Preparation of Standard Solution of Sodium Carbonate

A standard solution is a solution whose concentration has been accurately determined. Standard solutions are prepared from highly pure chemicals and the exact concentration is determined by a process called standardization. The substance available for standardization of a solution is highly pure is called a primary standard.

Aim

To prepare the 250 cm3 of N/10 standard solution of sodium carbonate.

Theory

Sodium carbonate is essentially insoluble in nearly saturated sodium hydroxide. The insoluble sodium carbonate will settle to the bottom of the container after the saturated NaOH has equilibrated for a couple of days. The supernatant can be withdrawn carefully to prepare diluted NaOH solution free of sodium carbonate. The water for preparing NaOH standard solution should be boiled to remove any dissolved CO2, because dissolved CO2 can cause a titration error. To prepare the standard solution of sodium carbonate, The equivalent weight of sodium carbonate = \(\frac{Molecular\ weight}{2} = \frac{106}{2} = 53\) !000cm3 of normal sodium carbonate solution requires 53g of sodium carbonate. Therefore, 250cm3 of \(\frac{N}{10}\) sodium carbonate requires \(\frac{53}{1000}\times\frac{250}{10}=1.325g\)

Materials Required

  1. Chemical balance
  2. Watch glass
  3. Weight box
  4. 250ml beaker
  5. Glass rod
  6. 250ml measuring flask
  7. Wash bottle
  8. Weighing tube
  9. Sodium Carbonate
  10. Funnel
  11. Funnel stand
  12. Distilled water

Apparatus Setup

Preparation of Standard Solution of Sodium Carbonate

Procedure

  1. Take a watch glass, wash it with distilled water and dry it.
  2. Weigh the exact amount of clean and dried watch glass and record its weight in the notebook.
  3. Weigh correctly on the watch glass 1.325 g of sodium carbonate and record this weight in the notebook.
  4. Using a funnel, transfer sodium carbonate softly and carefully from the watch glass into a clean and dry measuring flask.
  5. Wash the watch glass with distilled water to move the particles that stick to it into the foam with the assistance of a wash bottle.
  6. For this purpose, the volume of distilled water should not exceed 50 ml.
  7. Wash funnel several times with distilled water to move the sticking particles into the measuring flask using a wash bottle. Add water in tiny quantities while washing the funnel. The distilled water quantity used for this purpose should not exceed 50 mL.
  8. Using a wash bottle, wash the funnel carefully with distilled water to pass the solution attached to the funnel into the measuring flask
  9. Turn the flask of measurement until the sodium carbonate dissolves.
  10. Using a wash bottle, thoroughly add enough distilled water to the measuring flask just below the etched mark on it.
  11. Add the last few mL of distilled water drop into the measuring flask until the reduced meniscus level just touches the mark.
  12. Put the stopper on the mouth of the flask and shake softly to make the entire solution uniform. Calculate it as a solution of sodium carbonate N/10.

Observations

Weight of the watch glass W1g
Weight of the watch glass + Sodium carbonate W1 + 1.325 g
Weight of Sodium carbonate 1.325 g
Volume of distilled water 250 cm3

Results and Discussion

250cm3 of decimolar or N/10 standard solution of sodium carbonate is prepared.

Precautions

  1. While weighing do not spill the substance on balance pan
  2. While preparing the laboratory reagent apron should be used.
  3. Bases are highly corrosive so it should be handled with extreme care.
  4. Watch glass must be dry.
  5. Funnel should be washed thoroughly several times.
  6. Shaking of solution should be done thoroughly so that it may become uniform.
  7. While making solution the solvent should be added such that the lower meniscus of the solvent must be on the mark of the measuring flask.
  8. Last few drops should be added using a pipette to avoid extra addition of distilled water above the mark on the neck of the measuring cylinder.

Frequently Asked Questions on

Which indicator is used while titrating strong acid against strong base ?

Methyl orange or phenolphthalein.

Differentiate between molarity and molality.

Molarity of a solution is the number of moles of the solute present per litre of the solution, whereas molality is the number of moles of the solute present per kg of solvent.

What is acidimetry ?

The method used to determine the strength of an acid by titrating it against a standard alkali solution using suitable indicator is known as acidimetry.

What is basicity of an acid ?

Basicity of an acid is the number of replaceable hydrogen atoms present per molecule of acid.

Why is standard solution of NaOH cannot be prepared ?

NaOH is a hygroscopic substance. It absorbs moisture, therefore, it cannot be weighed and that is why its standard solution cannot be prepared directly.

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