Simplest (Empirical) Formula Simplest integer ratio of the atoms in a compound Assume 100 g of compound, %element is then g element in sample g element x 1 mol element = mol element g element CHCl3 10.061 g C x 1 mol C = 0.83765 mol C 12.011 g C Determine simplest integer mole ratio

EXAMPLE: Phosphorus burns in air to produce a white compound that is 43.7% P and 56.3% O by mass. What is the empirical formula of the compound? Assume 100 g of compound Relative Number of Atoms Multiply by Integer mass 43.7g P 56.3g O (mass/atomic mass) Divide by Smaller 43.7/30.97 = 1.41 56.3/15.9994 = 3.52 2  1.00  2 2  2.50  5 1.41/1.41 = 1.00 3.52/1.41 = 2.50 .25, .33, .5, .67, .75 ¼, ⅓, ½, ⅔, ¾ 1:1.25 = 4:5 Empirical Formula  P2O5

Molecular Formula The exact proportions of the elements that are contained in a molecule An integer multiple (X) of the empirical formula MF = X  EF

Molecular Formula from Simplest Formula empirical formula mass  FM sum of the atomic weights represented by the empirical formula molar mass = MM = X  FM

Molecular Formula from Simplest Formula first, knowing MM and FM X = MM/FM then MF = X  EF

EXAMPLE: Our phosphorus compound has a molar mass of ~285 EXAMPLE: Our phosphorus compound has a molar mass of ~285. What is the molecular formula? FM = 2 x 30.97 + 5 x 16.00 = 141.94 MM 285 X = = = 2 FM 141.94 thus MF = 2  EF P4O10

The empirical formula of a substance is found to be CH3O and its molecular weight is found to be roughly 61 g/mol. What is the true molecular weight of the substance? 30.5 g/mol 31.0 g/mol 61.0 g/mol 62.0 g/mol 124.0 g/mol 130 10

Biological Periodic Table

Carbohydrates Cx(H2O)y Glucose C6H12O6

Sucrose Glucose + Fructose  Sucrose + Water

Tristearin - Glycerol - Stearic Acid 3H2O+ +3

Quantities of Reactants and Products Chapter 4 Quantities of Reactants and Products

Balanced Chemical Equation Representation of a chemical reaction which uses stoichiometric coefficients (prefix numbers) to represent the relative amounts of reactants and products 2 H2 (g) + O2 (g)  2 H2O (l) Molecule to Molecule or Mole to Mole

balanced chemical equation EXAMPLE How much H2O, in moles results from burning an excess of H2 in 3.3 moles of O2? 2 H2 + O2  2 H2O (3.3 mol O2) (2 mol H2O) #mol H2O = = 6.6 mol H2O (1 mol O2) Mole ratio from balanced chemical equation

Reaction of H2 and Cl2 or H2 (g) + Cl2 (g)  2 HCl (g) one to one gives two or four to four gives eight

Types of Reactions synthesis or combination reactions decomposition reactions displacement reactions exchange reactions

Types of Chemical Reactions

Synthesis or Combination Reactions Formation of a compound from simpler compounds or elements.

Combination Reaction

Decomposition Reactions Separation into constituents by chemical reaction.

Dynamite

Electrolysis

Displacement Reactions Reaction of a compound with a more reactive element to produce a new compound and release a less reactive element

Displacement Reactions

Exchange Reactions Reaction where ion partners are exchanged

Pb(NO3)2 (aq) + K2CrO4 (aq)  PbCrO4 (s) + 2 KNO3 (aq)

When Zn(s) is placed in aqueous HCl, hydrogen gas is evolved and zinc chloride solution is obtained. Predict the reaction type. Combination Combustion Decomposition Displacement (single displacement) Exchange (double displacement) Instructor comment: The answers include the possible reaction types and any answer may be selected if the student is clueless. This question requires cumulative skills including writing correct formulas and identifying reaction type. The student must carefully examine the reactants and products and determine the net change during the reaction. The instructor can review these concepts when discussing the solution to the problem and emphasize the need to retain information by drill and practice outside class and reinforcement in class. 130 10

Writing and Balancing Chemical Equations Determine the type of reaction and formulae of the products Write an unbalanced equation with the correct reactants and products Balance the equation by the use of prefixes (coefficients) to balance the number of each type of atom on the reactant and product sides of the equation.

Example Iron is produced by the reduction of iron(III) oxide with CO which forms CO2 iron(III) oxide + carbon monoxide  iron + carbon dioxide Fe2O3 + CO  Fe + CO2 Fe2O3 + CO  2 Fe + CO2 Fe2O3 + 3 CO  2 Fe + 3 CO2

When aluminum reacts with sulfuric acid to yield aluminum sulfate and hydrogen what is the SUM of the coefficients in the balanced equation? 4 6 7 8 9 130 10