First slide

Hardness of water

Question

Different samples of water containing each 100 ppm of CaCl₂, MgSO₄, CaSO₄ and MgCl₂ among them which will have greater hardness

Moderate

Solution

The degree of hardness of water is measured in terms of CaCO₃.
→ The number of parts by weight of CaCO₃ (Or) its equivalent Ca,Mg salts present in 10⁶ parts by weight of water is called degree of hardness of water.
100gr of CaCo₃ = 111gr of CaCl₂
100gr of CaCo₃ = 95gr of MgCl₂
100gr of CaCo₃ = 120gr of MgSO₄
100gr of CaCo₃ = 136gr of CaSO₄
100ppm of each means,

$\large \mathop {100parts}\limits_{[grs]} \;of\;CaC{l_2}\;\xrightarrow{{present\;in}}\;{10^6}gr\;of\;water$

111gr of CaCl₂ → 100gr of CaCo₃
100gr of CaCl₂ → ?

$\large \frac{{100}}{{111}} \times 100\; = \;mass\;of\;CaC{o_{3\;}} = \;Degree\;of\;hardness\;of\;water\;[D.H.W]$

Similary, for MgCl₂
$\large D.H.W\; = \;\frac{{Weight\;of\;material\;in\;ppm}}{{GMW\;of\;material}} \times 100$

For MgCl₂

$\large D.H.W\; = \;\frac{{100}}{{95}} \times 100\; = \;Mass\;of\;CaC{O_3}$

For CaSO₄

$\large D.H.W\; = \;\frac{{100}}{{136}} \times 100\; = \;Mass\;of\;CaC{O_3}\$

For MgSO₄

$\large D.H.W\; = \;\frac{{100}}{{120}} \times 100\; = \;Mass\;of\;CaC{O_3}\$
Degree of hardness caused by MgCl₂ sample is high

Numerator vaule is low i.e,. Molecular weight is low for NgCl₂.

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