Chem1 - Stoichiometry

6.022 x 10²³

the mass of a sample divided by the volume of the sample

the density of a material relative to the density of water

gives the composition of molecular compounds; is chemical symbols and the number of each representing composition

• the simplest whole number ratio of the atoms in a molecule
• it does not necessarily represent the actual number of atoms & is non-positional

• gives only the number of each kind of atom present
• consist of chemical symbols & the number of each element in a compound
• denotes actual composition but not position

• shows which atoms are present & how they connect
• consists of chemical symbols & numbers of each element that represents both number & position

• the mass % of a particular element within a compound is found by dividing the mass of that element by the mass of the compound & then converting the fraction to a percentage
• M% = (atom mass / compound mass) * 100
• can never exceed 100% for any component element

• used to find mass % of e/a component element in an unknown compound

• a hydrocarbon is oxidized into CO₂ & H₂O, which are then separated

• one way this is done is by 1st passing the products over a hygroscopic salt (eg. CaCl₂, MgSO₄) which absorbs the H₂O & increases in mass

• the remaining CO₂ is passed over KOH → forming KHCO₃, which also increases in mass

• the mass percent of a solute is the mass of the solute divided by the mass of the solution
• units: mass solute/mass of solution
• remains constant as temperature changes

moles of a solute divided by volume of solution

*density x mass % = solute mass/solution volume; converting the solute mass → moles yields Molarity

units: mol solute/L solution

• moles of a solute per kilogram of solvent
• m does NOT change with temperature, so it is often used to determine a change in the solution's temperature when the change depends on concentration (eg. BP elevation, freezing-point depression)
• units: mol solute/kg of solvent

• the mass of solution per volume of solution
• it VARIES with temperature

• the addition of solvent to a solution, resulting in an increase in the volume of the solution & a decrease in the concentration of the solute in solution
• MinitialVinitial = MfinalVfinal is an eqn for simple dilution where a solvent is added to a solution

• Absorbance = εCl
• ε: constant for solute at λmax (wavelength of greatest absorbance)
• C: solute concentration
• l: width of the cuvette (length of the pathway through which light passes)
• Absorbance ~ Concentration

• the reactant that is exhausted first, not necessarily the reactant with the least number of moles
• need to know amount & mole ratio of all reactants to determine

• 1. find the moles of each reactant (using information provided in the problem, eg. grams of a substance)
• 2. divide the # of moles of each reactant by it’s coefficient in the BALANCED eqn
• *the compound with the lowest answer = the LR

• 2 aqueous salts added together form spectator ions + a solid salt precipitate that ppts out of solution
• Pb(NO₃)2_(aq) + 2KI_(aq) → PbI2_(s) + 2KNO_3(aq)
• net: Pb₂⁺_(aq) + 2I^-_(aq) → PbI_2(s)

1. alkali metal cation (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺) & ammonium (NH₄⁺) salts ARE water-soluble

2. nitrate (NO₃^-) salts ARE water-soluble

3. halide anion salts (CI^-, Br^-, I^-) ARE water-soluble (exceptions: heavy metals like Ag⁺ & Pb²⁺)

4. sulfate anion (SO₄²⁺) salts are water-soluble (exceptions: Ba²⁺, Pb²⁺, Hg²⁺, Ca²⁺)

5. hydroxide anion (OH^-) salts are slightly water-soluble (KOH & NaOH = soluble; Ca(OH)₂, Sr(OH)₂, & Ba(OH)₂ = fairly water-soluble)

6. carbonate anion (CO₃^2-), chromate anion (CrO₄^2-), phosphate anion (PO₄^3-), & sulfide anion (S^2-) salts are slightly water-soluble

• recognizable because products = salt + H₂O
• NaOH_(aq) + HCl_(aq) → NaCl_(aq)+ H₂O_(l)
• net: OH^-_(aq) + H⁺_(aq) → H₂O_(l)

• combining of reactants to form a product
• *Entropy decreases & more bonds are formed than are broken
• # of reactants > # of products [A + B → AB]

• single reactant, MORE than 1 product [AB → A + B]
• *Entropy increases & more bonds are broken than are formed

• electrons are transferred between reactants
• oxidation numbers of SOME elements change
• at least 1 element must increase & one MUST decrease in oxidation #
• single displacement rxns are ALWAYS redox reactions

• 1. Single Displacement: 1 element displaces another from a compound
• • AB + C → AC + B

2. Metathesis: AB+CD → AD+BC

• loss of electrons
• LEO the lion goes GER: Lose Electrons = Oxidation

• gain of electrons
• LEO the lion goes GER: Gain Electrons = Reduction

the atom or compound reduced, aka the one that GAINS electrons

the atom or compound oxidized, aka the one that LOSES electrons

• a special type of redox rxn where the oxidizing agent is O2 & the products are oxides
• eg. of such a rxn: oxidation of organic compounds like hydrocarbons or carbohydrates into CO₂ & H₂O

• O: -2
• H: +1
• Halide: -1
• sum of oxidation states of elements in a compound = overall charge

• group # – # of e- surrounding element
• if bonded, split bond in 2 element gets 1 e-
• (in the periodic table rows = periods & columns = groups)