Washing soda

Determination of the water of crystallization in washing soda.


sodium carbonate is a suitable chemical for preparing a standard solution (as a primary standard). The Molarity of the given hydrochloric acid can be found by titrating it against the standard sodium carbonate solution Prepared. We do this experiment To determine the molarity of a NaCO solution by titrating it with a standard HCl solution

The equation for the complete neutralization of Na2CO3 with dilute HCl is

Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + CO3(g) + H2O(l)


electronic balance ,burettes 50cm3 pipette 25cm3, conical flask 250cm3 dry weighing boat , beaker,100cm3,flomatric flask 250cm3


Health and safety: Wear safety glasses . Use bulb for pipette suction .washing soda powder is irritant.0.1 mol/dm3 hydrochloric acid is irritant .screened methyl orange is flammable .risk of cuts from glassware breakage .

1- Using a dry weighing boat , weigh out 5 g of the powdered washing soda crystals to three decimal places and record the weigh.

2- Transfer quantitatively ,using wash bottle ,into 100cm3 beaker .Stir to dissolve and transfer quantitatively to a 250cm3 volumetric flask and invert several times ti ensure it dissolves .

3- Rinse the 50cm3burette with 0.100 mol/dm3 hydrochloric acid before filling with the acid .Fill and run down to the zero mark.

4- Use pipette transfer to 25.0cm3of washing soda solution into a 250cm3coincal

5- Add screened methyl orane indicator and titrate until just at the end point .

6- Record the titer.

7- Repeat the titration until at least three concordant results are obtained.


First time

Second time

Third time









4.99+4.95+5.23=5 g


We have seen that colour was changed from green to dark blue (called the “endpoint”).


Na2CO3+2HCL 2NaCl +H2O+CO3

Mol of HCl from titter =36.91000x0.100=3.69x10-3

Mole of Na2CO3 =3.69x10-3x12=1.845x10-3 in 25 cm3

We have 250cm3 Na2CO3

Moles of Na2CO3=25025x1.845x10-3=0.01845

Mass of Na2CO3=0.01845X106=1.955g

Mass of water of crystallization = 5 -1.955=3

Mole of water =318=0.169

We have 0.01845 mol Na2CO3+0.169 mol of water

1 mol Na2CO3 +10 mol of water



We did this experiment to determine the concentration of an acid solution In base titration .

A few drops of an appropriate acid-base indicator is added to base. If the solution of unknown concentration is acidic, a standard base solution is added to the acid solution drop by drop until it is neutralized.

While doing an acid-base titration, we must be able to see the standard solution and A sudden change in color . At this point, indicates that neutralization has occurred. the number of ions from the HCL is equal to the number of Na_2 CO_(3.)

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