1.
Relate the structure of water to its function as the universal solvent
Electrolytes : pH-electrolytic behavior
2.
Relate the concentration of ions in a solution to the physical and chemical properties such as pH, electrolytic behavior, and reactivity 11 th grade only
In many ways, water is a miracle liquid. It is essential for all living things (on this planet at least), and it is often referred to as a universal solvent because many substances dissolve in it. These unique properties of water result from the ways in which individual
H
2
O molecules interact with each other.
Water has a dipole that forms across the water molecule as a result of the polar covalent bonding between hydrogen and oxygen. Because the bonding electrons are shared unequally by the hydrogen and oxygen atoms, a partial negative charge (ð-) forms at the oxygen end of the water molecule, and a partial positive charge (ð+) forms at the hydrogen ends. Since the hydrogen and oxygen atoms in the molecule carry opposite (though partial) charges, nearby water molecules are attracted to each other like tiny little magnets. The electrostatic attraction between the ð+ hydrogen and the ð- oxygen in adjacent molecules is called hydrogen bonding.
Electronic
Distribution in
H
2
O
Hydrogen Bonding between Water
Molecules
Hydrogen bonding makes water molecules 'stick' together. While hydrogen bonds are relatively weak compared to other types of bonds, they are strong enough to give water many unique properties. For example, hydrogen bonds sank the Titanic, and hydrogen bonds allow the Basilisk lizard to walk on water (as a result, the Basilisk has earned the nickname 'Jesus' lizard).
Just how does hydrogen bonding do this? Well, let's start with the Titanic. The Titanic sank because it hit an iceberg - a chunk of ice floating on the surface of the ocean. The reason ice floats is because of hydrogen bonding. In water's liquid form, hydrogen bonding pulls water molecules together. As a result, liquid water has a relatively compact, dense structure Liquid Water and Hydrogen Bonding
As water freezes into ice, the molecules become frozen in place and begin to arrange themselves in a rigid lattice structure.
Ice and Hydrogen Bonding
The structure that forms in the solid ice crystal actually has large holes in it.

Therefore, in a given volume of ice, there are fewer water molecules than in the same volume of liquid water. In other words, ice is less dense than liquid water and will float on the surface of the liquid. Throw in one really big chunk of ice and a cruise ship, and you begin to see the problems that can arise.
Surface Tension: As we just discussed, neighboring water molecules are attracted to one another. Molecules at the surface of liquid water have fewer neighbors and, as a result, have a greater attraction to the few water molecules that are nearby. This enhanced attraction is called surface tension. It makes the surface of the liquid slightly more difficult to break through than the interior.
When a small object that would normally sink in water is placed carefully on the surface, it can remain suspended on the surface due to surface tension. Surface tension is responsible for capillary action, which allows water (and its dissolved substances) to move through the roots of plants and through the tiny blood vessels in our bodies. The
Basilisk lizard makes use of the high surface tension of water to accomplish the incredible feat of walking on water's surface. The Basilisk can't actually walk on water; rather, it runs on water, moving its feet before they break through the surface
Solutions and Electrolytes:
• A solution is a homogeneous mixture
• The most abundant component in a solution is called the solvent

• Other components are called solutes
• When pure solute and a solution are placed in contact and no more solute dissolves (or comes out of solution) the solution is said to be saturated holds maximum amount of solute
• Solubility is different for different materials
• A solution with concentration less than a saturated solution is called unsaturated
• Supersaturated more solute than in a saturated solution unstable -Solutes drop out of supersaturated solutions that have been "seeded", e. g. with crystals or dust water is a polar molecule -electrons are shared unevenly between the oxygen & hydrogen in water -result: water molecules have a partial negative charge on O, and a partial positive charge on H water molecules can form strong electrostatic attractions to: other water molecules -other polar molecules-ions nonelectrolyte electrolyte
Solutes dissolved in water can be strong or weak electrolytes or non- electrolytes strong electrolytes
• completely breaks apart into ions
• solutions strongly conduct electricity
• typical compounds: soluble ionic compounds strong acids weak electrolytes
•
•
• incompletely breaks apart into ions solutions weakly conduct electricity typical compounds: weak acids nonelectrolytes
• does not break apart
•
• solutions don't conduct electricity typical compounds: molecular compounds
Water as a Solvent
The partial charge that develops across the water molecule helps make it an excellent solvent . Water dissolves many substances by surrounding charged particles and 'pulling' them into solution . For example, common table salt , sodium chloride, is an ionic substance that contains alternating sodium and chlorine ions .

When table salt is added to water, the partial charges on the water molecule are attracted to the Na + and Cl ions . The water molecules work their way into the crystal structure and between the individual ions, surrounding them and slowly dissolving the salt. The water molecules will actually line up differently depending on which ions are being pulled into solution . The negative oxygen ends of water molecules will surround the positive sodium ions; the positive hydrogen ends will surround the negative chlorine ions .
Table Salt Dissolving in Water
In a similar fashion, any substance that carries a net electrical charge, including both ionic compounds and polar covalent molecules (those that have a dipole ), can dissolve in water.
This idea also explains why some substances do not dissolve in water. Oil, for example, is a non-polar molecule . Because there is no net electrical charge across an oil molecule, it is not attracted to water molecules and, therefore, it does not dissolve in water.
Soap
In order to understand how soap works, we must first acknowledge what soap actually does. Firstly, soap dissolves in water. There is nothing special about this, since many substances have this property. Secondly, it dissolves in substances such as grease and oil.
This is special because oil and water don't "mix". Try adding soap and oil to water and check to see if I am telling the truth.
I take it that you have tried that and decided that you can trust me so here is an explanation. The phrase like dissolves like is referred to when discussing solubility. This basically means that polar molecules dissolve polar molecules and non-polar molecules dissolve non-polar molecules.

Water is polar, the H
2
O molecules have an attraction for other polar substances such as salt (NaCl). When salt is added to water, its ions are "dragged" away from the molecule causing them to become surrounded by the water molecules. This phenomenon is known as solubility.
Oil is non-polar, so only non-polar substances will dissolve in it. Therefore, oil and water do not mix. You might be beginning to wonder why I haven't discussed soap yet but don't worry, to understand the properties of soap you need to know this.
By definition, soap is a mixture of sodium or potassium salts and long chain organic acids. An example of such a soap is
Sodium Octadecanoate, C
17
H
35
COONa. As you can see, the soap molecule is long. It has an oxygen end which is polar and a fatty acid end, which is non-polar. In this way, soap is unique. It can dissolve in water due to the polar end and it can also dissolve in oil due to the non-polar end.
Now the explanation begins to get a little bit tricky. When soap is added to oil, it dissolves but the solution becomes slightly polar. This happens because the oxygen ends of the soap molecules are polar. These are available to help the solution dissolve in water. This explains the fact that, when soap is added to oil and water, they will mix.
This basically explains why soap is so effective as a cleaning agent. If soap is used to clean your hands, it will easily form lather and be washed off with water. See, chemistry actually is everywhere and in many cases, it is taken for granted!

Soft
Water
Hard
Water
Water with no dissolved compounds - lathers readily with soap and no scum is formed.
Water with dissolved compounds (a result of water flowing through different kinds of rock).The compounds are usually calcium and magnesium compounds. Doesn't lather readily with soap - the calcium and magnesium ions react with the soap to form a scum forms first
ACIDS AND BASES ARE EVERYWHERE
Look around you and every liquid you see will probably be either an acid or a base. The only exception would be distilled water. Distilled water is just water. That's it. Most water you drink has ions in it. It is those ions which make something acidic or basic.
In your body there are small compounds called Amino Acids. Those are acids (Duhh). In fruits there is something called Citric Acid. That's an acid too (Duhh again). But what about baking soda? When you put that in water it makes a base. Vinegar? Acid.
Scientists use something called the " pH " scale to measure how acidic or basic a liquid is.
The scale goes from "0" to "14". Distilled water is 7 (right in the middle). Acids are found between "0" and "7". Bases are from "7" to "14". Most of the liquids you find every day have a pH near "7", either a little below, or a little above. When you start looking at the pH of chemicals the numbers go to the extremes. If you ever go into a chemistry lab, you could find solutions with a pH of "1" and others with a pH of "14".
Those chemicals are very dangerous. There are pH values higher than 14 and lower than
0, but let's just start with 0-14.
Here are a couple of definitions you should know...
ACID : A solution that has an excess of H + ions.

BASE : A solution that has an excess of OH ions. Another word for base is ALKALI .
AQUEOUS : A solution which is mainly water.
STRONG ACID : An acid which has a very low pH (0-4). All of the acid becomes ions
(completely ionizes in water.
STRONG BASE : A base which has a very high pH (10-14). All of the base becomes ions. (completely ionizes in water.
WEAK ACID : An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (3-6).
WEAK BASE : A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10).
NEUTRAL : A solution which has a pH of 7. It is neither acidic nor basic.
WHAT REALLY HAPPENS
Acids are compounds which break into hydrogen (H placed in an aqueous solution. Bases are compounds which break up into Hydroxide
(OH -
+ ) ions and another compound when
) ions and another compound when placed in an aqueous solution.
If you have an IONIC compound and you put it in water it will break apart into two ions. If one of those ions is H + ... The solution is acidic. If one of the ions is OH ... The solution is basic. There are other ions which make acidic and basic solutions, but we won't be talking about them here.
That pH scale we talked about is actually a measure of the number of solution. If there are a lot of that means the number of H +
H +
ions is very low, so the pH is high.
H + ions in a
ions, the pH is very low. If there are a lot of OH ions,
That's basically it. (Ha Ha, get it?)

S ummary List of the Properties of Water Related to the Structure of Water
Hydrogen bonding of Water molecules: Due to the polar covalent bonds that hold a water molecule together, Hydrogen bonds form where the negative Oxygens and the positive
Hydrogens are located.
Drawings of Hydrogen bonded water molecules:
The results of these bonds are as follows:
1. Cohesion : is the sticking together of similar molecules. Water is very cohesive.
2. Surface Tension : cohesion allows water to pull together and form droplets or form an interface between it and other surfaces. The measure of how hard it is to break this interface is its surface tension.
3. Adhesion: The sticking of one substance to another. Water is a good adhesive. It will cling on to many objects and act as a glue. Capillary Action is an example of cohesion and adhesion working together to move water up a thin tube.
4. Imbibition : The process of soaking into a hydrophilic substance. Water being taken into a sponge, into a seed, into paper towels.
5 . High Specific Heat:
Specific heat of a substance is the heat needed (gained or lost) to change the temperature of 1g. of a substance 1degree Celsius. A Kilocalorie or large C equals 1,000 small calories.It takes 1,000 calories to raise 1,000g. of water 1 degree C.
This high specific heat allows water to act as a heat sink. Water will retain its temperature after absorbing large amounts of heat, and retain its temperature after losing equally large amounts of heat.
The reason for this is that Hydrogen bonds must absorb heat to break.
They must release heat when they form.The Ocean acts as a tremendous heat sink to moderate the earth's temperature.
6. High Heat of Vaporization:

Water must absorb a certain amount of additional heat to change from a liquid into a gas.
This extra heat is called heat of vaporization. In humans, this value is 576 cal/g.
This results in evaporative cooling of the surface. Alcohol has a value of 237cal/g. and chloroform 59cal/g.
As one can see water removes much more heat from a surface upon evaporation than does either alcohol or chloroform.
7 . Freezing and Expansion of Water : Water is most dense at 4 degrees C. At ) degrees
C. it is 10% less dense. Ice floats because maximum Hydrogen bonding occurs at 0 degrees C.
8. Versatile Solvent :
ƒ Water is a major solvent in nature. When water and another substance is mixed the resulting solution is called an aqueous solution.
9.
pH : Refers to the dissociation of water molecules.
The pH constant is K w
= 1.0 x 10 -14 (mol/L) 2
This constant shows that water dissociates at the rate of 1 molecule for every 554
million.
We have an even split of H +
If 1.0 x 10 -14 = H +
and OH ions.
and OH Then the conc. of the H ion is 1 x 10 -7 and the conc of the OH ion is also 1x10 -7
The true definition of pH is the negative log of the hydrogen ion concentration.