1. Colligative Properties

To illustrate the concept of colligative properties in chemistry when dealing with solutions, I created a tiered lesson plan incorporating a simulated experiment, a hands-on activity, and a student generated analysis of data.

Students will access the simulated experiment

Freezing point depression, one of the colligative properties illustrated in the simulation, is used in the making of ice cream. Students can make ice cream in class using rock salt, coffee cans, ice, and the standard recipe for ice cream. This hands-on activity will illustrate how the normal freezing point of a so

While performing the simulated experiment, students work in cooperative groups to record data. There are a variety of solutes, electrolytes and nonelectrolytes as well as varying solutes. The class is to be divided into groups, with each group being responsible for a unique category as follows:

- nonelectrolyte solute in water

- electrolyte solute in water, NaCl

- electrolyte solute in water, CaCl2

- electrolyte solute in water, KCl

- no solute in water

Each group's responsiblility is to perform the simulated experiment for their group, record data, and graph change in temperature with varying concentrations. As a whole class activity the data will be then shared collectively to generate understanding of colligative properties.

As a follow-up assignment, students are to complete the assessment questions and turn them in along with a short written conclusion describing what they learned.

 

2. Equilibrium and Le Chatelier's Principle

The above is a link to an excellent online virtual lab going through several different chemical experiments illustrating Le Chateliers Principle and Equilibrium. This interactive tutorial includes background information, interactive experiments as well as simulations, and postlab questions. Students are to complete the entire lab, creating data tables for each lab activity, answering all post lab questions, and to write a detailed conclusion summarizing what they learnt, and how they would improve the activty if they could.

3. Selective Precipitation

  1. Save Our Pond
    To help determine what substance(s) could be used to precipitate mercury (I) ions (Hg2+2) from a local
    contaminated pond.
    Mercury
    is a toxic metal that is contaminating the environment. Mercury can be introduced to the
    environment through several avenues including the incineration of municipal and hazardous waste, the
    burning of coal from power plants, or the throwing away of household items that contain mercury,
    such as thermometers, mercury batteries, and fluorescent lamps, which can end up in landfills. This
    EPA document gives a more complete list of household products containing mercury.
    Mercury in the atmosphere can be deposited into bodies of water in several forms including Hg+2 and
    Hg2+2. Bacteria in the pond convert the mercury ions into methylmercury. This very toxic form of
    mercury can be ingested by the fish and other forms of wildlife in and around the lake
    or pond. The mercury accumulates in the tissues of the fish and works its way up the food chain.
    According to a USGS website (last updated in 2002): “Forty states have issued advisories for
    mercury on selected water-bodies and 13 states have statewide advisories for some or all
    sportfish from rivers or lakes”.
    What are the effects on wildlife? According to the website mentioned above, studies have shown
    mercury to
    -cause reductions in loon chick production in lakes where mercury concentrations in eggs
    exceed concentrations that are toxic in laboratory studies.
    -affect the behavior of juvenile Great Egrets.
    -decrease the effectiveness of protective enzymes in mallards, great egrets and other aquatic
    birds.
    -affect diving ducks from the San Francisco Bay, herons and egrets from the Carson River in
    Nevada, and heron embryos from colonies along the Mississippi River.
    People who eat contaminated fish can also accumulate mercury in their bodies, leading to a condition
    similar to cerebral palsy with potential blindness and deafness. Children exposed to mercury before
    they are born can experience a decrease in their: attention span, fine motor skills, language skills,
    visual-spatial abilities, and verbal memory. “Other effects of methyl mercury poisoning can include:
    loss of appetite, diarrhea, gum inflammation, lack of coordination of movements, impaired speech,
    hearing and walking; muscle weakness, memory loss and possible brain damage.”
    (http://www.waterspecialists.biz/html/low_level_mercury_removal.html, accessed July 2006)
    The National Research Council, in its 2000 report on the toxicological effects of methylmercury,
    pointed out that the population at highest risk is the offspring of women who consumed large amounts
    of fish and seafood during their pregnancy. (USGS Science For a Changing World,
    http://www.usgs.gov/themes/factsheet/146-00/ , accessed July 2006)
    The EPA has published a pamphlet on what fish to avoid during pregnancy. They suggest avoiding:
    shark, swordfish, King Mackerel and Tilefish as they contain the largest amounts of mercury. Pregnant
    women and children can eat up to 12 ounces a week of shrimp, canned light tuna, salmon, pollock and
    catfish. You can access the pamphlet at: www.epa.gov/ost/fish
    Procedure
    1. Start Virtual ChemLab and click on the General Chemistry Laboratory door. Once inside, click on
    the Inorganic Lab Bench.
    2. Enter the stockroom by clicking inside the Stockroom window. Once inside the stockroom, drag a
    test tube from the box and place it on the metal test tube stand. Click on the bottle of Hg2+2 on the shelf
    and a sample will appear in the test tube. (An enlargement of the test tube will appear at the lower left
    of the screen.) Click Done to send the test tube back to the lab. Return to Lab.
    3. The mercury solution you prepared in the stockroom is in the blue test tube rack. Drag the test tube
    with the Hg2+2 solution to the metal test tube stand. Click on the Divide button on the bottom (with the
    large red arrow) and make five more test tubes of the solution. With one test tube in the metal stand
    and the five others in the blue rack, click on the Na2S bottle to add sodium sulfide to the mercury
    solution. You will observe what happens in the window at the bottom left corner of the screen. Record
    your observations. If the solution remains clear, write NR, for no reaction. Drag this test tube to the red
    disposal bucket.
    4. Place a second tube from the blue rack on the metal stand. Add a sample of sodium sulfate, Na2SO4,
    and record your observations. Discard the tube. Continue testing each sample of the mercury solution
    with the other reagents on the TOP SHELF of the lab bench that are listed in the table below.

    Conclusion
    Which of the reagents tested could be used to precipitate Hg2+2 from the lake?
    Extension
    1. Can you think of any adverse effects that might occur by using the reagents mentioned in your
    conclusion?
    2. What factors might you want to consider when choosing what reagent to use?
    3. The Ksp for HgS is 1.6 x 10-54. If [Hg+2] = 2.0 ? 10-12 and the concentration of Na2S that was added
    was 3.5 x 10-20 moles per liter, would the HgS precipitate?

 

Interactive Physics

(a) Basketball

b) Shooting gallery:

 

(c) Comparison of a spring with a pendulum

(d) Factors affecting the period of a pendulum.