Bio 189 Water, Aqueous Solutions, and Concentration

Why is water considered a polar molecule?

) Oxygen is more electronegative than hydrogen, creating partial charges

Which of the following best describes hydrogen bonding in water?

Weak attractions between the δ+ hydrogen of one water molecule and the δ– oxygen of another

What property of water allows it to stick to itself?

Cohesion

Which of the following is an emergent property of water?

c) It expands upon freezing

Why is water’s high specific heat capacity important to life?

It prevents organisms from overheating too quickly

Which of the following best describes adhesion?

Water molecules sticking to other substances

What is transpiration in plants?

The loss of water vapor through the leaves

Which process contributes most to evaporative cooling?

High-energy water molecules escaping as vapor

How does adding ice to a beverage lower its temperature?

Ice absorbs heat as it melts, lowering the temperature

Why does ice float on water?

Ice is less dense due to the hydrogen bonds forming a structured lattice

What happens to the density of water when it is heated?

It decreases

A solution is composed of:

A solute dissolved in a solvent

What is the molarity of a solution with 1 mole of solute dissolved in 1 liter of solution?

1 M

What happens to the rate of evaporative cooling in high humidity?

It decreases

Which of the following is the correct order of concentration terms from highest to lowest?

% > ‰ > ppm > ppb > ppt

Intracellular water

within cells; ~40% of adult
human biomass; primarily used as a solvent and
during chemical reactions (e.g., hydrolysis)

Extracellular water

outside cells (interstitial
water is extracellular water in-between cells);
~20% of adult human biomass

The resulting intermolecular force is

called a
hydrogen bond (┉)(not a chemical bond)

Hydrogen bonds underlie four emergent
properties of liquid water:

Cohesion/adhesion
• High specific heat capacity
• Decreasing density when frozen
• Power of solvency/dissociation

Cohesion

water molecules cling to one
another due to hydrogen bonding

Adhesion

water molecules cling to other
molecules due to hydrogen bonding

Results in surface tension

↑ force
needed to penetrate surface: walk on
water; droplets/beads; visceral pleura
associates with parietal pleura for proper
lung function and prevents lung collapse

Water heats slowly because

absorbed energy must first
overwhelm H-bonds before the kinetic activity/
temperature can ↑; Water cools slowly too

Water molecules that absorb the most heat energy (high
kinetic energy) are more prone

to evaporate (liquid➟gas)
than those with low kinetic energy resulting in ↓ temp

How can you replace loss ions?

Must replace lost ions (e.g., Na + , K+, Ca2+ ) by eating

Heat

total kinetic energy of the
matter in a defined mass; transfers
from warmer ➟ cooler matter

Temperature

average kinetic
energy of matter as sampled
from a particular location (e.g.
sublingual, anal, axillary)

Water density ↓ as it warms;

forms temp strata
in lakes; one reason why sea level is ↑

Its density also ↓ when it freezes (0 °C) and
is why ice floats

solid water has a stable
crystal lattice structure with greater
intermolecular distance than in liquid water).

Density

= mass/volume; if mass is constant,
then volume ↑ or ↓ with temperature changes
(↑ about 10% when frozen)

Solutes with polar bonds

(e.g., some proteins)

Solutes with ionic bonds

(e.g., Na + and Cl– in NaCl

Suspension

a heterogeneous mixture
whose solid particles eventually settle due to gravity (e.g., blood cells in a blood sample)