3.7 Questions

Figure 3.10. H2O-KCl equilibrium phase diagram. Phases at equilibrium for the system H2O-KCl are shown as a function of chemical composition (weight percent KCl) and temperature. The blue area indicates temperatures and compositions for which a single phase, brine, is present at equilibrium. The crystalline phases are the minerals ice (H2O) and sylvite (KCl). Click on the diagram to see a larger version and to get more information.

Diagrams like H2O-NaCl Equilibrium Diagram for other minerals and higher temperatures are used by petrologists to understand igneous processes. To make sure that you have a good understanding of these diagrams, look at the H2O-KCl Equilibrium Diagram for the minerals ice and sylvite in Figure 3.10. Use the enlarged version of Figure 3.10 and the "Coordinates" button (if needed) to help answer the following questions.

For the chemical system H2O-KCl, what phase or phases will coexist at equilibrium for a chemical composition of 10 weight percent KCl at -10°C?
Pick one.
Brine plus sylvite.
Ice plus brine.
Ice plus sylvite.
Ice plus brine plus sylvite.