2.2 (Topic 2)

Question 1

Describe the structure of an atom

Answer 1

• Atoms are composed of protons, neutrons and electrons. Protons have a positive charge, neutrons have no charge and electrons have a negative charge.
• Protons and neutrons are found in the atomic nucleus. Electrons are found in a cloud surrounding the nucleus.

Question 2

Contrast ion with atom.

Answer 2

Atoms have no net charge because the have equal numbers of protons (+) and electrons (-). If an atom gains or loses an electron it will have a net charge and be called an ion.

Question 3

Define anion and cation.

Answer 3

• A negatively charged ion because it has gained electrons

- A positively charged ion because it has lost electrons.

Question 4

Contrast covalent, ionic and hydrogen bonds.

Answer 4

• All bonding involves electrons or the charges that result from the giving/taking of electrons.
• Covalent bond: electrons are shared between two atoms
• Ionic bond: attraction between cation and anion (no sharing of electrons)
• Hydrogen bond: an attraction (not a true bond) between two polar molecules.

Question 5

Write the molecular formula for water and draw the atomic structure of the molecule.

Answer 5

H2O

Question 6

Describe the cause and effect of the polar nature of water.

Answer 6

• In water, the oxygen has a greater “pull” on the shared electrons than the hydrogen atoms. As a result, there is unequal sharing of the electrons, with the electrons drawn closer to the oxygen.
• As a result, the oxygen has a slightly negative charge and the hydrogens have a slightly positive charge.

Question 7

Describe where and how water is able to form hydrogen bonds.​

Answer 7

• Water forms hydrogen bonds between the partial positive hydrogen of one water molecule and the partial negative oxygen of ANOTHER water molecule.
• One water molecule is capable of forming up to four hydrogen bonds with other water molecules.

Question 8

Contrast adhesion with cohesion.

Answer 8

• Adhesion: Water molecules bonding to non-water molecules through hydrogen bonding or attraction to an ionic charge.
• Cohesion: Water molecules attach to other water molecules through hydrogen bonding.

Question 9

Outline an example of the cohesive property of water being of benefit to life.

Answer 9

• Water cohesion allows for surface tension, allowing some insects to stay on the surface of the water.
• Water cohesion creates a chain of water molecules that allows for the transport of water from the roots to the leaves of plants.
• Water cohesion is responsible for the high heat capacity of water, maintaining a relatively stable internal temperature and external environment for living organisms

Question 10

Outline an example of the adhesive property of water being of benefit to life.

Answer 10

Adhesion is needed for water to move from the roots to the leaves of plants. Water sticks to the sides of the xylem wall through adhesion.

Question 11

Explain three thermal properties of water that are useful to living organisms.

Answer 11

• This means water absorbs more heat before changing state (each H-bond has an average energy of 20 kJ/mol)
  
  • Water has a significantly higher melting and boiling point
  • Water has a higher specific heat capacity (energy required to raise the
    temperature of 1 g of substance by 1ºC)
  • Water has a higher heat of vaporization (energy absorbed per gram as it
    changes from a liquid to a gas / vapour)
  • Water as a higher heat of fusion (energy required to be lost to change 1 g
    of liquid to 1 g of solid at 0ºC)

Question 12

Outline a benefit to life of water’s high specific heat capacity.

Answer 12

It takes a relatively large amount of heat energy to raise the temperature of water. This is a benefit because the temperature of large bodies of water remains relatively constant, protecting life from potentially lethal temperature fluctuations.

Question 13

Outline a benefit to life of water’s high latent heat of vaporization.

Answer 13

• It takes a relatively high amount of heat energy to vaporize water (convert from liquid to gas) because hydrogen bonds must be broken.
• As the water evaporates, the surface it leaves becomes cooler. This is called evaporative cooling and allows organisms to cool with sweating

Question 14

Outline a benefit to life of water’s high boiling point.

Answer 14

• Water boils at a relatively high temperature for a compound made of such light elements; this is due to the hydrogen bonding between water molecules causing them to resist being pulled apart (which is what happens when water boils to become a gas).
• Without this, water would not be a liquid over much of the surface of the Earth and we would not have a liquid ocean

Question 15

Explain why water is such a good solvent.

Answer 15

Water is a good solvent because it can form hydrogen bonds with a variety of different substances. Water is called the “universal solvent” because it dissolves more substances than any other liquid.

Question 16

List the types of molecules that water will dissolve.​

Answer 16

Water will dissolve substances that are polar or ionically charged.

Question 17

State that polar and ionic molecules are hydrophilic.

Answer 17

• Water is a polar molecule that attracts other polar or ionic substances,
  making them hydrophilic
  
  • A molecule or substance that is attracted to water.

Question 18

State that non-polar, non-ionic molecules are hydrophobic.

Answer 18

• Nonpolar or non-ionic molecules are hydrophobic.

- A molecule or substance that is NOT attracted to water.

Question 19

Given a diagram of a molecular structure, determine if the molecule is hydrophilic or hydrophobic.

Answer 19

The negative charge found on a phosphate group makes it an ION. Water is attracted to ions, making them hydrophilic.

Question 20

Compare the physical properties of methane and water.

Answer 20

Methane (CH4)

• Gas at room temperature
• Lower heat capacity

Water (H2O)

• Liquid at room temperature
• Higher heat capacity (more energy to change temp)

Question 21

Explain why water and methane have different thermal properties based on their molecular structures.

Answer 21

• Methane is nonpolar whereas water is polar.
• Because water is polar, it is able to form hydrogen bonds with many types of molecules.
• As a nonpolar molecule, methane does not form hydrogen bonds with other molecules.

Question 22

Explain sweating as a mechanism to cool the body.

Answer 22

Sweat is mostly water. When the water evaporates from the surface of the skin, it takes heat with it. With the loss of the heat energy, the skin feels cooler.

Question 23

State if the following molecules are hydrophobic or hydrophilic: glucose, amino acids, cholesterol, fats, oxygen, and sodium chloride.

Answer 23

Glucose: Hydrophilic
- Glucose has many polar -OH groups which are able to form hydrogen bonds with water.
Amino Acids: Generally Hydrophilic
- Although variable, many amino acids have polar or ionic “R” groups which
are able to form hydrogen bonds with water.
Cholesterol: Hydrophobic
- Cholesterol is primarily a non-polar hydrocarbon and does not form hydrogen bonds with water.
Fats: Hydrophobic
- Fats are primarily non-polar hydrocarbons and do not form hydrogen bonds with water.
Oxygen:
- Gaseous oxygen does not react with water. It is water soluble depending on temperature and pressure conditions.
Sodium Chloride:
- Hydrophilic
- The ions are able to dissolve in water.

Question 24

Outline the mechanism of transport in the blood of the following molecules: glucose, amino acids, cholesterol, fats, oxygen, and sodium chloride.

Answer 24

Glucose: Blood is primarily water. Because it is hydrophilic, glucose can dissolve and be directly transported in the blood.

Amino Acids: Blood is primarily water. Because most are hydrophilic, amino acids can usually dissolve and be directly transported in the blood.

Cholesterol: Blood is primarily water. Because it is hydrophobic, cholesterol must be transported in the blood within “sacs” called lipoproteins. Lipoproteins are a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.

Fats: Blood is primarily water. Because it is hydrophobic, fats must be transported in the blood within “sacs” called lipoproteins. Lipoproteins are a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.

Oxygen: Oxygen is transported in the blood by binding to a protein transport molecule (hemoglobin) within the red blood cells.

Sodium Chloride: Blood is primarily water. Because they are hydrophilic. sodium and chloride ions can dissolve and be directly transported in the blood.