Q3 of 5 Page 211

Find the valency of the underlined element in the given formulae.

i) H2O ii) KCl iii) Al2O3 iv) Fe2O3 v) CH4

i) H2O

Valency of oxygen is 2


Let the valency of oxygen is x


We know that,


Charge on hydrogen is +1


Therefore, 2⨉1 + x = 0


2+x=0


x= -2


As the picture shows,



ii) KCl


Valency of potassium is 1


Let the valency of potassium is x


We know that,


Charge on chlorine is -1


Therefore, x + (-1) = 0


x – 1 =0


x= 1


As the picture shows,



iii) Al2O3


Valency of aluminium is 3


Let the valency of aluminium is x


We know that,


Charge on oxygen is -2


Therefore, 2⨉x + 3⨉(-2) = 0


2x – 6 =0


2x= 6


x =


x = 3


iv) Fe2O3


Valency of iron is 3


Let the valency of iron is x


We know that,


Charge on oxygen is -2


Therefore, 2⨉x + 3⨉(-2) = 0


2x – 6 =0


2x= 6


x =


x = 3


v) CH4


Valency of carbon is 4


Let the valency of carbon is x


We know that,


Charge on hydrogen is +1


Therefore, x+4⨉1 = 0


x+4=0


x= -4


More from this chapter

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1

Water is made up of two elements, hydrogen and oxygen. Water is a liquid, whereas hydrogen and oxygen are gases. Hydrogen catches fire easily. Oxygen helps in burning. Water is used to put off the fire.

From the above information, answer the following questions.


a) What are the elements present in water?


b) In which state do these elements exist?


c) Write the property of hydrogen.


d) Write the property of oxygen.


e) Do the properties of water differ from hydrogen and oxygen?

 2

Using the elements enclosed in the bottle, frame formulae for some compounds.

 4

Write the chemical name of the given formulae.

i) MgO ii) HCl iii) NH3 iv) ZnO v) NaCl

 5

Write the names of the planets (Greek God) after which these elements are named.

a) Plutonium b) Neptunium c) Uranium