Chapter 03 Atoms and Molecules Questions-03
Questions
1. Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
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Answer
(i) $Na_2 O$
(ii) $NH_4 Cl$
(iii) $Na_2 SO_4$
(iv) $Mg(OH)_2$
2. Write down the names of compounds represented by the following formulae:
(i) $Al_2(SO_4)_3$
(ii) $CaCl_2$
(iii) $K_2 SO_4$
(iv) $KNO_3$
(v) $CaCO_3$.
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Answer
(i) Aluminium sulphate
(ii) Calcium chloride
(iii) Potassium sulphate
(iv) Potassium nitrate
(v) Calcium carbonate
3. What is meant by the term chemical formula?
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Answer
Chemical formula of a compound (or element) is the symbolic representation of its composition. It represents
(i) The number and kind of atoms present per molecule of the compound,
(ii) One mole of the compound,
(iii) Molar mass of the compound.
4. How many atoms are present in a
(i) $H_2 S$ molecule and
(ii) $PO_4^{3-}$ ion?
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Answer
(i) 2 atom of hydrogen +1 atom of sulphur
$ =\text{ three (3) atoms (in a H2S molecule). } $
(ii) 1 atom of phosphorus +4 atoms of oxygen
$ =\text{ five (5) atoms (in aPO43-ion). } $
