Water

Water

• Most abundant compound in living things• Important to understanding the functions of

living things• Composed of 2 hydrogens and 1 oxygen• Atoms connected through a covalent bond =

sharing electrons; creates some unique properties

Water

• Polarity – happens because oxygen atom has greater attraction for electrons than the hydrogen atom; creates magnet-like polarity

Water

• Hydrogen bonding – happens due to polarity; attracts water molecules to each other

• Both responsible for many of water’s special properties.

Water

• Hydrogen bonding pulls water molecules together & creates cohesion

• Cohesion – attraction between molecules of same substance

• Water = extremely cohesive; allows bugs to “walk” on water

• Creates surface tension

Water

• Adhesion – attraction between molecules of different substances

• Makes water stick to sides of containers• Ex. Measuring cup, graduated cylinder• Also makes water rise in a narrow tube =

capillary action• Capillary action helps water get pulled up

from roots of plants to leaves.

Water• Has a high specific heat = amount of energy needed

to increase the temperature• In order for temperature to increase, the molecules

must move faster• Hydrogen bonds in water make it hard for the

molecules to move faster• Means that areas near water stay cooler in summer

because the water takes longer to heat and warmer in winter because the water holds a lot of heat.

Water

• Density anomaly – water is more dense as a liquid than as a solid

• Allows ice (solid) to float on surface of lakes & rivers

• Permits life to survive in liquid water below the surface

• Without this property – aquatic life would all die each winter as bodies of water freeze

Water

• Universal solvent – water is able to dissolve a lot of compounds

• Necessary for chemical reactions to take place in body = metabolism

• Without being dissolved, these reactions would not occur

Solutions

What are solutions?

• Solutions are homogeneous mixturesWhat does THAT mean?• Particles are EVENLY distributed or mixed• May exist as a SOLID, LIQUID or GAS

What are solutions?

• Particles are SMALL – about 0.1 to 1 nm• Will not separate if left standing• Will not separate by filtration• Do not display Tyndall effect = scattering of

light beam that is shone through the mixture

Examples• Air• Salt in water• Steel, brass (metal

alloys)

What is in a solution?• Solutions consist of:1. Solvent = the substance that does the

dissolving that is present in the GREATER amount

2. Solute = substance that is placed in solvent, present in SMALLER amount

How do solutions form?• When solvent particles are attracted to

solute particles

Hey, I really

am attracted to you!

Me too!

How do solutions form?• If the attractive forces between solvent &

solute particles are greater than or stronger than the attractive forces between particles of the SOLUTE, then the solute is called SOLUBLE and WILL DISSOLVE.

Ionic Solutes

• When an ionic substance dissolves in water, the ions separate and are able to move in the water.

• Process is called dissociation

The Dissociation ProcessNaCl (cr) + H2O Na+(aq) + Cl-(aq)

Dissociated ion

Ionic Solutes

• Because the ions can now move, the resulting solution can conduct electricity

• Conductivity requires 2 things:1. Charged particles2. Ability of the charged particles to move

• Before dissolving, these conditions do not exist

Ionic Solutes

• This property of conducting electricity when in solution classifies the solute as an electrolyte

• Electrolyte = substance that forms ions when it dissolves in water

Molecular Solutes

• Molecular solutes contain no charged particles• Most do not form ions when dissolved• Molecules tend to stay whole when they go

into solution• Process = dispersion• Dispersion = breaking into small pieces that

spread throughout the solution

Molecular Solutes

• After dispersion, some molecular compounds form ions by reacting with water to gain or lose electrons

• Ionization = process by which molecules gain or lose electrons

• Allows them to be electrolytes as well• Does not happen to all molecules

What affects the speed that something dissolves?

Think about it….

• In winter, you make a cup of hot tea and add a spoonful of sugar. When you finish drinking your tea, there is no sugar at the bottom of your cup.

• In summer, you have the same size cup of iced tea and add the same amount of sugar. Yet, at the bottom of the cup when you are done, there is some visible sugar “sludge” left.

• Why?

Temperature

• When the temperature of something increases the particles are moving faster

• So, if we heat up our solvent, the particles move faster and pull apart the solute faster

Surface Area

• The smaller the particle, the greater the surface area of that solute that is exposed to the solvent.

• Smaller particles = faster dissolving due to increased surface area

Surface Area

• So – which should dissolve faster:

Sugar cube Granulated sugar

• Why?• Greater surface area!

Stirring

• Stirring makes the solute and solvent particles have more contact with each other

• More contact = faster dissolving

Types of solutions

Saturated solution• A solution that contains the maximum amount

of solute.• So if I add more solute to this solution, no

more will dissolve

Unsaturated solutions

• A solution that contains less than the maximum amount of solute

• So if I add more solute to this solution, it WILL dissolve

Supersaturated Solutions• A solution that contains more than the

maximum amount of solute for a saturated solution at the same temperature

• How is this possible?• Make a saturated solution• Heat and add more solute• Cool slowly and carefully

So – how do I identify an unknown solution?

• Drop a small piece of the solute into the solution

• If it DISSOLVES RIGHT AWAY – the solution is unsaturated

• If it DROPS TO THE BOTTOM – the solution is saturated

• If it causes MORE CRYSTALS TO APPEAR – the solution is supersaturated

What do all ofthese have

in common?

APPLE BUTTER

GRAPEFRUIT

VINEGAR

MILK

VOMIT

BATTERIES

PEPSI WINE

ACIDS!!!

MALIC ACID

CITRIC ACID

BUTYRIC ACID

ACETIC ACID

HYDROCHLORIC ACID

TARTARIC ACID

LACTIC ACID

SULFURIC ACID

PHOSPHORIC ACID

What is an acid?

1. Acids (defined)A substance which forms a lot of H+ ions in solution with water

What is an acid?2. Characteristics

a) Taste sourb) Conduct electricity when in dissolved in water = electrolytec) React with bases to form water and a salt = neutralization reactiond) Change indicator colorse) More H+ than water.

What is a base?

1. Base (defined)A substance which forms a lot of OH- ions in water (or very few H+

ions)

What is a base?2. Characteristics

a) Bitter tasteb) Have a slippery or soapy feelingc) Are causticd) React with acids in a neutralization reaction.e) Conduct electricity when dissolved in waterf) Change indicator colorsg) Less H+ than water

What is pH?

1. A quantitative measure of the strength of acids and bases

2. Actually measures the amount of H+ (the acid ion) in a solution

pH scale

0---------------------7--------------------14

ACIDIC BASIC

NEUTRAL

[H+] > [OH--] [OH--] > [H+]

Why is water neutral?

H+ H+

H+

H+H+

OH—

OH—

OH—

OH—

OH—

The number of H+ ions = OH— ions

So solutionis neutral

pHpH between 1 & 7 = acidicMeans a lot of H+ ions in waterCreated by acidsThe lower the pH the stronger the

acid

Acidic Solution

H+ H+

H+

H+

H+

OH—

OH—

OH—

OH—

OH—

[H+] >[OH—]

Add HCl(add H+)

H+

H+

So solutionis acidic

H+

H+

pHpH between 7 & 14 = basic/alkalineMeans very few H+ ions in waterCreated by basesThe higher the pH, the stronger the

base

Basic Solution

H+ H+

H+

H+H+

OH—

OH—

OH—

OH—

OH—

[H+] <[OH—]

Add NaOH(add OH—)

So solutionis basic

OH—

OH—

Buffers

• Weak acids/bases that prevent sudden changes in pH• Example = blood, sea water

Buffers• Important to living organisms

because pH must be controlled in order for homeostasis to be maintained

Indicators

• Any substance that changes color in the presence of an acid or a base

• Color change happens at different pH levels depending on the indicator used

• Common indicators:1. Litmus – red in acid, blue in base2. Phenolphthalein – colorless in acid, pink in base3. pH paper – changes color & read according to

scale

Indicators

• Also have some natural indicators in nature• Ex. Beet juice – base turns purpleRed cabbage juice – red = acid, purple = neutral,

green/yellow = baseHydrangeas (flowers) – blue = acid, pink = base

Neutralization

• Occurs when an acid and a base react• The H+ of the acid combines with the OH- of

the base to form water• Leftover parts combine to form a salt• Ex.

HCl + NaOH → NaCl + HOH (H2O)• When this happens, the properties of the acid

and base disappear – including pH