bio 7/14: Chemistry of Life & Water Properties Lecture

Question-and-Answer flashcards covering bond strength, molecular geometry, water’s properties, pH, and introduction to carbohydrates from the lecture.

Which covalent bonds require the least energy to break?

Single bonds.

Which organisms in soil can break the triple bond of atmospheric N₂?

Nitrogen-fixing bacteria.

How does bond order relate to bond-breaking energy?

The more bonds between two atoms (double, triple), the more energy required to break them.

What is the molecular geometry of methane (CH₄)?

Tetrahedral.

What is the molecular geometry of carbon dioxide (CO₂)?

Linear.

What is the molecular geometry of a water molecule (H₂O)?

Bent (angular/planar-bent).

Why is water’s shape bent rather than linear?

Repulsion from two lone electron pairs on oxygen pushes the H–O–H bonds apart.

Approximately what percentage of a cell’s mass is water?

About 75 %.

Why is water considered an excellent natural solvent?

Its polarity allows it to surround and separate many polar or charged solutes.

What type of molecules dissolve readily in water?

Polar or charged (hydrophilic) molecules.

What type of molecules are repelled by water and do not dissolve well?

Non-polar, hydrophobic molecules such as lipids/oils.

What weak attractive force links one water molecule to another?

Hydrogen bonding between H (δ+) and O (δ−) atoms of adjacent molecules.

Are hydrogen bonds generally strong or weak?

Weak; they break and reform easily.

What is a “shell of hydration”?

A layer of water molecules that surrounds and stabilizes a dissolved ion or polar molecule.

How can table salt be recovered from saltwater?

Evaporate or boil off the water so the Na⁺ and Cl⁻ recombine as solid salt.

What are hydrophobic interactions?

Weak forces that aggregate non-polar molecules in water (often via Van der Waals attractions).

Which property of water lets some insects stride across its surface?

High surface tension.

Define cohesion in water.

Attraction between water molecules due to hydrogen bonding.

Define adhesion in water.

Attraction between water molecules and a different polar surface (e.g., glass).

What phenomenon in a graduated cylinder demonstrates adhesion and cohesion?

Formation of a meniscus (curved surface).

Does water become more or less dense when it freezes?

Less dense; it expands, so ice floats.

Why is the floating of ice vital for aquatic life?

The ice layer insulates liquid water below, allowing organisms to survive winter.

Does water have a high or low specific heat?

High specific heat.

What molecular feature gives water its high specific heat?

Extensive hydrogen bonding that must be disrupted to raise temperature.

What is evaporative cooling?

Heat removal as water absorbs energy to vaporize (basis of sweating/panting).

What is an acid in proton (H⁺) terms?

A substance that donates protons, increasing [H⁺]/[H₃O⁺] in solution.

What is a base in proton terms?

A substance that accepts protons, decreasing [H⁺] in solution.

What pH value is considered neutral?

pH 7, where [H₃O⁺] equals [OH⁻].

How does each unit change on the pH scale relate to proton concentration?

It is logarithmic; each whole pH unit represents a ten-fold change in [H⁺].

What is a buffer?

A compound or mixture that resists pH change by accepting or donating protons.

Give the general chemical formula for carbohydrates.

(CH₂O)ₙ, where n = number of carbon atoms.

Name two functional groups found in all carbohydrates.

Carbonyl group (C=O) and hydroxyl group (–OH).

Differentiate monosaccharide and polysaccharide.

Monosaccharide = single sugar unit; polysaccharide = many sugar units linked in a polymer.

How do aldose and ketose sugars differ?

Position of the carbonyl group—aldose at an end carbon, ketose on an internal carbon.

Why do most sugars form rings when dissolved in water?

Intramolecular reactions in aqueous solution cause the straight chain to cyclize into a ring, which is more stable.