Water Flashcards
What is hard water
Water in which it is difficult to form a lather with soap. It contains calcium and/or magnesium ions which react with soap to produce scum
What is scum
An insoluble solid formed when the dissolved compounds react with soap
What do soap less detergents do
Do not react with hard water to form scum
When water is in contact with rocks what happens
Some compounds dissolve
When is scale formed
When a type of hard water called temporary hard water is heated an insoluble solid called scale is produced
What caused blockages and reduces the efficiency of heating systems
Scale
What is the difference between scale and scum
Scum is formed when soap reacts with compounds in hard water. Scale is formed when temporary hard water is heated
What is calcium good for
Helping develop strong bones and teeth, reduces the risk of heart disease so hard water is better to drink than soft water
Why does soft water not produce scum
It may contain dissolved substances but I’d doesn’t contain dissolved salts which react with soaps to produce scum
How can hard water be made soft
Removing the dissolved calcium a den magnesium
Why is temporary water softened by heating
When it is heated the calcium and magnesium compounds form insoluble scale and this removes them from the water
Permanent hard water…..
Is not softened by boiling and does not produce scale when heated
What is meant by temporary hard water
Water that is softened by boiling and produced scale when heated
What kind of ions does temporary hard water have
Hydrocarbon ate ions
What do the hydrocarbon ate ions decompose to form
Carbonate ions, water, co2
What does the carbonate ions react with to form a precipitate which removes them from the water
The carbonate ions react with calcium and magnesium ions in the water to produce a precipitate of calcium carbonate and magnesium carbonate that are deposited as scale
Describe the method used to soften either type of water
By precipitating out the ions that cause hardness, this is done by adding washing soda (sodium carbonate). The sodium reacts with calcium and magnesium in the water to form solid calcium carbonate and magnesium carbonate that cannot react with soap
How does an ion exchange column work?
When the hard water passes through the resin calcium and magnesium ions become attached to the resin and sodium or hydrogen ions take their place in the water, these ions do not react with soap
What is the temporary hard water decomposition equation
2HCO3 - (aq) ———-> Co3 2-(aq) + H2O(l) + CO2 (g)
What should drinking water contain
No harmful substances and should have low levels of dissolved salts and microbes
How is water often treated
By sedimentation and filtration to remove solids followed by disinfection to kill microbes (chlorine is often used for this)
What are water filters used for
Improving the taste of water.
How do water filters work
They often contain carbon and an ion exchange resin that removes some soluble substances and silver or another substance to prevent bacterial growth
How is pure water obtained
Distillation,
Why is distillation expensive
which requires a large amount of energy to boil the water and so it expensive
Where must water be from t make it suitable to drink
An appropriate source
What does the hardness of water depend on
Where you live
What is a disadvantage of hard water
Can block and make heating systems less effective
What is an advantage of hard wate f
Has health benefits
If hard water is not suitable for a purpose what can be done
You can treate the water for an alternative supply
What is good about softening hard water
Use less soap, does not produce scum, reduces the effects on heating systems
DisAds of softening water
Reduces health benefits, expensive
What is chlorine good for
Killing microbes
Why is chlorine dangerous
It is poisonous and an produce toxic compounds
Why is fluorine added to toothpaste and water
Prevent tooth decay
Why are some people against adding Florida to water
People should Beatle to choose
What is soft water
water containing no dissolved calcium and/or magnesium so it easily forms a lather with soap
