2.2 Properties of Water

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

2.2 Properties of Water

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Life depends on hydrogen bonds in water.

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

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

2.2 Properties of Water

• Water has a variety of unusual properties because of attractions between these polar molecules.– The slightly negative regions of one molecule are

attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.

– Each water molecule can form hydrogen bonds with up to four neighbors.

A hydrogen bond is an attraction between a slightlypositive hydrogen atom & a slightly negative atom.

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

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

High specific heat is water’s ability to resist changes in temperature.

Water must absorb more heat energy to increase in temperature (compared to other substances).

2.2 Properties of Water

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

Cohesion is the attraction among molecules of a substance.

Water molecules stick to each other & cause surface tension.

2.2 Properties of Water

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

Adhesion is the attraction among molecules of DIFFERENT substances.

Water molecules stick to other things & is responsible for curves on the surface of water

2.2 Properties of WaterMany compounds dissolve in water.

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

solution

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.

Ions & other polar molecules dissolve in water whereas nonpolar molecules such as fats and oils do not.

2.2 Properties of WaterSome 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