The Nature of Solubility Structure of Water Properties of Solutions Factors Affecting Gas and Solid Solubility

What is a Solution? In your science notebooks, write down the definition of a solution as it applies to science. Yes, a solution is also the answer to a problem, but in science… Solutions: A solutions is a mixture of materials. One material is usually a fluid. A fluid is a material that flows, such as a liquid or a gas. The fluid of a solution is usually the solvent. The material other than the solvent is the solute. In science, we say that we dissolve the solute into the solvent. What are some examples of solutions you use daily? Syrup is a solution of sugar and water. The brine used in making pickles is a solution of salt and water. Sweet tea is a solution of powdered tea mix, sugar, and water.

What is a solute? Solutes: The material (or chemical) present in the lesser amount The substance which dissolves in the solvent to form a solution Any reagent that undergoes a change in state when it forms a solution

What is a solvent? Solvents: The material (or chemical) present in the greater amount The substance in which the solute dissolves to form a solution The most widely used solvent is water.

Some Properties of Solutions: The mixture does not separate upon standing. Once the solute and solute are completely mixed, the mixture is homogeneous. This means you could take a sample from anywhere in the solution and the proportions of the materials will be the same. The mixture will be transparent. (This doesn’t mean it is clear, or colorless. It means that the mixture is not cloudy.)

The Structure of Water Every water molecule has one oxygen atom and two hydrogen atoms. The chemical formula is H2O The hydrogen atoms are 105° apart from each other. The hydrogen atoms have a positive charge and the oxygen atom has a positive charge. Why does that matter? Like charges repel, unlike charges attract. There is an unequal distribution of charges on the water molecule. This makes the water molecule a polar molecule.

Polarity “Like dissolves like” One end of the water molecule is more negative (oxygen), and the other is more positive (hydrogen). The partial negative end of the oxygen atom is attracted to the partial positive end of the hydrogen atom on an adjacent molecule. The hydrogen bonds give water its unique properties.

Factors Affecting Solid Solubility The solubility of a solute at a particular temperature is the number of grams of a solute which must be added to 100 g of a solvent to produce a saturated solution. The solubility of a solid increases with temperature.

Why is the effect of temperature on gas solubility significant? What are the consequences of power plants (or other types of industries) releasing run-off water into a lake or stream that is either much higher or much lower than the normal temperature range? Consequences include suffocating fish, low dissolved oxygen, decreased fish population, altered food web.

Factors Affecting Gas Solubility As the temperature increases, the solubility of a gas decreases. More gas is present in a solution with a lower temperature than in a solution with a higher temperature. Gases increase in solubility with increasing pressure. Henry’s Law: “The solubility of a gas in a liquid is directly proportional to the pressure of that gas above the surface of the solution.” More gas molecules are soluble at higher pressure.

Factors Affecting Gas Solubility If the pressure is increased, the gas molecules are ‘forced’ into the solution since this is one way to relieve the pressure that has been applied. A real world application: Deep sea divers may experience a condition called the "bends" if they do not readjust slowly to the lower pressure at the surface. As a result of breathing compressed air and being subjected to high pressures caused by water depth, the amount of nitrogen dissolved in blood and other tissues increases. If the diver returns to the surface too rapidly, the nitrogen forms bubbles in the blood as it becomes less soluble due to a decrease in pressure. The nitrogen bubbles can cause great pain and possibly death. The number of gas molecules is decreased. The number of gas molecules dissolved in solution has increased. More gas molecules are soluble at higher pressure.

Universal Solvent Water is often described as a universal solvent. It is capable of dissolving a variety of different substances. Water can dissolve polar or ionic substances. Water cannot dissolve nonpolar substances. It is water's chemical composition and physical characteristics that make it such an excellent solvent. Water, as a universal solvent, is important to every living thing on Earth. Wherever water goes (through the air, ground, or our bodies), it carries valuable chemicals, minerals, and nutrients.

Unique Properties of Water Water is the universal solvent. It exists naturally on Earth as a solid, liquid, and gas. It exists at room temperature as a liquid. In its solid state (ice) is less dense than liquid water. Has a high surface tension (That’s why there can be water drops and waves in the ocean.). Has a high specific heat (It keeps the beach cool during the day and warm at night.).