DM - Formulae, equations and amount of substance *02 Flashcards

1
Q

what are acid-base titrations used for?

A

to find how much acid is needed to neutralise a base

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2
Q

How do you set up a titration?

A
  1. measure out some alkali using a pipette and put it into a flask
  2. add indicator, phenolphthalein
  3. do a rough titration to get an idea of where the end point is
    - add acid to alkali using a burette and swirl
  4. do an accurate titration
    - drop wise
  5. record the vol. of acid used to neutralise the alkali
    - repeat this until results are concordant (within 0.1cm^3 of eachother)
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3
Q

What are redox titrations?

A

used to find out how much oxidising agent is needed to exactly react with a quantity of reducing agent

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4
Q

What do you need to know when doing a redox calculation?

A

the conc. of either the reducing or oxidising agent

use titration value to work out conc. of the other

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5
Q

what redox titration do i need to know for the exam?

A

when manganate (VII) ions, MnO4- are the oxidising agent

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6
Q

method of redox titration using manganate (VIII) ions?

A
  1. measure vol. of reducing agent, (eg aq Fe2+ ions), using a pipette and put into a conical flask
  2. add some dilute sulfuric acid to the flask (in excess)
    - acid makes sure that there are plenty of H+ ions to allow the oxidising agent to be reduced
  3. add aq MnO4- (oxidising agent) to reducing agent using a burette, swirling conical flask
  4. stop when the mixture just becomes tainted with the colour of MnO4- (the end point) and record the vol. of the oxidising agent added - this is a rough titration
  5. now do accurate titrations until readings are within 0.10cm^3 of each other (concordant)
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7
Q

how do you know when the redox titration with Manganate (VII) ions is complete?

A

Manganate (VII) ions in aq potassium manganate (VII) - KMnO4 - are PURPLE

when they are added to the reducing agent they start reacting with the reducing agent, they get reduced to COLOURLESS Mn2+ ions.

the reaction continues until all of the reducing agent has reacted

the very next drop will give the mixture a PINK colour of the oxidising agent

need to spot exactly when this happens

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8
Q

How can you use titration results of find the conc. of a reagent?

A
  1. work out moles
  2. use mole ratio (in balanced equation) to work out moles in each reactant/product
  3. work out conc. (should be given vol. values)

concentration = moles / volume

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