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Preparation of sodium hydroxide solutions.

1. To prepare an approximate 1 molar solution of sodium hydroxide -


• dissolve 40 gm (1 mole) of NaOH (sodium hydroxide) in 1 L of distilled water
  
  It is more convenient to prepare an approximate NaOH solution at approximately 1 M strength, as 40 g of NaOH is a convenient quantity to weigh.
  
  Note: Only an approximate concentration of NaOH soln. can be prepared, which will then have to be standardised.
  
  
2. To prepare a 0.1M NaOH solution. -


• Dilute a standardised 1.0 M NaOH solution by a factor of 10
  
• or, Dilute a non standardised 1.0 M NaOH solution by a factor of 10 and then standardise.
  
• or, dissolve 4 gm NaOH in 1 L of distilled water (a less accurate option also requiring standardisation)


It is more convenient to prepare and store an approximate NaOH solution at ~ 0.1 M strength, as -


• this is the concentration used in the determination of juice and wine's titratable acidity.
  
• 0.1 M NaOH soln. is more stable then the weaker 0.01 M NaOH soln.
  
• the 0.1 M NaOH soln. can then be simply diluted down by a factor of ten to a 0.01 M NaOH solution and used in SO₂ analysis.


3. To prepare a 0.01M NaOH solution -


• Dilute a standardised 0.1 M NaOH solution by a factor of 10
  
• or, Dilute a non standardised 0.1 M NaOH solution by a factor of 10 and then standardise.
  
• or, dissolve 0.4 gm NaOH in 1 L of distilled water (a less accurate option also requiring standardisation)


All prepared and standardised NaOH solutions should be protected from the air as much as possible by -


• pouring your 1L of 0.1M NaOH in four 250mL bottles.
  
• Sealing the bottles when not in use.
  
• Re-standardise your NaOH soln. once a month or more frequently depending on exposure.
  
• Alternatively, using a burette, reservoir combination fitted with soda lime tubes, requiring less frequent standardisation.
  
  
Note: the 0.01M NaOH solution used in the determination of SO₂ should be prepared fresh, daily, as its low strength makes it subject to a higher percentage deterioration on air exposure (see NaOH).