Water Flashcards
What happens when hard water mixes with soap?
The calcium and magnesium ions in the water react with the soap to form scum which is insoluble.
What happens when hard water is heated?
It forms scale (calcium carbonate)
How can hard water reduce the efficiency if heating systems?
When hard water is heated it forms scale which can build up on the inside of pipes, boilers and kettles meaning they’re less efficient as scum cannot conduct the heat very well.
How is hard water form?
Hard water contains lots of calcium and magnesium ions which get into the water from rain falling on rocks (limestone, chalk) which dissolve compounds like magnesium sulfate and calcium sulfate.
What are the advantages of hard water?
Calcium ions are good for healthy teeth and bones.
Reduces risk of developing heart disease
What are the two kinds of hardness in water?
Temporary hardness caused by the hydrogencarbonate ion in calcium hydrogencarbonate.
Permanent hardness caused by dissolved calcium sulfate and magnesium sulfate.
How is temporary hardness removed?
Temporary hardness is removed by boiling. When heated calcium hydrogencarbonate decomposes to form carbonate ions which react to form calcium carbonate and magnesium carbonate which is insoluble. The solid formed is limescale
How are both types of hardness removed?
By adding washing soda(sodium carbonate, Na’2CO’3).
The added carbonate ions react with the calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate.
The ions are no longer dissolved so they can’t make it hard.
How do ion exchange columns work?
It is a cylinder filled with beads of resin containing sodium/hydrogen ions.
The magnesium an calcium are exchanged with the sodium ions meaning the calcium and magnesium ions are left in the resin.
What happens when an ion exchange column runs out of resin?
Run sodium chloride through the column to replenished the resin.
What does water go through in water treatment works?
Water from the reservoir passes through a mesh screen to remove debris like twigs, leaves.
The water then goes into a settlement tank where sand or soil can sink to the bottom and be removed.
Aluminium sulfate is then added to make solids and microbes stick together and fall to the bottom.
The water is then filtered through gravel beds to remove any insoluble solids.
Chlorine is then added to kill bacteria.
What else is added to drinking water in some areas?
Fluorine is added to drinking water in some parts of the country as it helps reduce tooth decay.
What are the disadvantages to adding fluorine or chlorine to drinking water?
Chlorine can react with other natural substances in water to form toxic by products which could cause cancer.
Fluorine can cause cancer and bone problems in humans.
Many think it is unethical as we should have the right to choose if we want it or not.
What should drinking water have low levels of?
Low levels of dissolved salts and microbes.
What does carbon and silver in water filters do?
Carbon removes the chlorine taste and silver discourages bacterial growth on the resin, kills bugs.
Both improving the taste.
