Unit 2

• Stoichiometry refers to relationships among amounts of substances in a chemical reaction, which are expressed in moles or masses.
• Stoichiometry depends on the Law of Conservation of Mass.
• Chemical equations include reactants, products, and miscellaneous information on or below the arrow such as catalysts, solvents, temperature, conditions.
• The periodic table can be used to predict reactions and members of a family react similarly.
• Combustion in air results in C,H compounds (hydrocarbons) + O2 → ?.
• Reaction types include combination (composition, synthesis) (1 product), decomposition (1 reactant), single replacement (displacement) (1 element + 1 compound), and double replacement (metathesis) (2 compounds).
• Atomic mass scale is a relative scale, now based on carbon, and measured in amu.
• Average atomic masses are the weights on the periodic table, which are weighted averages.
• Formula weight is the mass of formula = sum of average atomic weights of elements in formula.
• Molecular weight (amu) refers to molecules only, while molar mass applies to all kinds of substances and is measured in grams/mole.
• Percentage by mass can be calculated in a compound by using the formula: % composition = (mass of each element in compound / total mass of compound) x 100.
• Mass spectrometer breaks molecules into fragments, which are characteristic of the molecule, and these collide with detector and a spectrum is generated.
• The relative height of each peak on a spectrum corresponds to the % abundance for the isotope.
• Molar mass is the mass of formula in grams.
• Mass, moles, and # particles are all related.
• The empirical formula of a hydrate can be determined using mass data or percent composition data.
• Another method of determining the empirical formula by combustion analysis is by determining the percent by mass of each element.
• The theoretical yield of aluminum iodide can be determined assuming a complete reaction.
• The amount of product predicted by stoichiometry is called the theoretical yield.
• In stoichiometry, mass is converted to moles, moles to mole ratio, moles to grams.
• Percentage yield: % yield = actual yield x 100% theoretical yield.
• When 1.54 g of aluminum metal is added to 15.32 grams of iodine solid, a reaction occurs.
• When 2 reactants are involved in a reaction, one is often in excess, the reactant consumed first is the limiting reactant or limiting reagent.
• The limiting reactant can be identified in a reaction.
• If the actual yield is 12.5 grams of aluminum iodide, the % yield can be calculated.
• KClO3 decomposes when heated, hence the theoretical yield of oxygen gas can be determined when a certain amount of KClO3 is heated.
• The density of octane is 0.692g/mL at 20°C, hence the number of moles of O2 required to burn 1.00 gallon of octane can be calculated.
• The empirical formula from combustion analysis is determined by determining the percent by mass of each element.
• In the reaction 3 Cd + 2 P → Cd3P2, Cd is the limiting reactant.
• When octane, C8H18, is burned in air, it requires 1.50 mole of O2.
• The mass of excess reactant can be calculated if the actual yield is known.
• Aspartame, the artificial sweetener marketed as NutraSweet, has a molecular formula C14H18N2O5.
• A sample of glucose, C6H12O6, contains 2.03 x 1021 atoms of carbon.
• The mole, 6.022 x 1023 particles, is a fundamental concept in chemistry.
• Empirical formulas are determined from % composition.
• The molecular formula of a compound can be determined from the empirical formula and molar mass.
• Determining the formula of a hydrate involves finding the empirical formula from % composition and molar mass.