CHEM - Interpreting Solubility Curves

🚨Important Words You Should Understand for IGCSE Chemistry🚨

— Solvent: the liquid in which a solute dissolves

— Solute: the substance that dissolves in the solvent

— Solution: the mixture formed when a solute is dissolved in a solvent

— Saturated solution: the solution when the maximum amount of solute is dissolved in a solvent

For example,

• Saltwater is a solution of salt and water.
• Salt is the solute, and water is the solvent.
• If you keep adding salt to water at a constant temperature, you will notice that salt will not dissolve in water anymore and remain as a solid after you add a certain amount of salt. The saltwater that contains the maximum amount of dissolved salt is called saturated solution.

Another important term to understand for IGCSE Chemistry is.....

Solubility

• Solubility is the ability of a solute to dissolve in a solvent
• Solubility measures the maximum amount of solute that can be dissolved in a solvent at a given temperature
• Solubility is expressed in g of solute per 100 g of solvent
• For solids, solubility increases as temperature increases.
  • More amount of salt can be dissolved in hot water than in cold water.
• For gases, solubility decreases as temperature increases.
  • Sodas are basically a solution of carbon dioxide dissolved in water.
  • When the soda is kept at room temperature, there is less fizziness in the soda because solubility has decreased and carbon dioxide has left the soda.

👇 This graph shows the solubility curve of many different solutes. 👇

Examples of information you should be able to get from interpreting this graph:

• The solubility for solid salts, such as NaNO₃, KNO₃ and NH₄Cl, increases as temperature increases.
• The solubility for gases, such as NH₃, SO₂ and HCl, decreases as temperature increases.
• What is the solubility of NH₄Cl at 70°C?
  • The solubility of NH₄Cl is 60 g of solute / 100 g water at 70 °C.
• At 70°C, how many grams of NH₄Cl would I need to prepare a saturated solution if I had 300 g of water?
  • 60 x (300 / 100) = 180 g
• If I dissolved 20 g of KCl into 50 g of water at 75 °C, would the solution be saturated?
  • The solubility of KCl at 75 °C is approximately 50 g of KCl / 100 g water.
  • The maximum amount of KCl that can be dissolved in 50 g of water at 75 °C is 50 x (50 / 100) = 25 g.
  • Therefore, the solution is not saturated.

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