Question

please I need help with this one question.

Titration Procedure

1. Prepare your starch solution by dissolving 0.040g of vitex starch in 20 mL of water.

2. Prepare your 3%diluted commercial bleach solution (3% of the concentration of the commercial bleach, by volume.) Do not discard as you will use this solution for each of your trials.

   1. Dependingonyourinstructor’schosenmethod;deliverexactly3mLofcommercialbleach solution to a 100mL volumetric flask using the burette that contains the class’s supply of bleach, or pour some from the bottle into a small beaker and use a pipette at your lab station. Caution: Bleach is harmful to your skin, and it will bleach your clothes on contact.

   2. Dilutethebleachinthe100mLvolumetricflasktoatotalvolumeof100mLwithdeionized water and invert (turn upside down) several times to mix thoroughly.

3. Perform the titration

   1. Useavolumetricpipettetodeliverexactly10mLofthedilutedbleachsolutionthatyou made, into an empty Erlenmeyer flask that you will use for the titration (Solution shown in Picture 1)

   2. Addapproximately3gramsofsolidKIandswirltomix

   3. Youmayaddalittlebitofdeionizedwatertorinseanalytefromthewallsoftheflaskand

      make the volume more convenient if it is too small.

   4. Addapproximately2mL(40drops)ofHCl.Thesolutionwillturnorangebecausethe redox reaction between the bleach and iodide is producing iodine.(Solution shown in Picture 2.)

   5. Zerotheburettebyfillingitexactlytothe“0mL”markontopoftheburettewith0.0250M Na2S2O3 titrant and record it as your initial volume. If you didn’t zero the burette exactly, then you may have an initial volume other than “0.”

   6. Whilestirring,openthestopcocktodelivertitrant1mLatatime.Whenthesolution becomes pale yellow(Picture3), stop and add approximately 2mL (40 drops) of starch to turn the iodine black so it is easier to see. (Picture 4)

      1. Thereisnoneedtorecordthevolumeoftitrantyetbecauseyou’reonlyaddingstarch as an indicator to make the equivalence point that you’re about to reach easier to see.

   7. Continuethetitrationmoreslowly,untilthelastdropoftitrantcausesthesolution
      to stay colorless. (Picture 5) Record the final titrant volume from your burette (Picture 6). This is the equivalence point.

You are finished with the experiment when you have obtained trials whose volumes of titrant to reach equivalence are within 0.15mL of each other. Four or more trials may or may not be necessary to achieve the 0.15mL error tolerance.

1. Fill out the following information as determined by the data and pictures on the experiment PDF.  The stoichiometry of the reactions can be found on page 147.

Initial volume (mL) of 0.0250M S₂O₃^2-:                                 0 mL

Final volume (mL) of 0.025M S₂O₃^2-:                        

Moles of titrant S₂O₃^2- to equivalence point:              

Moles of I₂ present at equivalence point:                   

Moles of ClO^- in dilute bleach solution:                    

Volume of dilute bleach solution (L):                        

Molarity of dilute bleach solution:                             

Molarity of concentrated bleach solution: