why is it necessary to store AgNO3 solution in an amber bottle?
Why must volhard titration be carried out in strongly acidic medium?
Why is titration of AgNO3 with KSCN be done with vigorous swirling?
AgNO3 is sensitive to light. Ultraviolet light of a certain range of wavelengths reduces it to Ag; therefore, the molarity of the solution changes. Remember that Ag salts are one of the light sensitive materials in paper photography.
You don't want Ag2O (the end product of the formation of AgOH) to form but that will happen in basic solution.
Excess SCN^- can form a complex ion with Ag^+ so the idea is to minimize the concentration of SCN^-.
These may not be the only reasons for #2 and #3; i.e., there may be others.
The low pH is needed to prevent the Fe^+3(aq) indicator from hydrolyzing (forming hydroxy complexes and eventually iron(III) hydroxide). If the ferric salt indicator is altered, there is no clear end point during the titration.
To answer these questions, let's break down each one and explain the reasons behind them.
1. Why is it necessary to store AgNO3 solution in an amber bottle?
AgNO3 is a chemical compound commonly known as silver nitrate. It is sensitive to light and can undergo photochemical decomposition when exposed to UV light. This decomposition reaction may result in the formation of brown nitrogen dioxide gas and the precipitation of silver oxide. To prevent this degradation, it is necessary to store AgNO3 solutions in amber-colored bottles.
Amber-colored bottles provide protection against UV light, blocking most of the light from reaching the solution inside. This helps to maintain the stability of AgNO3 and prolong its shelf life. Therefore, storing AgNO3 in an amber bottle helps to preserve its integrity and prevent unwanted reactions caused by light exposure.
2. Why must volhard titration be carried out in strongly acidic medium?
Volhard titration is a method commonly used for determining the concentration of chloride ions (Cl-) in a solution. In this titration, a known quantity of silver ions from silver nitrate (AgNO3) is added to the solution containing chloride ions, forming a white precipitate of silver chloride (AgCl). The end of the titration is indicated by the excess silver ions that are not consumed by the chloride ions.
The reason why a strongly acidic medium is required for volhard titration is to prevent the formation of other silver precipitates. Without a strongly acidic medium (using nitric acid, for example), other anions present in the solution (such as bromide or iodide ions) can react with silver ions and form their respective silver halides (AgBr or AgI).
By adding an excess of nitric acid (HNO3) to the solution, the other halide ions (Br- and I-) are converted to their respective acids, which do not precipitate with silver ions. This ensures that only chloride ions react to form silver chloride. Hence, volhard titration is carried out in a strongly acidic medium to selectively determine the concentration of chloride ions.
3. Why is titration of AgNO3 with KSCN be done with vigorous swirling?
When performing a titration of AgNO3 with potassium thiocyanate (KSCN), a redox reaction occurs between silver ions (Ag+) and thiocyanate ions (SCN-). This reaction forms a reddish-brown complex, silver thiocyanate (AgSCN), which is sparingly soluble in water.
To ensure that the reaction is complete and that all silver ions have reacted with thiocyanate ions, vigorous swirling is necessary during the titration process. Swirling helps to improve the mixing of the reactants, ensuring that the reactants come into contact and react effectively.
Without vigorous swirling, localized concentrations of reactants may form in certain regions of the solution, leading to incomplete or slow reaction. This could result in inaccurate titration results. Therefore, by swirling the solution vigorously, the reaction proceeds more quickly, ensuring a complete reaction between AgNO3 and KSCN and providing accurate titration results.