Question 1
What is the empirical formula of a compound containing 40.0% sulfur and 60.0% oxygen by mass?
Ans: SO3
Question 2
A compound is found to contain 23.3% magnesium, 30.7% sulfur, and 46.0% oxygen. What is the empirical formula of this compound?
Ans: MgSO3
Question 3
What is the empirical formula for a compound containing 38.8% carbon, 16.2% hydrogen, and 45.1% nitrogen?
Ans: CH5N
Question 4
A sample of an oxide of nitrogen is found to contain 30.4% nitrogen. What is its empirical formula?
Ans: NO2
Question 5
A sample of an oxide of arsenic is found to contain 75.74% arsenic. What is its empirical formula?
Ans: As2O3
Question 6
What is the empirical formula for a compound containing 26.57% potassium, 35.36% chromium, and 38.07% oxygen?
Ans: K2Cr2O7
Question 7
A compound with an empirical formula of C2OH4 and a molar mass of 88. What is the molecular formula of this compound?
Ans: C4O2H8
Question 8
A compound with an empirical formula of C4H4O and a molar mass of 136. What is the molecular formula of this compound?
Ans: C8O2H8
Question 9
A compound that is 9.4% C, 14.9% F, 62.7% Br, and 6.3% Oxygen has a molar mass of 237.8. What is the molecular formula of this compound?
Ans: C2F2Br2O
Question 10
A carbohydrate on analysis gave the following composition: carbon = 40.0%; hydrogen = 6.71%, and oxygen made up the rest. Calculate the molecular formula of this organic compound which has a molecular mass of 181.
Ans: C6H12O6
Question 11
Nicotine is mainly responsible for the addictive nature of cigarettes. A typical cigarette contains 12.33 mg C, 1.45 mg H, and 2.87 mg N. If the molar mass of nicotine is 162 g/mol, what is the molecular formula of nicotine?
Ans: C10H14N2
Question 12
An unknown compound was found to have a percent composition as follows: 47.0 % potassium, 14.5 % carbon, and 38.5 % oxygen. What is its empirical formula? If the true molar mass of the compound is 166.22 g/mol, what is its molecular formula?
Ans: KCO2, K2C2O4
Question 13
NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O. Calculate the empirical formula of NutraSweet and find the molecular formula. (The molar mass of NutraSweet is 294.30 g/mol)
Ans: C14H18N2O5
Question 14
What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29% Oxygen? If the molar mass is 110 g/mol, what is the molecular formula?
Ans: C3H3O, C6H6O2
Question 15
Caffeine has the following percent composition: 49.47% C, 5.201% H, 28.84% N, and 16.48% O If the molecular mass of caffeine is 194.2 amu, what is it’s molecular formula?
Ans: C8H10N4O2
Question 16
The combustion of 3.42 g of a compound is known to contain only nitrogen and hydrogen gave 9.82 g of NO2 and 3.85 g of water. Determine the empirical formula of this compound.
Ans: NH2
Question 17
A 2.52 g sample of a compound containing carbon, hydrogen, nitrogen, oxygen, and sulfur was burned in excess oxygen gas to yield 4.36 grams of CO2 and 0.892 grams of H2O as the only carbon and hydrogen products respectively. Another sample of the same compound of mass 4.14 g yielded 2.60 g of SO3 as the only sulfur containing product. A third sample of mass 5.66 g was burned under different conditions to yield 2.80 g of HNO3 as the only nitrogen containing product. Determine the empirical formula of the compound.
Ans: C5H5NOS
Question 18
A compound with a known molecular weight (146.99 g/mol) that contains only C, H, and Cl was studied by combustion analysis. When a 0.367 g sample was combusted, 0.659 g of CO2 and 0.0892 g of H2O formed. What are the empirical and molecular formulas?
Ans: C6H4Cl2
Question 19
A 6.20-g sample of an unknown compound containing only C, H, and O combusts in an oxygen rich environment. When the products have cooled to 20.0 °C at 1 bar, there are 8.09 L of CO2 and 3.99 mL of H2O. The density of water at 20.0 °C is 0.998 g/mL.
Ans: C9H12O3