Test: JEE Previous Year Questions- Stoichiometry - JEE MCQ

No. of molecules = mass / molecular mass * Na . so according to the formula 2.01*10^23=mass /28 * 6.022*10^23 = mass =2.01*10^23 *28 /6.022 *10^23 = 9.3gm

Mass of 1 mole of compound = 108g.

Let the mass of C in 1 mole of compound = 9x.

mass of H in 1 mole of compound = x

mass of N in 1 mole of compound = 3.5x

therefore total mass = 9x+x+3.5x = 13.5x.

According to the question

13.5x=108

=> x=108/13.5 = 8.

mass of C=9x=72g = 12(6)

mass of H= x= 8g = 1(8)

mass of N=3.5x=28g = 14(2)

molar mass of C,H,N = 12, 1, 14.

therefore there are 6, 8, 2 molecules of C,H,N

MOLECULAR FORMULA = C₆H₈N₂.

560 g of Fe

For 70 g of N
14 g N = 1 mol of N -atom
70 g N = 5 mol of N -atom 

For 20 g of H
1 g H = 1 mol of H.-atom
20 g H = 20 mol of H-atom 

1mole of Mg₃ (PO₄ )₂
=> 3moles of Mg atom + 2 moles of P atom + 8 moles of O atom
8 moles of oxygen atoms are present in = 1mole of Mg₃ (PO₄)₂
0.25mole of oxygen atoms are present in = (1 x 0.25)/8
= 3.125 × 10^–2moles of Mg₃ (PO₄ ) ₂.

Correct Answer :- B

Explanation : 6 moles of HCl reacts with 3 moles of hydrogen.

Hence, 1 mole of HCl will react with 3/6 

= 0.5 moles of hydrogen.

At STP, 1 mole of hydrogen corresponds to 22.4 L.

Hence, 0.5 moles of hydrogen will correspond to 22.4/2 = 11.2L.

Thus, 11.2 L of hydrogen gas at STP is produced for every mole of HCl consumed.