HARDNESS OF WATER:

QUESTIONS:

1. Multiple choice: choose the most correct answer from the alternatives provided.

  (i) ______ is an example of the substance which causes permanent hardness of water.

     A: Calcium carbonate

     B: Calcium sulphate

     C: Magnesium carbonate

     D: Calcium hydrogen carbonate

   (ii) Washing soda(sodium carbonate) is added to hard water to replace ______ with sodium ions.

     A: chlorine ions

     B: aluminium ions

     C: calcium ions

     D: sulphate ions

   (iii) Boiling is an easy method of removing _______ in water.

          A: temporary hardness

          B: Scum

          C: permanent hardness

          D: ions

   (iv) _____ is an example of a compound that when dissolved in water it causes hardness.

       A: sodium chloride

       B: magnesium hydrogen carbonate

       C: calcium chloride

       D: lead nitrate

   (v) Soap becomes less active in hard water because

        A: it forms insoluble salt of calcium and magnesium

        B: it forms soluble salt with sodium derived from it

        C: it increase coldness of water

        D: it is also hardened by water

   (vi) Boiling temporary hard water

        A: promotes formation of scum

        B: Makes soap to react easily with water in formation of lather.

        C: promotes formation of carbonate to make soft water

        D: remove sulphate ions from water

    (vii) Boiling of permanent hard water may increase hardness of water because

         A: formation of vapour reduce volume of water in a container.

         B: boiling does not form carbonate ions

         C: it forms other substances that make water to be hard.

         D: it produce more sulphate ions because minerals become more soluble.

  (viii) It forms carbonate when added into hard water.

        A: Calcium sulphate

        B: sodium carbonate

        C: magnesium sulphate

        D: calcium hydrogen carbonate.

  (ix) Insoluble salt formed when soap is added into hard water.

       A: sodium chloride

       B: magnesium chloride

       C: Scum

       D: calcium chloride

  (x) One of the following is an advantage of soft water.

       A: form lather easily with soap

       B: prevents water pipes corrosion and addiction of poisonous metal salt into the water.

       C: it costs  more soap.

       D: forms strong shells in aquatic animals.

2. Match items in list A with responses in list B

      List A

(i) calcium sulphate and magnesium sulphate

(ii) Calcium bicarbonate and magnesium bicarbonate

(iii) sodium carbonate

(iv) ions exchanger

(v) soft water

   List  B

A: has hydrogen carbonate ions or sulphate ions.

B: has no sulphate ions or bicarbonate ions.

C: it turns hard water into soft when is added into it.

D: calcium or magnesium ions left in it when permanent hard water passes into it.

E: they cause permanent hardness of water.

F: they temporary hardness of water.

3. What is the meaning of the following terms?

     (i) Soft water

     (ii) hard water

     (iii) scum

4. Differentiate soft water from hard water(three points)

5. Explain, how hardness of water can be determined?

6. Outline three advantages of hard water.

7. Which method can be used to test if water is soft, temporary hard or parmanent hard.

8. Explain how iron exchanger remove hardness of water.

9. Mention two disadvantages of hard water.

10. Amina, Mwanaidi, Godfrey, Ntimizi and Magreth and Ester

    Performed an experiment to determine hardness of water by using soap and the following water sample.

      Water sample A=water from lembeli

                                B=water from mtakuja

                                C=water from kiloleli

                                G=water from ujega

Sample:        VOLUME OF SOAP SOLUTION USED(cm3)

             UntreatedH2O BoiledH2O  H2Opassed through ion exchanger.

    A            12         1.8                1.8

    B            17         17                 1.7

    C            26         20                 1.8

   D            1.6         1.6                 1.6

  (a) Which water sample is hardest? Give reason for your answer.

  (b) Which water sample behave as distilled water? Explain.

  (c) Name a chemical substance that could be that cause of hardness in

       (i) water sample A

       (ii) water sample

  (d)which problems may face people who are using water from lembeli, mtakuja and kjiloleli?

       ANSWERS:

1. (i) B    (vi) C

    (ii) C.   (vii) D

    (iii) A   (viii) B

    (iv) B    (iv) C

    (v) A     (ix) A

2. (i) E   (ii) F  (iii) C  (iv) D  (v) B

3. i) Soft water is water which do not have dissolved minerals of calcium or magnrsium sulphate or hydrogen carbonate.

  ii) Hard water is water which contains dissolved minerals of calcium or magnesium sulphate or hydrogen carbonate.

iii) Scum is insoluble salt formed when water hardness react with soap(sodium derived from the soap)

CaSO4(hardness) + Na stearate(soap)-----> Ca stearate(scum) + Na2SO4

NB.

    Stearate means salt or ester of stearic acid.

4. i) hard water does not form lather easily with soap While soft water forms lather easily with soap.

   ii) Hard water can't remove its hardness by boiling While soft water can be treated by boiling to remove its hardness.

iii) Hard water contains hydrogen carbonate or sulphate of calcium or magnesium While soft water does not contain such kind of mineral salts.

iv) Hard water tastes batter While soft water is tasteless.

5. Hard water determine by observing the following properties.

     a) if it does not form lather easily.

     b) if it leaves scummy deposits on clothing  and utensils.

     c) it it tastes better due to dissolved minerals.

6. Advantages of hard water

     i) it tastes better

   ii) it provides calcium for growth of bones and teeth.

  iii) it helps to form strong shells in some aquatic animals.

  iv) it prevents pipes corrosion and addiction of poisonous metal salts  to water.

7. - Soft water can be used by using soap,  if it forms lather easily without boiling that water is soft.

  -temporary hard water and permanent hard water tested by boiling  and after boiling soap is applied.

    If water forms lather easily after boiling it means that water is temporary hard but if it does not form lather even after boiling that water is permanently hard.

8. Iron exchanger remove hardness of water by passing water in it.  Magnesium or calcium ion attach on the beads or ion exchanger resin by exchanging with weakly attached ions such as sodium ions. Then calcium or magnesium ions left behind in the resin as soft water flows out with sodium.

9. Disadvantages of hard water.

   i) it makes boilers, hot pipes, kettles and other appliances less efficient.

  ii) it needs more soap.

iii) it leaves scummy deposits on clothing and utensils.

10. a) water sample C is hardest, because it remains hard even after boiling.

       b) water sample D behave as distilled water because it use Little volume of soap solution.

           It means that water contains no soluble substances.

      c) (i) Calcium hydrogen carbonate or magnesium hydrogen carbonate.

          (ii) Calcium sulphate or magnesium sulphate

     d) - using more soap during washing

         - destruction of boilers, hot water pipes and kettles.