Water (Practice Questions)

Question 1

Why is water polar?

Answer 1

Although covalently bonded, the hydrogen and oxygen molecules in water do not share the electrons equally, resulting in polarity.

Question 2

What property of oxygen causes polarity in water?

Answer 2

Oxygen has a higher electronegativity and attracts the electrons more strongly, resulting in an imbalance in charges in the poles of the water molecule.

Question 3

Slightly positive charge

Answer 3

δ+

Question 4

Slightly negative charge

Answer 4

δ-

Question 5

What is a hydrogen bond?

Answer 5

A bond between a hydrogen atom and a highly electronegative atom (F, O, and N); stronger than standard polar associations

Question 6

Which properties of water are hydrogen bonding responsible for?

Answer 6

Thermal, cohesive, adhesive, surface tension, and solvent properties

Question 7

Draw a diagram of a hydrogen bond

Answer 7

Make sure the line representing the hydrogen bond is dotted

Question 8

What is cohesion?

Answer 8

The attraction between water molecules through hydrogen bonding.

Question 9

How does surface tension occur?

Answer 9

The hydrogen bonding between water molecules allows the liquid to resist low levels of external force, creating surface tension.

Question 10

What is the importance of surface tension?

Answer 10

Smaller organisms can move across the surface of the water.

Question 11

What is adhesion?

Answer 11

Water molecules stick to other polar or charged molecules by forming polar associations.

Question 12

What is capillary action?

Answer 12

Capillary action is the process of water flowing in opposition to gravitational forces using the adhesive property of water.

Question 13

What determines the strength of capillary action?

Answer 13

The strength is dependent on the diameter of the pore through which the water moves (smaller diameter = more action).

Question 14

Why is capillary action necessary?

Answer 14

Capillary action is necessary to allow water to be transported up plant stems via a transpiration stream.

Question 15

How does water move up from the roots to the leaves of a plant?

Answer 15

The adhesive properties of water allow it to first stick to the xylem cell walls, and the cohesive properties of water allow the water to move against gravity and up into the plant.

Question 16

Which substances are soluble in water?

Answer 16

Substances that contain ions or electronegative atoms (polar) are soluble in water.

Question 17

What is a dispersive hydration shell?

Answer 17

The polar regions of the water molecules surround the oppositely charged molecules, creating dispersive hydration shells.

Question 18

What life-promoting properties do solutes dissolved in water have?

Answer 18

Solutes in aqueous solutions are more likely to collide with enzymes and undergo necessary chemical reactions.

Question 19

How does water promote enzyme activity?

Answer 19

The polarity allows aqueous solutions in which the solutes can react

Absorb heat from exothermic reactions and maintains acid-base neutrality

Question 20

What are hydrophilic substances?

Answer 20

Substances that freely associate and readily dissolve in water, such as all polar molecules and ions

Question 21

What are hydrophobic substances?

Answer 21

Substances that do not freely associate or dissolve in water, such as all large non-polar molecules (lipids)

Question 22

How are substances transported in animals?

Answer 22

Water-soluble substances—including amino acids, simple sugars, wastes, and a small amount of gases—are transported via blood plasma.

Question 23

How are substances transported in vascular plants?

Answer 23

Mineral ions are transported via xylem vessels, while sugars, proteins, and dissolved nutrients are transported via the phloem.

Question 24

How are non-soluble substances transported in living organisms?

Answer 24

In animals, lipids are packaged with proteins to form water-soluble lipoproteins that are transported via blood. In plants, lipids might conjugate to amino acids and be transported via the phloem.

Question 25

What is buoyancy?

Answer 25

Buoyancy is the upward force applied to an object in a medium and is determined by the density of the medium; because water is denser than air, it applies a greater upward force that allows objects to float in water.

Question 26

What is viscosity?

Answer 26

A measure of a liquid’s tendency to flow; more viscous means more resistant to flow

Question 27

Why is water more viscous than air?

Answer 27

Water forms hydrogen bonds, increasing the friction of flowing molecules. Water can also dissolve many solutes, which can increase the viscosity of the solution.

Question 28

What is thermal conductivity?

Answer 28

A measure of a medium’s ability to move heat across a temperature gradient; a medium’s ability to spread heat evenly

Question 29

Why does water have higher thermal conductivity than air?

Answer 29

Water absorbs and transfers heat more readily than air because water particles are packed more closely.

Question 30

What is specific heat capacity?

Answer 30

The amount of energy required to raise the temperature of 1g of substance by 1ºC

Question 31

Why does water have a higher specific heat capacity than air?

Answer 31

Water has the highest specific heat capacity of any liquid because its hydrogen bonds require additional energy to break, which means it doesn’t quickly move to extreme temperatures.

Question 32

What is the advantage of water being denser than ice?

Answer 32

Ice forms at the top of water bodies, allowing aquatic life to live freely below the surface (water’s high specific heat capacity also ensures that the water body does not freeze completely).