Lab 2: Alkanes and Alkenes Introduction Alkanes and Alkenes are the simplest groups of hydrocarbons in organic chemistry

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Lab 2: Alkanes and Alkenes Introduction Alkanes and Alkenes are the simplest groups of hydrocarbons in organic chemistry. Alkanes, also known as paraffins, have the generic formula C₂H2 They are saturated compounds, each carbon being bonded to four different atoms. There are many different alkanes and they have varied functions e.g. fuels, (commonly associated propane and butane, and gasoline); moisturizers/ skin softeners (alkanes with high molar mass act as emollients which cover the skin and prevent loss of water-commonly associated with petroleum jelly), and pheromones (ants release undecane C₁H₂4 and tridecane C₁H that act as alarm signals to other ants). Alkenes are unsaturated compounds, with one or more carbon double bonds found in each molecule. Monounsaturated alkenes have the formula C₂H₂ poly unsaturated alkenes have the formula C₂H2-2), X representing the number of double bonds in the structure. The presence of double bonds makes alkenes more reactive than alkanes, and they are often used as the precursors when making other compounds e.g. alkyl halides and alcohols. A number of biological molecules are polyunsaturated compounds. A few are shown below. beta carotene Equipment/Materials 5-8 Test tubes 5 test tube stoppers Test tube rack graduated droppers Foil Litmus paper lycopene Objectives: 1) To investigate physical properties of alkanes and alkenes. 2) To investigate chemical properties of alkanes and alkenes. 3) To compare chemical and physical properties of these different groups of hydrocarbons. Hexane Hexene Vitamin A اسلحہ خانہ جاتے Cyclohexane Cyclohexene Butane Potassium permanganate Dilute sulfuric acid Concentrated sulfuric acid Bromine water Distilled water (non-polar solvent e.g. heptane)

Procedures PHYSICAL PROPERTIES Appearance 1. Observe and record the color, state and odor of the organic compounds you will be handling today. (REMEMBER: do not directly inhale chemicals! Gently waft the vapour towards you and then describe any odor you detect.) Solubility 1. Place a ½ mL of hexane in a test tube and add a few drops of water. Shake and then stand the tube in a rack. Repeat using a non-polar instead of water. Compare the appearance of the mixtures. 2. Repeat the above steps using hexene then cyclohexene.. Questions a. Which combinations mix well? Which do not? b. Explain why the compounds behave this way. (Hint-relate to structure and polarity of molecules.) e. If two layers formed, which molecule is in the top layer in each case? How do you know? d. Compare the melting point of the four compounds tested in this exercise. Explain any difference you see. CHEMICAL PROPERTIES 1. Halogenation a. Wrap four separate test tubes with foil to prevent light from reaching their contents. Label the tubes 1-4, add 0.5 mL of bromine water to each test tube, and then stopper the tubes. (Make sure to note the color of the bromine water. Active bromine water has a brownish tinge. If your bromine water is colorless you should ask for a fresh sample.) b.Add 0.5 mL of hexane to the first test tube then re-stopper and shake for about a minute. Note any color change. c. Repeat step b. with your other hydrocarbons, placing 0.5 mL cyclohexane in the second test tube, 0.5 mL hexene in the third, 0.5 mL cyclohexene. d.If any solution retains a yellowish or brownish tinge, uncover and expose to sunlight for 5-10 minutes. Record any changes observed after this time. e. Unstopper the first mixture and test for the presence of acid gas by placing a strip of moistened blue litmus paper at the mouth of the tube. Record your results. f. Repeat step e. for the other mixtures. Questions g.Draw a sketch to represent the first test tube and its composition after adding bromine water. Indicate where the water is, where the bromine is, where the hydrocarbon is. Explain how you know the location of each of these components of the mixture. h.Explain the basis behind the color change in each case and what difference exposure to light makes. i. Show balanced chemical equations for any reaction that occurred. 2. Oxidation a. Label four clean test tubes. To each test tube, add Iml of water, three drops of acidified potassium permanganate solution. b. Add 10 drops of: hexane in one tube, cyclohexane in the second, cyclohexene in the third and hexane in the fourth. c. Shake well and record any observable changes.

Questions d.Explain the chemical basis for your observations. e. Show a chemical reaction to represent any reaction observed. 3. Addition reaction a. Label three clean test tubes. To each test tube, add Iml of concentrated sulfuric acid. b.Add 10 drops of: hexane to one tube, cyclohexane to the second, cyclohexene to the third. c. Swirl the contents gently to mix. Questions d.Touch the bottom of the tubes. Has there been any change in temperature for any of the mixtures? e. Observe the mixtures - have the contents completely mixed? f. Identify which compounds react in each case. Do your results agree with your predictions? Explain why/why not. g.For compounds that react, show equations that depict the likely reaction that took place. 4. Combustion (Demonstration) a. Place 10 drops of hexane in a crucible. Ignite the fluid with a lit splint. Record your observations of the flame (odor, clarity, presence of smoke, etc.). b. Repeat step a. for cyclohexene. c. Light a Bunsen burner. Slowly increase then decrease the amount of butane by turning the gas faucet. Record what you notice about the size of the flame as you change the amount of gas being released. d. Adjust the amount of air that mixes with the butane by slowly opening and closing the air holes on the Burner. Record your observations. e. Turn off the Burner. Questions f. Write balanced equations for complete combustion of the liquid compounds. Do you think that all the compounds experienced complete combustion? Why? g. Explain causes for differences in the appearance of the flame. h. Explain the differences in the appearance in the flame of the Bunsen burner when you 1) increased the amount of butane 2) increased the amount of air i. Assuming that the gas being burnt is propane, show the most likely chemical reaction occurring when the flame is: 1) clear/blue 2) yellow 3) yellow and smoky

Lab 2: Data Name: Table 1: Physical appearance of hydrocarbons Compound Observations Hexane Hexene Cyclohexane Cyclohexene Butane Heptane Table 2: Solubility Compound Hexane Hexene Cyclohexene Table 3: Halogenation Compound Halogenation Bromine water Hexane Hexene Cyclohexane Cyclohexene Solvent water Table 4: Combustion substance Hexane Litmus paper Description of flames Partner Non-polar solvent ( oxidation addition

Hexane Hexene Cyclohexane Cyclohexene Table 4: Combustion substance Hexane Cyclohexene Butane (effects of changing amount of gas) Butane (effects of changing amount of air) Description of flames Students will write a formal lab report to submit at the beginning of the next lab session.

Lab 2: Alkanes and Alkenes Introduction Alkanes and Alkenes are the simplest groups of hydrocarbons in organic chemistry. Alkanes, also known as paraffins, have the generic formula C,H- They are saturated compounds, each carbon being bonded to four different atoms. There are many different alkanes and they have varied functions e.g. fuels, (commonly associated propane and butane, and gasoline); moisturizers/ skin softeners (alkanes with high molar mass act as emollients which cover the skin and prevent loss of water-commonly associated with petroleum jelly), and pheromones (ants release undecane C₁H₂ and tridecane C₁H₂ that act as alarm signals to other ants). Alkenes are unsaturated compounds, with one or more carbon double bonds found in each molecule. Monounsaturated alkenes have the formula C,H... poly unsaturated alkenes have the formula C₂H0+2, X representing the number of double bonds in the structure. The presence of double bonds makes alkenes more reactive than alkanes, and they are often used as the precursors when making other compounds e.g. alkyl halides and alcohols. A number of biological molecules are polyunsaturated compounds. A few are shown below. beta carotene lycopene Equipment/Materials 5-8 Test tubes 5 test tube stoppers Test tube rack graduated droppers Foil Litmus paper Objectives: 1) To investigate physical properties of alkanes and alkenes. 2) To investigate chemical properties of alkanes and alkenes. 3) To compare chemical and physical properties of these different groups of hydrocarbons. Hexane Hexene Vitamin A Cyclohexane Cyclohexene Butane Potassium permanganate Dilute sulfuric acid Concentrated sulfuric acid Bromine water Distilled water (non-polar solvent e.g. heptane)

Procedures PHYSICAL PROPERTIES Appearance 1. Observe and record the color, state and odor of the organic compounds you will be handling today. (REMEMBER: do not directly inhale chemicals! Gently waft the vapour towards you and then describe any odor you detect.) Solubility 1. Place a ½ mL of hexane in a test tube and add a few drops of water. Shake and then stand the tube in a rack. Repeat using a non-polar instead of water. Compare the appearance of the mixtures. 2. Repeat the above steps using hexene then cyclohexene.. Questions a. Which combinations mix well? Which do not? b. Explain why the compounds behave this way. (Hint-relate to structure and polarity of molecules.) c. If two layers formed, which molecule is in the top layer in each case? How do you know? d. Compare the melting point of the four compounds tested in this exercise. Explain any difference you see. CHEMICAL PROPERTIES 1. Halogenation a. Wrap four separate test tubes with foil to prevent light from reaching their contents. Label the tubes 1-4, add 0.5 mL of bromine water to each test tube, and then stopper the tubes. (Make sure to note the color of the bromine water. Active bromine water has a brownish tinge. If your bromine water is colorless you should ask for a fresh sample.) b. Add 0.5 ml of hexane to the first test tube then re-stopper and shake for about a minute. Note any color change. c. Repeat step b. with your other hydrocarbons, placing 0.5 mL cyclohexane in the second test tube, 0.5 mL hexene in the third, 0.5 mL cyclohexene. d.If any solution retains a yellowish or brownish tinge, uncover and expose to sunlight for 5-10 minutes. Record any changes observed after this time. Questions e. Unstopper the first mixture and test for the presence of acid gas by placing a strip of moistened blue litmus paper at the mouth of the tube. Record your results. f. Repeat step e. for the other mixtures. g.Draw a sketch to represent the first test tube and its composition after adding bromine water. Indicate where the water is, where the bromine is, where the hydrocarbon is. Explain how you know the location of each of these components of the mixture. h.Explain the basis behind the color change in each case and what difference exposure to light makes. i. Show balanced chemical equations for any reaction that occurred. 2. Oxidation a. Label four clean test tubes. To each test tube, add Iml of water, three drops of acidified potassium permanganate solution. b. Add 10 drops of: hexane in one tube, cyclohexane in the second, cyclohexene in the third and hexane in the fourth. c.Shake well and record any observable changes.

Questions d.Explain the chemical basis for your observations. e. Show a chemical reaction to represent any reaction observed. 3. Addition reaction a. Label three clean test tubes. To each test tube, add Iml of concentrated sulfuric acid. b.Add 10 drops of: hexane to one tube, cyclohexane to the second, cyclohexene to the third. c.Swirl the contents gently to mix. Questions d. Touch the bottom of the tubes. Has there been any change in temperature for any of the mixtures? e. Observe the mixtures- have the contents completely mixed? f. Identify which compounds react in each case. Do your results agree with your predictions? Explain why/why not. g.For compounds that react, show equations that depict the likely reaction that took place. 4. Combustion (Demonstration) a. Place 10 drops of hexane in a crucible. Ignite the fluid with a lit splint. Record your observations of the flame (odor, clarity, presence of smoke, etc.). b. Repeat step a. for cyclohexene. c. Light a Bunsen burner. Slowly increase then decrease the amount of butane by turning the gas faucet. Record what you notice about the size of the flame as you change the amount of gas being released. d. Adjust the amount of air that mixes with the butane by slowly opening and closing the air holes on the Burner. Record your observations. e. Turn off the Burner. Questions f. Write balanced equations for complete combustion of the liquid compounds. Do you think that all the compounds experienced complete combustion? Why? g. Explain causes for differences in the appearance of the flame. h. Explain the differences in the appearance in the flame of the Bunsen burner when you 1) increased the amount of butane 2) increased the amount of air i. Assuming that the gas being burnt is propane, show the most likely chemical reaction occurring when the flame is: 1) clear/blue 2) yellow 3) yellow and smoky

Lab 2: Data Name: Table 1: Physical appearance of hydrocarbons Compound Observations Hexane Hexene Cyclohexane Cyclohexene Butane Heptane Table 2: Solubility Compound Hexane Hexene Cyclohexene Table 3: Halogenation Compound Halogenation Bromine water Hexane Hexene Solvent water Cyclohexane Litmus paper Partner Non-polar solvent ( oxidation addition

Hexane Hexene Cyclohexane Cyclohexene Table 4: Combustion substance Hexane Cyclohexene Butane (effects of changing amount of gas) Butane (effects of changing amount of air) Description of flames Students will write a formal lab report to submit at the beginning of the next lab session.