Determination of Single Electrode Potential using Calomel Electrode

Calomel Electrode ( Mercury-Mercurous electrode)- Secondary Reference Electrode

Calomel Electrode 

Standard Hydrogen electrode is a primary reference electrode, the usage is  difficult as it has many disadvantages. Other electrodes with constant electrode potential are called as secondary reference electrodes. Calomel electrode and Silver-Silver chloride electrodes are examples for such reference electrodes.


Calomel electrode cell representation is

Hg | Hg₂Cl₂ (s) | KCl or Hg , Hg₂Cl₂ (s) , KCl.  

Calomel electrode acts as an anode or cathode electrode depending on the nature of the other electrode.

Hardness of Water

1. The hardness of water is due to the presence of 
     (a) Na+ and K+     (b) Na+ and Al3+ 
     (c) K+ and Ca2+    (d) Ca2+ and Mg2+


Ans. (d)


2. Which of the following causes permanent hardness
    (a) NaCl          (b) MgCl2     (c)   KCl     (d)   MgCO3


Ans. (b)


3. Which of the following causes temporary hardness
       (a) NaCl          (b) MgCl2     (c)   KCl     (d)   MgCO3


Ans. (d)


4.  Which of the following does not cause permanent hardness
        (a)  NaCl         (b) MgCl2     (c)   CaCl2     (d)   MgSO4


Ans. (a)