Experiment Q1 titration Flashcards
Permanganate titration
Properties that make it a good primary standard:
Pure, water soluble, doesn’t effloresce, has a high relative molecular mass.
Indicator: none, self indicating
end point: Faint, pale, persistent pink colour
Necessary to use dilute sulphuric acid: Prevents oxidation of Fe2+ to Fe3+.
Necessary to add more dilute sulphuric acid to each portion, ensure the complete reduction of Mn7+ to Mn2+
Procedure to ensure accuracy of end point, swirl flask while titrating, read burette at eye level, read top of meniscus
Iron tablets are prescribed for: to prevent anaemia
why must the solutions be standardised: Not a primary standard
Why is it necessary to standardise the solutions: unstable, affected by light
what reagent was used to standardise these solutions: Ethanedioic acid
Sodium thiosulfate standardise against iodine
How is iodine, a non polar substance of very low water solubility is brought to an aqueous solution: reaction with potassium iodide, forms soluble potassium triiodide
indicator: starch
When is the indicator added: when colour in the conical flask is a pale yellow
Endpoint: blue-black to colourless
why is distilled water more accurate than deionised water: deionised water could contain non-ionic substances that could be oxidised or reduced
sequence of colour changes: reddish brown to straw yellow to blue-black to colourless
Hydrochloric acid solution and sodium carbonate
How the liquid level was adjusted to the zero mark: fill to 1-2 inches below graduated mark, remove funnel, add dropper wise
Why a pipette filler is sued to fill the pipette with sodium carbonate solution: safety, avoid solution getting into mouth
Indicator: Methyl orange
Colour change: yellow/orange to Red/pink
Ethnic acid in vinegar
Indicator: Phenolphthalein because weak acid-strong base
colour change: Pink to colourless
what two titrations are required to standardise a sodium hydroxide solution: anhydrous sodium carbonate titrated with a strong acid (hydrochloric acid) and acid titrated with sodium hydroxide
Why vinegar is diluted: Vinegar is too concentrated so it would required a large volume of NaOH to get an accurate titration
carboxylic acid that occurs in nettle stings and ant stings: Methanol acid
compound in white wine that is converted to ethnic acid in vinegar:
ethanol
chemical process that converts this compound to ethnic acid:
oxidation
Water of crystallisation
One precaution that should have been taken as the end of the titration was approached:
Swirl flask contents
how this precaution increased accuracy:
To ensure thorough mixing of reagents
Indicator:
Methyl orange
Colour change:
Orange/Yellow to red/pink
The primary standard solution that can be used: anhydrous sodium carbonate
why no more than 1-2 drops of indicator is added:
Indicator is a weak acid
Hardness of water
Two ions represented by M2+ that most commonly cause hardness when dissolved in water: Calcium ions and magnesium ions
what is total hardness of water: sum of all permanent and temporary hardness due to sum of all dissolved calcium and magnesium ions
Indicator: Solocrome black
Colour change: Wine red to blue
What pH does the buffer solution maintain in the mixture in the conical flask: 10
Why is it important to maintain this pH during the titration: To ensure only calcium ions are detected / for a sharp accurate end point is detected
Compound of calcium that can cause hardness of water:
Calcium chloride (CaCl2)
Another solution was added to the water samples before the titrations:
pH buffer 10
how to determine if the sample supply contains temporary hardness: boil water, scale as a result of boiling indicates temporary hardness
Full name of edta reagent: ethylenediamine
General purpose of pH buffers: To stabilise the pH of a solution
What would happen if the wrong pH was used: inaccurate end point
Is the water suitable for use as deionised water in the lab after passing through the deioniser:
No, because hardness remains after passing through the deioniser.
Bleach
Why must excess KI be added to dilute bleach: To ensure all hypochlorite reacts to form soluble triiodide
Colour change of first reaction:
First colourless
second brown
Indicator: starch
Final colour change: from pale yellow to blue-black to colourless
Reasons why excess potassium iodide was used: so that all bleach has reacted, to keep the iodine in the solution
indicator: starch
colour change: blue-black to colourless
Oxygen
Compound usually added to the water to provide the Mn2+ ions:
MnSO4 . 2H2O
Why was an excess of this compound required;
Ensures all O2 is detected
What colour is the Mn compounds:
brown
Indicator:
starch
colour change:
blue-black to colourless
Change observed when the concentrated sulfuric acid was added and mixed thoroughly: changes to brown
all colour changes:
brown to light yellow to blue-black to colourless
Why is it important to avoid trapped air bubbles: more oxygen would dissolve
What compound was added: MnSO4
What conclusion should have been reached had a white precipitate been observed instead of a brown precipitate: No loss in oxygen
Why is the immediate determination of dissolved oxygen considered best practice: biochemical reactions occur
Why should the solutions be concentrated when making additions: to minimise the amount of water that is displaced so that a small volume supplies excess
