The van't Hoff factor for CaCl2 is 2.71. What is its mass % in an...

Question

The van't Hoff factor for CaCl2 is 2.71. What is its mass % in an aqueous solution that has Tf = - 1.14 °C?

Accepted Answer

Hello. In this problem, we are told in an experiment, the van Hoff factor for sodium sulfate was calculated to be 2.80 in aqueous sodium sulfate solution has the freezing point of minus 2.35 degrees Celsius. We are asked to find the mass percent of sodium sulfate in this solution. The first thing we're going to do then is find the morality. And we will then convert morality to mass percent to find morality. We're going to make use of the formula for the depression of freezing point. For a solution which is given by the change in the freezing point is equal to the Van Hoff factor times a freezing point depression constant, times morality. We're told we have an aqueous sodium sulfate solution. So our Sullivan is water. Water has the freezing point depression constant at 1.86°C perm allow We were told that the calculated van Hoff factor was 2.80 and the change in the freezing point is equal to the freezing point for pure water minus the freezing point. For the solution, water has a freezing point of zero degrees Celsius. And we're told the freezing point of the solution was minus 2.35 degrees Celsius. So our change in freezing point is 2.35 degrees Celsius. So we can use the formula above To solve for morality, morality then is equal to the change in the freezing point divided by the Van Hoff factor divided by freezing point depression constant. The change of freezing point is 2.35 degrees Celsius. The Van Hoff factor is 2.80 and are freezing point depression constant is 1.86 degrees Celsius Permal al our unit's attributes, Celsius cancels. This works out to 0.4512, wow. We can write this out further. The morality then is equal to 0. moles of sodium sulfate per kilogram of water. Now that we know the morality, we can convert morality to mass percent. We will do that. Then by first assuming we have one kg of water. If we have one kg of water, then that tells us we have 0. moles of sodium sulfate. Since we are trying to find mass percent, we need to convert our moles of sodium sulfate to mass. So we'll make use of the molar mass of sodium sulfate. One more sodium sulfate Has a mass of 142. g. And we set up. So our moles of sodium sulfate cancel. And that leaves us with 64.09 g of sodium sulfate. We then find the percent by mass of sodium sulfate by taking the mass of sodium sulfate provided by the mass of our solution which is the mass of sodium sulfate plus the mass of water Times our percent by massive sodium sulfate. Then the mass that we found for the sodium sulfate was 64.09 g And Massive r. value, which is the sodium sulfate is 64.09g, assumed a kilogram of water. So that's equal to 1000 g And we multiply this by a 100 percent. So our percent by mass sodium sodium sulfate works out to 6.02 percent by mouse. So in this problem we made use of the formula for the depression of the freezing point for a solution to find the morality. Once we found the morality, we made an assumption about the quantity of water and then found the mass of our salute, the sodium sulfate. And we then calculate the mass percent of sodium sulfate In the solution, which turned out to be 6.02% by mass sodium sulfate. Thanks for watching. Hope this help.

The van't Hoff factor for CaCl2 is 2.71. What is its mass % in an aqueous solution that has Tf = - 1.14 °C?

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