Principle - Standardization Standardization of KMnO 4 (aq) with Na 2 - - PowerPoint PPT Presentation

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Principle - Standardization Standardization of KMnO 4 (aq) with Na 2 - - PowerPoint PPT Presentation

Nov 01, 2023 153 likes •280 views

Redox Titration with KMnO 4 (2020/05/08 revised) Collect: One 100 mL volumetric flask One magnetic stir bar (from TA) Four 250 mL Erlenmeyer flask One 25 mL burette One glass dropper Thermometer General apparatus Two

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SLIDE 1

1

Redox Titration with KMnO4

Collect:

  • One 100 mL volumetric flask
  • One magnetic stir bar (from TA)
  • Four 250 mL Erlenmeyer flask
  • One 25 mL burette
  • One glass dropper
  • Thermometer

General apparatus

  • Two 100 mL beaker
  • One 10 mL graduated cylinder
  • One 50 or 100 mL graduated cylinder

(2020/05/08 revised)

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SLIDE 2

2

Principle - Standardization

  • Standardization of KMnO4(aq) with Na2C2O4
  • McBride method

 Titrate with KMnO4 at 60~90 oC with stirring  The first persistent (ca. 30 s) pink color as the end point

  • Fowler-Bright method

 At room temp., add 80% KMnO4 to react with Na2C2O4  Stir until the purple color of MnO4

  • disappears

 Heat the solution to 55~60 oC then complete the

titration

2MnO4

  • (aq) + 5C2O4

2-(aq) + 16H+(aq) 

2Mn2+ (aq) + 10CO2(g) + 8H2O(l)

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SLIDE 3

Principle - Analyze the Iron(II) Content

  • Determine the percent composition of iron(II)

in an unknown sample with standard KMnO4 solution

3

8H+ (aq) + MnO4

  • (aq) + 5Fe2+(aq) 

5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

nFe2+ 5

=

nMnO4

−

1

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SLIDE 4

4

Step 1 Preparation of 0.02 M KMnO4

  • Weigh about 0.3 g KMnO4(s)
  • Dissolve the solid with deionized water
  • Dilute to 100 mL with volumetric flask

Dissolve the solid completely

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SLIDE 5

5

Step 2 Standardization by McBride Method

(2) Blank titration: titrate 50 mL 1 M H2SO4 at 80 oC (1) Weigh 0.1~0.15 g (to the nearest 0.1 mg) Na2C2O4 into 250 mL flask

 Dissolve with 50

mL 1 M H2SO4

  • Heat to ca. 80 oC
  • Titrate with KMnO4 till

the pink color persists 30 s to the end point

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SLIDE 6

6

Step 3 Standardization by Fowler-Bright Method

(1)

 Weigh 0.1~0.15 g Na2C2O4

into 250 mL flask

 Dissolve with 50 mL of 1 M

H2SO4

  • At room temp.
  • Add ca. 80% KMnO4
  • Stir until appears

colorless

  • Heat to 55~60 oC
  • Titrate with KMnO4

till the pink color persists 30 s to the end point (2) Blank titration: titrate 50 mL 1 M H2SO4 by same procedures

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SLIDE 7

7

Step 4 Determine the Percent Composition of Iron(II)

  • Unknown sample that contain Fe(II)
  • Odd no. explores unknown A; even no. examines unknown B

(1) Weigh ca. 0.2 g unknown sample in the flask

 Add 5 mL conc. HCl

and heat to nearly boiling

  • Add 10 mL Z-R

reagent and 100 mL H2O

 Titrate with

KMnO4

Incubate for 3 min.

(2) Blank titration: titrate blank solution (without unknown sample) by same procedures

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SLIDE 8

8

Notice

  • Manipulate the volumetric flask

 Use funnel to transfer the solution  Use a dropper to bring the liquid level to the mark

  • Remove the buret away from top of the hot plat while not

doing the titration to avoid heating the solution in buret

  • Heat the conc. HCl(aq) in fume food
  • Put the cotton gloves on to remove glassware from heating
  • Dispose the waste into heavy metals waste container
  • Calculation:

 Correct the titration data for the blank  Calculate [KMnO4] by McBride method  Calculate [KMnO4] by Fowler-Bright method  Calculate the percent composition of iron in unknown

sample

Condensed report

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SLIDE 9

9 

Place balance on stable, non-vibrating table where no sun/wind, and temperature is stable.

Do not overload the balance. Maximum load of an electric balance in lab is 610 g.

Make sure balance is level, clean, and dry before use.

Warm up the balance for 30 minutes before use.

Put weighed object in the center of weighing pan.

A baked object need to go back to room temperature before weighing, the buoyancy of convective airflow around the pan will affect object’s apparent mass.

T9 - Electronic Balance

Wipe balance clean with a damp cloth but do not use solvents.

Do not invert balance upside down to avoid damage to the parts inside.

Use folded paper, beaker or bottle as container while weighing, do not put chemicals on directly.

Analytical balance is a more precise balance having maximum load of 210 g, close its windshields while zeroing and weighing or the reading is inaccurate.

Analytical Balance (s.f. contains four decimal places)

T9 Video on YouTube (Click)

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SLIDE 10

10

T13 - Volumetric Flask

  • Wash a 100 mL volumetric flask

thoroughly and rinse with distilled water.

  • Transfer the solution to flask with the

help of a funnel.

  • Fill the flask about half full and swirl the

contents to achieve solution.

  • Bring the liquid level almost to the mark.
  • Use a dropper to add solvent to the mark.
  • Stopper the flask and invert repeatedly to

assure homogeneous.

  • Pour the solution in beaker for later use.
  • Wash immediately after use.

標線刻度 100

ml ±0.15 In 20

  • C

Mark

T13 Video on Youtube (Click)

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SLIDE 11

11

T14 - Titration

  • Rinse a 25 mL-buret with D.I. water thoroughly.
  • Rinse twice with ca. 5 mL titrant.
  • Transfer the titrant to buret via funnel.
  • Drain slowly until the tip is free of air bubbles and

completely filled with liquid.

  • Read and record initial (Vi) and final volume (Vf) of

buret to 0.01 mL.

  • Place buret tip well inside the receiving flask

during titration.

  • Swirl the flask with right hand and control the

stopcock with left hand (process done by one person).

  • Rinse the buret with tap water, inverted clamped,

and left to dry after the experiment.

T14 Video on Youtube (Click)