Unit 3: 2 - Hard Water Flashcards
What does hard water produce when exposed to soap? Why?
Scum. Metal ions in the water react with the soap to make scum.
What water lathers easily with soap?
Soft
Which ions make water hard?
Calcium and Magnesium ions.
Where do the ions in hard water come from?
The ground as it filters through. Different areas have different minerals in the ground.
How is scale formed?
By heating a certain type of hard water.
Why is scale a problem?
It is insoluble and it reduces the efficiency of heating systems. It also causes blockages.
Give some health benefits of hard water.
- Good calcium content for teeth and bones
- Calcium may reduce the risk of heart disease.
Give an industrial benefit of hard water.
Some brewers prefer the taste.
Give the 2 types of hard water.
Temporary hard water and Permanent hard water.
Which type of hard water causes scale?
Temporary hard water.
Which water is not softened by boiling?
Permanent hard water.
How is temporary hard water softened by heating?
It contains hydrogencarbonate ions, HCO3 (aq). These ions decompose when heated to produce carbonate ions, water and CO2.
Give a symbol and word equation of temporary hard water being softened by heating.
2HCO3- (aq) –> CO3 2- (aq) + H2O (l) + CO2 (g)
Hydrogrencarbonate –> Carbonate ions + Water + Carbon dioxide.
Give a method of softening either type of hard water. (precip)
Precipitating out the ions which cause hardness, using washing soda.
What is washing soda?
Sodium carbonate
How does washing soda soften water?
It reacts with the calcium ions and magnesium ions in the water to form solid calcium carbonate and magnesium carbonate which can’t react with soap.
Give a method of softening either type of hard water. (ion)
Using an ion-exchange column. This is packed with resin containing sodium or hydrogen ions. When hard water is passed through, Ca+ and Mg+ ions attach to the resin and sodium and hydrogen ions take their place in the water. H+ and Na+ ions don’t react with soap.
Name a substance used to treat water to make it safe for drinking.
Adding chlorine.
What can be used to improve the taste of water?
A filter containing carbon and an ion-exchange resin, which will remove silver and stop bacterial growth.
How can we make water completely pure?
Distillation, which requires lots of energy to boil the water.
What is a problem with adding chlorine to water?
Chlorine is poisonous and can produce other toxic compounds.
What is added to water in some places to help reduce tooth decay?
Flouride ions.
