WATER

Chapter 3: Water and the Fitness of the Environment

maima

(Hebrew) amane (Berber) amanzi (Zulu)

biyo (Somali) mizu

(Japanese)

jo (Warao) shouei (Chinese)

Paani (Hindi)

wasser

(German)

su (Turkish)

dlo (Haitian)

Water 2

• Cells are 70-90% water• Three-fourths of Earth’s surface is

covered by water• Water is the biological medium for

life on Earth• Water must be present for life (as

we know it)

Figure 3.1 Hydrogen bonds between water molecules 

Water’s polarity 5• Polar – opposite ends of molecule have

opposite charges– Opposing charges due to oxygen’s

electronegativity•Oxygen has partial negative•Hydrogens have partial positive

• Water forms H bonds (opposite charges attract)– ~15% water molecules in our body

are bonded to four partners

Four Properties of Water Allowing for Life 6

1. Cohesion/Adhesion2. Moderation of temperature3. Insulation of bodies of water by

floating ice4. The solvent of life

Figure 3.2x Trees

Figure 3.3 Walking on water

Cohesion 9

• Cohesion - H bonding keeps water molecules close together

• Makes water a “structured” liquid• Adhesion – the clinging of one substance

to another– Ex. water sticks to sides of a glass

• Both cohesion and adhesion help water move up from roots to plants to leaves

• Surface tension – measure of difficult it is to stretch or break the surface of a liquid– Water has a high surface tension due to

H bonds – almost like a thin film on the surface.

Moderation of Temperature

10• Heat – measure amount of total kinetic energy (cal, kcal, or J)– 1 cal = amount of heat needed to raise

the temp of 1g of water 1°C– 1000 cal = 1 kcal – 1 cal = 4.184 J

• Temperature – measures the intensity of heat due to average kinetic energy of molecules (°C)

• Specific heat – amount of heat that must be absorbed or lost for 1 g to change its temp by 1 °C – Specific heat of water = 1 cal/g/°C

– Compared to most substances, water’s specific heat is quite high.

– This means water will change its temp less when it absorbs or gives off heat.

– Why? H bonds need heat to break and heat is released when bonds are formed.

– High specific heat allows large bodies of water to absorb lots of heat in summer without raising temp too high. In winter, gradual cooling of water helps warm the air.

– High specific heat helps stabilize ocean temp to better support marine life.

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• Heat of vaporization – quantity of heat a liquid must absorb for 1 g to be converted to a gaseous state

• Water has a high heat of vaporization (580 cal heat needed to evaporate 1 g water at 25°C) because H bonds must be broken before molecules can change to gas.– Evaporative cooling – as liquid evaporates,

the surface cools because the hottest molecules leave as gas and cooler molecules are left behind• Why sweat? Evaporative cooling in

progress!• Why do we sweat more on humid days?

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Insulation of Bodies of Water by Floating Ice

• Water is more dense than ice. At 4°C water is at its most dense state, then as it cools to O°C, the molecules freeze. The H bonds keep the water molecules slightly apart (like a lattice) so air pockets form within ice.

• Lakes, oceans etc. would freeze solid if ice was more dense than water. During the summer, only upper few inches of ocean would thaw making life as we know it impossible (not to mention ice skating and hockey! )

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Figure 3.5 The structure of ice (Layer 2)

Figure 3.5x1 Ice, water, and steam

Figure 3.6 Floating ice and the fitness of the environment

Figure 3.6x1 Floating ice and the fitness of the environment: ice fishing

Figure 3.6x2 Ice floats and frozen benzene sinks

The Solvent of Life

• Solvent - dissolving agent in a solution

• Solute – the substance that is dissolved

• Aqueous solution – water is the solvent

• Water can dissolve many substances, but obviously not all!– Hydrophilic – likes water – Hydrophobic – repel water (nonpolar

and nonionic)

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Figure 3.7 A crystal of table salt dissolving in water

Figure 3.8 A water-soluble protein

Figure 3.x2 Moles

pH• H+ (protons) occasionally move from

one water molecules to another (disassociation).

• If water loses a H+ then it becomes OH- (hydroxide ion).

• If water gains a H+ then it becomes H3O+ (hydronium ion).

• In pure water, the OH- and H+

concentrations are equal.• Acid – increases H+ concentrations, nl• Base – lots of OH, decreases H+

concentrations

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Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift

Figure 3.9 The pH of some aqueous solutions

Buffers

• Buffers – minimize changes in pH by being able to release or take in H+

• Buffers keeps blood between 7 and 7.8

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Acid Rain

• Acid precipitation – below 5.6• Caused primarily by increased levels of

sulfur and nitrogen oxides released from the burning of fossil fuels

• Acid precip can damage lakes, streams, and soil.

• Acid can make harmful heavy metals more soluble in water.

Figure 3.10 The effects of acid precipitation on a forest

Figure 3.10x1 Pulp mill

Figure 3.10x2 Acid rain damage to statuary, 1908 & 1968