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)