2.2 Removing Hardness Flashcards
How can we make hard water soft?
Remove the calcium and magnesium ions
How is temporary hard water softened?
Boil the water so the ions form insoluble scale and are no longer in the water
What happens to the hydrogencarbonate ions when temporary hard water is softened?
The hydrogencarbonate ions decompose when heated to form carbonate ions, water and carbon dioxide. The carbonate ions react with calcium ions and magnesium ions in the water to produce precipitates of calcium and magnesium carbonate that are deposited as scale
Write a balanced equation for the reaction of calcium ions with carbonate ions
Ca(2+) (aq) + CO3(2-) (aq) –> CaCO3 (s)
Write a balanced equation for the decomposition of hydrogencarbonate ions
2HCO3(-) (aq) –> CO3(2-) (aq) + H2O (l) + CO2 (g)
What does soft water not contain?
Dissolved salts that react with soap to form scum or scale when it’s heated
What can be added to hard water to precipitate out the calcium and magnesium ions?
Washing soda/sodium carbonate
How does washing powder remove hardness of water?
The sodium carbonate reacts with calcium and magnesium ions in the water to form solid calcium carbonate and magnesium carbonate that cannot react with soap
What is the machine called that softens hard water?
Ion exchange column
What does the ion exchange column contain?
A resin containing sodium or hydrogen ions
What happens when hard water is passed through the resin?
Calcium and magnesium ions become attached to the resin and the sodium or hydrogen ions take their place in the water
Name a disadvantage of boiling temporary hard water to remove hardness
It is expensive so not suitable for large scale
Name an advantage of using washing powder to remove hardness of water
It is much cheaper using washing crystals
