Directed Reading: Water’s Unique Properties

Suggest how dolphins get freshwater if they live in a salty sea from information in this paragraph.

• Dolphins get freshwater from the food they eat - this is possible since marine organisms are mostly water, at 80% water.

• Dolphins drink seawater and filter out the salt using special organs.

• Dolphins absorb freshwater through their skin from rainwater.

• Dolphins get freshwater by swimming to rivers and drinking directly from them.

State the main salt found in seawater, along with 5 other types of solutes (things dissolved in water) found in seawater.

• The main salt in the ocean is sodium chloride. The 5 other solutes are: 1) other salts, 2) trace elements, 3) organic molecules, 4) dissolved gasses, 5) and nutrients.

• The main salt in the ocean is potassium chloride. The 5 other solutes are: 1) sugars, 2) vitamins, 3) proteins, 4) dissolved metals, 5) and sand.

• The main salt in the ocean is calcium carbonate. The 5 other solutes are: 1) dissolved plastics, 2) oils, 3) ammonia, 4) sulfur, 5) and clay.

• The main salt in the ocean is magnesium sulfate. The 5 other solutes are: 1) dissolved rocks, 2) carbon dioxide only, 3) methane, 4) iron filings, 5) and silt.

Distinguish between an atom and an element.

• An atom is the smallest form of an element, and an element is a substance found naturally on Earth, such as oxygen.

• An atom is a large molecule, and an element is a mixture of substances.

• An atom and an element are the same thing with no difference.

• An atom is a type of compound, and an element is a type of mixture.

Describe the sizes of the atoms involved in the water molecule.

• The water molecule consists of two small hydrogen atoms, and one much larger oxygen atom.

• The water molecule consists of two large hydrogen atoms, and one much smaller oxygen atom.

• The water molecule consists of three atoms of equal size.

• The water molecule consists of one small hydrogen atom, and two much larger oxygen atoms.

Describe a hydrogen bond.

• A hydrogen bond is a weak attraction of opposite charges, and they are not as strong as the bonds that hold the hydrogen atom to the oxygen atom in the water molecule.

• A hydrogen bond is a type of covalent bond that forms between two hydrogen atoms.

• A hydrogen bond is the sharing of electrons between hydrogen and carbon atoms.

• A hydrogen bond is a metallic bond found only in metals.

State why hydrogen bonds are SO important.

• The hydrogen bonds are responsible for water being a unique molecule!

• Hydrogen bonds make water heavier than most gases.

• Hydrogen bonds cause water to evaporate instantly.

• Hydrogen bonds prevent water from dissolving salts.

Use the caption of figure 3.1 on page 58 to describe the overall charge of each end of the water molecule.

• The oxygen end is negative, and the hydrogen end is positive.

• The oxygen end is positive, and the hydrogen end is negative.

• Both ends are positive.

• Both ends are negative.

State one special characteristic about water when it comes to the 3 states of matter.

• Water is the only substance that naturally exists on Earth in all 3 states - solid - liquid - and gas.

• Water can only exist as a liquid on Earth.

• Water never exists as a gas in nature.

• Water is always found as a solid in nature.

Describe the process of hydrogen bonding between different water molecules in the liquid phase.

• The water molecules are held in place in small groups, however they are not held in place constantly. The hydrogen bonds that hold them together are constantly breaking, and reforming.

• The water molecules are held together by permanent covalent bonds, which never break.

• The water molecules do not interact with each other at all in the liquid phase.

• Hydrogen bonds in water only form in the solid phase, not in the liquid phase.

State how long a hydrogen bond between two water molecules lasts for in the liquid phase, and explain how this is possible.

• The hydrogen bond only lasts for a trillionth of a second. This quick forming and breaking process is possible since the hydrogen bond is very weak, being able to be broken and formed easily.

• The hydrogen bond lasts for several minutes. This is possible because hydrogen bonds are extremely strong and rarely break.

• The hydrogen bond lasts for a few hours. This is possible because water molecules are very stable and do not move much in the liquid phase.

• The hydrogen bond lasts for a few seconds. This is possible because the bond is moderately strong and only occasionally breaks.