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Preparing a Standard Solution from Solid Solute

Let us discuss the preparation of a standard solution of sodium trioxocarbonate(IV) (say M/10) using water as the solvent.

Now sodium carbonate is a primary standard. Its molecular mass is 106.

To prepare M / 10 Na2C03 solution, 10.6 g of sodium carbonate should be dissolved per litre of the solution.

Normally in the laboratory we are required to prepare 250 dm3 of solution. Therefore, to prepare 250 cm3 of M / 10 NaCO3 10 solution 10.6 /4  = 2.650 g of sodium carbonate are dissolved in lesser quantity of water and the solution diluted to exactly to 250 cm3.

The apparatus required for the above preparation are weight box, chemical balance, watch glass, 250 cm3 beaker, glass rod, 250 cm3 measuring flask, wash bottle.

 

PROCEDURE

1. Take a watch glass, wash it with distilled water and then dry it.

2. Weigh the clean and dried watch glass accurately.

3. Weigh 2.650 g sodium trioxocarbonate (IV) on the watch glass accurately.

4. Transfer gently and carefully sodium carbonate from the watch glass into a clean 250 cm3 beaker. Wash the watch glass with distilled water with the help of a wash bottle to transfer the particles sticking to it into beaker (Fig. 11.1). The volume of distilled water for this purpose should not be more than 50 cm3.

Fig. 11.1. Washing of watch glass to transfer sticking particles to beaker.

 

5. Dissolve sodium trioxocarbonate (IV) crystals in the beaker by gentle stirring with a clean glass rod.

6. When the sodium trioxocarbonate (IV) in the beaker is completely dissolved, transfer carefully the entire solution from the beaker into a 250 cm3 measuring flask with the help of a funnel (Fig. 11.2).

Fig. 11.2. Transferring solution to measuring flask.

 7. Wash the beaker with distilled water. Transfer the washings into the measuring flask (Fig. 11.3).

Fig. 11.3. Transferring last traces of solution to measuring flask.

 

8. Finally wash the funnel thoroughly with distilled water with the help of a wash bottle to transfer the solution sticking to the funnel into the measuring flask (Fig. 11.4).

Fig. 11.4. Washing last traces of solution from funnel to the measuring flask.

 

9. Add enough distilled water to the measuring flask carefully up to just below the etched mark on it, with the help of wash bottle.

10. Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the measuring flask (Fig. 11.5).

Fig. 11.5. Using pipette to add last drop of water to make the volume up to the mark.

 

11. Stopper the measuring flask and shake gently to make the solution uniform throughout. Label it as M/10 sodium trioxocarbonate(IV) solution.