#7 The Chemistry and Qualitative Analysis of Cations: Group Separations and Separation of Group I Cations

Selectivity in precipitation

The ability to separate specific metal cations from a mixture by controlling solubility product constants.

Solubility product constant (Ksp)

The constant for the reaction of a sparingly soluble salt dissolving in water, representing its solubility.

Qualitative analysis

A procedure to determine the presence or absence of particular ions in a solution without quantifying their concentration.

Group I cations

Cations that form insoluble chlorides including Ag^+, Pb^2+, and Hg22^+.

Hydrochloric acid (HCl)

A strong acid used to provide chloride ions for precipitation of Group I cations.

Thioacetamide (CH3CSNH2)

A compound used to generate sulfide ions (S^2-) for precipitation reactions.

Dithionite ion (S2O4^2-)

A strong reducing agent used to reduce silver ions (Ag^+) to elemental silver (Ag) during cation detection.

Acid-base equilibria

Reactions involving the transfer of protons between acids and bases; important for managing ion concentrations.

Common-ion effect

The reduction in solubility of a salt due to the presence of a common ion from another source.

Precipitation method

A technique used to separate cations by converting them into an insoluble solid through the addition of specific reagents.

Copper (II) sulfide (CuS)

A precipitate formed from the reaction of copper ions with sulfide ions in solution.

Lead(II) chloride (PbCl2)

An insoluble salt formed during the precipitation of lead(II) ions from solution with chloride ions.

Ferrous sulfide (FeS)

An insoluble compound formed from the precipitation of ferrous ions with sulfide ions.

Mercury(I) chloride (Hg2Cl2)

A white precipitate formed during the precipitation of mercury ions from solution using chloride ions.

Confirmation test

A specific reaction conducted to verify the presence of a particular ion or compound in a solution.

Filtration

A method used to separate solid precipitates from liquid supernatants in a solution.

Colorimetric detection

Using color changes in solutions to confirm the presence of certain metal ions after precipitation.

Hexacyanoferrate (II) ion

A complex ion used to detect copper(II) ions by forming an insoluble precipitate.

Thiocyanate ion (SCN-)

An ion that forms a deep red complex with ferric ions (Fe^3+), used for detection.