C3 = Water Flashcards
How is scum produced?
When the dissolved compounds such as calcium or magnesium in hard water react with soap
How is scale produced?
When temporary hard water is heated
Can permanent hard water produce scale?
No, this is because it cannot be softened to remove the calcium and magnesium compounds unlike temporary hard water
What are the advantages and disadvantages of hard water?
Advantages : Calcium is good for bones and teeth and can reduce the risk of heart disease.
Disadvantages : When it’s heated it produces scale which clogs up pipes and stops appliances working efficiently.
How to remove the hardness from temporary hard water? A.k.a. Softening
When heated,
The hydrogencarbonate ions in temp hard water decompose when heated to produce carbonate ions (and water, co2) which react with the calcium/magnesium and leave a white precipitate behind called scale. Making the water soft.
How can adding washing soda to hard water make it soft?
It brings out the precipitates by using sodium carbonate to react with the calcium/ magnesium to produce solids such as calcium carbonate that doesn’t react with soap
How can an ion-exchange column make hard water soft?
The column is packed with a resin containing sodium or hydrogen ions. When hard water is passed through, the calcium and magnesium attach to the resin and the sodium/hydrogen take their place in the water, which don’t react with soap.
How is water made safe to drink?
Filtered to remove solids
Disinfected to kill microbes (chlorine is usually used)
Why is pure water rarely made?
Uses a lot of energy and so is very expensive
What’s one advantage and one disadvantage of using chlorine to kill microbes in water?
A : Effectively kills microbes so it’s safe for use
D : Poisonous, so must be used at the right concentration
What’s an advantage and a disadvantage of adding fluorine to toothpaste.
A : prevents tooth decay
D : People should have the choice to take fluorine or not
What is the difference between hard and soft water?
Soft water lathers easily with soap, hard water doesn’t
