Question

Consider the following reaction and based on the reaction answer the questions that follow :
\[\ce{(NH4)2Cr2O7 ->[heat] N2(g) + 4H2O(g) + Cr2O3}\] 
Calculate :
(i) The quantity in moles of (NH₄)₂Cr₂O₇ if 63 gm of (NH₄)₂Cr₂O₇ is heated.
(ii) The quantity in moles of nitrogen formed.
(iii) The volume in litres or dm³ of N₂evolved at STP.
(iv) The mass in grams of Cr₂O₃ formed at the same time
[Atomic masses : H = 1, Cr=52, N=14]

Answer 1

(i) Molecular mass of ammonium dichromate
= 2 (14 + 4) + 104 + 112 = 252g
Number of moles = `"weight"/"Molecular weight"` 
= `63/252` = 0.25 moles

(ii) 252 g of ammonium dichromate gives 22.4 dm³of N₂
63g of ammonium dichromate gives = `[63 xx 22.4]/252` =5.6L
No. of moles = `"Weight"/"Molecular weight"` 
= `5.6/22.4` = 0.25 moles
(iii) 252g of ammonium dichromate gives 22.4dm³ of N₂
63g of ammonium dichromate gives gives `[63 xx 22.4]/252` = 5.6L
(iv) 252g of ammonium dichromate gives 152g of CrO₃.
63g of ammonium dichromate gives `[63 xx 152]/252` = 38g.