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Chemistry LibreTexts

Sample Handling and Treatment

  • Page ID
    199369
  • Q10. (Sample Handling & Treatment) Answer Q1 – Q13 in the Chemical Equilibria and Sample Preparation section of the Lithia Water Springs document. After completing these questions, go online to the U.S. Environmental Protection Agency website (www.epa.gov) and search for documentation regarding the preservation of inorganic analytes in water samples.

    Q11. (Sample Handling & Treatment) Based on your search results on the U.S. EPA website and your answer to question 13 in the Chemical Equilibria and Sample Preparation section, develop a sampling plan for Lithia water so that all significant analytes can be determined.

    One general approach to preserving Lithia water without compromising the determination of bicarbonate is to obtain two samples of Lithia water in Nalgene bottles, and acidify the sample that will be used to determine the concentration of all cationic species. A 1.0 mL sample of 6 M HNO3 added to 60 mL of Lithia water should be sufficient to reduce the sample pH below 2.0. The unpreserved sample should be tightly capped until the bicarbonate ion determination is about to be performed.

    Activity #1: At this point, if you are going to have your students analyze some of the constituents of a local water source, it would be an appropriate time to have them collect the samples. If students are interested in investigating changes in sample appearance upon standing, students should obtain a small, clean Nalgene bottle (60 – 250 mL capacity) and rinse it thoroughly with the water sample. After rinsing, fill the bottle completely with water and cap it tightly. Students should record any observations regarding the appearance of the water immediately after collection and a day or two afterwards. They should measure the pH of the water sample and record that value in their laboratory notebook. If students have already developed a sampling plan, appropriate steps should be taken to properly clean sample containers and preserve samples as needed.

    Instructors should inform their students that any change in the appearance of their natural water sample may indicate the occurrence of a chemical reaction that changes the chemical composition of the water sample. Such changes include the appearance of turbidity or precipitate, gas evolution and/or a color change. In the case of Lithia water, the Lithia water piped into downtown Ashland, Oregon is clear and colorless with a pH of approximately 6.4 and a faint sulfurous smell. After 1 – 2 days, the Lithia water sample becomes slightly turbid with a light orange precipitate at the bottom of the sample container.

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