• Solubility is?a measurement of how much of a substance will dissolve in a given volume of a liquid
  • The liquid is called the solvent
  • The solubility of a gas depends on pressure and temperature

   

• Different substances have different solubilities
• Solubility can be expressed in?g per 100 g of solvent
• Solubility of solids is affected by temperature
  • As?temperature increases, solids usually become?more soluble

   

• Solubility of gases is affected by temperature and pressure; in general:
  • As?pressure increases, gases become?more soluble
  • As?temperature increases, gases become?less soluble

   

• Solubility graphs or curves represent solubility in g per 100 g of water plotted against temperature
• To plot a solubility curve, the maximum mass of solvent that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures

Solubility curve for three salts. While the solubility of most salts increases with temperature, sodium chloride, or common salt, hardly changes at all

Answers

Problem 1

At 40 °C the solubility is 68 g per 100 g of water

So scaling, 68 x (20 / 100) =?13.6 g?of potassium nitrate will dissolve in 20 g of water

Problem 2

Solubility of lead(II) nitrate at 90?^oC is 118 g / 100 g water, and 64 g / 100 g water at 20 °C.

Therefore for mass of crystals formed = 118 – 64 = 54 g (for 100 cm³?of solution).

However, 200 cm³?of solution was prepared,

So total mass of lead(II) nitrate crystallised = 2 x 54 =?108?g