Water A1.1 Study Guide

What must you be able to show when drawing two water molecules joined together?

Draw two H₂O molecules with bent shapes. Show the O–H bonds as polar covalent bonds, label O as δ⁻ and H as δ⁺, and show a hydrogen bond as a dashed line between the δ⁺ hydrogen of one molecule and the δ⁻ oxygen of the other.

What type of bonding occurs within a water molecule?

Polar covalent bonding. The oxygen and hydrogen atoms share electrons, but the electrons are shared unequally.

What type of bonding occurs between water molecules?

Hydrogen bonding. The δ⁺ hydrogen of one water molecule is attracted to the δ⁻ oxygen of another.

Why are the covalent bonds in water polar?

Oxygen is more electronegative than hydrogen, so it attracts the shared electrons more strongly.

What causes water to be a polar molecule?

Unequal sharing of electrons gives oxygen a partial negative charge (δ⁻) and the hydrogen atoms partial positive charges (δ⁺), creating an uneven distribution of charge.

What charge does the oxygen atom have in a water molecule?

Partial negative charge (δ⁻).

What charge do the hydrogen atoms have in a water molecule?

Partial positive charge (δ⁺).

How does the polarity of water allow hydrogen bonds to form?

The δ⁺ hydrogen of one water molecule is attracted to the δ⁻ oxygen of a neighbouring water molecule, forming a hydrogen bond.

What is cohesion?

Cohesion is the attraction between molecules of the same substance. In water, it is caused by hydrogen bonding between water molecules.

What is adhesion?

Adhesion is the attraction between molecules of different substances, such as water molecules and another surface.

What is the difference between cohesion and adhesion?

Cohesion is attraction between water molecules, whereas adhesion is attraction between water and another substance.

How does cohesion benefit organisms?

It allows water molecules to remain together, helping maintain continuous columns of water, such as in plant xylem.

How does adhesion benefit organisms?

It allows water to stick to other surfaces, helping water move through narrow structures such as plant vessels.

What are the four key properties of water in this unit?

Adhesion, cohesion, solvent properties, and thermal properties.

What does it mean that water has solvent properties?

Water can dissolve many substances, allowing molecules and ions to move and interact.

Why is water a good solvent?

Water is polar, so its partial charges allow it to interact with and dissolve many polar and charged substances.

How do the solvent properties of water support life?

Essential molecules such as amino acids and nucleotides can dissolve, move, and interact in water, allowing biochemical reactions and the development of early cells.

How does water act as a medium for life?

It provides the aqueous environment in which molecules can dissolve, move, and interact, allowing chemical and biochemical reactions to occur.

Why was water important for the development of early life?

Life is believed to have begun in aquatic environments such as oceans or primordial ponds. Water provided a stable environment where essential molecules could dissolve, move, interact, and undergo chemical reactions.

How does water provide a stable environment for chemical reactions?

Its solvent properties allow reactants to dissolve and interact, while its thermal properties help prevent rapid temperature changes.

What role could water have played in the formation of the first cells?

It allowed organic molecules such as amino acids and nucleotides to dissolve and interact, supporting the formation of increasingly complex molecules and early cells.

What is specific heat capacity?

The amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K).

What is the unit for specific heat capacity?

J kg⁻¹ K⁻¹.

Why does water have a high specific heat capacity?

Water requires a relatively large amount of energy to increase its temperature because energy is involved in disrupting interactions between water molecules.

What is the consequence of water having a high specific heat capacity?

Water resists rapid changes in temperature and therefore provides relatively stable thermal conditions.

How does the high specific heat capacity of water affect aquatic habitats?

Aquatic environments experience less rapid temperature change, providing a more stable environment for organisms.

Why is temperature stability important for aquatic organisms?

Organisms are adapted to particular temperature ranges, so reduced temperature fluctuations help maintain stable conditions for biological processes.

What are the consequences of the physical properties of water for organisms in aquatic habitats?

Water's high specific heat capacity helps maintain relatively stable temperatures, while its solvent properties allow substances to dissolve and move through the habitat. Cohesion and adhesion also influence how water behaves and moves.

How does water's thermal property benefit aquatic life?

Water can absorb substantial amounts of heat without a large increase in temperature, reducing rapid temperature fluctuations in aquatic habitats.

How are water's polarity and solvent properties connected?

Water's polarity gives it partial charges that allow it to interact with and dissolve many charged and polar substances.

How are water's polarity and cohesion connected?

Water's polarity allows hydrogen bonds to form between neighbouring water molecules, producing cohesion.

How are water's polarity and adhesion connected?

The polar nature of water allows it to be attracted to other polar or charged surfaces, producing adhesion.

Why is water described as essential for life?

Its combination of solvent, cohesion, adhesion, and thermal properties provides a suitable medium for biochemical reactions, transport, and stable living conditions.