Properties of WaterProperties of Water

Chapter 2, Section 2Chapter 2, Section 2

Water is a Polar MoleculeWater is a Polar Molecule

the uneven distribution of electrons between the the uneven distribution of electrons between the oxygen and hydrogen atoms creates the polarity oxygen and hydrogen atoms creates the polarity and gives water its bent shapeand gives water its bent shape

Hydrogen BondsHydrogen Bonds

the positive side of one water molecule is the positive side of one water molecule is attracted to the negative side of another water attracted to the negative side of another water moleculemolecule

water molecules can form up to four hydrogen water molecules can form up to four hydrogen bonds with adjacent water moleculesbonds with adjacent water molecules

Capillary Action (think roots!)Capillary Action (think roots!)

CohesionCohesion – attraction between molecules – attraction between molecules of same substanceof same substance

Very strong in water due to hydrogen Very strong in water due to hydrogen bonding!bonding!

AdhesionAdhesion – attraction between unlike – attraction between unlike moleculesmolecules

Because water is a polar molecule, it Because water is a polar molecule, it adheres very well to other polar moleculesadheres very well to other polar molecules

Temperature ModerationTemperature Moderation

Temperature is a measure of the random Temperature is a measure of the random motion of particles in a substance.motion of particles in a substance.

Water heats up slowly because hydrogen Water heats up slowly because hydrogen bonds keep water molecules from moving bonds keep water molecules from moving around.around.

As water cools, it gives off heat slowly as As water cools, it gives off heat slowly as hydrogen bonds reform.hydrogen bonds reform.

Low Density of IceLow Density of Ice

Unlike other liquids, water becomes less Unlike other liquids, water becomes less dense as it freezes. dense as it freezes.

Hydrogen bonds in ice keep water Hydrogen bonds in ice keep water molecules spaced in a regular patternmolecules spaced in a regular pattern

Water Can Dissolve Other Water Can Dissolve Other SubstancesSubstances

Water dissolves other Water dissolves other substances to form substances to form solutionssolutions

SolutionsSolutions are uniform mixtures are uniform mixtures of two or more substancesof two or more substances

Example: salt (NaCl) Example: salt (NaCl) dissolved in waterdissolved in water

Water is the Water is the solventsolvent NaCl is the NaCl is the solutesolute

Water can dissolve ionic Water can dissolve ionic compoundscompounds (salt) (salt)

Water can dissolve polar Water can dissolve polar covalent compoundscovalent compounds (sugar) (sugar)

Water cannot dissolve non-Water cannot dissolve non-polar substancespolar substances (oils) (oils) Fig 2-9 on p. 42

Acids, Bases, and pHAcids, Bases, and pH A small percentage of water molecules break apart into ions in A small percentage of water molecules break apart into ions in

aqueous solutionsaqueous solutionsHH22O HO H++ + OH + OH--

If a solute increases the concentration of H+ ions in the solution, it is If a solute increases the concentration of H+ ions in the solution, it is an an ACIDACID

If a solute decreases the concentration of H+ ions in the solution, it If a solute decreases the concentration of H+ ions in the solution, it is a BASEis a BASE

The The pH ScalepH Scale describes how acidic or basic a solution is: describes how acidic or basic a solution is:

Vinegar (pH of 3) is 10 times more acidic than tomato juice (pH of 4)Vinegar (pH of 3) is 10 times more acidic than tomato juice (pH of 4)