The Physical and Chemical Properties of Hydrocarbons

Chemistry II   Experiment 23: The Physical and Chemical Properties of Hydrocarbons   Although all hydrocarbons contain only carbon and hydrogen, they have a variety of different structural features. On the basis of their structural features, hydrocarbons can be divided into three groups: saturated hydrocarbons (alkanes), unsaturated hydrocarbons (alkenes and alkynes), and aromatic hydrocarbons (arenes). You will study the difference in reactivity among these classes of compounds in this experiment.   Prelab Questions:   What is the difference between a saturated hydrocarbon and an unsaturated hydrocarbon?   Give the name and structure of a saturated hydrocarbon and an unsaturated hydrocarbon, each having five carbons.   What are the characteristic structural features allow one to differentiate among an alkane, an alkene, and an alkyne, and an arene?   Explain how it is possible to distinguish between an alkane and an arene by the flammability test.   Of the following compounds, which reacts with bromine without the aid of uv light: ethane, ethene, and propane? What type of reaction takes place? Write the equation for this reaction.   How can one tell whether a compound reacts with bromine?   Hypothesis:   The physical properties and chemical reactivity of a hydrocarbon reflect the presence or absence of certain chemical bonds.   Objectives:   To examine the physical properties of hydrocarbons. To observe reactions characteristic of each of the three main classes of hydrocarbons   Materials and Equipment:   Heptane, cyclohexene, toluene, iron fillings, hydrocarbon unknown, 1% bromine in carbon tetrachloride, ethanol, carbon tetrachloride, eye dropper, small test tubes.   Procedure:   Perform the test described in Parts A and B on each of these compounds: heptane, cyclohexene, and toluene. Carry out the same tests with an unknown hydrocarbon.   Solubility. Place 5 drops of each hydrocarbon in a separate clean, dry test tube. Cautiously compare their odors. Add about 10 drops of water on each tube. Shake the tubes, and note in the data table any solubility. Repeat the solubility test using ethanol and carbon tetrachloride as solvents. CAUTION: Carbon tetrachloride is toxic. Avoid inhalation of the vapors or contact with the liquid. Remember to use clean, dry test tubes for each test.   Hydrocarbon Odor Solubility Water Ethanol CCl4 Heptane           Cyclohexene           Toluene           Unknown #             Reaction and with Bromine: Place 10 drops of each hydrocarbon in a separate clean, dry test tube. To each sample add 2 drops of a 1% solution of bromine in carbon tetrachloride. Shake each test tube, and record the results. If no reaction occurs, add a few iron fillings. CAUTION: Avoid breathing fumes from the bromine and carbon tetrachloride solution.   Hydrocarbon Observation Bromine in CCl4 Bromine in CCl4 + Fe Heptane       Cyclohexene       Toluene       Unknown #         Use your test results to classify your unknown as an alkane, alkene, or arene. Explain your reasoning.         Post lab questions:   Write the molecular formulas, condensed structural formulas, and full structural formulas for the three known hydrocarbons used in this experiment.   Write and balance the combustion to heptane.   Write a balanced chemical equation for each of the known hydrocarbons that reacted with the bromine solution in the absence of iron fillings.   What is the name and structure of the compound that reacts with bromine in carbon tetrachloride to give 1,2-dibromohexane?   Explain the difference between the reaction of bromine with cyclohexene and with benzene.