When 1 mol of HCl is added to 1 kg of water, the boiling point in...

Question

When 1 mol of HCl is added to 1 kg of water, the boiling point increases by 1.0 °C, but when 1 mol of acetic acid, CH₃CO₂H is added to 1 kg of water, the boiling point increases by only 0.5 °C. Explain.

Accepted Answer

Welcome back, everyone. Adding one mole of magnesium chloride in one kg of water will cause a greater increase in boiling point than adding one mole of glucose in the same amount of water. Explain why. So we're going to consider choices A through D where choice A says that magnesium chloride will produce more particles than glucose, which will cause a greater increase in boiling point. Choice B states that glucose will produce more particles than magnesium chloride which will cause a greater increase in boiling point. Choice C states that magnesium chloride is soluble in water. While glucose is only sparingly soluble and magnesium chloride will produce more dissolved particles causing a greater increase in boiling point. And choice D states that both magnesium chloride and glucose should cause the same increase in boiling point because one mole of both species is dissolved in water. Now, in order to get to our answer, we want to recall that boiling point of a solution is going to be dependent on our total number of particles that are dissolved in the solution. We can recall the following formula which relates our boiling point change, which is calculated from taking our Van Hoff factor represented by the variable I multiplied by our boiling point elevation, constant K B, which is dependent on our solvent used and then multiplied by our modality of our solution expressed by the variable M. And again, this is our boiling point elevation formula. Now, let's consider the two substances we're told of in the prompt beginning with magnesium chloride. M G C L two recognize that because this chemical formula consists of magnesium which is a metal and chlorine, which is a nonmetal. This compound is considered ionic. And we want to recall our solubility rules for chlorides where we would recognize that magnesium chloride is an example of a soluble chloride and therefore, is going to fully dissociate into the following ions where we form magnesium two plus Kion as a product, as well as two moles of our chloride anion as a product. And for our products, we can count a total of three moles of dissolved ions, which therefore corresponds to a van Hoff factor equal to three. Next, we consider glucose which were given the formula as C six H 12 06. And recognized that each atom making up this chemical formula, carbon, hydrogen and oxygen are all nonmetals. And therefore this is a molecular compounds and this will correspond to glucose being a non electrolyte. And we can recognize it as a sugar. And so it's just going to exist as sugar molecules which remain intact in solution with water where each molecule of glucose will count as just one molecule. And so because of all of these reasons, we would therefore say that we have a van Hoff factor equal to just one particle. So where magnesium chloride had a van hall factor of three particles, glucose just has a van Hoff factor of one particle. And if we see that for magnesium chloride, we have three particle, three moles of particles dissolved from our van Hoff factor of three. We therefore will have a higher increase in boiling point associated with magnesium chloride versus glucose, which only again has one particle for its van Hoff factor. So based on what we've outlined, we can go ahead and rule out choice B which states that glucose will produce more particles which will cause a greater increase in boiling point. We see that to not be true. Then in choice C we can also rule out choice C because it says that glucose is only sparingly soluble when glucose actually is just as soluble as magnesium chloride. It's just that it's a molecular compound. And then lastly choice D we can rule out as well because they will not our two compounds. Magnesium chloride and glucose will not cause the same increase in boiling point. And that is due to the fact that we saw that magnesium chloride has a vanhall factor of three, whereas glucose has a lower van half factor of just one. And so it will have a minimal impact on an increase in boiling point. And that leaves us with choice. A magnesium chloride will produce more particles than glucose, which will cause a greater increase in boiling point. As the correct choice to complete this example. As our final answer, I hope that this made sense and let us know if you have any questions.

When 1 mol of HCl is added to 1 kg of water, the boiling point increases by 1.0 °C, but when 1 mol of acetic acid, CH₃CO₂H is added to 1 kg of water, the boiling point increases by only 0.5 °C. Explain.

Key Concepts

Colligative Properties

Ionization of Solutes

Boiling Point Elevation Formula

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