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pH of a Solution

0.24 g sample...

Question

0.24 g sample of $M g$ react with 80.0 mL of $H C l$ solution whose $p H$ is 0.30. $p H$ after all $M g$ has reacted is:

0.3

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0.41

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0.24

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0.57

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Solution

The correct option is C 0.24
Given concentration of $H^{+} = 10^{- 0.3} = \frac{1}{2} = 0.5$
No. of moles of $H C l$ $=$ (Concentration) $\times$ Volume $=$ $(0.5) \times \frac{80}{100} = 0.04$ moles
No. of moles of magnesium $= \frac{0.24}{24} = 0.01$ moles
$M g + 2 H C l ⟶ M g {C l}_{2} + H_{2} ↑$
1 mole of $M g$ and 2 moles of $H C l$ is needed.
So, 0.02 moles are left.
$⟹ p H = - log (0.02 \times \frac{1000}{80}) = 0.24$

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0.24 g sample of Mg react with 80.0 mL of HCl solution whose pH is 0.30. pH after all Mg has reacted is:

0.24 g sample of $M g$ react with 80.0 mL of $H C l$ solution whose $p H$ is 0.30. $p H$ after all $M g$ has reacted is: