### E-AIM Tutorial

 Lesson 4: Properties of Solutions Containing Multiple Salts

### Introduction

In the first three lessons of this tutorial we examined the water content, phase state, and particle/vapour partitioning of single salt solutions, and mixtures containing both a salt and an acid. In the next three lessons we will study the behaviour of a two salt mixture. In this lesson we look at the water content at various relative humidities.

### Preparation

Before starting, ensure that this browser window occupies only the left half of your screen. You should leave enough space for another browser window where you can enter data into E-AIM and read the results. If your screen is too small for two windows, print out this tutorial and use this window to enter data and read E-AIM's results. In these lessons we assume that you will have two browser windows open.

Select this link to open a second browser window containing the data input page for "simple" calculations using Model III (http://www.aim.env.uea.ac.uk/aim/model3/model3a.php). Arrange the windows on your screen so that both are visible and the left window contains this text.

### The Lesson

This consists of the two sets of calculations described in the links below, which should be done in the order listed.

### Conclusion

You have completed Lesson 4, and learned that:
• The water content of particles increases as more compounds are added, and the total amount of soluble material increases.
• At relative humidities very close to 100% the water uptake of an NH4NO3/NaNO3 mixture is approximately equal to the water uptake of the same number of moles of NH4NO3 alone. This relationship breaks down at lower relative humidities where the solutions are more concentrated.
• The Zdanovskii-Stokes-Robinson equation predicts the water uptake of a mixed solution from the values for each of the individual solutes at the same water activity as the mixture. This relationship works well at low relative humidities.

Now proceed to Lesson 5, which examines how solids form in mixed aqueous aerosols.