What do nonvolatile solutes do

Image from Wikimedia. A knowledge of Latin helps us understand our own language better. Where did that come from? This helps you better understand some of the science terminology we use every day. A colligative property is a property of a solution that depends only on the number of solute particles dissolved in the solution and not on their identity.

Recall that the vapor pressure of a liquid is determined by how easily its molecules are able to escape the surface of the liquid and enter the gaseous phase. When a liquid evaporates easily, it will have a relatively large number of its molecules in the gas phase and thus will have a high vapor pressure.

Liquids that do not evaporate easily have a lower vapor pressure. The Figure below shows the surface of a pure solvent compared to a solution. In the picture on the left, the surface is entirely occupied by liquid molecules, some of which will evaporate and form a vapor pressure. On the right, a nonvolatile solute has been dissolved into the solvent. Her work has appeared on Forbes, Yahoo! News, Business Insider, Lifescript, Healthline and many other publications. TL;DR Too Long; Didn't Read A nonvolatile solute does not produce vapor pressure in a solution, which means the solute cannot escape the solution as a gas.

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Science Projects About Kitchen Chemistry. If you draw the saturated vapour pressure curve for a solution of a non-volatile solute in water, it will always be lower than the curve for the pure water. Note: The curves for the pure water and for the solution are often drawn parallel to each other. That has got to be wrong! Suppose you have a solution where the mole fraction of the water is 0. The vapour pressure of the solution will be 99 kPa - a fall of 1 kPa.

At a lower temperature, where the vapour pressure of the pure water is 10 kPa, the fall will only be 0. For the curves to be parallel the falls would have to be the same over the whole temperature range. They aren't! If you look closely at the last diagram, you will see that the point at which the liquid-vapour equilibrium curve meets the solid-vapour curve has moved. That point is the triple point of the system - a unique set of temperature and pressure conditions at which it is possible to get solid, liquid and vapour all in equilibrium with each other at the same time.

Since the triple point has solid-liquid equilibrium present amongst other equilibria , it is also a melting point of the system - although not the normal melting point because the pressure isn't 1 atmosphere. That must mean that the phase diagram needs a new melting point line a solid-liquid equilibrium line passing through the new triple point.

That is shown in the next diagram. Now we are finally in a position to see what effect a non-volatile solute has on the melting and freezing points of the solution.

Look at what happens when you draw in the 1 atmosphere pressure line which lets you measure the melting and boiling points. The diagram also includes the melting and boiling points of the pure water from the original phase diagram for pure water black lines.

We have looked at this with water as the solvent, but using a different solvent would make no difference to the argument or the conclusions. The only difference is in the slope of the solid-liquid equilibrium lines. For most solvents, these slope forwards whereas the water line slopes backwards. You could prove to yourself that that doesn't affect what we have been looking at by re-drawing all these diagrams with the slope of that particular line changed.

If this is the first set of questions you have done, please read the introductory page before you start. Asked 7 years, 2 months ago. Active 5 years ago. Viewed 52k times. This is what I have gathered so far: A non-volatile solute does not produce vapour at the boiling point of the solution. A volatile solute does produce vapour at the boiling point of the solution.

Can someone confirm these definitions? Improve this question. Community Bot 1. Amuna Amuna 1, 6 6 gold badges 22 22 silver badges 27 27 bronze badges. Volatile solutes must be accounted for. Add a comment.