There are three states of matter solid, liquid, and gas. As we have seen each state of matter has a certain number of particles with a certain degree of order. All particles are in constant random motion and there is an attractive force between these particles. These two things determine the order of the particle and thus whether the matter is in the gas, liquid, or solid state. Let's compare 25ml of a gas, liquid and a solid. In 25 ml of a gas the average kinetic energy or speed of the particles is much greater than the attraction between the particles. This allows the gas to expand and fill its container with a relatively small of particles. The particles are in total disorder and are far apart. This means there a very few number of particles in our 25-ml of gas. In 25 ml of a liquid the particles have more order but are still in disorder. They are also closer together than in a gas and thus, the particles are moving slower (have less kinetic energy). Because of the speed of the particles and their arrangement we will have more particles in 25 ml of a liquid than in 25 ml of a gas. In 25 ml of a solid the particles are in an ordered arrangement and close together. These particles are moving even slower than that of a liquid (low kinetic energy). Here we will have more particles in 25 ml than in either the gas or liquid.

As we have learned with the kinetic theory of matter all particles are in constant random motion. So whether matter is in the solid, liquid, or gas state the particles making up that matter are constantly moving. This motion is due to the particles kinetic energy. The process of dissolving is based on the principles learned from the kinetic theory of matter.

Let's look at the process of dissolving using water and sugar. Water is the dissolving medium, which is called the solvent. Sugar is the dissolved particles, or substance to be dissolved. This is called the solute. If a sugar crystal is placed in a beaker of water it will automatically dissolve with no out side forces acting upon it. In other words, we do not have to do anything to the water or the sugar in order for it to dissolve; the process is said to be spontaneous.

When a sugar is placed in water, the water molecules collide with the sugar molecule because of their kinetic energy. The process of dissolving the sugar involves the following three actions.

1. The solute (sugar) particles are separated from the solid, because of the attraction of the solute and solvent (water) particles. This attraction takes up energy (energy is required).
2. The solvent (water) particles are moved apart to allow solute particles to enter the liquid environment. This action also takes up energy.
3. The solute (sugar) particles are attracted to the solvent (water) particles. This gives up energy (energy is released).

When energy is released it is considered an exothermic reaction, and when energy is absorbed it is considered an endothermic reaction. Thus, the first two steps are endothermic because the take in energy, and the third step is exothermic.

Based on the kinetic theory of matter temperature is a measure of the average kinetic energy (speed) of all the particles in matter. If the temperature (average kinetic energy of the particles) increases as the dissolving process occurs, the exothermic process is greater than the two endothermic processes (negative heat of solution). The solubility of a substance with a negative heat of solution decreases with rising temperature.

If the temperature of the solution decreases as the dissolving process occurs, the endothermic processes are greater than the exothermic process (positive heat of solution). The solubility of the substance increases with rising temperature.

Any time a substance is dissolved in another substance we create a solution. If the dissolving medium (thing we dissolve in) is water we call these solutions aqueous. Solutions are mixtures and have certain properties. Solutions are made up of two substances; a solute, the substance being dissolved, and a solvent, the dissolving medium.

Solutions are homogeneous mixtures that are very stable. Solutions are physically blended and can only be separated by means of evaporation. They can not be separated with a filter paper. When a solution is placed in a filter both the solute and the solvent particles pass through the filter paper. Solutions will not settle over time.

Solutions can be made from many different substances. Many times when we think of a solution we think of dissolving a solid into a liquid. But this does not always have to be the case. Solvents and solutes may be gases, liquids or solids. For example, when making homemade root beer, dry ice is places in the liquid syrup. As the dry sublimates (goes from solid to gas) the gas is dissolved in the liquid. This is what gives root beer and other sodas their bubbles.

We saw in the element notes and labs the sugar will dissolve in water but that citric acid will not. Not all substances will dissolve in water or other substances. Their ability to dissolve has to do with the type of bonds. Substances that dissolve most readily in water are ionic compound and polar covalent molecules. These will form ionic solutions. Non-polar covalent molecules do not dissolve in water. A golden rule to remember is that likes dissolve likes. Water is a polar covalent molecule; thus other polar covalent molecules will dissolve in it.

If we were to try and dissolve oil into water what do you think will happen? They will not mix and no dissolving will occur. These two liquids are said to be immiscible (when two liquids can't dissolve in each other). Now if we were to take ethanol, it will dissolve in water. These two liquids are said to be miscible (when two liquids can dissolve in each other).

Now let's look at mixtures of water with substances that do not form true solutions. Two such mixtures are suspensions and colloids.

Suspensions are heterogeneous mixtures. These mixtures have particles that are larger than those of a solution. These larger particles will eventually settle over a period of time. The particles of a suspension when filtered will remain on the filter paper and just the water will pass through. An example of a suspension would be chalk in water.

Colloids are mixtures containing particles that are intermediate in size between those of suspensions and true solutions. The properties of a colloid differ form those of solutions and suspensions. Many colloids are cloudy or milky in appearance but look clear when they are very dilute. The particles of a colloid can not be removed by filter paper. The particles will pass through with the water much the same as solutions. The particles also will not settle over time. Colloids are based on the Brownian motion (remember back to the kinetic theory of matter). Examples include, blood, aerosol sprays and smoke.

There is a test that can be preformed in order to determine where a substance is a solution, colloid, or suspension. This test is called the Tyndall effect (the scattering of visible light in all directions). To do this test a beam of light passed through these mixtures. Within the container holding the solution there will be no light seen. The colloid will appear as a beam and the suspension will scatter the light. So the suspension and the colloid exhibit the Tyndall effect.

The particles move from the solid to the solvated state and back to the solid again. Yet there is no net change in the overall system. A state of dynamic equilibrium exists between the solution and the undissolved solute, provided that the temperature remains constant. The sodium chloride solution is saturated.

When the temperature of a saturated solution is raised, the excess solid will usually dissolve. If the system then cools slowly and undisturbed to its original temperature, the excess solute does not always immediately crystallize. A solution which contains more solute than it can theoretically hold at a given temperature is a supersaturated solution.

In such a solution, a dynamic equilibrium cannot exist between the dissolve solute and the undissolved solid because there is no undissolved solid. Crystallization in a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added. Crystallization can also occur on a rough surface such as the inside of the container if it is scratched.

The rate at which excess solute deposits upon the surface of a seed crystal can be impressively rapid. Scientific rainmaking is done by deeding clouds, which are made of air supersaturated with water vapor. Tiny silver iodide (AgI) crystals are dusted on a cloud. Water molecules that are attracted to the ionic particles come together and form droplets that act as seeds for other water molecules. The water droplets grow and eventually fall as rain when they are large enough. (Chemistry, pg. 376)

The solubility of gases behave opposite of solids. Agitation and increasing temperature decreases the solubility of a gas. Where as these two things will increase the solubility of a solid with a positive heat of solution? Henry's law states that at a given temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid.

Colligative properties of Solutions

Some of the physical properties of a solution are different form those of a pure solvent. Some of these differences are due to the mere presence of solute particles in the solution. These properties are called colligative properties (meaning depending on the collection). There are three important colligative properties of solutions, vapor pressure lowering, boiling point elevation, and freezing point depression.

Colligative properties depend on the number of particles dissolved in a given mass of solvent. The lowering of the freezing point and the raising of the boiling point are examples of physical properties of solutions that depend on the concentration but not the kind of solute particles.

The magnitude of the change is directly proportional to the concentration of solutes. A solute that dissociates into several particles, like sodium chloride, has an even greater effect of colligative properties. The more particles there are the more interference there is and thus a higher boiling point or a lower freezing point.

Proportions are relationships between things, so that when one number changes the other changes as a multiply of the first. For example, if we compare how many quarts are in a gallon we would say that there are 4 quarts in 1 gallon. If we wanted to know how many quarts are in 2 gallons we would double the quarts because the gallons were doubled. Proportions are easier to work with if we write them as a ratio. For example, 4 quarts/1gallon. It does not matter if proportions are flipped, for example, 4 quarts/1 gallon can also be written as 1 gallon/ 4 quarts.

Units are the labels that identify what a number is talking about. For example, you are about 5.0 x 10⁸ old. What?! Yes, you are about 5.0 x 10⁸ seconds old.

When solving problems that use proportions, it is necessary to make sure that all units cancel, except for those units in the answer. The picket fence is a tool used to make sure that the units cancel. We use straight lines to create a picket fence as shown -------|-------|-------.

When a number is on the top of the picket fence, it means the number is used to multiply other numbers by it. In other words, all of the numbers on top are multiplied together. When a number is on the bottom of the picket fence, it means the number is used to divide other numbers by it. This means that the number on top is divided by the number on the bottom. If there is more than one number on the bottom then all the numbers on the bottom are multiplied together before the division takes place.

Steps for using the picket fence:

Step 1: Write out any proportions given in the problem and any others that may be of use. This makes filling in the picket fence easier because all of the proportions needed to solve the problem are right where we can see them.

Step 2: Identify what units are needed to satisfy what the problem is asking.

Step 3: Start the picket fence in the upper left hand corner by filling it in with the number and the units that are not part of any proportions and is given to you in the problem.

Step 4: Fill in the picket fence form left to right, making sure to cancel the units as you go along. Units cancel when they are kiddy corner to each other.