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NEET · Chemistry · STD 12 -1. Solution and colligative properties

5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution?

  1. A The solution shows positive deviation.
  2. B The solution shows negative deviation.
  3. C The solution is ideal.
  4. D The solution has volume greater than the sum of individual volumes.
Verified Solution

Answer & Solution

Correct Answer

(B) The solution shows negative deviation.

Step-by-step Solution

Detailed explanation

\(\begin{array}{cc}X & Y \\ n_x=5 & n_y=10 \\ P_x^0=63 & P_y^0=78\end{array}\)
\(P_{s(\text { calc. })}=P_x^0 x_x+P_y^0 X_y \)
\( =\frac{63 \times 5}{15}+78 \times \frac{10}{15} \)
\( =21+52 \)
\( =73 \)
\( P_{s(\text { obs. })}=70 \)
\( P_{s(\text { obs. })}< P_{s(\text { calc. })} \)
\( \text {-ve deviation}\)