1. Water Hardness
Review its causes
Identify cations causing hardness
Classify differnet types of harness
Observe its effects â harmful and beneficial
Understand procedures to remove water hardness
2. Title: Hard and Soft Water
Objectives
âą â describe key features of hard and soft water.
âą - explain how to identify hard and soft waters
Starter â What has happened to these kettles and
this bathroom?
17. Water hardness in the UK by region
Where will your kettle last the longest?
Yorkshire
Cheshire
Peak District
Malvern
Somerset
Cornwall
Guildford
LO â to describe key features of
hard and soft water.
- To explain how to identify hard
and soft waters
43. The Water Cycle
Q - Where in this water cycle does our drinking
water come from?
ï Hard water contains dissolved compounds, usually of
calcium or magnesium. The compounds are dissolved when
acidic water comes into contact with rocks.
44. The Water Cycle and water hardness â the
chemistry
Hard water contains dissolved compounds, usually of
calcium or magnesium. The compounds are dissolved when
slightly acidic water comes into contact with rocks.
CaCO3(s) + H2O(l) + CO2(aq) ï Ca2+(aq) 2HCO3
-(aq)
45. Titel: Temporary and Permanent Hard Water
Lernziel
âą to be able to distinguish between temporary hard water and
permanent hard water
âą To be able to explain what happens when we heat temporary hard
water
Starter A â Does furring in kettles occur in all types of water?
B â what is needed for this
reaction?
Calcium ï calcium + carbon
carbonate oxide dioxide
46. Temporary hard water chemistry
this is caused by the presence of CaHCO3 compound â soluble in
water
LO â to be able to distinguish between temporary hard water and permanent hard water
- To be able to explain what happens when we heat temporary hard water
Ca2+(aq) 2HCO3
-(aq) CaCO3(s) + H2O(l) + CO2(g)
heat
(scale)(âhardnessâ)
Permanent hardness is caused by the presence of soluble Ca2+ and Mg2+ ions in water
47. Review â explaining how temporary hard water is
softened by boiling
Choice 1
Explain which ions are
missing from soft water
Choice 2
Explain the symbol
equation for the reaction
of calcium ions with
carbonate to form scale
in full sentences.
Choice 3
Write a balanced symbol
equation for the
reaction of Magnesium
ions with carbonate ions
to form scale
Compulsory
Write definitions for these key words
Permanent hard water
temporary hard water
LO â to be able to distinguish between temporary hard water and permanent hard water
- To be able to explain what happens when we heat temporary hard water
Hinweis der Redaktion
Although soaps are excellent cleansers, they do have disadvantages. As salts of weak acids, they are converted by mineral acids into free fatty acids:
CH3(CH2)16CO2-Na+ + HCl â CH3(CH2)16CO2H + Na+ + Cl-
These fatty acids are less soluble than the sodium or potassium salts and form a precipitate or soap scum. Because of this, soaps are ineffective in acidic water. Also, soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron.
2 CH3(CH2)16CO2-Na+ + Mg2+ â [CH3(CH2)16CO2-]2Mg2+ + 2 Na+
The insoluble salts form bathtub rings, leave films that reduce hair luster, and gray/roughen textiles after repeated washings. Synthetic detergents, however, may be soluble in both acidic and alkaline solutions and don't form insoluble precipitates in hard water. But that is a different story...
