Solubility and Solutions

Water is the most abundant liquid on the earth and is necessary for all life. Because of water's great dissolving properties, any sample is a solution containing solids, other liquids, and gases from the environment. This stream also carries suspended, ground-up rocks, called rock flour, from a nearby glacier.

Solutions

Introduction A solution is a homogeneous mixture of ions or molecules of two or more substances. Two parts Solvent is the component that is in the largest quantity Solute is the component that is dissolved in the solvent. If one of the components of a solution is a liquid it is usually the solvent. If the solvent is water then the solution is identified as an aqueous solution.

Above this city there are at least three kinds of solutions. These are (1) gas in gas-oxygen dissolved in nitrogen, (2) liquid in gas- water vapor dissolved in air, and (3) solid in gas-tiny particles of smoke dissolved in the air.

Concentration of Solutions The concentration of a solution describes the relative amounts of the solute and solvent. Concentrated solution contain large amounts of solute. Dilute solutions contain little solute. Different ways to express concentration Parts per million (ppm) Parts per billion (ppb) Percent by volume – the volume of solute per 100 volumes of solution Molarity – number of moles of solute per liter of solution

MOLARITY WHAT IS A MOLE ANYWAY???? ppt

There are different ways to express the concentration of a solution.

Three ways to express the amount of solute in a solution: (A) as parts (e.g., parts per million), this is 2 parts per 100; (B) as a percent by volume, this is 2 percent by volume; (C) as percent by weight, this is 2 percent by weight.

Salinity is a measure of the amount of salts dissolved in 1kg of solution. If 1,000 g of seawater were evaporated, 35.0 g of salts would remain as g of water leave.

Solubility A saturated solution is an equilibrium mixture that exists between solute and solvent where the rate of dissolving is equal to the rate at which the solute is coming out of solution. Solubility is the concentration of solute that can be dissolved to make a saturated solution at a given temperature. It is important to note that solubility varies with temperature Solubility of most ionic solids increases with increasing temperature Solubility of most gases decreases with increasing temperature.

Approximate solubility curves for sodium nitrate, potassium nitrate, potassium chloride, and sodium chloride.

Water Solutions

Properties of Water Molecules Water is a polar molecule since the oxygen has a greater electronegativity than the hydrogen. The electrons spend more time around the oxygen, giving it a partial negative charge and giving the hydrogen a partial positive charge. It is this charge differential that allows most water soluble compounds to dissolve in water.

The polarity of the water molecule allows it to set up intermolecular forces with other molecules. The positive end of the water molecule can attract the negative part of another molecule The negative end of water molecule can attract the positive end of another molecule. These types of attractions are called van der Waals forces. The intermolecular forces between a hydrogen atom and an electronegative atom such as oxygen is called a hydrogen bond. A hydrogen bond is a weak bond between a partial positive hydrogen and a partial negative atom on another molecule.

(A) The water molecule is polar, with centers of positive and negative charges. (B) Attractions between these positive and negative centers establish hydrogen bonds between adjacent molecules.

The Dissolving Process There is a limit to the solubility of any molecule in a solution Some substance do not dissolve to any appreciable amount in a solution. Fluids that can mix freely with one another are called miscible Fluids that cannot mix freely are called immiscible

Water is polar, and carbon tetrachloride is nonpolar. Since like dissolves like, water and carbon tetrachloride are immiscible.

Soap cleans oil and grease because one end of the soap molecule is soluble in water, and the other end is soluble in oil and grease. Thus, the soap molecule provides a link between two substances that would otherwise be immiscible.

IONIC COMPOUNDS What is an ionic compound? Would it dissolve in H20?

An ionic solid dissolves in water because the number of water molecules around the surface is greater than the number of other ions of the solid. The attraction between polar water molecules and a charged ion enables the water molecules to pull ions away from the crystal, a process called dissolving.

Properties of Solutions Electrolytes Ionic substances dissolved in an aqueous solution create a charge differential in the solution Since there is a charge differential there is a potential difference and electrical charge can flow between unlike charged areas. A solution which can conduct an electrical charge is called an electrolyte A solution which cannot conduct an electrical charge is called a nonelectrolyte. Ionic compounds ionize in water, disassociate to form their independent, charged particles. Acids ionize in water to protonate the water molecule and form a hydronium ion H 3 O +

(A) Water solutions that conduct an electric current are called electrolytes. (B) Water solutions that do not conduct electricity are called nonelectrolytes.

Three representations of water and hydrogen chloride in an ionizing reaction. (A) Sketches of molecules involved in the reaction. (B) Electron dot equation of the reaction. (C) The chemical equation for the reaction. Each of these representations shows the hydrogen being pulled away from the chlorine atom to form H 3 O +, the hydronium ion.