Names: ______Date: ______
Exploring Properties of Water Honors
Directions:Write all answers on a separate sheet of paper. You may hand in one answer sheet per pair. Use pages 39 – 44 in your text books to help you. Use complete sentences for credit.
1. Sodium Pentothal, also known as truth serum, is used by the C.I.A. to gather intel from high-profile criminals/terrorists. One way to inconspicuously get the criminal of interest to ingest the serum is to slip it into their drink. Sodium Pentothal is a compound created chemically combining a metal and a nonmetal. Your mom is a CIA agent, and you discovered some truth serum from her coat pocket. You suspect that your boyfriend or girlfriend is cheating on you after snooping through their phone. You then have an “Aha” moment, and decide to use the truth serum on your boyfriend/girlfriend. To use it, you must slip it into their water bottle without them knowing. Once they finish their water, they will tell you their deepest, darkest secrets within 30 minutes. When placed in a water-based liquid, the sodium pentothal compound disappears.
a. What type of mixture is formed when the sodium pentothal mixes with water? Explain.
b. Describe how the water causes the truth serum to disappear. Use the terms polar,
positive ions, negative ions, solute, and solvent in your answer.
2. The pygmy gecko is able to literally stand on a droplet of water. Its skin is covered in oil. What properties of water allow the gecko to avoid breaking through the droplet? Use the terms hydrogen bonds, cohesion, and surface tension. (hint: the gecko isn’t lighter than water
3. This Thorny Devil lives in the arid deserts of Australia. Scientists have observed that as it stands in the shallow water, it appears to be drinking through its feet. Upon closer inspection, it is revealed that water is actually traveling, against gravity, up the arms and legs of the lizard. The thorny devil is covered in scaly bumps, grooves and crevasses, which act as passageways that carry the water up the lizard’s body. Use the terms hydrogen bonds, adhesion, cohesion, and capillary action (capillarity) to describe how this occurs.
4. The land masses on Pandora are very broken up, creating more coastlines and fewer inland regions than on earth. Because so much of the land consists of coastline, the ocean reduces extremes in temperature across the entire continent. In other words, temperatures don’t fluctuate very much anywhere on the planet, and remain relatively consistent all year round. Explain.
1 a. A solution was formed when the sodium pentothal and water mixed. A solution is a mixture in which a solute is dissolved by a solvent, and the solute is evenly dispersed throughout the solvent. In this solution, water is solvent, which dissolves the solute sodium pentothal.
b. Water causes the truth serum to disappear by dissolving it. Sodium Pentothal is an ionic compound, meaning it is bound together by positively and negatively charged ions. Water is polar molecule, meaning it has an uneven sharing of electrons between the oxygen and hydrogen atoms. This gives water a partial negative, and partial positive charge within the molecule.
When sodium pentothal is stirred into water, the positive hydrogen end of water molecules surround the negative ions in sodium pentothal. Conversely, the negatively charged oxygen end of water molecules surround the positive ions in sodium pentothal. The ions in sodium pentothal become attracted to the water molecules charges, instead of to each other, and the truth serum is broken apart into extremely small particles. It becomes invisible to the naked eye, and the particles evenly spread throughout the water. It is not dissolved.
2. The pygmy gecko is not less dense than water. It is not floating on the surface of the water. Rather, it is able to walk across because the water molecules are polar. This means that each water molecule has a partial negative, and partial positive charge within it. The negative ends of one water molecule attract the positive ends of a neighboring water molecule, and vice versa. The attraction of water to other water is called cohesion. At the very surface of a body of water, the attraction of water molecules are slightly stronger. This is called surface tension. The strength of the surface tension is strong enough to hold the gecko without breaking the hydrogen bonds. Because the gecko is covered is oil, which is nonpolar, and has no charges in it, the water molecules do no attract to the oil. This helps to maintain the surface tension.
3. Capillary action is the ability of a liquid to travel against gravity, like how water moves up the skin of the thorny devil lizard. Capillary action is the result of cohesion, the ability of water to attract, or stick to other water molecules, and adhesion; the ability of water to attract and stick to other types of substances with charges (skin, metal, glass). There are charged molecules in the many small crevasses on the skin of the thorny devil. When the lizard steps into a shallow puddle, the water molecules "automatically" begin to move up its body because they are attracted to the charges in the skin (due to adhesion), and pull each other up in a chain (cohesion). Both cohesion and adhesion are the result of water's polarity, which causes water to form hydrogen bonds with other water molecules, and with other charged surfaces.
4. The temperature in the Mojave desert (deserts are very dry) is very hot in the day, and very cold at night. This is because of the lack of water in a desert. Water is able to absorb a lot of heat from the sun, and release some of that heat energy when it is cooler. When the Mojave desert is compared to the Jersey shore, the temperatures are much more moderate. The ocean absorbs lots of heat during the day, and releases it into the cooler night time air, making the land much more reasonable to live on. Since the land on Pandora is mostly surrounded by ocean, the small land masses will stay within a smaller range of temperatures day-to-day due to the ability of water to absorb and release thermal energy.