Question

What range of pH values could be aceved with a buffer consisting of nitrous acid (HNO2) and sodium nitrite (NO2 ‚àí)?

Answer 1

Answer:

The range of pH values that could be achieved with a buffer consisting of nitrous acid (HNO2) and sodium nitrite is 2.35 to 4.35.

Calculating the range

• The buffer consists of nitrous acid (weak acid) and sodium nitrite.
• Thus, it contains a weak acid and its salt.
• The buffer will act properly if the range of the ratio of the molar concentration of the salt and weak acid is between 0.1 to 10.
• [salt] / [weak acid]= 0.1 to 10
• [NaNO2] / [ HNO2] = 0.1 to 10
• If [NaNO2] / [ HNO2] = 0.1, using Henderson's equation we get,    

           pH  =pKa + log [salt] / [ acid]

           pH  =3.35 + log [NaNO2] / [ HNO2]

          pH  =3.35 + log 0.1

           pH = 3.35 + (-1)

           pH = 3.35 -1

          pH= 2.35

• If [NaNO2] / [ HNO2] = 10, using Henderson's equation we get,    
•          
•  pH  =pKa + log [salt] / [ acid]
•            
• pH  =3.35 + log
• [NaNO2] / [ HNO2]
•          
• pH  =3.35 + log
• 10
•            pH = 3.35 + 1
•            pH = 3.35 + 1
•          
• pH= 4.35

Thus, the range of pH values could be achieved with a buffer consisting of nitrous acid (HNO2) and sodium nitrite 2.35-4.35.