Water (Practice Questions) Flashcards
Remember examples of the black-throated loon and ringed seal (physical properties of water)
Why is water polar?
Although covalently bonded, the hydrogen and oxygen molecules in water do not share the electrons equally, resulting in polarity.
What property of oxygen causes polarity in water?
Oxygen has a higher electronegativity and attracts the electrons more strongly, resulting in an imbalance in charges in the poles of the water molecule.
Slightly positive charge
δ+
Slightly negative charge
δ-
What is a hydrogen bond?
A bond between a hydrogen atom and a highly electronegative atom (F, O, and N); stronger than standard polar associations
Which properties of water are hydrogen bonding responsible for?
Thermal, cohesive, adhesive, surface tension, and solvent properties
Draw a diagram of a hydrogen bond
Make sure the line representing the hydrogen bond is dotted
What is cohesion?
The attraction between water molecules through hydrogen bonding.
How does surface tension occur?
The hydrogen bonding between water molecules allows the liquid to resist low levels of external force, creating surface tension.
What is the importance of surface tension?
Smaller organisms can move across the surface of the water.
What is adhesion?
Water molecules stick to other polar or charged molecules by forming polar associations.
What is capillary action?
Capillary action is the process of water flowing in opposition to gravitational forces using the adhesive property of water.
What determines the strength of capillary action?
The strength is dependent on the diameter of the pore through which the water moves (smaller diameter = more action).
Why is capillary action necessary?
Capillary action is necessary to allow water to be transported up plant stems via a transpiration stream.
How does water move up from the roots to the leaves of a plant?
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.
Which substances are soluble in water?
Substances that contain ions or electronegative atoms (polar) are soluble in water.
What is a dispersive hydration shell?
The polar regions of the water molecules surround the oppositely charged molecules, creating dispersive hydration shells.
What life-promoting properties do solutes dissolved in water have?
Solutes in aqueous solutions are more likely to collide with enzymes and undergo necessary chemical reactions.
How does water promote enzyme activity?
The polarity allows aqueous solutions in which the solutes can react
Absorb heat from exothermic reactions and maintains acid-base neutrality
What are hydrophilic substances?
Substances that freely associate and readily dissolve in water, such as all polar molecules and ions
What are hydrophobic substances?
Substances that do not freely associate or dissolve in water, such as all large non-polar molecules (lipids)
How are substances transported in animals?
Water-soluble substances—including amino acids, simple sugars, wastes, and a small amount of gases—are transported via blood plasma.
How are substances transported in vascular plants?
Mineral ions are transported via xylem vessels, while sugars, proteins, and dissolved nutrients are transported via the phloem.
How are non-soluble substances transported in living organisms?
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.
What is buoyancy?
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.
What is viscosity?
A measure of a liquid’s tendency to flow; more viscous means more resistant to flow
Why is water more viscous than air?
Water forms hydrogen bonds, increasing the friction of flowing molecules. Water can also dissolve many solutes, which can increase the viscosity of the solution.
What is thermal conductivity?
A measure of a medium’s ability to move heat across a temperature gradient; a medium’s ability to spread heat evenly
Why does water have higher thermal conductivity than air?
Water absorbs and transfers heat more readily than air because water particles are packed more closely.
What is specific heat capacity?
The amount of energy required to raise the temperature of 1g of substance by 1ºC
Why does water have a higher specific heat capacity than air?
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.
What is the advantage of water being denser than ice?
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).
