Q3 of 8 Page 42

The oxidation state of oxygen is -2. Find the oxidation state of the other atoms in the following compounds.

1. H2O 2. H2CO3 3. HNO3 4. H3PO4

Note: the sum of oxidation numbers of all elements in a compound is zero.

Consider x is the oxidation number of atoms whose oxidation number is to be found. Oxidation number of oxygen is -2. Applying the above rule-


1. 2x + (-2) = 0 ; x = 1 ; oxidation number of hydrogen is 1.


2. 2(1) + x + 3(-2) = 0 ; x = 4 ; oxidation number of carbon is 4.


3. 1 + x + 3(-2) = 0 ; x = 5 ; oxidation number of nitrogen is 5.


4. 3(1) + x + 4(-2) = 0 ; x = 5 ; oxidation number of phosphorous is 5.


More from this chapter

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1

Complete the table given below and answer the following questions (Symbols used are not true.)


a) Which element in the table is the most stable one? Justify your answer.


b) Which element donates electrons in chemical reaction?


c) Write the chemical formula of the compound formed by combining element S with P.

 2

Examine the following chemical equations and answer the questions. (Hint: Atomic Number Mg=12 Cl=17)

Mg + Cl2→ MgCl2


Mg → Mg2+ + ……


Cl + 1e–→ …….


a) Complete the chemical equations.


b) Which is the cation? Which is the anion?


c) Which type of chemical bond is present in MgCl2?

4

Electronegativity values of some elements are given. Using these values, find whether the following compounds are ionic or covalent.

(Electronegativity of Ca=1.0, O = 3.5, C = 2.5, S = 2.58, H = 2.2, F = 3.98)


Sulphur dioxide (SO2) Water (H2O)


Calcium fluoride (CaF2) Carbon dioxide (CO2)

 5

Some elements and their valences are given.


a) Write the chemical formula of barium chloride.


b) Write the chemical formula of zinc oxide.


c) The chemical formula of calcium oxide is CaO. What is the valency of calcium?