5 Steps to a 5 AP Chemistry 2019

(^102) › STEP 4. Review the Knowledge You Need to Score High
(e) The one formula is double the formula of the other. Thus, the smaller molecule dimer-
izes to produce the larger molecule.
You get 1 point for pointing to any relationship between the two formulas. You get
1 point if you note the second formula is two of the lighter molecules added together.
Total your points. There are 10 points possible.
❯ Rapid Review
● The mole is the amount of substance that contains the same number of particles as
exactly 12 g of carbon-12.
● Avogadro’s number is the number of particles per mole, 6.022 × 1023 particles.
● A mole is also the formula (atomic, molecular) mass expressed in grams.
● If you have any one of the three—moles, grams, or particles—you can calculate the others.
● The empirical formula indicates which elements are present and the lowest
whole-number ratio.
● The molecular formula tells which elements are present and the actual number of each.
● Be able to calculate the empirical formula from percent composition data or quantities
from chemical analysis.
● Stoichiometry is the calculation of the amount of one substance in a chemical equation
by using another one.
● Always use the balanced chemical equation in reaction stoichiometry problems.
● Be able to convert from moles of one substance to moles of another, using the
stoichiometric ratio derived from the balanced chemical equation.
● In working problems that involve a quantity other than moles, sooner or later it will be
necessary to convert to moles.
● The limiting reactant is the reactant that is used up first.
● Be able to calculate the limiting reactant by the use of the mol/coefficient ratio.
● Percent yield is the actual yield (how much was actually formed in the reaction) divided
by the theoretical yield (the maximum possible amount of product formed) times 100%.
● A solution is a homogeneous mixture composed of a solute (species present in smaller
amount) and a solvent (species present in larger amount).
● Molarity is the number of moles of solute per liter of solution. Don’t confuse molarity,
M or [ ], with moles, n or mol.
● Be able to work reaction stoichiometry problems using molarity.
● Always use the balanced chemical equation in reaction stoichiometry problems.