The slide show includes the following topics: 1. hard water 2. soft water 3. causes of hardness of water 4. types of hardness (temporary and permanent) 5. methods to remove temporary hardness (heating and clarks method) 6. methods to remove permanent hardness (with washing soda, caustic soda and zeolite) 7. Heavy water 8. hygroscopic and deliquescent substances I have made this presentation for grade 9 students.

1. PREPARED BY MISS SALIHA RAIS
CLASS IX
CHEMISTRY

2.  Water containing dissolved impurities of
hydrogen carbonates, chlorides and
sulphates of calcium and magnesium is called
hard water.
 It does not give lather with soap.

3.  Water containing
dissolved impurities
but in small quantities
and easily produces
lather with soap is
called Soft water.

4.  Hard water produces
curds with soap and
affects the cleaning
action of soap.

6.  The rain water on its way to ground,
dissolves carbondioxide gas. This water
while flowing through beds of soil or rocks
containing carbonates react with dissolved
carbondioxide, and form bicarbonates. This
bicarbonate ions cause temporary hardness
in water.
CaCO3 + CO2 + H2O → Ca(HCO3)2
MgCO3 + CO2 + H2O → Mg(HCO3)2

9. TYPES OF
HARDNESS
Temporary
Hardness
Permanent
Hardness

10.  Due to presence of dissolved Calcium
Bicarbonate and Magnesium Bicarbonate.
 These salts are water soluble.
 They can ionize in water.
Ca(HCO3)2 ↔ Ca+2 + 2HCO3
-
Mg(HCO3)2 ↔ Mg+2 + 2HCO3
-

11.  Due to dissolved chlorides and sulphates of
Ca and Mg.
 E.g: CaCl2, MgCl2, CaSO4, MgSO4
 They are soluble in water.
 They can ionize in water.
CaCl2 ↔ Ca+2 + 2Cl-
MgSO4 ↔ Mg+2 + SO4
-2

13. METHODS
TO REMOVE
TEMPORARY
HARDNESS
1. BY
HEATING
2.
CLARK’S
METHOD

14. 1. By heating:
Temporary hardness can be removed by boiling.
Temporary hardness is caused by presence of
Ca(HCO3)2 and Mg(HCO3)2.
on heating they decompose into CaCO3 and MgCO3,
, which are insoluble in water.
Ca(HCO3)2 → CaCO3(ppt) + CO2 + H2O

15. 2. Clark’s Method:
Temporary hardness can also be removed by using
slaked lime Ca(OH)2.
This method is called Clark’s method.
The hard water is treated with slaked lime.
The calcium or magnesium bicarbonates are
converted into their carbonates, which are insoluble
in water.
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3(ppt) + 2H2O

17. METHODS
TO REMOVE
PERMANET
HARDNESS
1. BY USING
WASHING
SODA
(Na2CO3.10H2
O)
2. BY USING
CAUSTIC
SODA
(NaOH)
3. BY USING
ZEOLITE OR
PERMUTIT

18. 1. By using washing soda (Na2CO3.10H2O):
Permanent hardness is caused by dissolved
CaCl2, MgCl2, CaSO4 and MgSO4.
When washing soda is added to permanently hard
water, CaCO3 and MgCO3 are precipitated
out.
CaSO4 + Na2CO3 → CaCO3 + 2NaSO4

19. 2. By using caustic soda:
When NaOH is added in permanent hard water,
Mg(OH)2 is precipitated out.
MgSO4 + 2NaOH → Mg(OH)2 + Na2SO4

20. 3. By using zeolite or permutit:
Permutit- ion exchange resin.
When the hard water is passed through the
resins, the magnesium and calcium ions of
water are exchanged with sodium ions from
resins.
So the hardness is removed and soft water is
drawn out.
CaSO4 + sod-zeolite → Ca-zeolite + Na2SO4

23.  “Heavy water is a compound of oxygen
with heavy hydrogen, i.e. Deuterium. It is
also called deuterium oxide D2O.”
 Abundance: 1 part in 7000 parts of antural
water.
 D2O is 1.1 times heavier than H2O.

24.  Density of D2O (1.104g/cm3) is greater than H2O.
 Low vapour pressure than H2O.
 Melting point: 3.81oC.
 Boiling point: 101.42oC.
 Refractive index of D2O is smaller than H2O.
 Molecular mass: 20a.m.u.

26.  “The substances that absorb moisture on
exposure to air are called Hygroscopic
substances.”
 If the substance is a solid, it will not become
solution, but merely become sticke or moist.
 E.g. Sodium nitrate NaNO3,Copper oxide
CuO, Calcium oxide CaO.
 Uses: used as drying agent in the laboratory
since they have strong affinity to absorb
moisture.

27.  Deliquescent substances: they absorb large
amount of water, and eventually forms a
solution when exposed to air.