BPS 124L: Complexation and Redox reactions

Complexation

______ reactions between metals and ligands

Metal-ligand complexes

___________ are formed by coordinate covalent bonds wherein the ligand provides the lone pair/s in the reaction.

Complexing agents

___________ are used in pharmaceutical products to sequester metal cations that may affect product quality and stability.

Metallochromic indicators

_________ are ligands that undergo definite color transitions in the presence of specific metal cations.

• Change color when metal is removed by a stronger ligand (EDTA).

• These indicators can be used to indicate the presence of metal cations in different pharmaceutical products.

Monodentate ligands

They bind using one donor atom, can still form complex ions, and affect precipitation.

Chelating agents

form stable soluble complexes and prevent precipitation of metal hydroxides and salts.

disinfectants and antiseptics

Some of oxidizing agents have been routinely used as _____________.

Reducing agents

__________ are important pharmaceutical excipients. They act as antioxidants to prevent the oxidative decomposition of pharmaceutical products.

Color change (red to blue)

Ca²⁺ forms a complex with the indicator

Calcium-hydroxynaphthol complex

Calcium chloride + Hydroxynaphthol blue will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

return to the red color

EDTA binds Ca²⁺ more strongly

Ca–EDTA complex

Calcium chloride + Disodium edetate (EDTA) will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

formation of a red/pink color

Zn²⁺ complexes with dithizone

Zn–dithizone complex

Zinc Sulfate + Dithizone will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

disappearance of color or return to colorless

EDTA displaces dithizone

Zn–EDTA complex

Zinc Sulfate + Disodium Edetate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

color change (blue → wine red)

Mg²⁺ binds to the indicator

Mg–erichrome complex

Manesium Sulfate + Erichrome black will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

return to blue color

EDTA removes Mg²⁺

Mg–EDTA complex

Manesium Sulfate + Disodium Edetate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

Edetate (EDTA)

The strongest chelating agent that removes metals, not an indicator, that drives the reaction toward the endpoint.

Forms very stable complexes, used in complexometric titrations

• brings back the color to original color

Hydroxynaphthol blue

Eriochrome black

_________ & ________ are metallochromic indicators that change colors with alkaline metals

• red to blue to red

• blue to red to blue

Dithizone

The metallochromic indicator that changes color with heavy metals.

• Colorless to pink/red to colorless

formation of a blue precipitate

Cu²⁺ reacts with OH⁻, hydroxide is insoluble

Cuprous hydroxide

Copper(II) Sulfate + Sodium hydroxide will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

reduced or no precipitate

EDTA forms strong, soluble complexes with copper (II), even insoluble hydroxides can be dissolved.

Cu–EDTA complex

Copper(II) Sulfate + Sodium hydroxide + EDTA will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

formation of a white precipitate

Ca²⁺ reacts with PO₄³⁻, Phosphate is insoluble

Calcium Phosphate or Ca₃(PO₄)₂

Calcium chloride + Sodium phosphate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

decreased or no precipitate

citrate binds or removes Ca²⁺ = less Calcium phosphate precipitate forms

Ca-citrate complex

Calcium chloride + Sodium phosphate + Sodium citrate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

formation of a blue precipitate

Cu²⁺ reacts with OH⁻, hydroxide is insoluble

Cuprous Hydroxide

Copper(II) Sulfate + Sodium hydroxide will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

partially dissolved precipitation

tartrate complexes Cu²⁺, but not strong enough as EDTA

Cu–tartrate complex

Copper(II) Sulfate + Sodium hydroxide + Sodium tartrate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

Sodium tartrate

It can act as a mild chelating agent or masking agent, to dissolves precipitates.

Sodium citrate

It often used to mask calcium or magnesium, controls precipitation in phosphate reactions.

formation of a deep blue solution

Ammonia is a monodentate ligand that binds one lone pair of electrons to Copper (II)

Tetraamminecopper (II) complex

Copper(II) Sulfate + Sodium hydroxide + Ammonia will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

formation of a white precipitate

Zn²⁺ reacts with CO₃²⁻, carbonate is insoluble

Zinc Carbonate or ZnCO₃

Zinc Sulfate + Sodium carbonate will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

dissolution of precipitate

CN⁻ forms a stable complex, binds to zinc.

Tetracyanozincate (II) complex

Zinc Sulfate + Sodium carbonate + Sodium cyanide will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

formation of a red precipitate

formation of a red precipitate, has high bond with other and have low Ksp

Mercury iodide

Mercuric chloride + Potassium iodide will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.

dissolution of precipitate

excess iodide forms a complex so the precipitate dissolves

Tetraiodomercurate (II) complex

Mercuric chloride + Potassium iodide + Excess Potassium iodide will have a visible result of __________, because ___________.

• The product responsible is __________.

• The final product is ___________.