AP Chemistry

Pages
- Class
  Laboratory report rubric
  Notes
  1. Chemical foundations
  2. Atoms, molecules, and ions
  3. Stoichiometry
  4. Types of chemical reactions and solution stoichiometry
  5. Gases
  6. Thermochemistry
  7. Atomic structure and periodicity
  8. Bonding: general concepts
  9. Covalent bonding: orbitals
  10. Liquids and solids
  11. Properties of solutions
  12. Chemical kinetics
  13. Chemical equilibrium
  14. Acids and bases
  15. Acid-base equilibria
  16. Solubility and complex ion equilibria
  17. Spontaneity, entropy, free energy
  18. Electrochemistry
  Drug unit
  Basics
  Analgesics
  Antacids
  Anesthetics
  Depressants
  Stimulants
  Antibiotics
  Antiviral drugs
  Mind-altering drugs
- Textbook (incomplete)
  1. Chemical foundations
  2. Atoms, molecules, and ions
  3. Stoichiometry
  4. Types of chemical reactions and solution stoichiometry
  5. Gases
  6. Thermochemistry
  7. Atomic structure and periodicity
  8. Bonding: general concepts
- CED
  1. Atomic structure and properties
  2. Compound structure and properties
  3. Properties of substances and mixtures
  4. Chemical reactions
  5. Kinetics
  6. Thermochemistry
  7. Equilibrium
  8. Acids and bases
  9. Thermodynamics and electrochemistry

AP Chemistry

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3. Stoichiometry

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3. Stoichiometry

Counting by weighing

chemical stoichiometry: studying quantities of materials consumed and produced in chemical reactions

atoms are small; samples of matter contain huge numbers of atoms

determine number of atoms in a given sample by finding its mass

figure out average mass of atoms

Atomic masses

modern system of atomic masses: based on ¹²C (carbon twelve) as weighing exactly 12 atomic mass units (amu); all other atoms are relative to this standard

most accurate method for comparing masses of atoms: using mass spectrometer

determine mass values for individual atoms

atoms/molecules passed into beam of high-speed electrons

knock electrons off the atoms/molecules being analyzed; change into positive ions

applied electric field accelerates ions into magnetic field; interacts with applied magnetic field, changing path of ion

amount of path deflection depends on mass (more mass moves less), causing ions to separate

comparison of positions → relative masses

also used to determine isotopic composition of natural element

average atomic mass: relative average of atomic masses based on isotopic composition

finding

multiply percentage and mass value of each isotope

add values together

natural carbon does not contain a single atom with mass 12.01, but for stoichiometric purposes, we can consider carbon to be composed of only one type of atom with a mass of 12.01

The mole

mole (mol): number equal to number of carbon atoms in exactly 12 g of pure ¹²C

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also called Avogadro’s number

one mole of something consists of 6.022 ⨉ 10²³ units of that substance

sample of natural element with mass equal to the element’s atomic mass expressed in grams contains 1 mole of atomsd

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Molar mass

molar mass: mass in grams of 1 mole of the compound (also called molecular mass)

found by summing masses of component atoms

units

molecular compounds: molecules

ionic compounds: formula units

Solving problems

two ways to approach a problem

memorization/pigeonholing

label the problem (which pigeonhole fits)

requires new set of steps when problem changes

conceptual problem solving

understanding the big picture

looks within the problem for a solution

problem guides you as you solve it

ask questions and use knowledge to answer them

where are we going?

read the problem and decide on the final goal

sort through the facts given

focus on key words

draw diagram if appropriate

state problem as simply and visually as possible

how do we get there?

decide where to start (e.g. with chemical reaction in stoichiometry problem)

ask questions as you proceed

what are the reactants and products?

what is the balanced equation?

what are the amounts of reactants?

understanding of fundamental principles of chemistry will enable you to answer the simple questions and final solution

reality check: is the answer reasonable?

Percent composition of compounds

two common ways of describing the composition of a compound

numbers of constituent atoms

percentages (by mass) of elements

compare mass of each element present in one mole of compound compared to total mass of 1 mole of the compound

mass percent (or weight percent): proportion of a particular substance in a mixture as a percentage of the total mass

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Formula of a compound

often determined by taking weighted sample and decomposing it into component elements or reacting it with oxygen to produce substances to collect and weigh

for each element present:

determine molar mass of produced substances

determine fraction of element present by mass for the substance (mass of element divided by total mass of substance)

multiply fraction by given amount of substance

determine mass percent of element in the compound

convert masses of elements to numbers of atoms

base calculations on 100 g of compound

determine number of moles of each element present in 100 g of compound using atomic masses

divide each value of number of moles by smallest of the values

if numbers are not whole numbers, multiply by an integer so results are all whole

gives empirical formula: simplest whole-number ratio of elements in the compound

to specify molecular formula (exact formula of compound), must know molar mass

empirical formula mass and molar mass

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molecular formula from mass percent and molar mass

determine mass of each element in 1 mole of compound

determine number of moles of each element in 1 mole of compound

integers of step represent subscripts of molecular formula

Chemical equations

chemical reactions

chemical change involves reorganization of atoms

representation of a chemical reaction using chemical formulas and symbols

reactants on left side of arrow

products on right side of arrow

balancing a chemical equation: all atoms present in the reactants must be accounted for among the products

bonds broken; new ones formed

atoms are neither created nor destroyed

same number of each type of atom on the product and reactant sides

meaning of chemical equation

information given

nature of reactants and products

relative numbers of reactants and products

often give physical state

(s): solid

(l): liquid

(g): gas

(aq): aqueous solution; dissolved in water

atoms and mass are conserved

Information from combusting methane equation

Information from combusting methane equation

Reactants

Products

CH₄(g) + 2O₂(g)

CO₂(g) + 2H₂O(g)

1 molecule + 2 molecules

1 mole + 2 moles

6.022 × 10²³ molecules + 2 (6.022 × 10²³ molecules)

16 g + 2 (32 g)

44 g + 2 (18g)

80 g reactants

80 g products

There are no rows in this table

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Balancing chemical equations

the formulas of the compounds must never be changed in balancing a chemical equation

identities of reactants and products do not change

only change coefficients

when balancing, use trial and error and start with compounds with more atoms

Stoichiometric calculations

chemical equations can be used to determine masses of reacting chemicals

write balanced equation for the reaction

convert known mass of reactant/product to moles

use balanced equation to set up the mole ratios (ratio of moles of substances in reaction)

convert from moles back to grams if required

Limiting reactant

stoichiometric mixture: mixture that contains the relative amounts of reactants that match the numbers in the balanced equation

to determine how much product can be formed from a given mixture of reactants, find the limiting reactant

limiting reactant: reactant that runs out first and limits the amount of product that can form

finding limiting reactant

using reactant quantities (3 ways)

calculate moles of reactants present and compare to molar ratio

start with given amount of one element and calculate moles of other element needed

compare mole ratio of substances required by balanced equation with mole ratio of reactants actually present

using quantities of products formed

use amounts of reactants to determine how much product will form if each element is used up

smaller amount of product produced has limiting reactant

theoretical yield: amount of product formed when limiting reactant is completely consumed (maximum amount)

percent yield: actual yield often given as percentage of theoretical yield

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solving stoichiometry problem with masses of reactants and products

write and balance equation

convert known masses of substances to moles

determine which reactant is limiting

use amount of limiting reactant and appropriate mole ratios to compute number of moles of desired product

convert from moles to grams using molar mass