Tag: experiments with water

Questions Related to experiments with water

One litre of a sample of hard water contains 55.5 mg of $CaCl _2$ and 4.75 mg of $MgCl _2$. The total harness in terms of ppm of $CaCO _3$ is :

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. 9 ppm

  2. 10 ppm

  3. 20 ppm

  4. none of these

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Correct Option: D
Explanation:

$55.5$ mg of $CaCl _2$ in 1 litre of water corresponds to $55.5$ ppm.


$4.75$ mg of $MgCl _2$ in 1 litre of water corresponds to $4.75$ ppm.

Also $1 CaCl _2 = 1 CaCO _3$

$111$ ppm $= 100$ ppm

Hence, $55.5$ ppm $=\dfrac {100}{111} \times 55.5=50$ ppm.

Also $1 MgCl _2 = 1 CaCO _3$

$95$ ppm $= 100$ ppm

Hence, $4.75$ ppm $=\dfrac {95}{111} \times 4.75=5$ ppm.

Hence, the total hardness will be $5$ ppm.

In a permutit, the calcium and magnesium ions of hard water are exchanged by:

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. $CO^{2-} _{3} $and $HCO _3{^-}$ ions of permutit

  2. $Na^{+}$ ions of permutit

  3. $Al^{3+}$ ions of permutit

  4. $Si^{4+}$ ions of permutiti

Show answer
Correct Option: B
Explanation:
Permutit is an artificial zeolite. It is sodium aluminium orthosilicate $Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O$.
$\underset {\text { permutit}}{Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O} + Ca^{2+}(or Mg^{2+}) \rightarrow  \underset {\text { exhausted permutit }}{Ca Al _{2}Si _{2}O _{8}.xH _{2}O} + 2Na^{+}$

The molecular formula of a commercial resin used for exchanging ions in water softening is $C 8H _7SO _3 $ (Mol. wt. 206). Water would be the maximum uptake of $Ca^{2+} $ ions by the resin when expressed ____ in mole per gram of resin.

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. $\dfrac{2} {309} $

  2. $\dfrac{1} {412} $

  3. $\dfrac{1} {103} $

  4. $\dfrac{1} {206} $

Show answer
Correct Option: B
Explanation:

The chemical reaction for softening water can be given as:-


$2C _8H _7(SO _3)Na+Ca^{+2}\longrightarrow [C _8H _7(SO _3)] _2Ca+2Na^{+}$

$\therefore$  $2$ moles of resin$\equiv1$ mole of $Ca^{2+}$

$\therefore$  Mass of resin = $206\times 2=412g$

For $412g$ of resin, $1$ mole of $Ca^{2+}$ is required.

$\therefore$  Maximum uptake of $Ca^{2+}$ ions $= \cfrac {1}{412}$ mole/gram of resin.

The formula for permutit or zeolite which is used as softer in ion-exchange method is:

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. $NaAlSiO _{4}$

  2. $NaAlO _{2}$

  3. both $A$ and $B$

  4. $Na _{2}SO _{4}$

Show answer
Correct Option: A
Explanation:
Permutit is an artificial zeolite. It is sodium aluminium orthosilicate $Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O$.
$\underset {\text { permutit}}{Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O} + Ca^{2+}(or Mg^{2+}) \rightarrow  \underset {\text { exhausted permutit }}{Ca Al _{2}Si _{2}O _{8}.xH _{2}O} + 2Na^{+}$