Basic information about solutions and solubility

1. This project has received funding from the European Union’s Horizon 2020
research and innovation programme under grant agreement No 869993.
Solutions and
solubility

2. Solute, solvent, solution
• When you dissolve solute in
solvent, you will get solution.
• Water is the most common
solvent.
• The ability of the solute to
dissolve in solvent is called
solubility. It depends on physical
and chemical properties of the
solute and solvent and also
on temperature and pressure.

3. Soluble, insoluble, polar, non-polar
• Table salt (NaCl) dissolves in water,
so we say that NaCl is soluble in
water.
• NaCl does not dissolve in benzene,
so we say that NaCl is insoluble in
benzene.
• NaCl is a polar compound. Water is
also polar and that is why NaCl is
water-soluble.
• Benzene is a nonpolar molecule.
Therefore, NaCl is insoluble in
benzene.

4. Solubility and temperature
• Solubility is the property of a solute
to dissolve in a solvent at a specific
temperature.
• Solubility varies with temperature.
• Most substances are more soluble at
higher temperatures. For example,
solubility of sucrose in water
increases significantly with
temperature.
• Solubility of NaCl only slightly varies
with temperature.

5. Levels of saturation
Unsaturated solution Saturated solution Supersaturated solution
contains less than the maximum
amount of the solute that can be
dissolved at that temperature.
contains exactly the
maximum amount of the
solute that can be dissolved
at that temperature.
contains more than the
maximum amount of the solute
that can be dissolved at that
temperature.

6. Solubility curves
• Solubility in different temperatures
can be presented in solubility
curves.
• Temperature is on X-axis.
• On Y-axis is the solubility of the
solute in 100 grams of solvent.
• Saturation curve expresses
the saturation point at a specific
temperature.
• Below the saturation curve is
the unsaturated area and above it
the solution is supersaturated.

7. How to get a supersaturated solution of sucrose?
• If you mix 300 grams of sucrose in
100 grams of water at the
temperature of 90 °C, you have an
unsaturated solution (1).
• When you cool the solution to the
temperature of 20 °C, your solution
will get supersaturated (2).
• Cooling is one method for
supersaturation. It is a suitable
method, when the solubility of the
substance varies with temparature.
• Other methods are evaporation, anti-
solvent addition and precipitation.
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8. Units of concentration
• In solubility curves, the concentration
unit is usually grams of solute per
100 grams of solvent.
• There are plenty of other commonly
used expressions for
concentration. It is important to be
careful with the units to avoid
confusion.
• For example, if you mix 10 grams of
anhydrous sodium sulfate in 100
grams of water, all the concentrations
expressed in the next table mean the
same concentration.

9. This project has received funding from the European Union’s Horizon 2020
research and innovation programme under grant agreement No 869993.
References
Beckmann, W (ed.) 2013. Crystallization: Basic Concepts and Industrial Applications. Weinheim:
Wiley‐VCH Verlag GmbH & Co. KGaA. pp. 53-55.
Solubility of things. 2020. Solubility basics – What is solubility. Available at:
https://www.solubilityofthings.com/basics (Accessed 18.11.2020).
Videos
• Solutions: https://youtu.be/9h2f1Bjr0p4
• Solubility curves: https://youtu.be/7AZ2Z6_CQmA
• Solubility explained: https://youtu.be/TglqdJ2CkHA