Solubility
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saturated solution
one in which no more solid will dissolve in water at a particular temperature.
How are saturated solutions prepared?
by adding excess of the solid
Solubility
the mass of solute that can saturate 100g of water at a particular temperature.
units of solubility
g/100 g of water.
“Potassium chlorate(v), KCIO, has a solubility of 14 g/ 100 g water at 40°C” meaning
This means that 14 g of potassium chlorate (v) is required to saturate 100 g of water at 40°C
Mass measurement solubility
measured in g (grams).
Volume
measured in cm3
1 cm3
1 ml (millilitre)
Density of water
1 g/cm3
1 cm3 of water has a mass of?
1g
1 g of water has a volume of?
1 cm3
100 g of water is the same as?
100 cm3 of water.
The values for the solubility of most gases in water are low, so the units are usually mg/1 (milligrams per litre). 1 mg is 1/1000th of a gram.
1000 mg in 1 g.
1 litre = 1000 ml =
1000 cm3
recrystallised
• This process involves heating to evaporate some water (usually until half the volume of water is removed). • The solution is then left to cool and crystallise - crystallisation happens because the solubility of a salt decreases as the solution cools.
Why does crystallisation happen?
because the solubility of a salt decreases as the solution cools
What are not very soluble in water?
• Oxygen • carbon dioxide • hydrogen
How are O2, CO2 and H2 collected when they are prepared in the laboratory?
collected over water
Why are O2, CO2 and H2 collected over water?
This is because of their low solubility in water
general trends in the solubility of solids
As temperature increases, the solubility of a solid increases.
general trends in the solubility of liquids
As temperature increases, the solubility of a gas decreases.
method of determining the solubility of a solid
• Weigh a clean, dry boiling tube. • Add some solid (see step 7) and reweigh the boiling tube. • Add 10 cm3 of deionised water to the boiling tube from a pipette (a burette can be used). Using a pipette is an accurate way of measuring a volume of a liquid. Liguids are drawn up (sucked up) into the pipette using a pipette filler. • Put a thermometer in the boiling tube. • Heat the boiling tube in a water bath until all the crystals dissolve. Stir gently using the thermometer. • Allow the solution to cool slowly (while still stirring) and record the temperature when crystals appear. • For the most commonly used solids, between 1g and 5g of the solid is placed in 10 g of water. If no crystallisation was observed in step 6, try again with more solid - and if the solid did not all dissolve on heating then use less solid and try again.
method of determining the solubility of a solid step 1
• Weigh a clean, dry boiling tube.
method of determining the solubility of a solid step 2
Add some solid (see step 7) and reweigh the boiling tube.