Many compounds are only partially dissociated into ions in aqueou...

Question

Many compounds are only partially dissociated into ions in aqueous solution. Trichloroacetic acid (CCl₃CO₂H), for instance, is partially dissociated in water according to the equationCCl₃CO₂H (aq) → H⁺ (aq) + CCl₃CO₂⁻ (aq)For a solution prepared by dissolving 1.00 mol of trichloroacetic acid in 1.00 kg of water, 36.0% of the trichloroacetic acid dissociates to form H⁺ and CCl₃CO₂⁻ ions.What is the freezing point of this solution? (The freezing point of 1 kg of water is lowered 1.86 °C for each mole of solute particles.)

Accepted Answer

Hello everyone. Today we are being given the falling problem. Lactic acid partially associates according to this equation, a solution is formed by dissolving 1.5 moles of lactic acid in one kg of water where 1% of lactic acid associates two ions, calculate the freezing point of the solution. Given that the KF value for water is 1.86 degrees Celsius per morality. So first, we need to take into account how much associated. So We had 1% of our lactic acid associating. So 1% associated. And so what does that mean? That means that that one Times The 1.5 moles Produced 0.0, 1 5 moles of H plus or protons, We then had another product which that 1% times one .5 moles is that zero, moles of our lactate ion. So that means that if 1% divided into those two, the other 99 divided it into that 1.5 moles, gives us 1.4, 85 moles of our lactic acid. Excellent. And from here, we can calculate our morality. Morality is going to be moles of solute, divided by kilograms of solvent are moles of solute. We had three, we had a point 0.0 moles plus 0.0 15 moles plus 1.4, 8, 5 most. And then of course, our kilogram of solvent was just one kg. So this is going to give us one .5, We could then calculate our freezing point. That's going to be the freezing point is equal to the morality times our K F constant. A freezing point, depression, constant. So If we were to do that, we would have our morality which was 1.5, 15 times RKF value, which is 1.86°C per morals. This would give us 2.87 degrees Celsius Celsius as our freezing point. And the last thing that we have to do to calculate the freezing point of our solution is that we must take the freezing point of our solvent and subtract that by our freezing point depression. And so the freezing point of our solvent, which is water is going to be zero degrees Celsius. And that can be found in the reference text minus R 2.87 degrees Celsius that we have giving us a freezing point of our solution being negative 2.87 degrees Celsius as our final answer. And with that, we have solved the problem overall, I hope this helped ahead until next time.

Key Concepts

Dissociation of Acids

Colligative Properties

Molality and Freezing Point Depression

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