Water Unit 2 Topic 2 Flashcards
How much of the earth is covered in water?
70%
2 chemical tests for water?
Anhydrous copper sulfate - white to blue
Anhydrous cobalt chloride - blue to pink
2 physical tests for water?
Melts at 0c
Boils at 100c
What is hard water?
Water that doesn’t lather easily with soap
What ions cause hard water?
Magnesium and Calcium cations
How is scum formed from hard water & soap?
Calcium ions (water) + stearate (soap) ions to form insoluble calcium stearate (scum)
Does hard water affect detergents?
Example of a detergent?
No
Cilit bang
Word equation for the formation of scum
Ionic equation for the formation of scum
Sodium Stearate + hard water -> Calcium Stearate
2C17H35COONa (aq) + Ca 2+ (aq) -> (C17H35COO)2Ca (s) + Na +
Describe how you would identify whether a sample of water was hard or soft/
10cm3 waer sample. Add 1cm3 soap solution & shake 30 secs. Continue to add soap until permanent lather formed. Record volume of soap needed. More soap = harder water
What is a permanent lather?
Lather lasting more than 30 seconds
How is temporary hard water formed?
Calcium/magnesium hydrogencarbonate in it are caused by limestone reacting with carbonic acid in rainwater.`
What is permanent hard water?
Hard water that can’t be softened by boiling.
Equation for formation of temporary hard water?
Carbonic acid + Calcium Carbonate -> Calcium Hydrogencarbonate
H2CO3 (aq) + CaCO3 (s) -> Ca(HCO3)2 (aq)
How is permanent hard water formed?
Rain water passes over rocks containing calcium compounds (calcium sulphate) which dissolves into water
4 features of hard water areas?
Pot holes
Caverns
Stalagmites (up) & stalactites (down)
Word equation for heating temporary hard water?
Calcium hydrogencarbonate -> CO2 + H20 + Calcium carbonate
Symbol equation for heating temporary hard water?
Ca(HCO3)2 (aq) -> Co2 (g) + H20 (l) + CaCO3 (s)
2 methods to remove permanent hardness?
Washing soda & ion exchange column
Explain how washing soda removes permanent hardness?
Sodium carbonate = washing soda Na2CO3
Sodium carbonate added to water, calcium ions combine with carbonate ions and precipitate out as insoluble calcium carbonate
Word & symbol equation for washing soda + hard water?
Calcium Chloride + Sodium carbonate -> Calcium Carbonate + Sodium Chloride
CaCl2 (aq) + Na2CO3 (aq) -> CaCO3 (s) + 2NaCl (aq)
Explain how an ion exchange column works?
Glass tube filled with resin with sodium ions attached.
Hard water contains calcium ions.
Calcium ions removed & replaced with sodium ions as water flows through. Water is softened.
What is a precipitation reaction?
Ions in 2 solutions react to make an insoluble substance
How is an ion exchange column regenerated/
Pour sodium chloride (salt) solution through. Replaces calcium ions for sodium ions.
Advantages of hard water (4)
Tastes better
Provides calcium ions for bones & teeth
Better for tanning leather
Better for brewing beer
Disadvantages of hard water (4)
Fur & scale in kettles & pipes
Wastes soap, expensive
Dishwasher soap to remove limescale expensive
Produces scum
What is a dessicant?
A substance which absorbs moisture
What is a deliquescent?
A substance that absorbs so much moisture from air that it dissolves in it, forming a solution
Example of dessicant & use?
Silica gel
Leather & electrical goods
Medical use of barium sulphate?
To examine digestive tract in x-rays. Doesn’t allow ray through. Barium toxic but sulfate insoluble & safe. Passes through body without being digested (low solubility)
Fluoridation of drinking water?
Too much = fluorosis (mottled tooth enamel)
Helps bone & teeth strength
