Qualitative and Quantitative Chemical Analysis: Anions, Cations, and Stoichiometry

Vocabulary practice flashcards covering qualitative detection of anions and cations, group reagents, precipitate characteristics, and quantitative stoichiometry fundamentals.

Concentrated Sulphuric Acid Group Anions

A group of acid radicals consisting of chloride ($Cl^-$), bromide ($Br^-$), iodide ($I^-$), and nitrate ($NO_3^-$) that are detected using concentrated sulphuric acid ($H_2SO_4$) with gentle heating.

Detection of Chloride Anion ($Cl^-$)

The reaction of a solid chloride salt with concentrated $H_2SO_4$ evolves colorless hydrogen chloride gas ($HCl_{(g)}$), which forms dense white fumes of ammonium chloride ($NH_4Cl_{(s)}$) when exposed to a glass rod wet with ammonia ($NH_{3(g)}$).

Confirmatory Test for Chloride ($Cl^-$)

The addition of silver nitrate solution ($AgNO_3$) to a chloride salt solution forms a white precipitate of silver chloride ($AgCl$), which turns violet upon exposure to sunlight and is completely soluble in ammonia solution.

Detection of Bromide Anion ($Br^-$)

The reaction of a solid bromide salt with concentrated $H_2SO_4$ evolves colorless hydrogen bromide gas ($HBr_{(g)}$), part of which is oxidized by $H_2SO_4$ into orange-red bromine vapors ($Br_{2(g)}$) that turn starch paper yellow.

Confirmatory Test for Bromide ($Br^-$)

The addition of silver nitrate solution ($AgNO_3$) to a bromide salt solution produces a yellowish-white precipitate of silver bromide ($AgBr$), which turns dark upon exposure to sunlight and is sparingly soluble in ammonia solution.

Detection of Iodide Anion ($I^-$)

The reaction of a solid iodide salt with concentrated $H_2SO_4$ evolves colorless hydrogen iodide gas ($HI_{(g)}$), part of which is oxidized by $H_2SO_4$ into violet iodine vapors ($I_{2(v)}$) that turn starch paper blue.

Confirmatory Test for Iodide ($I^-$)

The addition of silver nitrate solution ($AgNO_3$) to an iodide salt solution produces a yellow precipitate of silver iodide ($AgI$) that is insoluble in ammonia solution.

Detection of Nitrate Anion ($NO_3^-$)

The reaction of a solid nitrate salt with concentrated $H_2SO_4$ produces nitric acid ($HNO_3$), which decomposes upon heating to evolve reddish-brown vapors of nitrogen dioxide ($NO_{2(g)}$); vapor evolution increases upon adding copper ($Cu$) turnings.

Brown Ring Test

A confirmatory test for nitrate ($NO_3^-$) where adding freshly prepared acidified iron(II) sulfate ($FeSO_4$) and concentrated $H_2SO_4$ carefully down the tube wall forms a brown ring of $FeSO_4 \times NO$ at the liquid junction, which is removed by shaking or heating.

Barium Chloride Group Anions

A group consisting of phosphate ($PO_4^{3-}$) and sulphate ($SO_4^{2-}$) anions that do not react with dilute $HCl$ or concentrated $H_2SO_4$, but form distinct precipitates with barium chloride solution ($BaCl_2$).

Detection of Sulphate Anion ($SO_4^{2-}$)

The reaction of a sulphate salt solution with barium chloride ($BaCl_2$) forms a white precipitate of barium sulphate ($BaSO_4$) that is insoluble in dilute hydrochloric acid ($HCl$).

Confirmatory Test for Sulphate ($SO_4^{2-}$)

The reaction of a sulphate salt solution with lead(II) acetate solution ($(CH_3COO)_2Pb$) produces a white precipitate of lead(II) sulphate ($PbSO_4$).

Detection of Phosphate Anion ($PO_4^{3-}$)

The reaction of a phosphate salt solution with barium chloride ($BaCl_2$) yields a white precipitate of barium phosphate ($Ba_3(PO_4)_2$) that is soluble in dilute hydrochloric acid ($HCl$).

Confirmatory Test for Phosphate ($PO_4^{3-}$)

The reaction of a phosphate salt solution with silver nitrate solution ($AgNO_3$) forms a yellow precipitate of silver phosphate ($Ag_3PO_4$) that is soluble in both ammonia solution and nitric acid ($HNO_3$).

Acid Stability Hierarchy

The classification of acids into unstable acids ($H_2CO_3, H_2S, H_2SO_3, H_2S_2O_3, HNO_2$), intermediate acids ($HCl, HBr, HI, HNO_3$), and stable acids ($H_2SO_4, H_3PO_4$), where a more stable acid displaces a less stable acid from its solid salt.

General Salt Solubility Rules

Solubility principles stating all nitrates and bicarbonates dissolve in water; chlorides, bromides, and iodides dissolve except with $Ag^+, Hg^+, Pb^{2+}$; sulphates dissolve except with $Ca^{2+}, Pb^{2+}, Hg^+, Ag^+$; carbonates, sulphites, and phosphates do not dissolve except with $Na^+, K^+, NH_4^+$.

Basic Radicals (Cations)

The electropositive radicals of salts whose chemical detection is more complicated than acid radicals due to their high diversity and the existence of multiple oxidation states for single elements (e.g., $Fe^{2+}$ and $Fe^{3+}$).

First Analytical Group of Cations

A group containing mercury(I) ($Hg^+$), silver(I) ($Ag^+$), and lead(II) ($Pb^{2+}$) cations, precipitated as insoluble white chlorides using dilute hydrochloric acid ($HCl$) as the group reagent.

Second Analytical Group of Cations

A group containing copper(II) ($Cu^{2+}$), precipitated as a black precipitate of copper(II) sulphide ($CuS$) using hydrogen sulphide ($H_2S$) in an acidic medium ($HCl$); the precipitate dissolves in hot nitric acid ($HNO_3$).

Third Analytical Group of Cations

A group comprising iron(II) ($Fe^{2+}$), iron(III) ($Fe^{3+}$), and aluminium ($Al^{3+}$) cations, precipitated as insoluble hydroxides using ammonium hydroxide ($NH_4OH$) as the group reagent.

Detection of Iron(II) Cation ($Fe^{2+}$)

Reaction of an $Fe^{2+}$ salt solution with ammonium hydroxide ($NH_4OH$) or sodium hydroxide ($NaOH$) produces a white precipitate of iron(II) hydroxide ($Fe(OH)_2$) that turns greenish-white in air and dissolves in dilute acids.

Detection of Iron(III) Cation ($Fe^{3+}$)

Reaction of an $Fe^{3+}$ salt solution with ammonium hydroxide ($NH_4OH$) or sodium hydroxide ($NaOH$) yields a reddish-brown gelatinous precipitate of iron(III) hydroxide ($Fe(OH)_3$) that is soluble in dilute acids.

Detection of Aluminium Cation ($Al^{3+}$)

Reaction of an $Al^{3+}$ salt solution with $NH_4OH$ or $NaOH$ forms a white gelatinous precipitate of aluminium hydroxide ($Al(OH)_3$), which dissolves in excess caustic soda ($NaOH$) to form colorless sodium meta-aluminate ($NaAlO_2$).

Fifth Analytical Group of Cations

A group represented by calcium ($Ca^{2+}$), which precipitates as a white precipitate of calcium carbonate ($CaCO_3$) using ammonium carbonate ($(NH_4)_2CO_3$) as the group reagent.

Flame Test for Calcium ($Ca^{2+}$)

A dry confirmatory test where volatile calcium cations exposed to a non-luminous Bunsen flame impart a distinct brick red coloration.

Molar Mass

The mass in grams of one mole of a chemical substance, calculated by taking the sum of the atomic masses of all elements indicated by its molecular formula.

Avogadro's Number ($N_A$)

A fundamental chemical constant equal to $6.02 \times 10^{23}$, representing the exact number of atoms, molecules, or ions present in one mole of any substance.

Molar Gas Volume at STP

The standard physical volume occupied by one mole of any gas at standard temperature and pressure, equal to $22.4\,L$.

Mole-Mass Relationship

The stoichiometry formula defined by $\text{Number of moles} = \frac{\text{Mass}\,(g)}{\text{Molar mass}\,(g\,mol^{-1})}$.

Mole-Gas Volume Relationship

The stoichiometry formula for gaseous substances at standard conditions defined by $\text{Number of moles} = \frac{\text{Volume}\,(L)}{22.4\,L}$.