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Salt X is mixed with an equal amount of K2Cr2O7 in a test tube and concentrated H2SO4 is added. On heating, red fumes of compound Y are obtained. These red fumes are passed into NaOH solution, which turns yellow due to formation of compound Z. What is the sum of the total number of atoms present in one formula unit each of Y and Z?
- 10
- 12
- 14
- 8
Correct answer: 12
Solution
Salt X = NaCl (or any chloride). Reaction: 4NaCl + K2Cr2O7 + 6H2SO4 -> 4CrO2Cl2 (Y, red fumes) +.... CrO2Cl2 is chromyl chloride (boiling point 117 C, red-orange fuming liquid). CrO2Cl2 + 4NaOH -> Na2CrO4 (Z, yellow) + 2NaCl + 2H2O. Atoms in Y (CrO2Cl2) = 1 + 2 + 2 = 5. Atoms in Z (Na2CrO4) = 2 + 1 + 4 = 7. Total = 12.
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