Polarity of Water and other Special Properties!

I. Facts about water Water is the most common liquid on Earth Water must be present for life to exist Water makes up 50 – 90% of living things Water is 75% of the human body

Water is Polar. What is polarity?

Matter is made up of electrons (- charge) and protons (+ charge) Usually, the + and - charges are evenly spread out.

However, if the charges are concentrated in different areas... - + This is now the negative pole This is now the positive pole …the object is said to have polarity.

…water is slightly polar. Because the atoms in each molecule of water are not arranged in a straight line... + This is the positive pole This is the negative pole - …water is slightly polar.

- + Water obeys the Laws of Electrostatics: Opposite charges attract each other...

The negative sodium is attracted to the positive chlorine The negative sodium is attracted to the positive chlorine. This is table salt. Na- Cl+

+ + …while like charges repel.

2H + O  H2O H O H H O + H + -

+ + - “Micky Mouse” look

+ So if anything with a positive charge is put in water... - - - …the negative poles of water molecules are attracted to it. - + - +

Of course, water’s positive pole will be attracted to negative charges. - + - + - - - + - + - +

The polarity of water explains why water dissolves more chemicals than any other liquid.

Many chemicals are ionic compounds, made of negative and positive ions: - +

When these ionic compounds are mixed in water, the water molecules surround both the negative and positive ions, forcing them apart, and dissolving the compound.

+ - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + +

Ionic compounds that dissolve in water include: Salts Acids Bases

Some molecules that are not ionic compounds are like water: They are polar also, with a positive and a negative end: + - + - + - + - + - + - + - + -

Water molecules will be attracted to the poles of these molecules, separating them from each other, and thus dissolving them. - + - + + - + - - + - + - + - + + - - + - + - + - +

Polar compounds that are dissolved by water this way include sugars, amino acids, nucleic acids, alcohols, and many other molecules important to life. Some molecules are neither ionic, nor polar. Usually, these will not dissolve in water.

- + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - +

Fats and oils, gasoline, kerosene, and waxes are some examples of compounds that will not dissolve in water. These are called NONPOLAR

Nonpolar molecules: No negative or positive charges Will not mix with polar substances Exs: oil, wax

Water has unique properties because of its polarity.

Hydrogen bonds – weakest bond of attraction between hydrogen and other polar molecules

Cohesion (“Co-”) – means “sticking together” Attraction between molecules of the same substance Caused by hydrogen bonds

3. Adhesion Water molecules sticking to other items with a charge. ex: capillary action ex: a meniscus

Ex: Water strider insect or floating paperclip on water 4. Surface tension – forms a film- like boundary on the surface of water, can support light objects. Ex: Water strider insect or floating paperclip on water

A fluid that dissolves another material is call a solvent. Solvent – the dissolving substance, usually a liquid, that makes up most of the solution The material that is dissolved is called a solute. Solute – substances that are being dissolved

A mixture in which a solute is dissolved in a solvent is called a solution.

A Glass of Saltwater Solution – saltwater Solvent – water Solute - salt

A Muddy Stream Solution – stream Solvent – water Solute – dirt, pollution, chemicals

A Cup of Coffee Solution – coffee Solvent – water Solute – coffee, sugar, cream, milk

Substances that do NOT dissolve in a solvent, are said to be Insoluble.

Water is the best solvent known Water is the best solvent known. It will dissolve more substances than any other fluid.

Water - Density

Density – the ratio of mass of matter to its volume. What can you infer about the density of these liquids? O O O O O O Oil O O O O O O O O O O O O Water O O O O O O O O O O O O O O O O O O O O O O Soap oooooooooooooooooooooooooooooooooooooooooooo Syrup

The 3 states of water

Solid – molecules expand to form a 6 sided crystal

Liquid – molecules contract

Gas – molecules separate; hydrogen bonds are broken

Changes in the state of water are due to the addition or removal of Heat. Solid absorbs heat Liquid absorbs heat Gas Solid releases heat Liquid releases heat Gas

The Density of Water

Least dense A. gas B. solid Most dense C. liquid

The unique properties of water density Why oceans and lakes don’t freeze solid Facts: Water is densest at 4o C Water contracts as it cools to 4o C As water goes from 4o C to freezing (0o C) it expands to become less dense than liquid As water molecules bond together to form ice, they release heat

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Lab book Entry Date: 9-15-06 Title: Properties of Water Table of Contents: add it in What are the ingredients in the following solutions that act as the solute and solvent? a. Lemonade b. 409 Cleaner

2.Why does the polarity of water make it such a good solvent 3. Draw 5 water molecules as they would line up next to each other. Show the partial charges on each atom.

4. Explain why fish and other aquatic life do not die when the top of a pond is frozen in winter. Less dense ice forms heat released Cold water sinks 4o C at bottom Thermal inversion