JEE Main 2023 · 10 April · morning · Numerical answer · +4 / −0
In the following reactions, the total number of oxygen atoms in X and Y is ___________.
Na₂O + H₂O → 2X
Cl₂O₇ + H₂O → 2Y
Answer and solution
Answer 5
Solution
Chemistry ma’am · 3 steps
Balance each equation to find one formula unit of X and of Y, then count oxygens in just those two.
- Find X. Na₂O is a basic oxide, so with water it gives a base: Na₂O + H₂O → 2NaOH. The atoms balance (2 Na, 2 O, 2 H on each side), so X is NaOH, with 1 oxygen atom.
- Find Y. Cl₂O₇ is the anhydride of perchloric acid, with Cl in the +7 state. With water it gives Cl₂O₇ + H₂O → 2HClO₄. Count the atoms: 2 Cl, 8 O and 2 H on each side, so Y is HClO₄, with 4 oxygen atoms.
1_(NaOH) + 4_(HClO₄) = 5
- So. The question asks for oxygens in one X and one Y, not in 2X and 2Y. The total is 5.
The common slip: 10. Counting the oxygens in 2X and 2Y, that is all product oxygens, gives 2 + 8 = 10. The question wants one X and one Y.
The idea to keep. A non-metal oxide plus water gives the oxoacid with the same oxidation state. A metal oxide plus water gives the hydroxide. Balance first, then read off one formula unit.
Answer from the NTA final answer key. Solution by PrepWiser.