Commonly asked questions in Chemical Practical Exam

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regarding titration 

1. why do we wash all glasswares with lots of tap water followed by DI water? 

- this gets rid of residual chemicals, preventing any trace of possibly interferring chemicals

- Di water removes other ions present in the tap water

- absence of contaminations gives accurate titration results 

2. why do we need to rinse the burette/pipette with solution before using it to measure the volume of solution? 

- to remove any remaining DI water as presence of DI water dilutes solution to be filled into burette/pipette for titration.

- this results in titration results being higher than the actual results, leading to inaccuracy

3. why do we only add 2-3 drops of indicator to acid/base in conical flask during acid-base titration? 

- as inidicators are also weak acids and bases, excessive amount reacts with acid/base of titration.

- this affects the accuracy of the expt

4. why do we not rinse conical flask (where final sol. will be present) with the same reagent (eg. conc. HCL/ Fe (II) sol. ) before adding titre solution into flask?

- there will be additional amount of mols of that solution present, causing titration results to be larger than actual, and causing inaccuracy in results 

- more titire sol. will be required to titrate reagent than before rinsing

5. why is sulfuric acid added in an expt where Fe (II) ions is titrated against KMnO4 solution ? 

- Sulfuric acid provides H+ ions to enable MnO4- ions to be reduced to Mn2+ ions, causing a more significant colour change to

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