Chemistry Practicals For Class IX (Science Group) - Experiment No. 5: To prepare the standard solution of Oxalic acid

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EXPERIMENT NO.5
TO PREPARE THE STANDARD SOLUTION OF OXALIC ACID

APPARATUS:

• Measuring flask
• Filter paper
• Funnel
• Beaker
• Glass rod
• Pipette
• Physical balance
• Weight box

CHEMICALS:

• Oxalic acid (COOH)₂.2H₂O
• Distilled water

THEORY:

CONCENTRATION:
The amount of solute present in definite volume of solution is called concentration of a solution.

MOLARITY:
It is defined as, the number of moles of solute dissolved per litter or per cubic decimetre of solution. lt is denoted by "M".

FORMULA OF MOLARITY:

FORMULA OF MASS:
1. Mass of substance = Molarity x gram mol mass x volume in dm³
2. Mass of substance = Molarity x gram molecular mass x volume in cm³ / 1000

CALCULATIONS FOR 0.5 M SOLUTION OF OXALIC ACID

1. MOLECULAR FORMULA OF OXALIC ACID
(COOH)₂.2H₂O

2. CALCULATION OF MOLECULAR MASS OF OXALIC ACID
(COOH)₂.2H₂O
= (12 + 16 + 16 + 1)₂ + 2 (2 + 16)
= ( 24 + 32 + 32 + 2) + 2(18)
= 90 + 36
= 126 gm

3. MASS OF OXALIC ACID REQUIRED FOR 100 ML

4. MASS OF OXALIC ACID REQUIRED FOR 250 ML

METHOD:

• Adjust physical balance.
• Place filter paper in left hand pan.
• With the help of forceps place standard weights of weight box in right hand pan, till the pointer oscillates equally about centre zero, when the centre rod is raised.
• Record mass of filter paper.
• Now place the weighed filter paper in right hand side pan and weights in left hand side pan.
• Place additional weights (6.3 gm for 100 ml or 15.75 gm for 250 ml in left hand pan.
• Put oxalic acid in right hand pan equivalent to the weights (6.3 gm or 15.75 gm).
• Transfer weighed oxalic acid into a beaker and dissolve it in a minimum quantity distilled water by stirring with a glass rod.
• Take a 100 ml flask for 6.3 gm or 250 ml flask for 15.75 gm oxalic acid.
• Transfer the solution from beaker into the flask.
• Wash the beaker and transfer the weighing to the flask.
• Add more water into the flask till the level of solution reaches very close to mark on the neck.
• Now continuously add water with the help of pipette, dropper or wash bottle till the lower meniscus touches the required mark.
• This is 0.5 M solution of oxalic acid.

PRECAUTIONS:

• Physical balance must be adjusted.
• Air bubbles must be removed.
• The weighing should be accurate.
• The beaker should be washed and washing should be added to the solution of flask.
• Final addition of water should be cautiously done.
• Lower meniscus A solution should be read.

Special Thanks to Sir Sajjad Akber Chandio