# Chem1 - Stoichiometry

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1. How many molecules in 1 mole?
6.022 x 1023
2. Density
the mass of a sample divided by the volume of the sample
3. Specific Gravity
the density of a material relative to the density of water
4. chemical formula
gives the composition of molecular compounds; is chemical symbols and the number of each representing composition
5. Empirical Formula
• the simplest whole number ratio of the atoms in a molecule
• it does not necessarily represent the actual number of atoms & is non-positional
6. Molecular Formula
• 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
7. Structural Formula
• shows which atoms are present & how they connect
• consists of chemical symbols & numbers of each element that represents both number & position
8. Mass Percent (% Composition by Mass)
• 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
9. Combustion Analysis (an Experimental Procedure)
• 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
10. Mass Percent (%)
• 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
11. Molarity (M)
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
12. Molality (m)
• 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
13. Density (ρ)
• the mass of solution per volume of solution
• it VARIES with temperature
14. Dilution
• 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
15. Beer's law
• 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
16. Limiting Reagent (LR)
• 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
17. How To Determine Which Compound is the LR
• 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
18. Precipitation Rxn (Double-displacement)
• 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) + 2KNO3(aq)
• net: Pb2+(aq) + 2I-(aq) → PbI2(s)
19. Solubility Rules
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 (CO32-), chromate anion (CrO42-), phosphate anion (PO43-), & sulfide anion (S2-) salts are slightly water-soluble
20. Acid-Base Rxn (Neutralization)
• recognizable because products = salt + H2O
• NaOH(aq) + HCl(aq) → NaCl(aq)+ H2O(l)
• net: OH-(aq) + H+(aq) → H2O(l)
21. Composition Rxn (Combination, Condensation)
• combining of reactants to form a product
• *Entropy decreases & more bonds are formed than are broken
• # of reactants > # of products [A + B → AB]
22. Decomposition Rxn (Cleavage)
• single reactant, MORE than 1 product [AB → A + B]
• *Entropy increases & more bonds are broken than are formed
23. Oxidation-reduction Rxn (Electron-transfer, Redox)
• 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
24. The 2 Types of Exchange Rxns
• 1. Single Displacement: 1 element displaces another from a compound
• • AB + C → AC + B

25. Oxidation
• loss of electrons
• LEO the lion goes GER: Lose Electrons = Oxidation
26. Reduction
• gain of electrons
• LEO the lion goes GER: Gain Electrons = Reduction
27. Oxidizing Agent (oxidant)
the atom or compound reduced, aka the one that GAINS electrons
28. Reducing Agent (reductant)
the atom or compound oxidized, aka the one that LOSES electrons
29. Combustion Rxn
• 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
30. How to Assign Oxidation States
• O: -2
• H: +1
• Halide: -1
• sum of oxidation states of elements in a compound = overall charge
31. Formal Charge
• group # – # of e- surrounding element
• if bonded, split bond in 2 element gets 1 e-
• (in the periodic table rows = periods & columns = groups)
 Author: mse263 ID: 287145 Card Set: Chem1 - Stoichiometry Updated: 2014-10-26 23:09:00 Tags: GeneralChemistry Folders: General Chemistry Description: chapter 1 Show Answers: