Question

Prepare the standard solution of 0.1M oxalic acid

Answer 1

We have to prepare the standard solution of oxalic acid [ 250ml / 0.1 M ]

molar weight of oxalic acid $H_2(C_2O_4).2H_2O$ = 1 × 2 + 2 × 12 + 4 × 16 + 2(1 × 2 + 16) = 2 + 24 + 64 + 36 = 126g/mol
mole = molarity × volume/1000 
= 0.1 × 250/1000 = 0.1/4
mass of $H_2(C_2O_4).2H_2O$ = 0.1/4 × 126 = 3.15g

Use an electronic balance, we will weigh about 3.15 g of $H_2(C_2O_4).2H_2O$ crystals in a weighing bottle and transfer these into a 250ml beaker. 

wash the bottle two - three times, using distilled water and transfer all the washings into the beaker. Dissolve $H_2(C_2O_4).2H_2O$ crystals in the beaker by gentle stirring with a clean glass rod.

when $H_2(C_2O_4).2H_2O$ crystals dissolve completely in the beaker, transfer entire solution into 250ml standard flask through a funnel , using a glass rod. 

wash the beaker two to three times with distilled water and transfer all the washings into the standard flask and finally wash the funnel thoroughly with distilled water.  This transfers the solution completely into the standard flask.

now use a wash bottle, add enough distilled water to the standard flask so that the level is just below the calibration mark on it. Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the standard flask.

stopper the measuring flask and shake gently to make the solution uniform throughout.