A1.1 Water

Question 1

structure of water, electron sharing and polarity

Answer 1

two hydrogen atoms covalently bonded to oxygen atom (H2O), The electrons are not shared equally between atoms,
- oxygen side has two partial negative charges
- each hydrogen atom is positively charged
resulting in polarity.

Question 2

define polarity in the case of water

Answer 2

Water is a polar molecule, although water as a whole is electrically neutral, due to the unequal sharing of electrons between oxygen and hydrogen.
- Oxygen becomes slightly negative (δ⁻) and hydrogen slightly positive (δ⁺), creating partial charges at opposite poles.

• polarity occurs when molecule has one end negatively charged and one positive charged caused by uneven electron distribution

Question 3

why does oxygen have δ⁻ and hydrogen δ⁺

Answer 3

oxygen (due to higher electronegativity) attracts the electrons more strongly causing them to be closer, forming slightly negative charge).
The hydrogen atoms have a weaker attraction towards the electrons, resulting in slightly positive charge

-this results in the molecules asymmetrical shape

Question 4

dipole

Answer 4

the separation of charge due to the electrons in the covalent bonds being unevenly shared.

Question 5

what does the polarity of water allow in terms of bonding/associations?

Answer 5

it allows it to form weak associations with other polar molecules or charged ions.

• The slightly negative poles will attract the slightly positive poles of other molecules and vice versa

Question 6

what does the delta symbol indicate? δ

Answer 6

a charge is very small

Question 6

define hydrogen bonds
why do they form between water molecules?

Answer 6

• Hydrogen bonds are intermolecular associations that form due to the polar covalent bonds within water molecules.
• As a result of water’s polarity, hydrogen bonds form between the partially positive hydrogen of one molecule and the partially negative oxygen of an adjacent molecule.

Question 7

Explain why hydrogen bonds are stronger than other polar intermolecular forces

Answer 7

Hydrogen bonds are stronger than standard dipole-dipole (polar) interactions due to the high electronegativity of fluorine (F), oxygen (O), and nitrogen (N).
When hydrogen is covalently bonded to one of these atoms, the resulting partial charges are strong enough to create a significant intermolecular attraction between molecules.

Question 8

what is the result of weak hydrogen bonds

Answer 8

when there are few, and they are weak, they are constantly breaking and reforming.

• when there are a large number they form a strong structure

Question 9

unique properties of water caused by hydrogen bonds

Answer 9

• cohesion
• adhesion

SOLVENT PROPERTIES:
- high specific heat capacity
- high latent heat of vaporization
-high boiling point
- solvent properties

Question 9

what type of molecule is water?

Answer 9

an inorganic, polar molecule

Question 10

number of hydrogen bonds each water molecule can dorm with adjacent water molecules

Answer 10

4

Question 11

What property of water causes cohesion?

Answer 11

Polarity. water is cohesive, The polarity allows water molecules to form hydrogen bonds with each other, leading to cohesion — the tendency of water molecules to stick together.

Question 12

How does cohesion contribute to surface tension in water?

Answer 12

Cohesion creates surface tension at the air–water interface, as hydrogen bonds resist external force and hold water molecules together at the surface, forming a stable layer.

Question 12

What is cohesion and why is it important in plants?

Answer 12

Cohesion is the attraction between water molecules due to hydrogen bonding. It allows columns of water to move under tension in the xylem, enabling efficient mass transport from roots to leaves.

Question 13

What is surface tension and how does it support small organisms?

Answer 13

Surface tension is the tendency of the surface of a liquid to resist external force.

• caused by hydrogen bonding between water molecules, creates a film-like surface at the air–water interface. This allows small organisms, such as pond skaters and water striders, to move across water without sinking.

Question 14

How do water striders stay on the water surface?

Answer 14

Water striders have long legs with thousands of microscopic hairs that trap air and distribute weight, increasing buoyancy and allowing them to walk on water supported by surface tension

Question 15

How does detergent pollution affect surface tension and insects?

Answer 15

Detergents lower surface tension by disrupting hydrogen bonding. This makes it harder for insects like water striders to stay afloat, as the film becomes too weak to support their weight.

Question 16

define solvation

Answer 16

the process by which solvent molecules surround and interact with solute molecules

Question 17

What is adhesion and how is it caused in water?

Answer 17

Adhesion is the ability of water to stick to polar or charged surfaces due to hydrogen bonding. This allows water to cling to substances like cellulose in plant cell walls.

Question 18

Why is water a good solvent, and how does it interact with polar and non-polar substances?

Answer 18

Water is an excellent solvent due to its polarity and ability to form hydrogen bonds.

• It can dissolve substances with charged particles (ions) or polar regions (most biological molecules), as the polar water molecules form hydration shells around them.
• Non-polar (hydrophobic) molecules lack charge and do not interact with water; instead, they cluster together due to hydrophobic interactions, while water molecules form hydrogen bonds among themselves.

Question 19

What is capillary action and how does it relate to water’s properties?

Answer 19

Capillary action is the movement of water through narrow spaces against gravity, caused by adhesion to the surface and cohesion between water molecules. It is stronger in smaller diameters.

Question 20

How does capillary action support water movement in plants and soil?

Answer 20

In plants, capillary action helps pull water up xylem vessels during transpiration, with adhesion to cell walls and cohesion between molecules. In soil, it draws water from the water table through narrow pores, affecting plant hydration and agriculture.

• The loss of water vapour from the leaves (via evaporation) and the absorption of water into the roots (via osmosis) creates a pressure gradient

Question 21

What are some key thermal and chemical properties of water?

Answer 21

• Water freezes at 0 °C and boils at 100 °C at standard pressure.
• It has a high boiling point due to hydrogen bonds, which require significant energy to break.
• Water can act as an acid or a base (amphoteric), as each molecule can donate or accept a proton (H⁺).

Question 22

ions formed when water donates/accepts a proton

Answer 22

water is amphoteric accept: Hydronium ion H3O+ donate: hydroxide ion OH-

Question 22

Why is water an important medium for metabolic reactions?

Answer 22

Water - dissolves a wide range of substances, allowing solutes and enzymes to collide more frequently, facilitating chemical reactions. It also helps absorb heat from exothermic reactions and maintain acid–base neutrality, supporting enzyme function.

Question 23

How does solubility affect the transport of biological molecules?

Answer 23

Highly soluble molecules (e.g., urea, glucose) are freely transported in aqueous solutions. Even amino acids with hydrophobic R-groups are soluble enough for transport. Insoluble molecules (e.g., fats) require special transport mechanisms.

Question 23

How do hydrophilic and hydrophobic substances differ in water?

Answer 23

Hydrophilic: Polar or charged substances that dissolve in water (e.g., glucose, salts, amino acids). Hydrophobic: Non-polar substances (e.g., lipids) that do not dissolve in water and tend to group together.

Question 24

How are non-water-soluble molecules transported in animals and plants?

Answer 24

In animals: Lipids are carried in the blood as lipoproteins (lipid-protein complexes). In plants: Lipid transport may involve conjugation to amino acids and movement via the phloem (mechanism not fully understood).

Question 25

How does water support enzyme structure and function?

Answer 25

Water stabilizes enzyme shape, allows reactions to occur in aqueous solutions, and hydrogen bonds facilitate enzyme-substrate binding, forming an enzyme–substrate complex.

Question 26

Why does oxygen need assistance for transport in animals?

Answer 26

Oxygen is sparingly soluble in water and less soluble at body temperature (37°C) than at 20°C. To transport sufficient oxygen, it binds to haemoglobin, allowing effective oxygen delivery to body cells. Oxygen still dissolves in aquatic environments for respiration

Question 27

What substances does water transport in the blood plasma?

Answer 27

Blood plasma carries amino acids, glucose, urea, and small amounts of oxygen and carbon dioxide in dissolved form.

Question 27

physical properties of water

Answer 27

- specific heat capacity - thermal conductivity - buoyancy - viscosity

Question 27

What substances are transported by water in vascular plants?

Answer 27

Xylem: Transports water and mineral ions. Phloem: Transports dissolved nutrients such as sugars and amino acids.

Question 28

What is specific heat capacity and how does it apply to water?

Answer 28

Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1°C. Water’s high specific heat capacity (4200 J/kg/°C) is due to hydrogen bonds, which require a lot of energy to break and form.

Question 28

What are the biological advantages of water’s high specific heat capacity?

Answer 28

- Water temperature changes more slowly than air, providing stable aquatic habitats. - Water helps maintain constant internal temperatures, allowing for optimal enzyme activity. - Ringed seals (Pusa hispida) can survive year-round in Arctic environments due to stable sea temperatures.

Question 29

How does the black-throated loon (Gavia arctica) adapt to water’s thermal conductivity?

Answer 29

The loon’s feathers trap air to create an insulating layer, helping it retain body heat while diving in cold water.

Question 29

What is thermal conductivity and how does it apply to water?

Answer 29

Thermal conductivity is a substance’s ability to transfer heat. Water has 30× higher thermal conductivity than air due to the close packing of water molecules.

Question 30

How does thermal conductivity affect ringed seals and their habitat?

Answer 30

- Seals use blubber to insulate against high thermal conductivity in water and low temperatures. - Ice acts as an insulator over the sea, reducing heat loss below and helping keep water temperatures stable.

Question 31

What is buoyancy and how does it apply to water?

Answer 31

Buoyancy is the upward force exerted by a fluid, allowing objects to float. Water is more dense than air, so it provides greater buoyant force.

Question 32

How do loons overcome buoyancy for diving?

Answer 32

Loons have solid bones (unlike most birds), making them heavier. This helps increase body density, so they can sink and dive more easily.

Question 32

How does the ringed seal use buoyancy to its advantage?

Answer 32

The seal’s blubber increases buoyancy, helping it float in water while also serving as insulation against the cold.

Question 33

What is viscosity and how does it apply to water?

Answer 33

Viscosity is a fluid’s resistance to flow. Water has a higher viscosity than air due to hydrogen bonding and dissolved solutes.

Question 34

How is the ringed seal adapted to move through viscous water?

Answer 34

Streamlined body reduces resistance. Flippers provide efficient movement through water.

Question 35

What physical properties of water make it essential for life?

Answer 35

Specific heat capacity: thermal stability Thermal conductivity: heat transfer Buoyancy: supports floating/diving Viscosity: affects movement These influence the adaptations of organisms like the black-throated loon and ringed seal.

Question 35

Why do scientists believe water on Earth has an extraplanetary origin?

Answer 35

When Earth formed (~4.5 billion years ago), it was too hot for water to condense. Scientists believe asteroids or meteorites delivered water to Earth, since many contain ice and organic material.

Question 36

What should students remember about hypotheses for the origin of water on Earth?

Answer 36

Although multiple hypotheses exist, IB students only need to study the asteroid hypothesis for exams.

Question 36

What meteorite evidence supports the asteroid water hypothesis?

Answer 36

Carbonaceous chondrites have hydrogen isotopes similar to seawater. Eucrite achondrites have hydrogen isotope ratios similar to those on Earth. These meteorites may have released water vapor during impact, which condensed into liquid water and was retained by Earth’s gravity.

Question 37

Why is water essential in the search for extraterrestrial life?

Answer 37

Life depends on water, so the presence of water is considered a key indicator of potential life on other planets.

Question 38

What is the Goldilocks zone and why is it important for life?

Answer 38

It’s the region around a star where temperatures are "just right" for liquid water to exist — not too hot or too cold. A planet in this zone is more likely to support life.

Question 38

What are exoplanets and how do scientists study them for signs of water?

Answer 38

Exoplanets are planets outside our solar system. Scientists use transit spectroscopy to analyze the light passing through their atmospheres. The light reveals elements or molecules, including a possible water signature.

Question 39

Why is water crucial for life processes?

Answer 39

In liquid water, dissolved molecules can move freely, collide, and react. This allows most biological processes to occur efficiently — which is why water is considered the medium of life.

Question 39

What are the key characteristics of an exoplanet that could support life?

Answer 39

- A water signature - Located in the Goldilocks zone - Large enough to support an atmosphere

Question 40

How did water contribute to the origin of the first cells on Earth?

Answer 40

Life likely began in deep ocean hydrothermal vents, where water and solutes were trapped in membrane-bound structures, allowing chemical reactions that led to the evolution of cells.

Question 41

What is transit spectroscopy and how is it used to detect water on exoplanets?

Answer 41

the technique analyzes light passing through the planets atmosphere as it passes in front of its nearest star based on the wavelength of the light being absorbed or deflected, an analysis can be made about the elements and molecules present in the atmosphere. If it indicates water may be present, the planet is said to have a water signature