BIOB111 - Tutorial activities for session 7 I. Tutorial Organic Chemistry II. Vitamin C Experiment

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1 BIOB111 - Tutorial activities for session 7 I. Tutorial Organic Chemistry II. Vitamin C Experiment General topics for the week 4 Session 7 Structure of organic compounds Students are given the molecular models to explore and learn about organic compounds Useful links: Log on to the following site and learn about organic chemistry General tutorial questions: 1. Which of the following statements concerning organic compounds is correct? a) Organic compounds are found only in non-living systems b) Organic compounds are always soluble in water c) Organic compounds cannot be found in nature; they must be synthesized in the laboratory d) Organic compounds always contain the element carbon 2. The distinction between a saturated hydrocarbon and an unsaturated hydrocarbon relates to: a) Boiling points b) Volatility c) Number of carbon atoms present d) The number of carbon to carbon bonds present Conceptual multiple choice questions: 3. Concept: Organic compounds Context: Organic compounds are wide spread in nature. In fact important compounds for our health like carbohydrates, lipids and proteins are all classed as organic compounds. Last updated on 23-Feb-18 Page 1 of 11

2 Question: Which of the following is correct for organic compounds? a) Organic compounds can only be derived in the laboratory b) An organic compound will always contain at least one carbon atom c) Organic compounds can only be derived in nature d) An organic compound may or may not contain carbon atoms 4. Concept: Organic vs inorganic compounds Context: There are two broad classes of compounds, organic and inorganic. Organic compounds are much more numerous, making up about 85% of all compounds. Inorganic compounds are much fewer, making up 15% of all compounds. Question: Which of the following provides the best explanation to why organic compounds are more numerous than inorganic compounds? a) All organic compounds contain carbons, with each carbon forming four separate covalent bonds, meaning there is great diversity in the possible combinations of atoms to create different compounds b) Organic compounds are made up of metal and non-metal atoms, whereas organic compounds are made up of only metal atoms c) All inorganic compounds contain carbons, with each carbon forming four separate covalent bonds, meaning there is great diversity in the possible combinations of atoms to make different compounds d) Organic compounds are made up of non-metal atoms, whereas organic compounds are made up of only metal atoms 5. Concept: Individual atoms vs atoms within a compound Context: Multiple atoms come together to form compounds. Within a compound there are multiple atoms are attached to each other via chemical bonds. For example, to form a H 2O molecule, an oxygen atom forms a covalent bonds to two separate hydrogen atoms. Question: Are the oxygen and hydrogen atoms more stable within the H 2O compound or as separate atoms and why? Last updated on 23-Feb-18 Page 2 of 11

3 a) The atoms are more stable as individual atoms, as all of their electrons are paired, whereas as within compounds the atom are more reactive as some of the electrons are unpaired b) The atoms are equally stable when in the compounds and as individual atoms c) The atoms are more stable within the compound, as all of their electrons are paired, whereas as within the individual atoms some of the electrons are unpaired and reactive d) The atoms are more stable as individual atoms as they can move about more freely than when they are a part of a compound 6. Concept: Covalent bonding of a carbon atom Context: The outer shell of a carbon atom contains four unpaired valence electrons. The number of unpaired valence electrons an atom contains is equal to the number of covalent bonds the atom is capable of forming. Question: Which of the following accurately describes the covalent bonding of a carbon atom? a) Each of the four unpaired valence electrons must form a covalent bond with another carbon atom to become more stable b) Each of the four unpaired valence electrons within the carbon atom can covalent bond to each other to become more stable c) Each of the four unpaired valence electrons of a carbon atom can form a covalent bond via electron sharing with other atoms such as hydrogen and carbon d) Each of the four unpaired valence electrons of a carbon atom can covalent bond to more than one different atom simultaneously 7. Concept: Saturated vs unsaturated hydrocarbons Context: Compounds composed of carbon and hydrogen are referred to as hydrocarbons. Hydrocarbon derivatives can also have additional atoms such as nitrogen and oxygen. Hydrocarbons are grouped into those that are saturated and those that are unsaturated. Question: Which of the following best describes the difference between a saturated and an unsaturated hydrocarbon? Last updated on 23-Feb-18 Page 3 of 11

4 a) The carbons within saturated hydrocarbons are connected to other carbons by single bonds, whereas at least one carbon in an unsaturated hydrocarbon connects to another carbon atom through a double or triple bond b) Saturated hydrocarbons contain only single carbon-carbon bonds, whereas unsaturated hydrocarbons contain only double or triple carbon-carbon bonds c) The carbons within unsaturated hydrocarbons are connected to other carbons by single bonds, whereas at least one carbon in an saturated hydrocarbon connects to another carbon atom through a double or triple bond d) Unsaturated hydrocarbons contain only single carbon-carbon bonds, whereas saturated hydrocarbons contain only double or triple carbon-carbon bonds 8. Concept: Straight chain vs ring structured hydrocarbons Context: Hydrocarbons that contain only carbon and hydrogen atoms can adopt either straight chain-like structures or ring-like structures. For example, a six carbon containing hydrocarbon can exist in both the straight chain or ring form (below). Question: Which of the following correctly describes the major difference between the straight chain (acyclic) and ring structured (cyclic) hydrocarbons? a) Cyclic hydrocarbons have carbons at the end of the structure that bond to only one other carbon atom, whereas all of the carbons in an acyclic structure bond to two other carbon atoms b) All of the carbons in a cyclic hydrocarbon are connected to only one other carbon atom, whereas all of the carbons in an acyclic structure connect to two carbon atoms c) Acyclic hydrocarbons have carbons at the end of the structure that bond to only one other carbon atom, whereas all of the carbons in a cyclic structure bond to two other carbon atoms d) All of the carbons in an acyclic hydrocarbon are connected to only one other carbon atom, whereas all of the carbons in an acyclic structure connect to two carbon atoms 9. Concept: Straight chain vs ring structured hydrocarbons Last updated on 23-Feb-18 Page 4 of 11

5 Context: Both straight chain (acyclic) and ring structured (cyclic) hydrocarbons can form structures that contain the same number of carbon atoms. However, these acyclic and cyclic compounds contain different numbers of hydrogen atoms, even though they have the same number of carbon atoms. Question: Which of the following best describes why acyclic and cyclic versions of hydrocarbons contain different numbers of hydrogen atoms? a) Acylcic hydrocarbons have more hydrogen atoms than cyclic hydrocarbons, as acyclic hydrocarbons have defined end carbons which attach to three hydrogen atoms b) Cyclic hydrocarbons have carbons that always attach to two other carbons, meaning they have more hydrogen atoms in total than acyclic hydrocarbons c) Cyclic hydrocarbons have more hydrogen atoms than acyclic hydrocarbons, as cyclic hydrocarbons have defined end carbons which attach to three hydrogen atoms d) Acyclic hydrocarbons have carbons that always attach to two other carbons, meaning they have more hydrogen atoms in total than cyclic hydrocarbons 10. Concept: Properties of a functional group Context: A functional group is a characteristic set of atoms used to distinguish one set of atoms from another. For example, the thiol functional group is R-SH (R = connection to other atoms). There are a variety of functional groups that compounds may contain such as the ester, amide and aldehyde. Question: Once you ve identified that a compound contains a certain functional group, what do you now know about the compound? a) The compound will only react with other compounds that contain the same functional group b) The compound is stable and unreactive, so it won t participate in chemical reactions Last updated on 23-Feb-18 Page 5 of 11

6 c) The compound will react similarly to other compounds with the same functional group d) The compound will have a specific function that is the same as all other compounds that contain the same functional group 11. Concept: Number of functional groups in a compound Context: Compounds can be divided into different groups based on the functional groups that they contain. For example, each amino acid (many of which connect to make up proteins) contains a carboxylic acid and amide functional group. Question: Which of the following is true about the number of functional groups a compound can contain? a) Each compound only contains one functional group b) A compound may either contain many or very few functional groups c) Each compound only contains two functional groups d) Compounds may either contain one or two functional groups 12. Concept: Stereoisomers Context: There are two distinct classes of isomers, structural isomers and stereoisomers. Two compounds that are structural isomers have the same type and number of atoms but have different bonding arrangements, which gives the compounds a different shape. In contrast, two compounds that are stereoisomers have the same type and number of atoms with the same bonding arrangements. However, stereoisomers have differences in the spatial arrangement of their atoms. Question: Which of the following best describes stereoisomers? a) H 2O and CO 2 are stereoisomers as they have different shapes due to the different atoms and bonding arrangements present b) 2-metylpropane and butane are structural isomers that have different shapes due to the different bonding arrangements within the four carbon and 10 hydrogen atoms present in each c) cis-butane and trans-butane are stereoisomers that have different arrangements in space but have the same bonding arrangements d) Compounds that have similar spatial arrangements are classed as stereoisomers Last updated on 23-Feb-18 Page 6 of 11

7 Vitamin C Experiment Determination of Vitamin C Concentration Introduction Vitamin C is a water-soluble compound that is essential for life. It is involved in many processes in the human body, including: the production of collagen in the connective tissue; the synthesis of dopamine, noradrenaline and adrenaline in the nervous system; and the synthesis of carnitine, which is important in the transfer of energy to the cell mitochondria. A deficiency in vitamin C causes scurvy, a disease that affected sailors in the 16th - 18th centuries. It was discovered that fresh fruit, e.g. limes and oranges, or sauerkraut (preserved cabbage) provided the sailors with protection from scurvy. In Australia and New Zealand, the recommended daily intake (RDI) of Vitamin C is 60 mg. Vitamin C is often used as an antimicrobial and antioxidant in foodstuffs. Vitamin C is the L-enantiomer of ascorbic acid, as shown in Figure 1. Ascorbic acid is a stable solid that does not react with air, however, it is rapidly oxidised on exposure to air and light when in aqueous solution. The product of this oxidation is dehydroascorbic acid, as shown in Figure 2. Figure 1: The two enantiomers of ascorbic acid. Last updated on 23-Feb-18 Page 7 of 11

8 Figure 2: The oxidation of ascorbic acid to dehydroascorbic acid. DESCRIPTION This method determines the vitamin C concentration in a solution using a redox reaction. In the redox reaction, iodine oxidises the ascorbic acid to dehydroascorbic acid, as the iodine is reduced to iodide ions (below). In the above reaction the iodine is reduced to iodide by vitamin C (ascorbic acid), which is itself oxidised. Only when all of the ascorbic acid has been oxidised is iodine free to react with the starch indicator to form the starch-iodine complex. The starch-iodine complex is blue/black in colour and causes a drastic colour change in the solution. The point at which the starch-iodine complex is formed is dependent on the amount of vitamin C in the solution, with solutions containing more vitamin C requiring more iodine to be added before the blue/black colour change. The method is suitable for determining the Vitamin C content in tablets, fresh or packaged fruit juices and solid fruits and vegetables. GOALS FOR THE EXPERIMENT. Observe the colour change as the redox reaction proceeds Estimate the vitamin C concentration of each sample by counting the number of drops of iodine solution needed to create the blue-black starch-iodide complex Present data in the format of table for each vitamin C source sample (fresh or preserve) Materials mL pipette mL conical flasks mL and 100-mL measuring cylinders mL syringe Last updated on 23-Feb-18 Page 8 of 11

9 5. Orange juice samples, dissolved tablet of vitamin C 6. Starch indicator 7. Iodine solution Conical flask 20-mL pipette Measuring Cylinder Juice samples Safety Precautions Always wear safety goggles and a lab apron Report any spills to your teacher Do not taste, eat, or drink any materials used in the lab Wash your hands after the experiments Pre-Lab 1. What do you expect to observe when the chemical reaction between ascorbic acid and iodine begins? Last updated on 23-Feb-18 Page 9 of 11

10 2. Why do we need the starch indicator in the experiment, even though it is not part of the redox reaction? Procedure 1. Pipette 20 ml of orange juice sample to a 250 ml conical flask 2. Add two drops of starch indicator 3. Add iodine solution to a syringe and start to add the iodine solution to the orange juice solution one drop at a time (counting each drop) 4. Count the number of drops added until the colour of orange juice sample turns dark blue and then record the number of drops required in the table below Last updated on 23-Feb-18 Page 10 of 11

11 Data Table: Fill out the table for different samples. Sample name Number of drops of iodine needed to turn the solution blue Conclude and Apply 1. Why does the orange juice change colour during the experiment? Does the orange juice contain vitamin C? 2. Why does the number of drops of iodine solution required to change the colour of the sample solution to a blue/blue black colour differ between the different samples? Last updated on 23-Feb-18 Page 11 of 11