Molar Ratios and Mass Relationships in Chemical Equations
H 209
Everett Community College Tutoring Center
Student Support Services Program
Given the reaction: CaCl2 (
aq
) + Na2C2O4 (
aq
) CaC2O4 (
s
) + NaCl (
aq
)
a) If 0.043g of oxygen was produced, how many grams of chlorine reacted?
b) How many moles of CaCl2 reacted?
c) How many moles of NaCl were produced if 4.39g of Na2C2O4 reacted?
STEP 1: Make sure the equation is balanced!
The equation is not balanced. Adding a 2 in front of NaCl in the products yields:
CaCl2 (
aq
) + Na2C2O4 (
aq
) CaC2O4 (
s
) + 2 NaCl (
aq
)
Ca
1
1
Ca
Cl
2
2 1
Cl
Na
2
2 1
Na
C2O4
1
1
C2O4
Now the equation has equal numbers of each atom in both reactants and products.
a) If 0.043g of oxygen was produced, how many grams of chlorine reacted?
STEP 2: Set up the units going from what we have to what we want.
0.043 g O = ? g Cl
what we
have
what we
want
g O
g O
mole O
mole O
mole CaC2O4
mole CaC2O4
mole CaCl2
mole CaCl2
mole Cl
mole Cl
g Cl
Cancel the units until the desired unit is the only one left.
STEP 3: Calculate any molar masses (formula weights) needed and fill in the numbers using the
balanced equation to find the molar ratios.
0.043 g O
16.00 g O
1 mole O
4 mole O
1 mole CaC2O4
1 mole CaC2O4
1 mole CaCl2
1 mole CaCl2
2 mole Cl
1 mole Cl
35.45 g Cl = 0.048 g Cl
molar mass molar ratio molar massmolar ratiomolar ratio
