Name ______________________________ Class ______________ Date __________
More Practice
Calculate the Mass of a Product
Step-by-Step Practice
1. Calculate the number of grams of Mg3N2 produced by the reaction of 246.5 g of
magnesium with an excess of nitrogen. The balanced equation is:
3Mg(s) + N2(g) → Mg3N3(s)
1. Analyze List the knowns and the unknown.
Knowns
Unknown
mass of Mg = 246.5 g Mg
mass of Mg3N2 = ?
molar mass of Mg = 24.3 g/mol
molar mass of Mg3N2 = 100.9 g/mol
2. Calculate Solve for the unknown.
Identify the steps needed to convert
g Mg → mol Mg → mol Mg3N2 → g Mg3N2
mass of Mg to mass of Mg3N2.
1 mol Mg3 N 2
3 mol Mg
Use the coefficients of Mg3N2 and Mg in the balanced
equation to find the mole ratio.
Start with the known mass of Mg.
Use conversion factors to
calculate the mass of
Mg3N2.
246.5 g Mg 
1 mol Mg
24.3 g Mg

1 mol Mg 3 N 2
3 mol Mg

100.9 g Mg3 N 2
1 mol Mg 3 N 2
 341.2 g Mg3 N3
3. Evaluate Does the
result make sense?
You might expect the mass of Mg3N2 to be about four times the mass of Mg, or about
1000 g, because Mg3N2 has about four times the molar mass of Mg. However, only one
mole of Mg3N2 is produced for every 3 moles of Mg. So a result of about 1/3 of 1000 g
makes sense.
2. Find the number of grams of sodium chloride (NaCl) produced when 82.4 g of aluminum
chloride (AlCl3) reacts with it.
2AlCl3(aq) + 3Na2CO3(aq) → Al2(CO3)3(s) + 6NaCl(aq)
Chemistry Skills and Math Workbook •
Name ______________________________ Class ______________ Date __________
1
Calculate List the knowns and the unknown.
Knowns
Unknown
mass of AlCl3 = _________
mass of Nacl = ?
mole ratio = 6 mol NaCl / ________
molar mass of AlCl3 = _________
molar mass of Nacl = ________
2 Calculate Solve for the unknown.
Identify the steps needed to convert
g AlCl3 

 g NaCl
mass of AlCl3 to mass of NaCl.
6 mol NaCl3
Start with the known mass ofAlCL3.
82.4 g AlCl 3 


Use conversion factors to calculate the
mass of NaCl.

g NaCl
3 Evaluate Does the result make
sense?
For each mole of AlCl3, how many moles of NaCl are produced? ______
The molar mass of NaCl is about what fraction of the molar mass of AlCl3 _______
Is the calculated mass of NaCl close to the mass of AlCl3 × the moles of NaCl and the
molar mass fraction? Explain.
_____________________________________________________________________
On Your Own
3. Crime scene investigators can make fingerprints more visible by spraying them with zinc
chloride (ZnCl2). This compound can be produced by the reaction of zinc with
hydrochloric acid (HCl). How many grams of zinc chloride are produced when 15.4 g of
zinc reacts with HCl? The balanced equation is:
Zn(s) + 2HCl(aq)  H2 ( g )  ZnCl2 (aq)
4. The reaction of aluminum and magnetite (Fe304) produces iron and aluminum oxide
(Al203) a compound used in toothpaste to polish teeth. Write the balanced equation for
this reaction. Then determine how many grams of Al203 are produced by a reaction of
26.3 g of Fe304 with aluminum.
Chemistry Skills and Math Workbook •