Stoichiometry Stoicheion from Greek which means first principle or element and metron is a measure Stoichiometry is the quantitative relationship among elements and compounds and among substances as they undergo chemical changes

The Limiting Reactant Concept In any chemical reaction, if there is a presence of one substance in excess, then the other substance is used up first. This is called the limiting reactant. Suppose you have 6 slices of bread and only 2 pieces of ham. Then the ham is the limiting reactant May problems in chemistry are based on the concept of a limiting reactant

The Limiting Reactant Concept Let us try a few problems using this concept: –What mass of carbon dioxide is formed by the reaction of 16.0g of methane with 48.0g of oxygen? –Chemical equation for the above reaction: CH 4 + 2O 2  CO 2 + H 2 O –One mole of methane = 16.0 g –Two moles of oxygen = 64.0g –One mole of carbon dioxide = 44.0 g –Two moles of water = 36.0 g

The Limiting Reactant Concept The reaction is a 1 to 2 reaction, which means that 1 mole of methane combines with 2 moles of oxygen to give 1 mole of CO 2 and 1 mole of water We are given that 16.0 g of methane reacts with 48.0 g of oxygen. Looking at the reaction, we know that 16.0 grams of methane represents 1 mole and 48.0 g of oxygen represents 1.5 moles. Returning to the equation, we can calculate the number of moles of oxygen that are required to react with methane. That would be 2.00 moles. But we only have 1.5 moles. Therefore oxygen is our limiting reactant as we need more than we have. Now use that information to determine the answer Since the question asks for the mass of carbon dioxide, we have to determine the ratio of oxygen and carbon dioxide in the reaction

The Limiting Reactant Concept Looking at the equation, we see that they are in a 2 to I ratio. But we have only 1.5 moles instead of 2. Therefore we will only get moles of carbon dioxide Finally, the mass of moles of carbon dioxide needs to be calculated. One mole of carbon dioxide = 44.0 grams Therefore mass of carbon dioxide = 0.750*44.0g = 33.0 g THE ANSWER IS 33.0 g OF CARBON DIOXIDE IS FORMED IN THE REACTION

Water 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

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.

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

A solution is a homogeneous mixture. A solution consists of a solvent, the substance in which something is dissolved, and one or more solutes the substance(s) dissolved in the solvent. In this chapter we will focus on aqueous solutions in which water is the dissolving medium, or solvent.solutionsolventsolutes aqueous solutions Solutes come in two varieties: electrolytes and nonelectrolytes Solutions of electrolytes such as NaCl and HNO 3 contain ions and thus conduct electricity. Solutions of nonelectrolytes such as sucrose (C 12 H 22 O 11 ) and methanol (CH 3 OH) do not form ions in solution and thus do not conduct electricity.electrolytes nonelectrolytes

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

An electrolyte may be either a strong electrolyte or a weak electrolyte. A strong electrolyte exists in solution completely (or almost completely) as ions, while a weak electrolyte produces only a small concentration of ions when it dissolves in solution.strong electrolyteweak electrolyte Ionic compounds that are soluble in water dissociate completely and exist in solution entirely as ions. Soluble ionic compounds are strong electrolytes. Molecular compounds such as sugar and alcohol are non-electrolytes. They have no tendency to come apart, and they exist in solution entirely as aqueous molecules.dissociate Some molecular compounds, most notably acids and weak bases, are electrolytes.

–Boiling Point The boiling point of a solution is the point at which enough energy has been added to overcome the intermolecular forces that hold the solute in the solution. At this point, the molecules gain enough kinetic energy to produce a pressure that is greater than the atmospheric pressure keeping them in solution Once this point is reached, the solution vaporizes (becomes a gas)

The rate of evaporation, and thus the vapor pressure, is less for a solution than for a solvent in the pure state. The greater the solute concentration, the less the vapor pressure.

–Freezing Point The freezing point of a solution is the point where enough energy has been removed from the solution to slow the molecules down and increase intermolecular forces so the solution becomes a solid

Acids, Bases, and Salts

Properties of Acids and Bases –The properties of acids are: Sour taste Change blue litmus paper to red. React with metals to release hydrogen gas. Neutralize bases, forming water and salts –The properties of bases are: Bitter taste Bases turn red litmus paper blue. Feel slippery to the skin. Neutralize acids, forming water and salts.

–Strong and Weak Acids and Bases Strong acids ionize completely in water Weak acids ionize only partially in water Strong bases ionize completely in water. Weak bases ionize only partially in water.

–The pH Scale Acid base strength is a measure of relative H 3 O + and OH - concentrations. Acidic solutions have concentrations of H 3 O + above 1 X Neutral solutions have H 3 O + concentrations equal to 1 X Basic solutions have H 3 O + concentrations less than 1 X A neutral solution has a pH of 7, acidic solutions have pH below 7, and basic solutions have pH above 7. Each division of the pH scale is an increase or decrease in concentration to a power of 10, which makes the scale a logarithmic scale

The pH scale.

The pH increases as the acidic strength of these substances decreases from left to right. Did you know that lemon juice is more acidic than vinegar? That a soft drink is more acidic than orange juice or grapefruit juice?

Properties of Salts –A salt is produced by a neutralization reaction between an acid and a base. A salt is any ionic compound, except for hydroxide or oxides –Hard and Soft Water A solution of Ca 2+ and Mg 2+ ions is called hard water because soap does not lather up very well in it. –The Ca 2+ and Mg 2+ replace the sodium or potassium ions in the soap and become insoluble

–Buffers A buffer is a mixture of a weak acid with the salt of the acid. A buffer has the ability to resist changes in pH when small amounts of acids or bases are added to the solution If small amounts of acid is added, hydronium ions are neutralized by reacting with the salt in solution If small amounts of base is added, hydroxide ions are neutralized by reacting with the acid.