Chemistry formulas/equations

• Empirical formula?

  (given mass of element/given total mass of compound) x 100 = %

  %/atomic mass of element = moles

  moles/smallest # of moles found = empirical formula unit
• Molecular formula?

  Given total mass/molecular mass of empirical formula = scale factor

  Scale factor x empirical formula = molecular formula
• Molar concentration (in mol/dm3)

  moles of solute/dm3 of solvent (C=n/V)

  if no volume given, assume V=1
• How to identify the number of ions in a molecule

  First, apply the swap and drop rule for charges

  (Take for example Mg(NO3)2 -> swap+drop -> Mg^2+ NO3^- (bcs Mg's initial denominator was 1 and NO3's denominator was 2)

  Then, add the absolute value of the charges together for the # of ions

  (|2|+|-1| = 3 ions)

  Lastly, multiple it by Avogadro's number

  (3 x (6.02x10^23))
• Moles

  grams/atomic mass
• Concentration of a newly diluted solution

  C1V1=C2V2
• Percentage yield

  (actual yield/theoretical yield) x 100
• 2 ways to find limiting reactants

  a ) Find the theoretical yield of product created by each reactant value. The one with the smallest yield is limiting reactant

  b ) Convert grams to moles and divide by their coefficient. Then compare the resulting values as the smaller one is the limiting reactant
• Volume of a gas product

  Use limiting reactant to find moles of product then plug into V=nRT/P
• Find theoretical yield

  Indentify for which product the actual yield is given. Use the limiting reactant to multiply it with the (moles of the product/moles of the LR) and then with its molecular mass
• Ionization energy

  E=hv where E is energy in Joules, v is frequency in (s^-1) and h is Plank's constant

  C=vl where C is the speed of light, v is frequency in (s^-1). and l is wavelength in meters
• Paper chromatography Retention factor (Rf)


  distance moved by solute up the paper/distance moved by solvent up the paper
• Percentage by mass of element in a compound


  Multiply the atomic mass of element with its mole coefficient then divide that amount with the compound's molecular mass. This amount is then multiplied by a 100 to find the value of percentage composition
• Atoms of an element in a compound given total amount of compound in moles

  Identify coefficient of element and multiply it to the total amount of compound in moles. Then, multiply it with Avogadro's constant (6.02x10^23)
• Equation for nth electron ionization

  X^((n-1)+) -> X^(n+) + e^-
• Equation for nth electron affinity

  X^((n-1)-) + e^(-) -> X^(n-)
• Combustion analysis is finding composition of hydrocarbon from combustion data

  1. take mass of CO2/H20 divided by its molecular mass and then multiplied by its coefficient in the molecule (ex. H20 holds 2 hydrogen, CO2 holds 1 carbon)

  2. divide by smallest amount found then multiple both to get whole

  numbers (if needed) = molecular formula
• 0.5 x 2=1

  0.333... x 3 =1

  0.25 x 4 =1

  0.2 x 5 =1

  0.4 x 5 =2
• The total potential difference (E[total]) of the electrochemical cell is calculated as follows: E[cathode] - E[anode]
• 0.0821 is R for dm3 atm/mol K units
• A is mass number
• Z is atomic number
• X is actual element