Question

preparation of standars solutions for beer's law plot

Obtain and clean four 50 ml volumetric flasks

Obtain from side bench abut 15ml of stock fe2+ solution in a clean, dry 20ml beaker - recor concentration of this solution

Rinse 1,3 and 5 ml pipets with stock fe2+ solution

Pipet 1ml of stock fe2+ solution into a clean 50ml volumetric flask as well as the 3ml and 5ml in diffrernt 50ml volumetric flasks

To all four volumetric flasks add 5ml saturated sodium acetate solution and 10% hydroxylamune hydrochrolide solution using a grad cylinder, swirl and wait 5 mins.- the flask with no fe2+ is your blank

Add 5ml 0.1% 1,10-phenanthroline to each flask and swirl. Wait 10 mins, then make up the volumetric flasks to mark with distilled water

****Please explian the reasons behind adding solutions to prepare the standard solution*****

i.e. why the 5ml saturated sodium actetate solution was added when it was added etc...

Answer 1

Objective of the experiment: The experiment deals with the determination of Iron by 1,10-phenanthroline to form a colored complex and further measuring the amount of light (A) that this comples absorbs.

From the Beer's Lambert law, A = bC we further determine the Concentration of Iron.

ε is the extinction coefficient (M^-1cm^-1) and b is the solution path length in cm.

Chemistry:

In the preparation of a Standards Solution, we react the starting solution Fe⁺³ with hydroxylamine hydrochloride in a Buffer (sodium actetate in the question) to reduce Fe⁺³ in to Fe^+2.

4 Fe⁺³ + 2 NH₂OH•HCl        →      4 Fe⁺² +N₂O + 4 H⁺ + H₂O

Fe⁺² further reacts with with 1,10-phenanthroline to form a colored chelate complex ion :

So we can view the ingradient as,

Fe⁺³ : Starting solution, whose concentration is to be determined.

Hydroxylamine hydrochloride : Reducing agent, reduce Fe⁺³ (Ferric ions)in to Fe⁺² (Ferrous ions).

Sodium actetate : Buffer

1,10-phenanthroline : Titrator