Question

post - lab questions. 1. use the word polar or nonpolar to complete the following: a. molecules are also hydrophilic. b. molecules can be either partially charged or fully charged. c. since polar molecules like water, then molecules must not. 2. use the word hydrophobic or hydrophilic to complete the following: a. molecules like to interact with water. b. molecules do not like to interact with water. c. molecules like to interact with hydrophobic molecules. 3. explain why water is called a polar molecule. 4. how does water dissolve sodium chloride (nacl) salt? 5. draw the phospholipid bilayer of the cell membrane (find a picture in the textbook or online). label the hydrophobic part and the hydrophilic parts. knowing that the cells cytoplasm (cytosol) is made up of a lot of water and that the environment outside the cell is very watery, explain why the phospholipid bilayer is oriented this way.

Explanation:

1. a. Polar molecules are hydrophilic and can interact with water. b. Non - polar molecules are hydrophobic and do not interact with water. c. Polar molecules are either partially or fully charged.
2. Water is a polar molecule. Polar molecules like water can dissolve polar substances. Sodium chloride (NaCl) is an ionic compound which dissociates into ions in water. Water molecules surround the ions through ion - dipole interactions, thus dissolving NaCl.
3. Water is called a polar molecule because it has a bent molecular shape with an oxygen atom at the center. Oxygen is more electronegative than hydrogen, creating a partial negative charge on the oxygen and partial positive charges on the hydrogens, resulting in a net dipole moment.
4. Sodium chloride (NaCl) is an ionic compound. When added to water, the polar water molecules surround the sodium (Na⁺) and chloride (Cl⁻) ions. The negatively charged oxygen ends of water molecules are attracted to Na⁺, and the positively charged hydrogen ends are attracted to Cl⁻. This process, called hydration, separates the ions and dissolves the salt.
5. The cell membrane has a phospholipid bilayer. The hydrophilic heads of phospholipids face the watery environments (cytosol inside the cell and extracellular fluid outside the cell) because they can interact with water. The hydrophobic tails face each other in the interior of the bilayer to avoid contact with water.

Answer:

1. a. Polar molecules are hydrophilic and can interact with water. b. Non - polar molecules are hydrophobic and do not interact with water. c. Polar molecules are either partially or fully charged.
2. Water is polar and can dissolve NaCl through ion - dipole interactions.
3. Water is polar due to its bent shape and electronegativity difference.
4. Water dissolves NaCl via hydration of its ions.
5. The phospholipid bilayer is oriented with hydrophilic heads facing water and hydrophobic tails away from water.