WORKSHEET- STOICHIOMETRY AND CHEMICAL FORMULA CALCUATIONS
SET A: (Time required, 1 hour)
1. A compound with the formula, BxH20O3, contains 36.14 % by mass oxygen. What is the
value of the integer, x ? 1) Ans: x = 6
2. A mixture of cobalt(II) oxide and cobalt(III) oxide contains 32.50 % by mass cobalt (II)
oxide. What is the total number of oxide ions in a 122 g of the mixture?
24
2) Ans: 1.22 x 10 oxide ions
3. A sulfur containing compound is treated chemically to convert all its sulfur into barium
sulfate. A 8.19 mg sample of the compound gave 5.46 mg barium sulfate.
a) What is the percentage of sulfur in the compound? 3a) Ans: 9.18 % S
b) If there is one sulfur atom in the molecule, what is the molar mass of the compound ?
3b) Ans: 349 g/mole
4. An alloy of Co, Rh and Mn contains these elements in the atomic ratio of 2 : 5 : 2 ,
21
respectively. What is the mass of a sample of this alloy containing a total of 8.75 x 10 atoms ?
4) Ans: 1.20 g
5. The percent of aluminum in the compound, Al2X3, is 18.56 %. What is the molar mass of
element X ?
5) Ans:79.00 g/mole
6. 3.9104 g sample of a compound made of carbon, hydrogen, nitrogen, and oxygen is
burned completely. 3.820 g CO2 and 3.125 g H2O are produced.
Analysis of nitrogen showed that the compound contains 46.62 % by mass nitrogen. The molar
mass of the compound is about 170 + 15 g/mole.
a) Calculate the empirical formula of the compound. 6a) Ans: C2H8N3O
b) What is the molecular formula of the compound? 6b) Ans: C4H16N6O2
7. 169 g FeCr2O4, 298 g K2CO3 and an excess of O2 (g) are sealed in a reaction vessel and
allowed to react at high temperature. The amount of K2CrO4 obtained is 194 g. Calculate the
percent yield of K2CrO4.
4 FeCr2O4 + 8 K2CO3 + 7 O2 8 K2CrO4 + 2 Fe2O3 + 8 CO2
( Molar mass: FeCr2O4 = 223.84, K2CO3=138.21, K2CrO4 =194.19 g/mole )
7) Ans: 66.2 %
SET B: (time required, 1 hour)
1. Excess amount of HCl is added to a mixture of CaCO3 and K2CO3. The mixture reacted
completely.
CaCO3 + 2 HCl CaCl2 + H2O + CO2
K2CO3 + 2 HCl 2 KCl + H2O + CO2
4.48 g CO2 and 3.57 g KCl are produced along with some CaCl2 and H2O. Calculate the mass of
the mixture.
1) Ans: 11.10 g mixture
2. The percent of manganese in the compound, Mn5X2, is 42.10 %. What is the molar mass
of element X ?
2) Ans: 186.9 g/mole
3. A mixture of potassium phosphate and potassium nitrate contains 36.55 % by mass
potassium nitrate. What is the total number of potassium ions in 83.5 g mixture?
23
3) Ans: 6.32 x 10 ions
4. A carbon containing compound was treated chemically to convert all its carbon into
2
SrCO3. A 31.23 g sample of the compound gave 1.203 x 10 g SrCO3.
a) What is the percentage of carbon in the compound? 4a) 31.3 % C
b) If there are three carbon atoms in a molecule of the compound, what is the molar mass of the
compound?
4b) Ans: 114.8 g/mole
5. 80.0 g KClO3 are mixed with 59.5 g HCl and allowed to react according to the equation:
2 KClO3 + 4 HCl 2 KCl + 2 ClO2 + Cl2 + 2 H2O
( Molar mass: KCl = 74.6, KClO3 = 122.6, HCl = 36.5, ClO2= 67.5, Cl2 = 71.0, H2O = 18.0 g/mole)
The amount of Cl2 produced is 18.7 g. Calculate the percent yield of Cl2.
5) Ans: 80.6 %
6. 28.50 g sample of a compound of carbon, sulfur, hydrogen, and oxygen is burned. 35.25
g CO2 and 14.65 g SO2 are produced. Analysis of hydrogen showed that the compound contains
8.514 % hydrogen by mass. The molar mass of the compound is 500 + 5 g/mole.
a) Calculate the empirical formula of the compound. 6a) Ans:C7H21S2O5
b) What is the molecular formula of the compound? 6b) Ans: C14H42S4O10
SET C:
1. A phosphorus containing compound is treated chemically to convert all its phosphorus
into Mg3(PO4)2. A 7.88 g sample of the compound gave 4.75 g Mg3(PO4)2. What is the
percentage by mass of phosphorus in the compound?
1) Ans: 14.2 % P
2. The percent by mass of boron in the compound, B7X3, is 42.1 % . What is the molar
mass of X ?
2) Ans: 34.7 g/mole
3. A 39.11 g sample of a compound containing Cr is analyzed to show the presence of 86.22
% Cr. It is found that there are five chromium atoms per molecule of the compound. What is the
molar mass of the compound?
3) Ans: 301.6 g/mole
4. The percent by mass of silicon in the compound, Si8X3, is 72.33 %. What is the molar
mass of element X ?
4) ans: 28.65 g/mole
5. Consider the following reaction:
3 CaBr2 + 2 Na3PO4 Ca3(PO4)2 + 6 NaBr
A reaction mixture contained 22.44 g of CaBr2 and 16.85 g Na3PO4.
( Molar mass: CaBr2 = 199.9, Na3PO4 = 164.0, Ca3(PO4)2 = 207.2, NaBr = 102.9 g/mole)
a. What is the mass of Ca3(PO4)2 produced after the reaction is complete ?
6a) Ans: 7.753 g
b. How many grams of each reactant is left after the reaction is complete?
6b) Ans: zero grams of CaBr2
-2- and 4.58 g Na3PO4
