and propanol? (4) Acetone Methanol Ethanol Propanol Isopropyl Alcohol

5. Methane is a gas at room temperature, however, methanol is a liquid at room temperature and they both contain only one carbon atom. Explain why alcohols tend to have higher boiling points than their hydrocarbon counterparts (hydrocarbons that have the same number of carbon atoms). (4)

6. Alcohols with less than 10 carbon atoms are able to dissolve in water, however, hydrocarbon chains that exist as liquids at room temperature and have less than 10 carbon atoms are not. Explain why this occurs based on what you know about bonding. (4)

7. Why do ketones with the same number of carbon atoms as their alcohol counterpart have lower boiling points? (2)

8. Using what you have observed with the boiling points of alcohols and ketones and what you know about the boiling points of hydrocarbons, explain the two key factors to a substances boiling point. (4)

9. We have wrapped up the material for the organic chemistry unit. What is one question you still have about organic chemistry? (1)

Organic Chemistry Lab.pdf

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