Hydrogen
1.0 Basic Information
2.0 Atomic and Physical Properties of Hydrogen (reference: NCERT)
3.0 Dihydrogen
4.0 Physical Properties
5.0 Chemical Properties
6.0 Uses of Dihydrogen
7.0 Compounds of Hydrogen
8.0 Hard and Soft Water
9.0 Hydrogen Peroxide
10.0 Volume strength of Hydrogen Peroxide
8.2 Degree of hardness
It is expressed as parts per million (ppm) and is defines as the number of parts of $CaCO_3$ or equivalent to various calcium and magnesium salts present in $10^6$ parts of water by mass.
Illustration 1. In a $100ml$ sample of water containing $1ml$ $CaCl_2$ and $1mg$ $MgCl_2$, the total hardness in terms of $CaCO_3$ will be calculated as
$$\begin{equation} \begin{aligned} 111g{\text{ }}CaC{l_2} = 100g{\text{ }}CaC{O_3}{\text{ and}} \\ 95g{\text{ }}MgC{l_2} = 100g{\text{ }}CaC{O_3} \\ \therefore (1mg{\text{ }}CaC{l_2}) + (1mg{\text{ }}MgC{l_2}) = \left( {\frac{{100}}{{111}}} \right) + \left( {\frac{{100}}{{95}}} \right){\text{ }}mg{\text{ of }}CaC{O_3} \\ 1litre({10^3}{\text{ parts) water = }}1.95mg{\text{ }}CaC{O_3} \\ {10^6}{\text{ parts water = }}1.95g \\ \therefore {\text{Degree of Hardness }} = 1.95ppm \\\end{aligned} \end{equation} $$
