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SS2: CHEMISTRY - 2ND TERM

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  1. Water & Solution I | Week 1
    10 Topics
    |
    1 Quiz
  2. Water, Solution and Solubility | Week 2 & 3
    9 Topics
    |
    1 Quiz
  3. Air | Week 4
    4 Topics
    |
    1 Quiz
  4. Pollution | Week 5
    6 Topics
    |
    1 Quiz
  5. Rate of Chemical Reaction | Week 6 & 7
    6 Topics
    |
    1 Quiz
  6. Energy and Energy Effect I | Week 8 & 9
    7 Topics
    |
    1 Quiz
  7. Energy and Energy Effect II | Week 10 & 11
    6 Topics
    |
    1 Quiz
  8. Chemical Equilibrium | Week 12
    8 Topics
    |
    1 Quiz

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SS2: CHEMISTRY – 2ND TERM Water & Solution I | Week 1 SS2: Chemistry Theory Questions – Water & Solution
Lesson 1, Topic 10
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SS2: Chemistry Theory Questions – Water & Solution

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Question 1:

(a) (i) Define hard water
(ii) Give one difference between hard and soft water 

(b) State two methods that can be used to remove hardness in a sample of water caused by Ca(HCO3)2

(c) Write an equation for the reaction involved in the removal of temporary hardness of water by
(i) Boiling 
(ii) With slaked lime 

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Question 2:

(a) List two methods of removing both permanent and temporary (total) hardness at the same time 
(b) i. List two advantages and two disadvantages of hard water
ii state the effect of hard water on laundry
(c) Explain the terms stalagmites and stalactites

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Question 3:

(a)  Describe how river water is treated and rendered suitable for human consumption 
(b) Some samples of hard water can be softened easily by boiling, while others require chemical treatment for softening. Justify the statement. Give three chemical methods for removing the hardness of water. Write the respective equation.
(i) Ca(HCO3)2(aq) boil→ CaCO3(s) + H2O(l) + CO2(g)
(ii) Ca(OH)2(aq) + Ca(HCO)2(aq) CaCO3(s) + H2O(l)

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Question 1

(a) (i) Define hard water

Answer:

Hard water is a type of water that contains an appreciable quantity of dissolved minerals (Calcium and Magnesium).

(ii) Give one difference between hard and soft water

Answer:

Hard water contains dissolved minerals (Ca and Mg) while soft water does not

(b) State two methods that can be used to remove hardness in a sample of water caused by Ca(HCO3)2

Answer:

(i) Boiling
(ii) Addition of slaked lime

(c) Write an equation for the reaction involved in the removal of temporary hardness of water by

(i) Boiling 

Answer:

Ca(HCO3)2(aq) \( \overset{boil}{\rightarrow} \) CaCO3(s) + H2O(l) + CO2(g)

(ii) With slaked lime 

Answer:

Ca(OH)2(aq) + Ca(HCO)2(aq) → CaCO3(s) + H2O(l)

Question 1

(a) List two methods of removing both permanent and temporary (total) hardness at the same time

Answer:

(a.i) Distillation
(a.ii) Addition of Washing Soda


(b) i. List two advantages and two disadvantages of hard water

Answer:

Advantages

– It can be supplied in lead pipes as it does not dissolve lead
– It is suitable for use in the beer brewing industry because of its characteristics taste

Disadvantages

– It wastes soap. (because it can’t lather easily).
– It causes fuming of kettles and boilers

ii state the effect of hard water on laundry

Answer: It damages fabric by removing dyestuff


(c) Explain the terms stalagmites and stalactites

Answer:

Stalagmites and stalactites are mineral deposits in a cave. The Ca(HCO3)2 in water becomes decomposed by heat in the cave. This leaves mineral deposits on the floor and on the roof of the cave.

The deposition growing downwards from the roof (stalactite)

The deposition growing upwards from the ground (stalagmite)

Question 3

(a)  Describe how river water is treated and rendered suitable for human consumption

Answer:

(i) It is aerated to remove iron (III) ions and other volatile chemicals like H2S and CO2 and to add oxygen to the water.
(ii) The particles in the water are then coagulated using potash Alum (KAl(SO4)3)
(iii) It is sedimented to remove big particles
(iv) It is passed through sand beds to remove further fire particles
(v) It is disinfected with Chlorine, Fluorine and Iodine are also added.
(vi) CaO is used to maintain the pH
(vii) It is friendly distributed free from germs

(b) Some samples of hard water can be softened easily by boiling, while others require chemical treatment for softening. Justify the statement. Give three chemical methods for removing the hardness of water. Write the respective equation.

Answer:

By Adding Washing Soda
NaCO3(s) + Ca(HCO3)2(aq) → CaCO3 + 2NaHCO3(aq)
NaCO3(aq) + CaSO4(aq)  →  CaCO3 + Na2SO4(aq)
NaCO3(aq) + MgSO4(aq) →  MgCO3 + Na2SO4(aq)

By Adding Caustic Soda
2NaOH + CaSO4(aq) →  Ca(OH)2 + Na2SO4
2NaCOH + MgSO4(aq) →  Mg(OH)2 + Na2SO4

Permutit or Zeoulite

\( \scriptsize \underset{Soluble}{CaSO_{4(aq)}} \: + \: \underset{Permutit}{Na_2P_{(s)}} \rightarrow \underset{Insoluble}{CaP_{(s)}} \: + \: \underset{Soluble}{Na_2SO_{4(aq)}} \)
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