Inorganic chemical language

1. a) Write the chemical formula of the following binary compounds: titanium dioxide, dihydrogen sulfide and cobalt(III) bromide.
2. b) Assign a systematic compositional or Stock name to the following formulas: $\mathrm{Cu_2O}$, $\mathrm{NH_3}$ and $\mathrm{SnH_4}$. State explicitly, for the compound $\mathrm{Cu_2O}$, the oxidation state of the copper.

In the draft of a chemical quality-control report, the following five formulation or nomenclature proposals appear:

1. "Iron(III) sulfate" associated with the formula $\mathrm{Fe_3(SO_4)_2}$.

2. "Potassium(I) oxide" to designate the substance $\mathrm{K_2O}$.

3. "Chloric acid" assigned to the formula $\mathrm{HClO_2}$.

4. "Calcium nitrite" for the formula $\mathrm{Ca(NO_3)_2}$.

5. "Sulfuric(VI) acid" for $\mathrm{H_2SO_4}$.

1. a) Distinguish formulation errors or errors in identifying a species, redundant indications and unnecessary mixing of nomenclatures. Do not assume that all cases have the same type of problem.
2. b) Provide a simple and correct formulation or name for each case: write the actual formula corresponding to the intended name in 1 and 4, and assign the unambiguous IUPAC name to the formulas in 2, 3 and 5.

1. a) Write the formulas of the following inorganic chemical species: iron(II) hydroxide, ammonium chloride and lead(IV) selenide.
2. b) Name the following compounds using compositional or Stock nomenclature: $\mathrm{Al(OH)_3}$, $\mathrm{Mg_3N_2}$ and $\mathrm{Fe_2S_3}$. Specify the ions (cation and anion) that formally make up each of them.

1. a) Write the molecular or empirical formula of the following oxygen-containing compounds: nitric acid, potassium sulfate and sodium dihydrogenphosphate.
2. b) Give a valid IUPAC name (accepted traditional or systematic compositional/hydrogen) for: $\mathrm{HClO_4}$, $\mathrm{NaIO_3}$ and $\mathrm{CaCO_3}$. Also state the oxidation state of the central non-metal in the acid and in the anions of the two salts.

Acid salts derived from polyprotic oxoacids retain hydrogen atoms with acidic character in their anion.

1. a) Write the formula of barium hydrogen sulfite, first deducing the oxidation state of all the elements present in the salt and applying the formal charge balance.
2. b) Write the complete ionic dissociation equation of this salt when it dissolves in water at $25\,^\circ\text{C}$, identifying the solvated cationic and anionic species. Explain whether the resulting anion shows amphiprotic behavior according to Brønsted-Lowry theory.

Observe the schematic two-dimensional representation of the structural arrangement in an inorganic solid made up of monatomic ions $A^{2+}$ and $B^{2-}$:

1. a) Deduce the minimum stoichiometric ratio between the two ions in the lattice and write the resulting empirical formula of the compound.
2. b) Explain why it has no physical meaning to refer to the molecular mass of this solid compound, and distinguish its continuous lattice nature from a discrete neutral molecular substance made up of covalently bonded atoms, such as sulfur dioxide, $\mathrm{SO_2}$.

In the lab, four pure substances I, II, III and IV are identified at $20\,^\circ\text{C}$ and $1\,\text{atm}$:

• I: A gas made up of molecules in which chlorine has oxidation state $+1$ with respect to oxygen in an atomic ratio $2:1$.

• II: A white solid with a high melting point ($1418\,^\circ\text{C}$), an electrical insulator as a solid but a conductor when molten, whose small fraction dissolved in water dissociates into ions $\mathrm{Ca^{2+}}$ and $\mathrm{F^-}$.

• III: An inorganic solid with an extremely high melting point ($>1600\,^\circ\text{C}$), insoluble and non-conducting, with silicon and oxygen atoms covalently bonded in the stoichiometric ratio $1:2$.

• IV: A homonuclear diatomic gas with a triple covalent bond.

1. a) Write the formula and assign a systematic IUPAC name to substances I, II and III.
2. b) Classify each substance (I to IV) as: molecular substance, ionic lattice or covalent lattice.

A pure sample of a hydrated nickel and sulfur oxysalt is thermally analyzed to determine its exact stoichiometric formula. $4,742\,\text{g}$ of hydrated nickel(II) sulfate, of formula $\mathrm{NiSO_4 \times } x\,\mathrm{H_2O}$, is weighed. After the solid is heated for a prolonged time at $280\,^\circ\text{C}$ in a dry atmosphere until constant mass, an anhydrous residue of $\mathrm{NiSO_4}$ is obtained, with a mass of $2,788\,\text{g}$.

Relative atomic mass data: $\mathrm{H} = 1,008$; $\mathrm{O} = 16.00$; $\mathrm{S} = 32.06$; $\mathrm{Ni} = 58.69$.

1. a) Calculate the amount of substance (in moles) of anhydrous salt and of water released, deducing the value of the integer hydration coefficient $x$.
2. b) Write the stoichiometric formula of the hydrated compound and name it according to the IUPAC systematic compositional nomenclature for hydrates.

Diphosphoric acid (or pyrophosphoric acid) and peroxydisulfuric acid are condensed oxoacids of industrial and analytical importance.

1. a) Determine the oxidation state of the central atom (phosphorus and sulfur) in the molecular formulas $\mathrm{H_4P_2O_7}$ and $\mathrm{H_2S_2O_8}$, justifying in detail the nature of the bridging bonds between the nonmetals in each of the two structures (oxo bridge $-\mathrm{O}-$ versus peroxo bridge $-\mathrm{O-O}-$).
2. b) Write the formula of potassium peroxydisulfate, write the balanced equation for the formation of $\mathrm{H_4P_2O_7}$ by loss of water from two molecules of phosphoric acid, $\mathrm{H_3PO_4}$, and state which stable hydrated ionic species coexist in the aqueous medium when the potassium salt dissolves completely at $25\,^\circ\text{C}$.

Topic challenge. Quality control: does your antiseptic do what it promises?

Imagine you work in a quality-control laboratory and must validate the concentration of a bottle of hydrogen peroxide from your home medicine cabinet.

1. Data and nomenclature: Check the label of a commercial bottle of hydrogen peroxide at home, note its declared concentration (in $\%$ by mass or "volumes", taking $d = 1.01\,\text{g/mL}$) and write the formula and IUPAC name of the solute ($\text{H}_2\text{O}_2$) and the auxiliary reagents of the test.

2. Solution and mole: Convert the commercial concentration to molarity ($M$) and design the technical protocol to prepare $250\,\text{mL}$ of a dilute solution $0.050\,\text{M}$, detailing the stoichiometric dilution calculations and the laboratory equipment needed.

3. Redox titration: Model the titration of $20.0\,\text{mL}$ of your prepared solution against potassium permanganate ($\text{KMnO}_4$) $0.020\,\text{M}$ in acidic medium ($\text{H}_2\text{SO}_4$). Balance the overall ionic equation by the ion-electron method and calculate the exact volume of titrant consumed at the equivalence point.

Write a short technical report (maximum two pages) with the analytical work, your results, and a critical assessment of the purity of the product.

Assessment criteria:

• Correctness and rigor in inorganic chemical language and in the ion-electron redox balancing.

• Accuracy in calculations of molar quantities, preparation of solutions, and titration stoichiometry.

• Clarity and methodological coherence in the design of the experimental procedure.