Ch.XI - Titration Experiments Flashcards
Manganate-Iron titrations
-What is placed in the burette, pipette and conical flask?
-Why is this acidic solution in the conical flask used and none else?
-Why is acid used in the preparation of ammonium iron(II) sulphate?
-What colour change is seen?
-Why must KMnO4 solutions be standardised?
-Why is it necessary to standardise the solution immediately before titration?
-What reagent is used for this purpose?
-The potassium manganate (VII) solution is placed in the burette. The iron (II) solution is placed into the conical flask using a pipette. The sulphuric acid is placed into the conical flask as well.
-Sulphuric acid is used to enable complete reduction of Mn(VII) to Mn(II). Without acidic conditions, the brown precipitate of Mn(IV) appears rather than Mn(II). HCl reacts with potassium manganate(VII) and nitric acid is an oxidising agent.
-To prevent oxidation of Fe2+ to Fe3+.
-Colourless to pale pink.
-Potassium manganate(VII) isn’t a primary standard.
-It’s unstable.
-Ammonium iron(II) sulphate.
HCl-Na titrations
-What is placed in the burette, pipette and conical flask?
-What colour change is seen?
-Why is the specific indicator used?
-Why should no more than 2 drops of indicator be used?
-The HCl solution goes into the burette. The sodium carbonate solution goes into the pipette along and is placed into the conical flask. The methyl orange indicator is placed into the conical flask.
-Yellow to pink is seen.
-Methyl orange is used because a strong acid weak base titration is involved.
-The methyl-orange is a weak acid.
Ethanoic acid in vinegar titrations
-What is placed in the burette, pipette and conical flask?
-What colour change is seen?
-Why is the vinegar diluted?
-Why is the specific indicator used?
-Sodium hydroxide solution is placed into the conical flask using a pipette. The phenolphthalein indicator is placed into the conical flask. The diluted vinegar solution is placed in the burette.
-Pink to colourless.
-The vinegar is diluted to suit the concentration of the NaOH solution.
-Phenolphthalein is used because a weak acid strong base titration is involved.
Iodine-thiosulfate titration
-What is placed in the burette, pipette and conical flask?
-What colour change is seen?
-Why is excess KI used?
-Potassium iodate solution is placed in the conical flask using the pipette. Sodium thiosulfate solution is placed in the burette. Sulphuric acid and potassium iodide are added to the conical flask. Later starch indicator is added to the conical flask.
-Starts off colourless then turns brown, then as sodium thiosulfate is added, turns pale yellow, addition of starch indicator turns it blue-black, further addition of sodium thiosulfate makes it colourless. Colourless, brown, straw yellow, blue-black, colourless.
-Excess potassium iodide is used to ensure that all the iodate ions are used up in the reaction between them. In this way, iodine, a non-polar substance of low water solubility is kept in solution. In the reaction I2 + I- =(eq.) I3-, iodine dissolves as triiodide(more soluble) when reacted with iodide.
Estimation of the total-hardness of a water sample using ethylenediaminetetraaceticacid(edta).
-What is placed in the burette, pipette and conical flask?
-What indicator is used?
-What colour change is seen?
-What ions cause hardness?
-Why is an alkaline buffer solution used?
-The edta solution is placed in the burette. Hard water is placed into the conical flask using a pipette. A few drops of pH10 buffer solution is also placed in the conical flask.
-Eriochrome Black T is the indicator, it is mixed into the conical flask until a wine-red is formed. At the end point of the titration, a dark blue colour forms.
-Ca2+ and Mg2+
-The metal-edta complex (MY2-) is only stable at a high pH for Ca and Mg.
Determination of the w/v percentage of hypochlorite in bleach.
-What is placed in the burette, pipette and conical flask?
-What indicator is used?
-What colour change is seen?
-Why is excess KI used?
-Why should distilled water be used rather than deionised water?
-Sodium thiosulfate is placed in the burette. Using a pipette, diluted bleach solution is placed in the conical flask. 10cm^3 of dilute sulfuric acid and 1g of potassium iodide is placed in the conical flask. The iodine solution formed turns solution from colourless to red-brown colour.
-Titration is carried out until red-brown turns to pale yellow. Then starch indicator is added. The pale yellow turns blue-black. Then Na2S2O3 is added dropwise until the solution turns colourless.
-Excess potassium iodide is used to ensure that all the iodate ions are used up in the reaction between them. In this way, iodine, a non-polar substance of low water solubility is kept in solution. In the reaction I2 + I- =(eq.) I3-, iodine dissolves as triiodide(more soluble) when reacted with iodide.
-Deionised water could contain non-ionic substances that can be oxidised or reduced.
Estimation of dissolved O2 by redox titration.
-What is placed in the burette, pipette and conical flask?
-How is water collected and why is it done so?
-What is added to the bottle of water?
-Why is excess mangenese(II) sulfate added?
-What indicator is used?
-What colour change is seen?
-What is the ratio of dissolved oxygen to thiosulfate?
-Sodium thiosulfate is placed in the burette. The brown water is placed in the conical flask using a pipette.
-The water is collected by submerging a reagent bottle in a basin of water. It is important that no air is present in the bottle as this would raise the O2 level.
-Solutions of manganese(II) sulfate and alkaline potassium iodide(they sink and form a brown precipitate). Shake, then concentrated H2SO4 is added. Shake again.
-To ensure that all the O2 is reacted.
-Starch indicator is used. When the brown turns to pale yellow, starch indicator is added and a blue-black is formed. The titration is continued until the solution becomes colourless.
-1:4, there’s 4 times as much thiosulfate as there is oxygen.
