Question

Using Avogadro's Number (6.02*10^23): Calculate the number of molecules in 3.00 moles H2S . Express your answer numerically in molecules.. Calculate the number of moles of Cl atoms in 1.81×10^24 formula units of magnesium chloride,MgCl2 .

Answer 1

`1.81x10^2^4~molecules~of~H_2S`

`3~mol~Cl`

Step-by-step explanation:

For this question we have to take into account that the ratio between moles and molecules:

`1~mol~H_2S~=~6.023x10^2^3~molecules~of~H_2S`

Then, using this ratio we can do the conversion:

`3.00~mol~H_2S(6.023x10^2^3~molecules~of~H_2S)/(1~mol~H_2S)`

`1.81x10^2^4~molecules~of~H_2S`

For the next question we have to keep in mind that the formula units are a synonym for molecules and we have to use two ratios:

`1~mol~MgCl_2=2~mol~Cl`

`1~mol~MgCl_2~=~6.023x10^2^3~molecules~of~MgCl_2`

Using these two ratios:

`1.81x10^2^4~molecules~MgCl_2(1~mol~MgCl_2)/(6.023x10^2^3~molecules~of~MgCl_2)(2~mol~C)/(1~mol~MgCl_2)`

`3~mol~Cl~`

Answer 2

Avagadro's number is just a measurement. One mole is 6.022 X 10^23 of anything - atoms, molecules, marbles... anything.
1) If one mole = 6.022 X 10^23, then 8.00mol of H2S is:
(3.00mol H2S) (6.022 X 10^23 molecules H2S / 1 mol H2S) = 1.8060 X 10^24 molecules H2S.
Rounded to 3 sig figs =1.81 X 10^24 molecules H2S
part2.
This one uses moles in the stoichiometric sense as well as the measurement. One formula unit of MgCl2 contains 1 mole Mg and 2 moles Cl.
First, figure out how many moles of formula units there are.
(1.81 X 10^24 FU's) (1mol MgCl2 / 6.022 X 10^23 FU's) = 3.0056mol MgCl2.

Now, we know that there are 2 moles of Cl in every mole of MgCl2 (2 Cl atoms in every unit of MgCl2). From this we can determine how many moles of Cl atoms there are:
(3.0056mol MgCl2) (2mol Cl atoms / 1mol MgCl2) = 6.0112mol Cl atoms.
Now round to 3 sig figs = 10.0mol Cl atoms