Water The Universal Solvent

What is Water? Water - compound– H 2 O – 2 hydrogens, 1 oxygenWater - compound– H 2 O – 2 hydrogens, 1 oxygen  This ratio never changes no matter what is dissolved in it or what state water is in (liquid, solid, or gas).

Water Water makes up 66% of the human body by massWater makes up 66% of the human body by mass We lose it by breathing, perspiration and in our wasteWe lose it by breathing, perspiration and in our waste If you are inactive you probably lose 25 – 100 ml/hourIf you are inactive you probably lose 25 – 100 ml/hour This increases to 3000 ml/hour if you are exercising!This increases to 3000 ml/hour if you are exercising! Therefore, you need to replenish your water often when exercising to prevent dehydrationTherefore, you need to replenish your water often when exercising to prevent dehydration

Water  Water is a molecular molecule because there is a sharing of electrons between the 2 hydrogen atoms and the oxygen atom.

Water  The hydrogen and oxygen atoms are held together by covalent bonds (result of the sharing of electrons).

Water  The water molecule has a positive end (hydrogen) and a negative end (oxygen). This makes water polar.

Water  Because of its molecular structure, water will dissolve most any substance. Water will dissolve polar and ionic solutes. Water is the "universal solvent".

Water  Solvent means that water does the dissolving.  Solutes are the substances that you mix with the water.

Water  In order for the water to dissolve something, there must be an attraction between the opposite charges of the water molecule and the solute molecule.

Water  The molecules of the solute are pulled away into solution and the solute dissolves.

Water  The positive end of the water molecule (H+) is attracted to the negative end of the solute molecule. Remember: Opposites always attract!!!

Water  For plants and animals to live in water, they must have oxygen. If something happens to the water to cause it not to dissolve enough oxygen, plants and animals will die.

Water  Example: Hot water discharged into rivers and lakes causing less oxygen to be dissolved in the water.

Water  During the winter, fish survive frozen lakes and ponds because the ice is less dense than the water and floats on top of the water. This forms an insulating layer to protect the fish from freezing.

Water  If the ice were more dense and did not float, no insulating layer would be formed and the fish would die.

ELECTROLYTES  Electrolytes are compounds that will conduct electricity when they are dissolved in water.

ELECTROLYTES  Water will conduct electricity if ions or minerals are dissolved in it. Example: Tap water (water from your sink or bathtub) has minerals (ions) dissolved in it, so it will conduct electricity.

ELECTROLYTES  Pure water or distilled water has no minerals in it, so it will not conduct electricity.

ELECTROLYTES  Examples of electrolytes include: minerals, salts (salt water and seawater), and acids.

KEYS TO REMEMBER  The one property of water that does not change is its formula (ratio of hydrogen to oxygen)  Water will dissolve almost anything because of its molecular structure (polar) Look for the word "polar" in the answer.

KEYS TO REMEMBER  When a solute dissolves in water, the negative molecules of the solute are attracted to the positive hydrogen end of the water molecule;

KEYS TO REMEMBER Cont. the positive molecules of the solute are attracted to the negative oxygen end of the water molecule.

KEYS TO REMEMBER  For questions regarding fish in ponds during the winter, look for "ice as an insulating layer" in the answers.

KEYS TO REMEMBER  Electrolytes cause water to conduct electricity.  Pure or distilled water will not conduct electricity.

KEYS TO REMEMBER  Tap water will conduct electricity because of minerals or ions in it. Look for "minerals or ions" in the answer.  Look for the word "acid" when asked about specific electrolytes.

The Water Cycle

Surface Tension Liquid water acts like it has a skin.Liquid water acts like it has a skin. Water forms round drops.Water forms round drops. All because water hydrogen bonds to other water molecules.All because water hydrogen bonds to other water molecules.

Surface Tension One water molecule H bonds to another.One water molecule H bonds to another. Can H bond to molecules all around.Can H bond to molecules all around. H H O ++ ++ -- H H O ++ --

Surface Tension Ever noticed that you can fill a glass so that the liquid bulges above the rim?Ever noticed that you can fill a glass so that the liquid bulges above the rim? Insects can walk on water as if it has a skin, but a needle will break through water immediately and sink?Insects can walk on water as if it has a skin, but a needle will break through water immediately and sink? These are examples of surface tensionThese are examples of surface tension

Surface Tension Water drops are round because all the molecules on the edge are pulled to the middle.Water drops are round because all the molecules on the edge are pulled to the middle.

Meniscus Water curves up along the side.Water curves up along the side. This makes the meniscus.This makes the meniscus.

Ice Most liquids contract (get smaller) as they are cooled.Most liquids contract (get smaller) as they are cooled. They get more dense.They get more dense. When they change to solid they are more dense than the liquid.When they change to solid they are more dense than the liquid. Solid metals sink in liquid metal.Solid metals sink in liquid metal. Ice floats in water.Ice floats in water. Why?Why?

Ice Water becomes more dense as it cools until it reaches 4ºC.Water becomes more dense as it cools until it reaches 4ºC. Then it becomes less dense.Then it becomes less dense. As the molecules slow down they arrange themselves into honeycomb shaped crystals.As the molecules slow down they arrange themselves into honeycomb shaped crystals. These are held together by H-bonds.These are held together by H-bonds.

H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O Liquid Solid

Ice 10% less dense than water.10% less dense than water. Water freezes from the top down.Water freezes from the top down. It takes a great deal of energy to turn solid water to liquid water.It takes a great deal of energy to turn solid water to liquid water.