Stoichiometry

is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions.



Stoichiometry Calculations
step 1. Write a balanced equation
step 2. Map the solution
step 3. Calculation


Mole-Mass Calculations
A chemical equation is written in terms of moles of reactants and products. However, in the lab, substances are measured in units of mass. So you will need to translate the mole to mass or mass to mole.


Example
Zn + 2 HCl --> ZnCl2 + H2
a)How many grams of Zn will react with 1.05 moles of HCl?
step 1: Zn + 2 HCl --> ZnCl2 + H2
step 2:   1.05 moles of HCl ------------------------> grams of Zn
                                                   moles of Zn
step 3:  1.05molHCl x 1molZn/2molHCl x 65.4gZn/mole = 34.3g Zn


b) How many moles of HCl are needed to form 6.12 grams of ZnCl2?
step 1:  Zn + 2 HCl --> ZnCl2 + H2
step 2: 6.12 grams of ZnCl2---------------------->moles of HCl
                                                 moles of ZnCl2
step 3: 6.12g ZnCl2 x 1mole/136.4g ZnCl2 x 2mol HCl/1mol ZnCl2 = 0.0897 mol HCl


Mass-Mass Calculations
When you calculate the number of grams of product yielded by a certain mass of reactant.


Example video:
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<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/y3SstUNwEHk" frameborder="0" allowfullscreen></iframe>


Molarity and Stoichiometry
molarity (M) = moles of solute/liter of solution (mole/L)



Example:
How many grams of Cu will be formed when 120mL of 0.3M CuSO4 is reacted with sufficient Zn?
Step 1:  1CuSO4 + 1Zn -------> 1ZnSO4 + 1Cu
Step 2: 120mL of 0.3 M CuSO4-------------------------->grams of Cu
                                             moles CuSO4---> moles Cu
Step 3: 0.12L x 0.3 mol CuSO4/1L x 1mol Cu/1mol CuSO4 x 63.5gCu/mole = 2.29g Cu