Water and Life - Flashcards

A set of Q&A flashcards covering key concepts from the Water and Life lecture notes (polarity, hydrogen bonding, phase changes, temperature and heat properties, cohesion/adhesion, solvent properties, and solubility).

What is a thermocline and what causes it?

A thermocline is a layer in the ocean where temperature changes with depth, separating warmer surface water from cooler deeper water due to water’s density differences with temperature.

Which oceanic zone lies at the surface and is warmed by sunlight?

The epipelagic zone, the sunlit surface layer where temperature decreases with depth.

What is the relationship between water temperature and density?

Cold water is generally denser than warm water; density increases as temperature decreases until the coldest temperatures reach a point.

What is the most dense state of water?

Liquid water near 4°C (39°F) is the densest state.

Why does ice float on liquid water?

Because ice is less dense than liquid water due to the crystalline lattice formed by hydrogen bonding.

What causes water’s polarity?

Unequal sharing of electrons in the O–H bonds; oxygen is more electronegative, giving partial negative charge on O and partial positive charge on H.

Why is the water molecule bent?

The lone pair electrons on oxygen repel each other, giving a bent molecular shape.

What are hydrogen bonds in water?

Intermolecular attractions where the partially positive hydrogen of one molecule interacts with the lone pair on a neighboring electronegative atom (often oxygen).

What is cohesion?

Attraction between like molecules (water–water), enabling surface tension and droplet formation.

What is adhesion?

Attraction between water and unlike substances (water–surfaces), driving capillary action.

What is surface tension and how is it related to cohesion?

Surface tension is the cohesive force at the surface of a liquid, arising from water–water hydrogen bonding, enabling droplets and surface stability.

What is capillary action?

The movement of water upward in narrow spaces against gravity, driven by adhesion to surfaces and cohesion within water.

What is a solvent?

A substance that dissolves other substances; water is a common solvent in biology.

What is a solute?

A substance dissolved in a solvent to form a solution.

What is a solution?

A homogeneous mixture of solute dissolved in solvent.

What happens when salts dissolve in water?

Ions dissociate and water forms hydration shells around the ions.

Can water dissolve polar molecules?

Yes; water dissolves many polar molecules (e.g., ammonia).

Can water dissolve nonpolar molecules?

No; nonpolar molecules (e.g., oil) are not soluble in water.

What is specific heat?

The amount of heat required to raise the temperature of 1 g of a substance by 1°C.

Why does water heat up slowly?

Because significant energy is needed to break hydrogen bonds, giving water a high specific heat.

What is heat of vaporization?

The amount of energy required to convert a liquid to a gas.

What is evaporative cooling?

Cooling that occurs when a liquid evaporates and absorbs heat; for example, sweating cools the body as water absorbs heat to vaporize.

What is a hydration shell?

A layer of water molecules surrounding a dissolved solute or ion.

What is the role of water as a solvent in biology?

Water’s polarity allows it to dissolve ions and polar molecules and form hydration shells; nonpolar molecules are not soluble.