Mole (unit)?

Question

how many molecules in 10 grams of Cl2, PCl5, HNO3, S04,H2O2, C3H8 and C2H5OH

how do u work it out

and how do u calculate the mass of one atom of zinc gold and helium

Answer 1

Last one first.  Since the average atomic mass is the mass of a mole of molecules, you can divide the average atomic mass by Avogadro's number to the average mass of a single atom.

For example, the average atomic mass is 55.845 g/mol

Divide by Avogadro's number, 6.022 x 10^23

And get the average mass of a single atom of iron: 9.273 x 10^-23 grams

For the first part of your question you must compute the molar mass of each of the compounds and then use a conversion factor to calculate the number of molecules:  The conversion factor is constructed from the premise that a mole of particles which is an Avogadro's number of particles has a mass equal to the molar mass.

10.0 grams Cl2 x (6.022 x 10^23 molecules / 71.0 g Cl2) = 8.48 x 10^22 molecules Cl2

10.0 grams PCl5 x (6.022 x 10^23 molecules / 208.5 g PCl5) = 2.89 x 10^22 molecules PCl5

10.0 grams HNO3 x (6.022 x 10^23 molecules / 63.0 g HNO3) = 9.56 x 10^22 molecules HNO3

Get the idea?  The answers to the rest are below, but you have to supply the setups.

SO4^2- -- 2.27 x 10^22 molecules

H2O2 -- 1.17 x 10^22 molecules

C3H8 -- 1.37 x 10^23 molecules

C2H5OH - 1.31 x 10^23 molecules

Answer 2

1) number of molecules in a certain compound

formula:    mass (g)  

      MM

***but first before you use this formula, you should know each of the compound’s Molar Mass (MM). here’s how: (also, you should have your periodic table with you…)

        2) Molar Mass

Formula: MM = (atomic weight) (subscript included**) + (atomic weight.) (subscript included**)…

**sorry. I forgot what’s the right term for it….

Its unit is   g/mol.

Example:

> MM:    H2O   H = 1 (2)                        O = 16 (1)  

         18 g/mol

                                    then add (the one u'l multiply with 1 is how many Hydrogen are there in the compound)

*so the MM of H2O is 18 g/mol. We’ll use this for finding its number of molecules.

> Number of Molecules: H2O

Mass is given (e.g.)  10 grams

           H2O =   10g / 18g/mol   = 0.55566 mol   (divide these and mol is left: unit)

LET’S TRY:

1) how many molecules are there in 10 g of Cl2?

First, we’ll find their MM.

MM = Cl2      Cl = 35 (2) = 70 g/mol



Second, we’ll now use the formula for finding its (how many) molecules.

No. of molecules in Cl2 =       10g        (divide these

                                   70 g/mol      and mol is

                                                              0.1428 mol    left as the unit)

2) how many molecules are there in 10g of PCl5?

First, we’ll find their MM.

MM = PCl5 P = 31 (1)        (add)

Cl = 35 (5)

       206 g/mol

Second, we’ll now use the formula for finding its (how many) molecules.

No. of molecules in PCl5 =  10g/ 206g/mol    (divide, mol is left for the unit)

2) (I think you know now and can follow and can answer the others??)

AND I THINK FOR THE CALCULATION OF THE MASS OF ONE ATOM A CERTAIN ELEMENT??

In grams of a mole of (element).



Formula: no. of mole =    g / MM

For GOLD

MM = Au = 197 (1) = 197 g/mol



No. of mole =      1 g / 197g/mol = 0.005076 mol (g is cancelled leaving you mol as the unit)



g = (no. of mole) (MM)

   = (0.00507614213197 mol) (197 g/mol)  

  = 0.99999999999809 grams

NOW, ALSO THE SAME WITH THE OTHER ELEMENTS…

  \m/