Mole to Mass & Mass to Mole

- questions may contain an amount of moles and ask you to determine the mass.
- Converting moles to mass only requires one additional step.


Steps:

1) Write the equations of the given formula
2) Balance the equations

Example:

Zn + HCl = ZnCl2 + H2

Then balance the equation

Zn + 2HCl = ZnCl2 + H2

then let's say the mole od zinc was 3.5, what is the mass of hydrogen?

3.5 mol x

multiply it over what you need over what you have!!

3.5 mol x  1   
                 1

Then you multiply it by the molar mass of the element you need, in this case, you need to find the molar mass of hydrogen. (remember the subscripts)

3.5mol x 1 x   2          =
               1   1 mol

 Multiply the whole equation and you get:

3.5 mol x 1  x   2    = 7 grams of hydrogen
                1    1 mol

Easy right?
Wait, we're not done yet...let's do the reverse.

How many moles are there in barium nitrate are consumed when 2.55 grams of silver chloride completely reacts?

First, remember to write the balanced equation:

Ba(NO3)2 + 2AgCl = BaCl2 + 2AgNO3

You do the reverse now, you use the molar mass of what you have. I repeat, what you have:

2.55 grams x 1 mol    x
                     143.3 g

Then multiply it by what you need over what you have!:

2.55 grams x 1 mol   x    1  =  0.00890 moles
                       143.3 g     2

http://www.youtube.com/watch?v=JIw_BmFZdhI
http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH4104

-Candace Chan