Question 1

A compound composed of only C and H contains 79.88 % C by mass.What is its empirical formula?

Accepted Answer

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Question 2

Chlorine was passed over 1.41 g of heated titanium,and 4.54 g of a chloride-containing compound of Ti was obtained.What is the empirical formula of the chloride-containing compound?

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Question 3

The analysis of an organic compound showed that it contained 0.105 mol of C,0.315 mol of H,and 0.0350 mol of N.Its molecular mass is 59 amu.How many atoms of carbon are there in the empirical formula for the compound,and how many are in the molecular formula?

Accepted Answer

To find the empirical formula, divide the moles of each element by the smallest number of moles: C (0.105/0.0350 = 3), H (0.315/0.0350 = 9), N (0.0350/0.0350 = 1), giving CH3N. The empirical formula mass is approximately 59 amu, matching the molecular mass, so the molecular formula is the same as the empirical formula, with 3 carbon atoms.

Question 4

The empirical formula of styrene is CH; its molar mass is 104.1 g/mol.What is the molecular formula of styrene?

Accepted Answer

The empirical formula mass of CH is 13.01 g/mol. Dividing the molar mass of styrene (104.1 g/mol) by the empirical formula mass (13.01 g/mol) gives approximately 8, indicating the molecular formula is C₈H₈.

Question 5

A given hydrocarbon is burned in the presence of oxygen gas and is converted completely to water and carbon dioxide.The mole ratio of H₂O to CO₂ is 1.125:1.00.The hydrocarbon could be

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Question 6

The analysis of an organic compound showed that it contained 0.630 mol of C,0.0300 mol of H,0.420 mol of O,and 0.210 mol of N.How many nitrogen atoms are there in the empirical formula for this compound?

Accepted Answer

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Question 7

The empirical formula for a group of compounds is CHCl.Lindane,a powerful insecticide,is a member of this group.The molar mass of lindane is 290.8.How many atoms of carbon does a molecule of lindane contain?

Accepted Answer

Since the empirical formula is CHCl, we know that there is one carbon atom in the molecule of lindane. To determine the number of hydrogen and chlorine atoms, we need to consider the molar mass of lindane (290.8 g/mol). If we assume that there are 6 carbon atoms in the molecule, we can calculate the expected molar mass as follows:
Molar mass = (6 x 12.01 g/mol) + (10 x 1.01 g/mol) + (6 x 35.45 g/mol) = 290.16 g/mol
Since the actual molar mass is slightly higher than this value, it is reasonable to assume that there are some additional chlorine atoms in the molecule. However, we cannot assume that there are more than 6 carbon atoms (since this would result in a higher molar mass than observed). Therefore, the only possible answer is D, which corresponds to a molecule of lindane containing 6 carbon atoms.

Question 8

A compound is composed of only C and Cl.It contains 18.42 % C by mass and has a molar mass of 260.76 g/mol.What is its molecular formula?

Accepted Answer

The molar mass of C is 12.01 g/mol, and Cl is 35.45 g/mol. The percentage of C in the compound is 18.42%, which corresponds to approximately 48 g of C in 260.76 g of the compound. This suggests a ratio of 4 C atoms to 6 Cl atoms, giving the molecular formula C₄Cl₆.

Question 9

A compound has a molar mass of 319.9g/mol and contains 30.01 % oxygen atoms by mass.How many oxygen atoms are in each molecule of this compound?

Accepted Answer

The mass of oxygen in the compound is 30.01% of 319.9 g/mol, which is approximately 96.0 g/mol. The molar mass of one oxygen atom is about 16.0 g/mol, so the number of oxygen atoms is 96.0 g/mol divided by 16.0 g/mol, which equals 6.

Question 10

An organic compound that has the empirical formula CHO has a molecular mass of 174 amu.Its molecular formula is

Accepted Answer

The empirical formula CHO has a molar mass of 29 amu (C=12, H=1, O=16). Dividing the molecular mass (174 amu) by the empirical formula mass (29 amu) gives approximately 6, indicating the molecular formula is C6H6O6.

Question 11

A hydrocarbon,subjected to elemental analysis,was found to contain 79.89 % carbon and 20.11 % hydrogen by mass.What is the empirical formula of the hydrocarbon?

Accepted Answer

The empirical formula is determined by dividing the percentage of each element by its atomic mass and then simplifying the ratio. For carbon: 79.89/12.01 ≈ 6.65, and for hydrogen: 20.11/1.008 ≈ 19.95. The simplest ratio is approximately 1:3, giving the empirical formula CH₃.

Question 12

What is the empirical formula of an oxide of nitrogen that contains 25.93 % nitrogen by mass?

Accepted Answer

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Question 13

A 4.94-g sample of an oxide of chromium contains 3.06 g of chromium.Calculate the simplest formula for the compound.

Accepted Answer

First, calculate the mass of oxygen in the sample: 
Mass of oxygen = Mass of the compound - Mass of chromium 
Mass of oxygen = 4.94 g - 3.06 g = 1.88 g

Next, convert the masses to moles: 
Moles of chromium = 3.06 g / 52.0 g/mol = 0.0588 mol 
Moles of oxygen = 1.88 g / 16.0 g/mol = 0.1175 mol

Divide both moles by the smaller value to get the mole ratio: 
Moles of chromium / 0.0588 = 1 
Moles of oxygen / 0.0588 = 2

Round these ratios to the nearest whole number to get the subscripts in the empirical formula: 
CrO2

Reduce the subscripts, if necessary: 
The formula cannot be reduced further, so the empirical formula is CrO2. However, the question asks for the simplest formula, so we can divide both subscripts by 2 to get the simplest formula: 
CrO

Question 14

An organic compound has a molecular mass of 324.2 amu and contains 66.63% carbon by mass.How many carbon atoms are in each molecule of this compound?

Accepted Answer

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Question 15

The empirical formula of butadiene is C₂H₃.An experimental determination of the molar mass of butadiene by a student yields the value of 54 g/mol.What is the molecular formula of butadiene?

Accepted Answer

The empirical formula mass of C₂H₃ is 27 g/mol. The molar mass of butadiene is 54 g/mol, which is twice the empirical formula mass. Therefore, the molecular formula is C₄H₆.

Question 16

A given hydrocarbon is burned in the presence of oxygen gas and is converted completely to carbon dioxide and water.Equal numbers of moles of CO₂ and H₂O are produced.The hydrocarbon could be

Accepted Answer

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Question 17

A compound is composed of only C and H.It contains 92.26 % C.What is its empirical formula?

Accepted Answer

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Question 18

An organic compound has a molar mass of 169.3 g/mol and contains 10.63 % hydrogen atoms by mass.How many hydrogen atoms are in each molecule of this compound?

Accepted Answer

The mass of hydrogen in one mole of the compound is 10.63% of 169.3 g/mol, which equals 18 g/mol. Since the molar mass of hydrogen is approximately 1 g/mol, there are 18 hydrogen atoms in each molecule of the compound.

Question 19

A sample containing 0.400 mol of a compound is composed of 2.41 × 10²³ atoms of sodium,14.19 g of chlorine atoms,and 19.22 g of oxygen atoms.The formula of the compound is

Accepted Answer

The correct answer is A because the ratio of the number of moles of sodium to the number of moles of chlorine to the number of moles of oxygen is 1:1:3, which corresponds to the formula NaClO3.

Question 20

A certain compound has a molar mass of 270 g/mol.Which is a possible empirical formula for this compound?

Accepted Answer

The empirical formula CH₂O has a molar mass of 30 g/mol. Multiplying this by 9 gives 270 g/mol, matching the compound's molar mass.

Quiz 3: Calculations With Chemical Formulas and Equations