151F09Lab03D2L

151F09Lab03D2L - GenChem 3rd Class Today's Agenda: Develop...

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GenChem 3 rd Class Chemical Separations Today’s Agenda: Develop the problem of the day. Perform first challenge: extract pigments. Discuss the challenge of chemical separations. Perform second challenge: determine the best solvent for the problem. Develop a consensus on the best answer. Discuss writing the report.
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GenChem Chemists use their knowledge and understanding of the properties of substances to separate the different components of materials. Why separate substances? Identification Characterization Elimination Quantitation Application Transformation
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GenChem In particular, biological materials tend to be mixtures of hundreds of different substances. What do you know about the properties of substances that cause leaves and flowers to be colored? They absorb visible light of certain colors and reflect others. Chlorophyll , for example, absorbs red and blue light. Carotene absorbs green and blue light.
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GenChem Let′s think! . In your groups: Discuss what properties of pigments in a leaf or a flower you could use to extract them; Propose an experimental strategy to extract the different pigments in a plant; Chlorophyll Carotene
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GenChem Let′s explore! Many chemical separations are based on differences in the strength of the interactions between particles of different substances.
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GenChem The solubility of one substance in another depends on the relative strength of the attractive forces between their particles AA , BB >> AB Insoluble, Immiscible AA, BB <= AB Soluble, Miscible What is going on? Could we use water or acetone or petroleum ether to extract the pigments from spinach leaves? Demo
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Why does simply sticking a leaf in a beaker of solvent not work? What do you know about the structure of leaves? Where are the pigments located? How can you get them out? Pigments are located in chloroplast walls inside cells. Solvent can’t get to them. Need to break down cell walls.
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151F09Lab03D2L - GenChem 3rd Class Today's Agenda: Develop...

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