Some Basic Concepts of Chemistry - Result Question 89
####27. The compound $YBa _2 Cu _3 O _7$, which shows super conductivity, has copper in oxidation state ………. Assume that the rare earth element yttrium is in its usual +3 oxidation state.
$(1994,1 M)$
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Solution:
- The balanced chemical reaction is
$$ 3 BaCl _2+2 Na _3 PO _4 \longrightarrow Ba _3\left(PO _4\right) _2+6 NaCl $$
In this reaction, 3 moles of $BaCl _2$ combines with 2 moles of $Na _3 PO _4$. Hence, 0.5 mole of of $BaCl _2$ require
$$ \frac{2}{3} \times 0.5=0.33 \text { mole of } Na _3 PO _4 $$
Since, available $Na _3 PO _4(0.2$ mole $)$ is less than required mole $(0.33)$, it is the limiting reactant and would determine the amount of product $Ba _3\left(PO _4\right) _2$.
$\because 2$ moles of $Na _3 PO _4$ gives 1 mole $Ba _3\left(PO _4\right) _2$
$\therefore 0.2$ mole of $Na _3 PO _4$ would give $\frac{1}{2} \times 0.2=0.1$ mole $Ba _3\left(PO _4\right) _2$
