chem u2 aos 1

CHAPTER 10 — WATER AS A UNIQUE CHEMICAL

Chapter 10 — Water as a unique chemical

What is the focus of Chapter 10?

Water as a unique chemical, including its states, availability, anomalous properties, hydrogen bonding, density, specific heat capacity and latent heat

What are the three states of water found at Earth's surface?

Solid, liquid and gas

What is potable water?

Water that is fit for drinking

What is brackish water?

Water that is slightly salty

What is the chemical formula of water?

H₂O

Is water polar or non-polar?

Water is a polar molecule

Why is water polar?

Oxygen is more electronegative than hydrogen, so the bonding electrons spend more time near oxygen, giving oxygen a partial negative charge and hydrogen atoms partial positive charges

What partial charge does oxygen have in water?

δ−

What partial charge do the hydrogen atoms have in water?

δ

What is an intramolecular bond in water?

The polar covalent O–H bond within a water molecule

What is an intermolecular force between water molecules?

Hydrogen bonding

What is hydrogen bonding?

An intermolecular attraction involving a hydrogen atom covalently bonded to N, O or F and a lone pair on N, O or F of another molecule

Which atoms can hydrogen be covalently bonded to for hydrogen bonding to occur?

Nitrogen, oxygen or fluorine

What is the difference between a hydrogen bond and a covalent bond?

A covalent bond holds atoms together within a molecule, while a hydrogen bond is an intermolecular attraction between molecules

Why does water have an unusually high boiling point?

Water molecules form strong hydrogen bonds with each other, so a large amount of energy is required to separate them

What is the boiling point of water?

100 °C at standard atmospheric pressure

Why does H₂O have a much higher boiling point than H₂S?

H₂O forms hydrogen bonds while H₂S mainly has weaker intermolecular attractions

What is surface tension?

The tendency of a liquid surface to resist being stretched due to cohesive intermolecular forces

Why does water have high surface tension?

Strong hydrogen bonding makes water molecules highly cohesive

What does cohesive mean?

Attraction between molecules of the same substance

What does hydrophobic mean?

Having little or no attraction to water and tending not to dissolve in it

Why does water dissolve many substances?

Its polarity allows it to interact strongly with many ionic and polar substances

What is the rule describing the solubility of polar substances?

Like dissolves like

What types of substances generally do not dissolve well in water?

Non-polar substances

What is the structure of ice?

Water molecules form an ordered, open hydrogen-bonded crystalline structure

Why is ice less dense than liquid water?

The hydrogen-bonded structure of ice holds water molecules farther apart than in liquid water

What happens to water when it freezes?

It expands and becomes less dense

Why does ice float on liquid water?

Ice has a lower density than liquid water

What is the biological importance of floating ice?

The surface ice layer insulates the liquid water below, allowing aquatic organisms to survive

At approximately what temperature is liquid water most dense?

About 4 °C

Why is the density of water anomalous?

Water reaches maximum density near 4 °C and becomes less dense as it freezes because freezing produces an open hydrogen-bonded structure

What is density?

Mass per unit volume

What is the formula for density?

d = m/V

What does d represent in d = m/V?

Density

What does m represent in d = m/V?

Mass

What does V represent in d = m/V?

Volume

What are common units for density?

g mL⁻¹, g cm⁻³ or kg m⁻³

What is the relationship between g mL⁻¹ and g cm⁻³?

1 g mL⁻¹ = 1 g cm⁻³

How do you rearrange the density formula to find mass?

m = dV

How do you rearrange the density formula to find volume?

V = m/d

Why does the density of a substance change with temperature?

Density changes because volume can change as particles move closer together or farther apart

What is specific heat capacity?

The amount of energy required to raise the temperature of 1 gram of a substance by 1 °C or 1 K

What is the symbol for specific heat capacity?

c

What is the specific heat capacity of water?

4.18 J g⁻¹ °C⁻¹

What is the formula for heat energy required to change temperature?

q = mcΔT

What does q represent in q = mcΔT?

Heat energy in joules

What does m represent in q = mcΔT?

Mass in grams

What does c represent in q = mcΔT?

Specific heat capacity in J g⁻¹ °C⁻¹

What does ΔT represent in q = mcΔT?

Change in temperature

What is the formula for change in temperature?

ΔT = T_f − T_i

What does T_f represent?

Final temperature

What does T_i represent?

Initial temperature

Why does water have a high specific heat capacity?

A large amount of energy is required to increase the temperature of water because energy is absorbed by the hydrogen-bonded system

What is the consequence of water's high specific heat capacity?

Water heats and cools relatively slowly

Why is the high specific heat capacity of water important for oceans?

Oceans can absorb large amounts of heat while experiencing relatively small temperature changes

What is latent heat?

Energy required to change the state of a substance without changing its temperature

Why does temperature remain constant during a phase change?

Energy is used to overcome or form intermolecular attractions rather than change the kinetic energy of the particles

What is latent heat of fusion?

The energy required to change a substance from solid to liquid at its melting temperature

What is the latent heat of fusion of water?

6.01 kJ mol⁻¹

What is latent heat of vaporisation?

The energy required to change a substance from liquid to gas at its boiling temperature

What is the latent heat of vaporisation of water?

40.7 kJ mol⁻¹

What is the formula for latent heat using moles?

q = nL

What is the formula for latent heat using mass?

q = mL

What does L represent in q = nL or q = mL?

Latent heat

What does n represent in q = nL?

Amount of substance in mol

Why is water's latent heat of vaporisation high?

Strong hydrogen bonds between water molecules require a large amount of energy to overcome

How does sweating cool the body?

Water evaporating from the skin absorbs energy because of its high latent heat of vaporisation

What happens when water changes from liquid to gas?

Energy is absorbed and intermolecular attractions are overcome

What happens when water changes from gas to liquid?

Energy is released as intermolecular attractions form

What happens during melting?

Energy is absorbed to disrupt the ordered solid structure

What happens during freezing?

Energy is released as molecules form an ordered solid structure

What happens during evaporation?

Water molecules gain enough energy to escape the liquid and become gas

What happens during condensation?

Water vapour loses energy and molecules come together to form liquid water

How does water's high specific heat capacity affect Earth's climate?

It allows oceans to absorb and redistribute large quantities of thermal energy

What is the enhanced greenhouse effect?

An increase in heat trapped by increased greenhouse gases in the atmosphere

What human activities increase greenhouse gases?

Activities including burning fossil fuels and land clearing

What are possible consequences of climate change?

Changes in rainfall patterns, increased storm severity and impacts on ecosystems and biodiversity

CHAPTER 11 — ACID–BASE (PROTON TRANSFER) REACTIONS

Chapter 11 — Acid–Base (proton transfer) reactions

What is the main focus of Chapter 11?

Brønsted–Lowry acids and bases, conjugate pairs, amphiprotic species, polyprotic acids, acid/base strength, concentration, pH, neutralisation, indicators, ionic equations and applications of acid–base reactions

What is an acid according to Brønsted–Lowry?

A proton donor

What is a base according to Brønsted–Lowry?

A proton acceptor

What is a proton?

H⁺

What are common properties of acids?

They generally have pH below 7, turn blue litmus red, may be corrosive and react with bases

What are common properties of bases?

They generally have pH above 7, turn red litmus blue, may be corrosive or caustic and react with acids

What is an alkali?

A base that is soluble in water

What are common types of bases?

Oxides, hydroxides, carbonates and hydrogen carbonates of metals

What are examples of bases?

MgO, NaOH, CaCO₃ and KHCO₃

What are examples of acids?

HCl, H₂SO₄, HNO₃, H₃PO₄ and CH₃COOH

What is the general reaction of a strong acid with water?

Acid

What is the Brønsted–Lowry equation for nitric acid in water?

HNO₃(aq)

What is the Brønsted–Lowry equation for hydrochloric acid in water?

HCl(aq)

What is the Brønsted–Lowry equation for ethanoic acid in water?

CH₃COOH(aq)

What is a conjugate acid?

The species formed when a base accepts a proton

What is a conjugate base?

The species formed when an acid donates a proton

What happens to an acid when it donates H⁺?

It becomes its conjugate base

What happens to a base when it accepts H⁺?

It becomes its conjugate acid

How do conjugate acid–base pairs differ?

They differ by exactly one proton, H⁺

What is the conjugate base of HNO₃?

NO₃⁻

What is the conjugate acid of NH₃?

NH₄⁺