Question

Given,$268 \times {10^{ - x}}$ moles of $Zn{(Fe{S_2})_2}$ can be made from 2 g of Zn, 3 g of Fe and 4 g of S. What is the value of x?

Answer 1

Hint: First find the weight of the compound formed by the given weights of the elements. Then you can find the number of moles of the compounds by using the molecular weight of the compound.

Complete answer:
Here, we need to find the number of moles of the given compound and the specific weights of the respective atoms is given.
- It is given that the sample can be made from 2 g of Zn, 3 g of Fe and 4 g of S.
So, we can say that the compound $Zn{(Fe{S_2})_2}$ formed will have a weight of 2+3+4 = 9 g
Now, we need to find the molecular weight of $Zn{(Fe{S_2})_2}$.
- Molecular weight of $Zn{(Fe{S_2})_2}$ = Atomic weight of Zn + 2(Atomic weight of Fe) + 4(Atomic weight of S)
Molecular weight of $Zn{(Fe{S_2})_2}$ = 65.3 + 2(56) + 4(32) = 241.2 $gmo{l^{ - 1}}$
Now, we know that one mole of any compound or species contains weight equal to its molecular or atomic weight. So, 1 mole of $Zn{(Fe{S_2})_2}$ will contain 241.2 g of weight.
- We can say that if weight $Zn{(Fe{S_2})_2}$ is 241.2 g, then the number of moles is 1.
If weight if $Zn{(Fe{S_2})_2}$ is 9 g, then number of moles = $\dfrac{9}{{241.2}} = 0.0272$
We know that 0.0272 = $272 \times {10^{ - 4}}$ $ \simeq 268 \times {10^{ - 4}}$

Thus, we can say that the value of x is (-4).

Note:
Remember that the atomic weight of Zn is 65.3 $gmo{l^{ - 1}}$ . Atomic weight of Fe and S is $65gmo{l^{ - 1}}$ and $32gmo{l^{ - 1}}$ respectively. Note that molecular weight is the weight of $6.022 \times {10^{23}}$ particles which is equal to the 1 mole.