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Using chemistry processes

Dynamic chemical equilibrium

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The adhering to video, animations and activity sheet represent the reaction in between iron(III) nitrate solution and potassium thiocyanate solution to form the iron(III) thiocyanate complex ion. This complicated ion undergoes reversible exchange the water molecules and thiocyanate ions bonded to the iron(III) leading to a dynamic equilibrium. The equilibrium can be uncomfortable by introducing another ion (fluoride) the competes an ext strongly 보다 both water and also thiocyanate for the iron(III) to type a new complex ion.

You are watching: Potassium thiocyanate and iron(iii) nitrate

The video shows the whole sequence of reactions utilizing the animations and laboratory clips, which display the colour transforms involved. These are connected to the corresponding chemical formulas and also equations. The separation, personal, instance animations space also obtainable and detailed below for inclusion right into your very own multimedia presentation.

Sample questions, with argued solutions, room also obtainable below. These require students to draw molecular-level representations, and also predict if a molecular-level device is in ~ equilibrium.

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Video: reversible competition between water molecules, thiocyanate ions and also fluoride ions for iron(III)


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This video portrays what happens once iron(III) nitrate solution and also potassium thiocyanate solution are combined to type the iron(III) thiocyanate facility ion, leading to a red solution. The reactants, potassium thiocyanate solution and iron(III) nitrate solution, and also the reaction at equilibrium, are depicted at the three reasoning levels – observational, molecular and symbolic. The crucial point is the competition in between water molecules and the thiocyanate ion to bond come the iron(III) ion, leading to a dynamic equilibrium. The equilibrium is uncomfortable by the addition of potassium fluoride solution, which outcomes in the development of a new complex. Development of the new complicated is signal by a adjust in the colour of the solution.

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A script is easily accessible to companion this video.

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Animations: the reactants


Aqueous potassium thiocyanateAqueous KSCN solution – different hydrated ions amongst water moleculesClick hereto download


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Potassium ion (aq), K+(aq)


Thiocyanate ion (aq), SCN–(aq)


This animation portrays one aqueous potassium thiocyanate equipment (KSCN(aq)). The hydrated potassium (K+(aq)) and also thiocyanate (SCN–(aq)) ions relocate randomly amongst the water molecules. The ion collide occasionally and type a transient ion pair. The water molecules promptly rehydrate the ions and also separate them:

K+(aq) + SCN–(aq)


Aqueous iron(III) nitrateHydrated iron(III) ions and nitrate ions collide in solutionClick hereto download


Iron(III) ion (aq), Fe3+(aq)


Nitrate ion (aq), NO3–(aq)


This animation portrays character language iron(III) (Fe3+(aq)) and also nitrate (NO3–(aq)) ions moving randomly among the water molecules. The ions collide occasionally and type a transient ion pair. The water molecules quickly rehydrate the ions and also separate them:

Fe3+(aq) + 3 NO3–(aq)


Aqueous iron(III) nitrate (ions)Hydrated iron(III) ions and nitrate ion collide in solution, solvent water omittedClick hereto download


Iron(III) ion (aq), Fe3+(aq)


Nitrate ion (aq), NO3–(aq)


This animation portrays character language iron(III) (Fe3+(aq)) and also nitrate (NO3–(aq)), ions, in a 1:3 ratio, relocate randomly amongst the water molecules. The ions collide occasionally and form a transient ion pair. V the intervening water molecules removed, girlfriend can obtain a feel for the crowding of ion in a 1 M solution:

Fe3+(aq) + 3 NO3–(aq)


Water exchange ~ above aqueous iron(III)Exchange that water molecules external inspection to iron(III) ionsClick hereto download


Iron(III) ion (aq), Fe3+(aq)


Nitrate ion (aq), NO3–(aq)


This animation shows that in an aqueous equipment solvent water molecules space in consistent exchange v water molecules bonded in character language cations and anions. The price of this exchange determines just how quickly brand-new complexes deserve to form.

Animations: separate reversible reactions


Iron(III) thiocyanate complexationFormation of 2+(aq) from Fe3+(aq)Click hereto download


Iron(III) ion (aq), Fe3+(aq)


Thiocyanate ion (aq), SCN–(aq)


This animation portrays the complexation of iron(III) (Fe3+(aq)) with the thiocyanate ion (SCN–(aq)) to form a nitrogen-bound isothiocyanate complicated (2+(aq)). One of the water molecules external inspection to Fe3+ is substituted through a SCN– ion to type the ion complex, the chemical types responsible because that the red colour in a solution when it is formed. This reaction is really favourable, forming lots that 2+(aq) prior to equilibrium is attained.

Fe3+(aq) + SCN–(aq) → 2+(aq) + H2O


Iron(III) thiocyanate dissociationFormation the Fe3+(aq) indigenous 2+(aq)Click hereto download


Iron(III) ion (aq), Fe3+(aq)


Thiocyanate ion (aq), SCN–(aq)


This animation portrays the relax of the thiocyanate ion (SCN–) and also iron(III) (Fe3+(aq)) from the nitrogen-bound isothiocyanate facility (2+(aq)). 2+(aq) is substituted through a water molecule native the solvent to type Fe3+(aq), publication SCN–(aq) ion come the solution. This reaction is not very favourable:

2+(aq) + H2O → Fe3+(aq) + SCN–(aq)

Animations: formation and dissociation of 2+(aq) in dynamic equilibrium


Iron(III) thiocyanate equilibriumFormation and dissociation of 2+(aq) in dynamic equilibriumClick hereto download


Iron(III) ion (aq), Fe3+(aq)


Thiocyanate ion (aq), SCN–(aq)


This computer animation shows that, at equilibrium, the rate of development of the nitrogen-bound isothiocyanate facility (2+(aq)) is equal to the release of iron(III) (Fe3+(aq)). The substitution price of water molecules by thiocyanate ions (SCN–) to type 2+(aq) ion is equal to the substitution rate of SCN– ion by water molecule to form Fe3+(aq). Back the concentration the 2+(aq) ions is much greater when equilibrium is lastly attained due to the fact that it is an ext stable than Fe3+(aq), the concentration of both ions does not adjust when dynamic equilibrium is reached:

2+(aq) + H2O ↔ Fe3+(aq) + SCN–(aq)


Iron(III) thiocyanate equilibrium (no solvent)Formation and also dissociation the 2+(aq) in dynamic equilibrium, through solvent molecules faded outClick hereto download


Iron(III) ion (aq), Fe3+(aq)


Thiocyanate ion (aq), SCN–(aq)


This animation shows that, at equilibrium, substitution price of water molecules by thiocyanate ion (SCN–) to kind the nitrogen-bound isothiocyanate facility (2+(aq)) is equal to the price of substitution the SCN– ions by water molecules to kind Fe3+(aq). The concentrations of both complexes stay constant. Watch closely to view that the in its entirety numbers the 2+(aq) ions and Fe3+(aq) ions execute not change when the reaction is in dynamic equilibrium. Formation and also dissociation are emerging at the same rate:

2+(aq) + H2O ↔ Fe3+(aq) + SCN–(aq)


Iron(III) thiocyanate ion – ball-and-stickBall-and-stick version of the 2+(aq) complicated ionClick hereto download


Iron(III) ion (aq), Fe3+(aq)


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Thiocyanate ion, SCN–


This animation shows the the thiocyanate ion (SCN–) is nitrogen bound once the isothiocyanate complicated ion (2+(aq)) is formed. The N-end that SCN– bonds more strongly than the S-end. Notification one of the external inspection water molecules is lacking an H atom since these molecules are quite acidic and also at the very least one is ionised in solution.

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Animations: development of an even more stable complicated with fluoride ions


Iron(III) fluoride complexFormation of 3–(aq) from Fe3+(aq)Click hereto download


This animation shows that fluoride ions (F–) form strong bonds to hydrated iron(III) (Fe3+(aq)) therefore they kind a secure iron(III) fluoride complex ion (3–(aq)) in systems if sufficient F–(aq) ions space available:

Fe3+(aq) + 6 F–(aq) → 3–(aq) + 6 H2O

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Iron(III) ion (aq), Fe3+(aq)Fluoride ion (aq), F–(aq)Hexafluoroiron(III) ion

Other resources: sample student concerns with solutions

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Student activity: equilibrium or not

Is the reaction at equilibrium?

This activity uses a molecular-level depiction of a reaction at 2 time points and asks if the reaction is in ~ equilibrium.

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