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3. ATOMS AND MOLECULES
easy
Calculate the formula unit masses of $Z n O,\, N a_{2} O,\, K_{2} C O_{3}$ given atomic masses of $Zn=65\,u $. $N a=23\,u $, $K=39\,u $, $C=12\,u $ and $O=16\,u $.
A
$4\,u $, $18\,u $ and $24\,u $
B
$81\,u $, $62\,u $ and $138\,u $
C
$36\,u $, $71\,u $ and $108\,u $
D
$12\,u $, $24\,u $ and $36\,u $
Solution
$(i)$ Formula unit mass of $ZnO$ (zinc oxide) $=65+16=81\,u $
$(ii)$ Formula unit mass of $Na_2O$ (sodium oxide) = $(23 \times 2)+(16 \times 1)=46+16=62\,u $
$(iii)$ Formula unit mass of $K_2 CO_3$ (potassium carbonate) $=(39 \times 2)+(12 \times 1)+(16 \times 3)=78+12+48=138\,u $
Standard 9
Science
