Core Practical 11

Question 1

Titrations using transition element ions are…

Answer 1

Redox titrations

Question 2

An oxidising agent ….. electrons and gets …..

Answer 2

Oxidising agent accepts electrons and gets reduced

Question 3

A reducing agent …… electrons and gets ….

Answer 3

Reducing agent donates electrons and gets oxidised

Question 4

How can you work out the concentration of reducing agent?

Answer 4

Titrate a known volume of it against an oxidising agent of known concentration. therefore how much oxidising agent needed to exactly react with reducing agent

Question 5

How can you find out how many manganate (VII) ions are needed to react with a reducing agent

Answer 5

measure out quantity of reducing agent e.g. Fe2+ ions
add dilute sulfuric acid (so lots of H+ to allow oxidising agent to be reduced)
rough titration. stop when purple colour appears (end point) + record volume

Question 6

What is the purple in a redox?

Answer 6

MnO4-

Question 7

What is the general rule for which way round oxidising/ reducing agent you put in burette and conical flask

Answer 7

Tend to add substance of known concentration (burette) to the substance of unknown (conical flask)

Question 8

What would the colour change be from MnO4 - to Mn2+

Answer 8

purple to colourless

Question 9

Other than KmnO4 what else can you use as an oxidising agent? What colour is this and what is it reduced to?

Answer 9

K2Cr2O7

[Cr2O7]2- reduced to Cr3+ = orange to green

Question 10

How to increase accuracy of end point?

Answer 10

Use white tile

Question 11

What is a redox titration?

Answer 11

titration of a reducing agent by an oxidising agent (or vice versa)

Question 12

How would you find the amount of iron in a iron tablet experimentally?

Answer 12

Titrate potassium manganate solution against acidified (H2SO4) crushed iron tablets.
Calculate the mean titre from concordant results
calculate number of moles of MnO4 - and use equation to = Fe2+ in original solution. use this to calculate mass of Fe2+ in solution and mass per tablet.

Question 13

How would you reduce the uncertainty in this experiment?

Answer 13

Use balance with greater resolution
Use pipettes and burettes with greater resolution
use larger masses and volumes so % uncertainty reduced

Question 14

What is the ionic equation for the reaction between acidified iron and potassium manganate?

Answer 14

5Fe​2+​ + MnO​4​−​ + 8H​+​ → 5Fe​3+​ + Mn​2+​ + 4H​2​O