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AIIMS 2008
Exam
AIIMS
Year
2008
Subject
Chemistry
Chapter
p Block Elements (Group 15, 16, 17 & 18)

AIIMS 2008 · Chemistry · p Block Elements (Group 15, 16, 17 & 18)

What is the correct relationship between the (pH) of isomolar...

What is the correct relationship between the (\mathrm{pH}) of isomolar solutions of sodium oxide (\left(\mathrm{pH}_1\right)), sodium sulphide (\left(\mathrm{pH}_2\right)), sodium selenide (\left(\mathrm{pH}_3\right)) and sodium telluride (\left(\mathrm{pH}_4\right)) ?

Options

  1. A(\mathrm{pH}_1>\mathrm{pH}_2=\mathrm{pH}_3=\mathrm{pH}_4)
  2. B(\mathrm{pH}_1 < \mathrm{pH}_2 < \mathrm{pH}_3 < \mathrm{pH}_4)
  3. C(\mathrm{pH}_1 < \mathrm{pH}_2>\mathrm{pH}_3 < \mathrm{pH}_4)
  4. D(\mathrm{pH}_1>\mathrm{pH}_2>\mathrm{pH}_3>\mathrm{pH}_4).

Correct answer

D. (\mathrm{pH}_1>\mathrm{pH}_2>\mathrm{pH}_3>\mathrm{pH}_4).

Step-by-step solution

 I Na2O+H2O→2NaOH II Na2 S+H2O→2NaOH+H2 S III Na2Se+H2O→2NaOH+H2Se IV Na2Te+H2O→2NaOH+H2Te\begin{array}{ll}\text{ I } & \mathrm{Na}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaOH} \\ \text{ II } & \mathrm{Na}_2 \mathrm{~S}+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{~S} \\ \text{ III } & \mathrm{Na}_2 \mathrm{Se}+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{Se} \\ \text{ IV } & \mathrm{Na}_2 \mathrm{Te}+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{Te}\end{array} I will have the highest pH\mathrm{pH}. Among H2 S,H2Se\mathrm{H}_2 \mathrm{~S}, \mathrm{H}_2 \mathrm{Se}, H2\mathrm{H}_2 Te acidity goes on increasing on going down the group as bond length increases on increasing size of central atom. So, pH4<pH3<pH2\mathrm{pH}_4 < \mathrm{pH}_3 < \mathrm{pH}_2 Overall order is pH1>pH2>pH3>pH4\mathrm{pH}_1>\mathrm{pH}_2>\mathrm{pH}_3>\mathrm{pH}_4
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