Some Basic Concepts of Chemistry - Result Question 19

####19. The number of moles of $KMnO _4$ that will be needed to react with one mole of sulphite ion in acidic solution is

(a) $\frac{2}{5}$

(b) $\frac{3}{5}$

(c) $\frac{4}{5}$

(d) 1

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Solution:

  1. Molarity $=\frac{\text { Moles of solute }}{\text { Volume of solution (L) }}$

Moles of urea $=\frac{120}{60}=2$

Weight of solution $=$ Weight of solvent + Weight of solute

$$ \begin{array}{rlrl} & =1000+120=1120 g \ \Rightarrow & \text { Volume } & =\frac{1120 g}{1.15 g / mL} \times \frac{1}{1000 mL / L}=0.973 L \ \Rightarrow & \text { Molarity } & =\frac{2.000}{0.973}=2.05 M \end{array} $$



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