Task today you will study the responses of several

This preview shows page 116 - 118 out of 128 pages.

Task:Today you will study the responses of several chemical systems at equilibrium to differentkinds of stress. The practical consists offour partsdealing with the following reactions atequilibrium:the dissociation of CH3COOH (Part A);the formation of [FeIII(SCN)]2+(Part B);the dissolution of NH4Cl (Part C);the dissolution of Ca(OH)2(Part D).ProcedureCollect the required reagents stored under the fume hoods as indicated by your TeachingAssistant: do not queue in front of the fume hoods and wait for your turn.1.We start by preparing a suspension of the sparingly soluble solid calcium hydroxide (Ca(OH)2).Add ~0.5 g of Ca(OH)2to a labelled conical flask and subsequently add ~50 mL of distilledwater. Seal the flask and shake vigorously for 2 minutes. Put the flask aside to allow itscontents to settle and proceed to the next tests before returning to the Ca(OH)2solubilityproduct test (Steps 14-16).Part A. Dissociation of Acetic Acid (Steps 2-4)Acetic acid (CH3COOH) is a weak acid and dissociates at the equilibrium according to the followingreaction:CH3COOH + H2OCH3COO-+ H3O+Since all the dissociation components are colorless, you will add the methyl orange indicator to theequilibrium mixture in order to visualize the chemical changes that occur as the result of a stress: itturns red in the presence of high concentrations of H3O+ion (i.e.acidic pH) and turns yellow at lowconcentrations of H3O+ion (i.e.basic pH). In particular, you will determine the effect of addingeither sodium acetate (CH3COONa) or sodium hydroxide (NaOH) to the equilibrium mixture.2.Dispense ~1 mL of dilute CH3COOH into a clean test tube (volume should be the height ofyour thumbnail). Add 1 drop of methyl orange indicator and record the color.
1153.Use a spatula to add 2 or 3 crystals of CH3COONa to the test tube and mix the solution untilthe crystals dissolve. Continue to add individual crystals, stirring after each addition, until youobserve a change in the equilibrium mixture. Record, and comment on, your observations.4.Dispense an additional ~1 mL of dilute CH3COOH into a second clean test tube. Add 1 drop ofmethyl orange indicator and stir. Add 1 drop of dilute NaOH to the second test tube and stir.Continue adding NaOH dropwise, stirring after each addition, until you observe a change inthe equilibrium mixture. Record, and comment on, your observations.Part B. Formation of Iron(III) Thiocyanate Complex (Steps 5-10)When potassium thiocyanate (KSCN) is mixed with iron(III) nitrate (Fe(NO3)3) in water, the complexion [FeIII(SCN)]2+forms according to the following reaction:Fe3+(aq)+ SCN-(aq)[Fe(SCN)]2+(aq)yellowcolorlessdark redNote that the reaction isexothermic. The solution also contains potassium (K+) and nitrate (NO3-)ions, but these are “spectator” ions, that is, they do not participate actively to the reaction.You will determine the response of this system at the equilibrium to heating and to the separateadditions of Fe(NO3)3, AgNO3and NaOH.

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 128 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Spring
Professor
N/A
Tags
Chemistry, laboratory supervisor

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture