Top 10 viva/interview questions on Acidity of wastewater test

Acidity is a measure of the capacity of water to neutralise bases. Acidity is the sum of all titrable acid present in the water sample. Strong mineral acids, weak acids such as carbonic acid, acetic acid present in the water sample contributes to acidity of the water. Usually dissolved carbon dioxide (CO2) is the major acidic component present in the unpolluted surface waters. 

The volume of standard alkali required to titrate a specific volume of the sample to pH 8.3 is called phenolphthalein acidity (Total Acidity). The volume of standard alkali required to titrate a specific volume of the water sample (wastewater and highly polluted water) to pH 3.7 is called methyl orange acidity (Mineral Acidity).

Hydrogen ions present in a sample as a result of dissociation or hydrolysis of solutes reacts with additions of standard alkali (NaOH). Acidity thus depends on end point of the indicator used. The colour change of phenolphthalein indicator is close to pH 8.3 at 25ºC corresponds to stoichiometric neutralisation of carbonic acid to bicarbonate.

1. Acidity is _____. 

a) Base neutralizing capacity 
b) Acid neutralizing capacity 
c) Quantity of acid present 
d) Quality of acid present 

2. An Indicator is a substance that facilitate colour change at the end point. 

a) True 
b) False 

3. The indicators used in the titration are 

a) Methyl orange and phenolphthalein 
b) Methyl red and phenolphthalein 
c) Methyl orange and Methyl red 
d) Bromocresol green and Methyl red 

4. To prepare 100 mL of 0.02 N of NaOH from 1 N NaOH, dilute ________ of NaOH. 

a) 20 mL 
b) 2 mL 
c) 0.2 mL 
d) 0.02 mL 

5. The major acidic component of surface water is 

a) Dissolved oxygen 
b) Dissolved carbon di oxide 
c) Dissolved sulphur di oxide 
d) Dissolved nitrous oxide 

6. The end point determination in titration will be based on the __________. 

a) Temperature 
b) Hardness 
c) Residual Chlorine 
d) Conductivity 

7. The methyl orange acidity is at pH ______. 

a) 3.7 
b) 3.9 
c) 4.5 
d) 4.7 

8. The phenolphthalein acidity is at pH is 8.3 

a) 8.3 
b) 9.3 
c) 4.3 
d) 7.3 

9. For dilution purposes, ____________ type of distilled water is used. 

a) Organic free 
b) CO2 free 
c) O2 free 
d) Ordinary 

10. Acidity can be electrometrically measured by_______________ 

a) pH meter 
b) Conductivity meter 
c) Turbidity meter 
d) Spectrometer

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