2.2 Properties of Water

Do Now

• Describe and draw a picture of a ionic bond• Describe and draw a picture of a covalent bond

2.2 Properties of Water

KEY CONCEPTWater’s unique properties allow life to exist on Earth.

2.2 Properties of Water

OHH

_

++

Life depends on hydrogen bonds in water.

• Water is a polar molecule.– Polar molecules have slightly charged regions, due to

uneven pull on electrons.

– Nonpolar molecules do not have charged regions.– Hydrogen bonds form between slightly positive    hydrogen atoms and slightly negative atoms.

2.2 Properties of Water

• Hydrogen bonds are responsible for three important properties of water.

– high specific heat– cohesion– adhesion

2.2 Properties of Water

Properties of water related to hydrogen bonds

• High Specific Heat - Large amount of energy needed to produce an increase in temperature.– Important in regulating temperature of cells

• Cohesion - water molecules “stick” to each other– Beads of water– Surface tension

• Adhesion - water molecules “stick” to other substances– Helps transport water from roots to leaves in plants

2.2 Properties of Water

Many compounds dissolve in water.

• A solution is formed when one substance dissolves in another.– A solution is a homogeneous mixture.– Solvents dissolve other substances (greater

concentration).– Solutes dissolve in a solvent (lower concentration).

solution

2.2 Properties of Water

Do NOW

• What does “like dissolves like” mean?

2.2 Properties of Water

• “Like dissolves like.”

– Polar solvents dissolve polar solutes.– Nonpolar solvents dissolve nonpolar solutes.– Polar substances and nonpolar substances generally

remain separate.– Oil and Water

2.2 Properties of Water

Acids and Bases

• Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases.

• Bases feel slippery, change litmus blue, and become less basic when mixed with acids.

2.2 Properties of Water

Some compounds form acids or bases.

• An acid releases a hydrogen ion when it dissolves in water.– high H+ concentration– pH less than 7

more acidic

stomach acid pH between 1 and 3

2.2 Properties of Water

• A base removes hydrogen ions from a solution.

– low H+ concentration– pH greater than 7

bile pH between 8 and 9

more basic

2.2 Properties of Water

• A neutral solution has a pH of 7.

pure water pH 7

2.2 Properties of Water

QuickTime™ and a decompressor

are needed to see this picture.

2.2 Properties of Water

How do Acids and Bases work?

• Water can dissolve compounds into their individual ions

• Acids– Compounds that contain hydrogen and release a

hydrogen ion when put in an aqueous (water) solution• Bases

– Substances that dissolve in water and release hydroxide ions (OH-) into solution.

• Neutralization– acids release H+ into solution and bases release OH-.

If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water

- Always produces water and a salt