BENCHMARK REVIEW

BENCHMARK SC.912.L.18.12
Discuss the special properties of water that contribute to Earth’s suitability as an environment for life: cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent. AA

Water has many unique properties that make it an important substance for life. One such property is its ability to store heat energy. Water absorbs heat more slowly and retains this energy longer than many other substances do. Many organisms release excess heat through water evaporation. For example, humans cool themselves by sweating. The water vapor lost through the evaporation of sweat carries heat away from the body.

Two other important properties of water are cohesion and adhesion. Cohesion is an attraction between substances of the same kind. The hydrogen bonds between water molecules cause the cohesion of liquid water. Because of cohesion, water and other liquids form thin films and drops. Adhesion is an attraction between different substances. Water molecules are attracted to many other similarly polar substances. Adhesion powers a process, called capillary action, in which water molecules move upward through a narrow tube, such as the stem of a plant.

Another important property of water is its ability to dissolve many substances. A solution is a mixture in which one or more substances are evenly distributed in another substance.

The polarity of water enables many substances to dissolve in water. Ionic compounds and polar molecules dissolve best in water. Nonpolar molecules, however, do not dissolve well in water.

Benchmark Practice

  1. When water in a lake freezes, the ice that forms floats on top of any water that is still liquid. Why does the ice float?
  1. Ice is less dense than liquid water, so it floats.
  2. Air bubbles trapped in the ice cause the ice to float.
  3. Ice crystals are polar, and they float on top of non-polar water.
  4. The ice forms at the top of the water, so it stays there and floats.
  1. When the oxygen atom in one water molecule is close to a hydrogen atom in another water molecule, what is most likely to happen?
  1. The water molecules will draw toward each other.
  2. The two water molecules will form a larger molecule.
  3. The like charges of the water molecules will repel each other.
  4. The two water molecules will gain energy and vaporize, becoming water vapor.
  1. When trees pull water in through their roots, they must then move the water up to their leaves in order to carry out photosynthesis. Since the water molecules cling to each other and to the inner surface of the xylem, the water can pull itself up through the tree by capillary action.
    Which property of water molecules allows them to cling together?
  1. Water molecules are polar molecules.
  2. Water molecules are small molecules.
  3. Water molecules have an odd number of atoms.
  4. Water molecules have covalent bonds between atoms.
  1. In Florida, daytime and nighttime temperatures usually only differ by 5 to 10°C, while temperatures in the desert often differ by as much as 40°C. What role does water play in keeping temperatures in Florida from fluctuating dramatically?
  1. Bodies of water store heat during the day and release it at night.
  2. Humid air releases heat as it rises, keeping temperatures constant.
  3. Evening rain brings heat from the upper atmosphere back to Earth.
  4. Water cools the land around it so that it never gets as hot as a desert.
  1. When salt is mixed with water and stirred, the salt will dissolve, forming a solution. When sand is mixed with water, the sand will not dissolve. Why will salt form a solution with water but sand will not?
  1. Sand is much harder than salt and so it will not form a solution with water.
  2. Salt is pulled apart into two ions by the polar water molecules, and sand is not.
  3. Salt consists of only 2 atoms and is small enough to dissolve, while sand is too large.
  4. Sand forms complex crystals which dissolve much more slowly than non-crystalline salt.

Test Practice SC.912.L.18.12

  1. A florist places a bouquet of white carnations in water containing blue dye. After a time, the flowers turn blue. What process helped the carnations to change color?
  1. water’s ability to form crystals
  2. ability of H2O to dissolve NaCl
  3. cohesion and adhesion of water molecules
  4. formation of covalent bonds between hydrogen and oxygen molecules
  1. Which of these statements correctly explains why water is a good solvent for many ionic compounds?
  1. Water is a polar compound.
  2. Water is an ionic compound.
  3. Water molecules are nonpolar.
  4. Water molecules completely separate into ions in solution.

3

  1. What is the attractive force between two of the same kind of particle?
  1. adhesion
  2. capillary action
  3. cohesion
  4. polarity

4.Which of the following is not a unique property of water?

  1. Water molecules stick together by cohesion.
  2. Frozen water is less dense than liquid water.
  3. Water molecules stick to other polar substances.
  4. Hydrogen bonds allow water to heat and cool very quickly.
  1. Water has the ability to store heat longer than other substances. What benefit does this property of water provide to organisms?
  1. It provides the ability to dissolve nonpolar compounds.
  2. It provides the appropriate catalyst for chemical reactions.
  3. It enables organisms to function with a higher cellular pH.
  4. It allows organisms to maintain a stable internal temperature.

6

  1. Many fish and aquatic plants can survive a cold winter because the layer of ice that forms at the top of a lake insulates the water below and prevents the lake from freezing solid. What unique property of water contributes to this effect?
  1. Water absorbs heat when it evaporates and forms a gas.
  2. Water expands and becomes less dense when it freezes.
  3. Water molecules completely separate into ions in solution.
  4. Water forms hydrogen bonds with ions and other polar substances.