Q2 of 11 Page 94

Explain by writing a word equation.

Hard water gets softened on mixing with a solution of washing soda.

Hard water can be softened by the help of a chemical change. Hard water contains chloride and sulphides of calcium and magnesium in a dissolved state. It can be removed by precipitating out the dissolved salts by adding washing soda. The salts of calcium and magnesium on the addition of washing soda precipitates in its carbonate salts form and hence the water becomes softened. The word equation for the change can be given as:
Calcium Chloride + Sodium Carbonate Calcium carbonate + Sodium chloride
Magnesium Chloride + Sodium carbonate Magnesium carbonate + Sodium chloride


More from this chapter

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1

Complete the statement by filling the gaps using an appropriate term from the terms given in the bracket. (slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign)

a. An ................ is drawn in between the reactants and products while writing the equation for a chemical reaction.


b. Rusting of iron is a ..................... chemical change.


c. The spoiling of food is a chemical change which is recognized from the generation of certain ............ due to it.


d. A colourless solution of calcium hydroxide in a test tube turns ..... on blowing in it through a blow tube for some time.


e. The white particles of baking soda disappear when put in lemon juice. This means that it is a .......... change.


f. Oxygen is a ................. in respiration.


g. Sodium chloride is ........... compound while hydrogen chloride is ......... compound.


h. Electron ......... is complete in each hydrogen in a hydrogen molecule.


i. Chlorine (Cl2) molecule is formed by ............... of electrons between two chlorine atoms.

 2

Explain by writing a word equation.

Respiration is a chemical change

 2

Explain by writing a word equation.

Lime stone powder disappears on adding to dilute hydrochloric acids.

 2

Explain by writing a word equation.

Bubbles are seen on adding lemon juice to baking soda.