1 Chapter 3: Water and the Fitness of the Environment THINK, PAIR, SHARE:

Chapter 3: Water and the Fitness of the Environment

THINK, PAIR, SHARE:

Chapter 3 Water and the Fitness of the

Environment

AIM: Why is water important to life?

Chapter 3 – Water and the Fitness of the Environment

Figure 3.1

wants to fill this

Covalent Bonding

Chapter 2 – The Chemical Context of Life AIM: Why is water important to life?

Chapter 3 – The Chemical Context of LifeAIM: Why is water important to life?

Name(molecularformula)

Electron-shell

diagram

Structuralformula

Space-fillingmodel

Hydrogen (H2). Two hydrogen atoms can form a single bond.

Oxygen (O2). Two oxygen atoms share two pairs of electrons to form a double bond.

Figure 2.11 A, B

AIM: How do atoms interact with each other?

Name(molecularformula)

Electron-shell

diagram

Structuralformula

Space-fillingmodel

Methane (CH4). Four hydrogen atoms can satisfy the valence ofone carbonatom, formingmethane.

Water (H2O). Two hydrogenatoms and one oxygen atom arejoined by covalent bonds to produce a molecule of water.

Figure 2.11 C, D

Oxygen

––

Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen.

This results in a partial negative charge on theoxygen and apartial positivecharge onthe hydrogens.

Chapter 2 – The Chemical Context of Life

Fluorine has the highest

electronegativity. Why not neon or helium?Neon/Helium have a full

valence shell and therefore are already

stable all by themselves and will not attract

electrons to be stable.In biology, we will focus on elements with high

electronegativity like oxygen and nitrogen.

Polar Covalent Bond

Non-polar covalent bond

Hydrogen Bonds

ionsCation vs Anion

The sodium and chloride ions are now attracted to each other and form an

ionic bond.ionic bond = bond between two

oppositely charged ions

Ionic Bond

Salt crystals

-Na+Cl- crystals are repeating arrays of Na+ and Cl- held together by the

electromagnetic force.-general name given to ANY ionic compound (not just sodium chloride

(Na+Cl-) held together in a lattice structure. Ex:

Na+Cl-

Mg2+Cl2-

Van der waals interactions• Even non-polar molecules can have some positively and negatively charged region briefly and can very weakly bind to another.

Figure 1. Two non-polar molecules (say H2) come into close proximity

Figure 2. By chance, the position of the electrons around one of the molecules (the one to the left) are more on one side of the molecule than the other causing one side to be slightly negative and the other side to be slightly positive.

Figure 3. This will then induce a dipole in the neighboring molecule as the neighboring molecule’s electrons will be attracted to the slightly positive region of the first molecule resulting again in an ever so slightly negative side and an ever so slightly positive side. Of

course, the negative and positive will form a very weak interaction.

◦ Reinforce the shapes of large molecules◦ Help molecules adhere to each other

Plasma membrane are stabilized by the additive affect of Van der Waals interactions between non-polar fatty acid tails of

phospholipids.

H bonds

The two strands of a DNA molecule are held together tightly by the additive affect of many, many weak

Hydrogen Bonds

Fig. 2-UN7

Fig. 2-UN11

Water-conductingcells

Adhesion

Cohesion150 µm

Directionof watermovement

How is water transported against gravity in plants?

Water-conductingcells

Adhesion

Cohesion150 µm

Directionof watermovement

How is water transported against gravity in plants?

A measure of how well a substance resists change in temperatures

1 kcal = 1,000 calories; amount of heat needed to raise the temp of 1kg of water

Specific heat of iron: 0.1 cal/g/oC

Water, because of it H-bonding (cohesive nature) has a very high specific heat

relative to other molecules.

It is difficult to get the water molecules to vibrate since they are all sticking to each

other. The H-bonds need to be broken.

Think about this analogy: is easy to push a single student and get them moving fast,

but if you all hold hands, it becomes more difficult as I would need to break those

bonds.

Helps organisms resist change in temperature!!

Water has a relatively high heat of vaporization because the hydrogen

bonds of the water that must be overcome in order for evaporation to

Liquid waterHydrogen bonds

constantly break and re-form

IceHydrogen bonds are stable

Hydrogen bond

Solvent: the dissolving agent in a solution

Solute: the substance being dissolved

Solution: a homogeneous mixture Aqueous solution: water is the solvent

“Cage” of water molecules surrounding each dissolved substance

Hydration shell

This oxygen is

attracted to a

slight positive

charge on the

lysozyme

molecule.This oxygen is attracted to a slight negative charge on the lysozyme molecule.

(a) Lysozyme molecule

in a nonaqueous

environment

(b) Lysozyme molecule (purple)

in an aqueous environment

such as tears or saliva

(c) Ionic and polar regions on the protein’s

Surface attract water molecules.

Figure 3.7

Rule of thumb: LIKE DISSOLVES LIKE

How would you make a 0.5-molar (0.5 M) solution of sodium chloride (NaCl)?

1. Find moles 2. Convert moles to grams (factor label method)3. Add enough water to make 1 L

Molarity = moles of solute liter of solution

Moles = M * L

1. Moles = 0.5 M * 1 L

= 0.5 moles

2. 0.5 moles * _________g 1 mole

Remember 1 mole = formula mass

58.5 = 29.3 g of NaCl and fill with water to 1 L

ck72+nerd

How many grams of acetic acid (C2H4O2) would you use to make 10 L of a 0.1 M aqueous solution

of acetic acid? 1. Find moles 2. Convert moles to grams (factor label method)

Moles = M * L

1. Moles = 0.1 M * 10 L

= 1 mole

2. 1 mole * _________g 1 mole

= 60 g of acetic acid 60

What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make

125 ml of solution? 1. Convert grams to moles2. Find molarity

1. 2.5 g * 1 mole g

58.5 = 0.0427 moles

2. Molarity = 0.0427 moles 0.125 L

Molarity = 0.34 M NaCl

AIM: How does pH affect living organisms?

H2O H+

Hydrogen ion(aka… a proton)

Hydroxide ion

The oxygen atom is more electronegative than the hydrogens and pulls the shared electrons away from them, which can cause one of the hydrogens (a proton) to fall off.

Hydroniumion (H3O+)

Hydroxideion (OH–)

Figure on p. 53 of water dissociating

H2O H+ +

It will transfer from one water to another to form H3O+

This change can significantly change the pH of an aqueous solution

Chapter 2 - The Chemical Basis of Life AIM: pH?

Logarithms (logs)The log of a number is simply

how many powers of 10 you can pull out of that number.

Ex. log 1000= 3 because you can pull three powers of 10 out

of 1000 (10 x 10 x 10) or 103 = 1000

Logarithms (logs)Ex. Log 100,000

= 5 because you can pull out 5 powers of 10 from 100,000 or 105 =

100,000.

Logarithms

log 102= log 100 =

log 103= log 1000 =

log 104= log 10,000 =

log 105=

log 106=

log 10-1= log .1 =

log 10-2=

log 10-3=

log 10-4=

23456-1-2-3-4

Then if you take the negative log…

The signs switch

-log 102=

-log 103=

-log 104=

-log 105=

-log 106=

-log 10-1=

-log 10-2=

-log 10-3=

-log 10-4=

-2-3-4-5-61234

pH = -log [H+]

What if the pH is 10 X higher?

pH = -log [H+][H

+] = 10-6 M

pH = -log [H+]

x = -log [10-6M]pH = 6

pH = -log [10-7M]pH = 7

[H+] = 10-7 M

What if the pH is 10 X higher?

1. As [H+] goes up, pH goes DOWN

3. A change in 1 pH corresponds to a 10-fold change in [H+]2. As [H+] goes down, pH goes UP

How many times more

acidic is lemon juice than urine? 10,000X more acidic

How many times more basic is

milk of magnesia (pH

11) compared to seawater (pH

8)? 1000X more basic

Neutral[H+] = [OH–]

Oven cleaner

pH Scale

Battery acid

Digestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juice

Black coffee RainwaterUrine

Pure waterHuman blood

Seawater

Milk of magnesia

Household ammonia

Household bleach

Figure 3.8

1. What does the pH value tell us about the

solution? 2. What happens to the

pH as the [H+] increases?

3. If the pH of a solution is increased by three pH units, how has the [H+]

changed?

The H+ (free proton) concentration [H+]

decreases

1000x lower [H+]

Moreacidic

AcidrainNormalrain

Morebasic

Figure 3.9

1 Chapter 3: Water and the Fitness of the Environment THINK, PAIR, SHARE:

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