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Conductivity MP BP and Electronegativity (Group 2)

A sample of w...

Question

A sample of water has a hardness expressed as 80 ppm of $C a^{2 +}$ . This sample is passed through an ion exchange column and the $C a^{2 +}$ is replaced by $H^{+}$ . What is the pH of the water after it has been so treated?
[Atomic mass of $C a = 40]$

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2.7

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5.4

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2.4

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Solution

The correct option is D 2.4
The concentration of calcium ions is 80 ppm. This means that 80 g of calcium ions are present in $10^{6}$ ml of water.
This corresponds to $C a^{2 +} = \frac{80}{40} m o l e s = 2 m o l e s o f C a^{2 +} = 2 \times 2$ .
This also corresponds to $= 2 \times 2 m o l e s$ of $H^{+}$ ions.
1 L (or 1000 ml) of water will contain $4 \times 10^{- 3} m o l e s$ of $H^{+}$ ions.
Hence, $p H = - l o g [H^{+}] = - l o g (4 \times 10^{- 3}) = 3 - l o g 4 = 3 - 0.6 = 2.4$ .

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A sample of water has a hardness expressed as 80 ppm of Ca2+. This sample is passed through an ion exchange column and the Ca2+ is replaced by H+. What is the pH of the water after it has been so treated?[Atomic mass of Ca=40]

A sample of water has a hardness expressed as 80 ppm of $C a^{2 +}$ . This sample is passed through an ion exchange column and the $C a^{2 +}$ is replaced by $H^{+}$ . What is the pH of the water after it has been so treated?
[Atomic mass of $C a = 40]$