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$"8.855 g/L"$


This is just asking you to calculate the new molar (i.e. molar solubility) at a different pressure, i.e. use the . (We'll end up converting it later back to $"g/L"$.)

$bb(PV = nRT)$

where:

  • $P$ is the pressure in $"atm"$.
  • $V$ is the volume in $"L"$.
  • $n$ is the mols of gas in $"mol"$s.
  • $R = "0.082057 L"cdot"atm/mol"cdot"K"$ is the universal gas constant in the appropriate units.
  • $T$ is the temperature in $"K"$.

Solving for molar density, we get:

$n/V = P/(RT)$

Since we have two solubilities to consider, we must have two states.

$n_1/V_1 = P_1/(RT)$

$n_2/V_2 = P_2/(RT)$

Therefore, we have:

$RT = (P_1V_1)/(n_1) = (P_2V_2)/(n_2)$

Solving for the new molar density, we get:

$n_2/V_2 = n_1/V_1 ((P_2)/(P_1))$

At this point, we can convert the mass-based solubility to mols. We assume that the $"CO"_2$ was as dissolved into the water as possible for the initial pressure, and that it doesn't change the volume of the water.

$n_1/V_1 = (0.161 cancel("g CO"_2) xx "1 mol CO"_2/(44.009 cancel("g CO"_2)))/("0.100 L water")$

$=$ $"0.0366 mol/L"$

Therefore, the new solubility is:

$"0.0366 mol/L" xx ("5.50 atm")/("1.00 atm")$

$=$ $"0.2012 mol/L"$

In the original units, we have:

$(0.2012 cancel("mols CO"_2))/"L solution" xx "44.009 g CO"_2/cancel("mol CO"_2)$

$=$ $color(blue)("8.855 g/L")$

Hence, the solubility increased by a factor of $8.855/1.61 = 5.5$, which is the ratio of the pressures. Does it make sense that a gas at a higher external pressure is more soluble?

(Note that we could have simply used the initial mass-based solubility as it is and avoided converting to molar solubility. But it is a good exercise to use the molar mass for conversions, so I avoided skipping that step.)

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