Inorganic Formulation and Chemical Reactions

Posted on Feb 9, 2025 in Chemistry

Inorganic Formulation

Valences and Common Elements:

  • +1: H (+/-1), Li, Na, K, Rb, Cs, Ag
  • +2: Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd
  • +3: B, Al, Tl, Ga, Bi
  • +1, +2: Cu, Hg
  • +1, +3: Au
  • +2, +3: Fe, Co, Ni, Mn (+4, +7), Cr (+6), Mo (+6)
  • +2, +4: Sn, Pb, Pt
  • +/-4: C (+2), Si
  • +/-3, +5: N (+1), P (+1), As, Sb
  • +/-2, +4, +6: O (always -2), S, Se, Te
  • +/-1, +3, +5, +7: F (always -1), Cl, Br, I

Nomenclature Codes:

1-Mono, 2-Di, 3-Tri, 4-Tetra, 5-Penta, 6-Hexa, 7-Hepta…

Suffixes:

Hypo…ous / -ic, …ous / -ic, …ic / -ate, Per…ic/-ate. 1 valence: -ic, 2 valences: -ous, -ic. 3 valences: hypo- -ous, -ous, -ic. 4 valences: hypo- -ous, -ous, -ic, per- -ic.

Common Chemical Compounds

Hydride: (Hydrogen acts with valence -1. Named with the word “hydride” followed by the name of the metal. Hydrogen is placed on the right.)

Example: FeH2 = Iron dihydride

Oxide: (In basic oxides (metal), valences of metal and oxygen are exchanged and simplified if possible. Acidic oxides are traditionally called anhydrides.)

Example: Cr2O3 = Chromium trioxide

Binary Salts: (The more electronegative element is placed on the right, named with the suffix “-ide”.)

Example: FeBr3 = Ferric bromide

Hydroxide:

Example: Cr(OH)2 = Chromium dihydroxide

Oxoacids:

Example: H2SO4 = Sulfuric acid

Oxisales:

Example: Fe2(SO4)3 = Ferric sulfate

Laboratory Techniques

Item 2: Conservation of Mass and Stoichiometry

Law of Conservation of Mass: In every chemical reaction, the mass remains unchanged; the sum of the masses of the reactants is equal to the sum of the masses of the products.

First Practice: Lead Nitrate and Potassium Iodide Reaction

Materials: Three watch glasses, pipette, cylinder, two beakers, funnel, filter paper, three beakers.

Substances: Lead nitrate (Pb(NO3)2) and potassium iodide (KI). Hazards: Oxidizer and harmful.

Procedure:

  1. Prepare 20 mL of a Pb(NO3)2 solution with a concentration of 18 g/L.
    • Calculation: 18 g/L = msolute / 0.02 L => msolute = 0.36 g
  2. Prepare 40 mL of a KI solution with a concentration of 9 g/L.
    • Calculation: 9 g/L = msolute / 0.04 L => msolute = 0.36 g
  3. Mix both solutions and note the observations.
    • Observation: The mixture turns yellow.
  4. Construct a filter and weigh it: 1.83 g
  5. Filter the precipitate produced.
  6. Let the precipitate dry.
  7. Once dry, reweigh the filter with the precipitate.
    • Mass of precipitate: 2.27 g – 1.83 g = 0.44 g

Theoretical Calculations:

Write and balance the reaction:

Pb(NO3)2 + 2KI -> 2KNO3 + PbI2

The precipitate corresponds to lead iodide (PbI2).

Calculate the mass and moles of Pb(NO3)2:

  • Mass: 0.36 g (as calculated above)
  • Moles: n = 0.36 g / 331.2 g/mol = 0.0011 mol

Calculate the mass and moles of KI:

  • Mass: 0.36 g (as calculated above)
  • Moles: n = 0.36 g / 166 g/mol = 0.0021 mol

Stoichiometric calculations show that there is just enough of each reactant. The expected moles of PbI2 are equal to the moles of Pb(NO3)2.

Calculate the theoretical mass of PbI2:

  • mPbI2 = 0.0011 mol * 461 g/mol = 0.461 g

The theoretical mass (0.461 g) does not exactly match the experimental mass (0.44 g) because some precipitate remained attached to the vessel walls.

Acid-Base Reactions

What are acidic and basic substances?

Acids:

  • Turn litmus paper red.
  • Leave phenolphthalein colorless.
  • Produce effervescence with carbonates, releasing CO2.
  • Produce effervescence with many metals, releasing H2.
  • Have a sour taste.
  • Are corrosive.
  • Examples: Oxoacids, most hydrides with metals, and organic substances possessing the -COOH group.

Bases:

  • Turn litmus paper blue.
  • Turn phenolphthalein pink.
  • Do not react with metals or carbonates.
  • Are corrosive.
  • Examples: Most hydroxides and ammonia.

When an acid and a base react, they lose their characteristic properties.

Neutralization:

AH + H2O -> A– + H+

BOH + H2O -> B+ + OH–

Neutralization Reaction: AH + BOH -> BA + H2O (Acid + Base -> Salt + Water)

pH Scale:

  • pH = 7: Neutral
  • pH > 7: Basic
  • pH < 7: Acidic

If we want to determine the concentration of an HCl solution, we can use a solution of NaOH of known concentration.

Write the reaction:

HCl + NaOH -> NaCl + H2O

We add a few drops of phenolphthalein to the HCl solution (it will be colorless). We then add the NaOH solution drop by drop from a burette. When the moles of base added equal the moles of acid, the equivalence point is reached. If one more drop of base is added, the solution will turn pink, indicating an excess of base. The concentration can then be calculated: CM = nHCl / V(L)