Capter 5 Water We Drink - Dwi S

7/30/2019 Capter 5 Water We Drink - Dwi S

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Kevin Carters 1994 Pulitzer prize winning

photo of a vulture waiting for a child to die,

so that it will eat it epitomizes not only the

hunger crises in Sudan but also in the

whole of Africa. (Photo source: Pulitzer)

Water scarcity

(Sudan, Africa)


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Water has never lost its mystery. After at least two and

a half millennia of philosophical and scientific inquiry,the most vital of the worlds substances remains

surrounded by deep uncertainties. Without too muchpoetic license, we can reduce these questions to asingle bare essential: What exactly is water?

Philip Ball, in Lifes Matrix: A Biography of Water,University of California Press,

Berkeley, CA, 2001, p. 115

Do you know where your drinking water comes from?

Do you know if your drinking water is safe to drink?

How would you know?


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While normally free of pollutants, groundwater can be

contaminated by a number of sources:

Abandoned mines Run off from fertilized fields

Household chemicals poureddown the drain or on the ground.

Poorly constructed landfills and septic systems


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http://catharsiscorner.wordpress.com/2009/01/26/peta-air-

tanah-dunia-sumber-kesejahteraan-dan-potensi-konflik/

Water distribution in Indonesia


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The average water use in the world:

70 % for agricultural needs,

8 % for domestic needs and

22 % for industry.

Afghanistan and India >95% of water use for agriculture,

Britain and Canada > 70% for industry.

Japan, Indonesia and Brazil 60% of water use for

agriculture, the Americans use the 42 per cent for agriculture and 46

percent for industrial use.

Global Water Usage


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Solution

A solution is a homogeneous mixture of uniformcomposition.

Solutions are made up ofsolvents and solutes.

Solvent = Substances capable of dissolving other

substances- usually present in the greater amount. Solutes = Substances dissolved in a solvent- usually

present in the lesser amount.

When water is the solvent, you have an aqueous solution


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Theimportance

of water as

a solvent in

our bodies


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Water in the Environment


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Concentration Terms

Parts per hundred (percent)

Parts per million (ppm)

Parts per billion (ppb)

20 g of NaCl in 80 g of water is a 20% NaCl solution

2 ppb Hg

2 g Hg

1109 g H2O

210-6 g Hg

1103 g H2O

2 g Hg

1 L H2O


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Molarity (M) = moles solute

liter of solution[ ] = concentration of

5.4

1.0 M NaCl solution

[NaCl] = 1.0 M = 1.0 mol NaCl/L solution

Alsothis solution is 1.0 M in Na+ and 1.0

M in Cl-

[Na+] = 1.0 M and [Cl-] = 1.0 M


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What is the molarity of glucose (C6H12O6) in a

solution containing 126 mg glucose per 100.0 mLsolution?

6.99 x 10-3 M


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5.4

How to prepare a 1.00 M NaCl solution:

Note- you do NOT add

58.5 g NaCl to 1.00 L of

water.

The 58.5 g will take up

some volume, resulting in

slightly more than1.00 L

of solution- and the

molarity would be lower.

mol soluteL of solution

M =


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5.5

Different Representations of Water

Lewis structures Space-filling Charge-

density

Charge-density

Region of partial negative charge

Regions of partial positive charge


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5.5

EN Values assigned by Linus Pauling,

winner of TWO Nobel Prizes.

Electronegativityis a measure of an atoms

attraction for the electrons it shares in a covalent

bond.

On periodic

table, EN

increases


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5.5

HH

O

A difference in the

electronegativities of the atoms in

a bond creates a polar bond.

Partial charges result

from bond polarization.

A polar covalent bond is a

covalent bond in which the

electrons are not equallyshared, but rather displaced

toward the more

electronegative atom.


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5.5

H HH

2has a non-polar

covalent bond.

NaClNaCl has an ionic

bond-look at the

EN difference.

Na = 1.0

Cl = 2.9

DEN = 1.9

A water molecule is polar due to

polar covalent bonds and the

shape of the molecule.


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5.6

Polarized bonds

allow hydrogen

bonding to occur.

H

bonds are intermolecularbonds. Covalent bonds are

intramolecular bonds.

A hydrogen bond is an electrostatic attraction between anatom bearing a partial positive charge in one molecule and

an atom bearing a partial negative charge in a neighboring

molecule. The H atom must be bonded to an O, N, or F

atom.

Hydrogen bonds typically are only about one-fifteenth as

strong as the covalent bonds that connect atoms together

within molecules.


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+ 1 e-Na Na

Na atom Na+

ion

Forming ions

+ 1 e-

Cl atom

Cl- ion

ClCl

5.7


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5.7

When ions (charged particles) are in aqueous

solutions, the solutions are able to conduct

electricity.

(a) Pure distilled water (non-conducting)

(b) Sugar dissolved in water (non-conducting): a nonelectrolyte(c) NaCl dissolved in water (conducting): an electrolyte


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5.7

Substances that will dissociate in solution are called

electrolytes.

Dissolution of NaCl in Water

The polar water molecules stabilize the

ions as they break apart (dissociate).

Ions are simply charged

particles-atoms or groups of

atoms.

They may be positivelychargedcations.

Or negatively charged-

anions.

NaCl(s) Na+ (aq) + Cl-(aq)H2O


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Some atoms form more than one stable ion

5.7


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Naming simple ionic compounds is easy-

Name the metallic element (cation) first,

followed by the non-metallic element (theanion) second, but with anide suffix.

5.7

MgO Mg is the metal, O is the non-metal

magnesium oxide

NaBr Na is the metal, Br is the non-metal

sodium bromide


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5.7

Ions that are themselves made up of more than

one atom or element are called polyatomic

ions.

NaSO4

(sodium sulfate) dissociates in water to form:

Na+

Sodium ions

and

Sulfate ions

The sulfate group

stays together in

solution.


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Naming polyatomic ionic compounds is also easy-

Name the cation first, followed by the anion

second.

5.7

MgOH Mg+ is the cation, OH- is the anion

magnesium

hydroxide

NH4Br NH4+is the anion, Br- is the anion

ammonium

bromide


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5.8

Simple generalizations about ionic

compounds allow us to predict their water

solubility.Ions

Solubility of

Compounds

Solubility Exceptions Examples

sodium, potassium,

and ammonium

All soluble None NaNO3 is soluble

KBr is soluble

nitrates All soluble None LiNO3 is soluble

Mg(NO3)2 is soluble

chlorides Most soluble Silver, some mercury, and

lead chlorides

MgCl2 is soluble

PbCl2 is insoluble

sulfates Most soluble Strontium, barium, and lead

sulfate

K2SO4 is soluble

BaSO4 is insoluble

carbonates Mostly insoluble* Group IA and NH41 carbonates

are soluble

Na2CO3 is soluble CaCO3

is insoluble

hydroxides and

sulfides

Mostly insoluble* Group IA and NH41

hydroxides and sulfides are

soluble

KOH is soluble Al(OH)3 is

insoluble

*Insoluble means that the compounds have extremely low solubility in water (less than 0.01 M).

All ionic compounds have at least a very small solubility in water.


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5.9

Covalent molecules in solution

A sucrose moleculewhen dissolved in water,sugar molecules interact with and become

surrounded by water molecules, but the sucrose

molecules do not dissociate like ionic

compounds do; covalent molecules remain

intact when dissolved in solution.

They will not conduct electricity; they are

non-electrolytes.


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Like dissolves like

5.9


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5.10

Maximum Contaminant Level Goal (MCLG)

and Maximum Contaminant Level (MCL)

5.10


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A pipe with hard-water scale build up

Hard watercontains high concentrations of dissolved

calcium and magnesium ions.

Soft watercontains few of these dissolved ions.

Not in 6th ed.


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Because calcium ions, Ca2+, are generally the largest

contributors to hard water, hardness is usually expressed in

parts per million of calcium carbonate (CaCO3) by mass.

It specifies the mass of solid CaCO3 that could be formed

from the Ca2+ in solution, provided sufficient CO32- ions were

also present:

Ca2+(aq) + CO32(aq) CaCO3(s)

A hardness of 10 ppm indicates that 10 mg of CaCO3 could beformed from the Ca2+ ions present in 1 L of water.

Not in 6th ed.


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5.11

Schematic drawing of a typical municipal water treatment facility


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5.12

Getting the lead out:

Schematic of a typical spectrophotometer

Using a plot of

absorbance vs. concentration

Calibration graph


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AAS =

Atomic

absorption

Spectro-photometer


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Access to safe drinking water varies widely across the world


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5.14

Access to safe drinking water varies widely across the world.


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Two water purification techniques:

Distillation Reverse osmosis

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Capter 5 Water We Drink - Dwi S