Question

Data about three gases at STP is given:
(A) $16gC{H}_4$
(B) $11.2LC{O}_2$
(C) $6.022\times {10}^{23}$ molecules of $N{H}_3$
(a) The number $6.022\times {10}^{23}$ is known as .............
(b) Calculate the number of $C{H}_4$ molecules present in 16 g $C{H}_4$.
(c) Arrange $A,B$ and $C$ in the increasing order of their mass in grams.
[given: At mass: $H=1,C=12,N=14,O=16$]

Answer 1

(a) Avogadro's number
(b) The molecular mass of $C{H}_4=1\times 12+4\times 1=16g$
i.e. 16 g $C{H}_4$ means one mole of $C{H}_4$
So, no. of molecules in 1 mole $=1\times 6.022\times {10}^{23}=6.022\times {10}^{23}$ molecules.
(c) A: $16$ g $C{H}_4$
B: $11.2$ L $C{O}_2$ means $22$ g of $C{O}_2$. It is because at STP, one mole of $C{O}_2$ having $22.4$ L volume will have mass $44$ g.
C: $6.022\times {10}^{23}$ molecules of $N{H}_3$, means one mole of $N{H}_3$.
(As one mole of any gas at STP contains $22.4$ L and has $6.022\times {10}^{23}$ molecules)
The gram molecular mass of $N{H}_3=1\times 14+3\times 1=17g$
$\therefore$ The required order is $A,C,B$.