Mass Mass
Ch 8 Blue Book
Mass-Mass problems are done when
we want to find the amount of a
compound made from a known
amount of another compound.
Stoichiometry
Example
 Zinc metal and hydrochloric acid react to
form zinc chloride and hydrogen gas. How
many grams of H2 are made from 10.0 g HCl?
 Step 1: Write out and balance the chemical
equation.
Zn + 2HCl  ZnCl2 + H2
Step 1.5 – identify your known and unknown,
draw an arrow going from your known amount
to your unknown amount.
Step 2: Convert grams of given  mols
Step 3: Determine mole to mole ratio from
balanced equation & convert moles of given to
moles of required (unknown amt. you are trying to
find)
Step 4: Convert moles of required (unknown)
grams
 Zinc metal and hydrochloric acid react to form
zinc chloride and hydrogen gas. How many
grams of H2 are made from 10.0 g HCl?
Zn + 2HCl  ZnCl2 + H2
Answer: 0.27 g H2
Example
 Calculate the grams of NaOH required to
produce 15.0 grams of Na2SO4 by the
neutralization of NaOH with excess H2SO4.
Step 1: Write & Balance Equation
Step 1.5: I.D. known & unknown
Step 2: mass of known  mols of known
Step 3: mols of known  mols of unknown
(Stoichiometric Ratio)
Step 4: mols of unkown  mass of unknown
8.45 g NaOH
Example
Washing soda (sodium carbonate decahydrate)
is a hydrated compound used for washing, water
softening and bleaching. If a sample of sodium
carbonate decahydrate has a mass of 20.0
grams and 10.0% of this 20.0 gram sample is
inert, what mass of sodium carbonate will be left
when the material is heated to drive off the water
of hydration?
6.67 g Na2CO3
HW Assignment
 #1-8
 #9-16
Due 4/8 pg. 79
Due 4/10 pgs. 82-83