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A soft drink was bottled with a partial pressure of CO_{2} of 3 bar over the liquid at room temperature. The partial pressure of CO_{2} over the solution approaches a value of 30 bar when 44\; g of CO_{2} is dissolved in 1\; kg of water at room temperature, The approximate pH of the soft drink is ______\times 10^{-1}. (First dissociation constant of H_{2}CO_{3}=4.0\times 10^{-7}; \; log\; 2=0.3; density of the soft drink =1\; g\; mL^{-1})
 

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The partial pressure of CO_{2} over the solution approaches a value of 30 bar when 44\; g of CO_{2} is dissolved in 1\; kg of water at room temperature.

Then, \textup{Molarity }= \frac{\textup{mole}}{\textup{Volume(L)}}

\textup{Molarity }= \frac{\frac{\textup{Mass}}{\textup{Molar mass}}}{\textup{Volume(L)}}

and density = Mass/volume

so, Volume = density X Mass = 1 x 1 = 1 litre

Then,\textup{Molarity }= \frac{\frac{\textup{44}}{\textup{44}}}{\textup{1}}=1\textup{ mole /litre}

Now,

A soft drink was bottled with a partial pressure of CO_{2}  of 3 bar over the liquid at room temperature.

Reaction : \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{2} \mathrm{CO}_{3}

For,  30 Bar        →     1 mol/litre

Then, 3 Bar          →     0.1 mol/litre

 

Now,

First dissociation constant :

4 \times 10^{-7}=\frac{0.1 \alpha^{2}}{1-\alpha}

4 \times 10^{-7}=0.1 \alpha^{2} \quad \because {(1-\alpha\approx 1)}

\begin{aligned} &\alpha^{2}=4 \times 10^{-6} \\ &\alpha=2 \times 10^{-3} \end{aligned}

So, 

\left[\mathrm{H}^{+}\right]= 0.1 \alpha = 2 \times 10^{-4} \mathrm{M}

Now, we pH = - log([H+])

\mathrm{pH}=\mathrm{-log[2\times 10^{-4}]}

\mathrm{pH}=-[\log(2) + (-4)\log (10)]

\mathrm{pH}=-[0.3 + (-4)]

\mathrm{pH}=3.7=37 \times 10^{-1}

Ans = 37

Posted by

Kuldeep Maurya

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