Question 1

A compound containing bromine and fluorine used in the production of UF₆ is 58.37% Br by mass.What is the empirical formula for the compound?

Accepted Answer

Assuming a 100 g sample of the compound, it contains 58.37 g Br and 41.63 g F. 
Converting to moles: 
Br: 58.37 g / 79.904 g/mol = 0.73 mol Br 
F: 41.63 g / 18.998 g/mol = 2.19 mol F 
Dividing by the smaller number of moles (0.73): 
Br: 0.73 mol / 0.73 mol = 1 
F: 2.19 mol / 0.73 mol = 3 
The empirical formula is therefore BrF3, which corresponds to choice C.

Question 2

Ibuprofen is 75.69% C,8.80% H,and 15.51% O by mass.What is its empirical formula?

Accepted Answer

The answer of Ibuprofen is 75.69% C,8.80% H,and 15.51% O...

Question 3

A compound known to contain platinum,nitrogen,and hydrogen was analyzed and found to contain 74.1% Pt and 21.3% N; the remainder was hydrogen.What is the empirical formula for the compound?

Accepted Answer

To find the empirical formula, calculate the moles of each element based on their percentages and atomic masses. For Pt (195.08 g/mol), N (14.01 g/mol), and H (1.008 g/mol): Pt: 74.1% / 195.08 = 0.38 moles, N: 21.3% / 14.01 = 1.52 moles, H: 100% - 74.1% - 21.3% = 4.6% / 1.008 = 4.56 moles. The ratio of Pt:N:H is approximately 1:4:12, making the empirical formula PtN4H12.

Question 4

Which of the following does NOT share the same empirical formula as the others?

Accepted Answer

The answer of Which of the following does NOT share...

Question 5

A 2.00 g sample of methamphetamine was found to contain 1.61 g C,0.203 g H,and 0.188 g N.What is its empirical formula?

Accepted Answer

The answer of A 2.00 g sample of methamphetamine was...

Question 6

Alkanes share a general chemical formula of C_nH₂_n₊₂.What is n of an alkane with a molar mass in the range of 125-130 g/mol?

Accepted Answer

The molar mass range of 125-130 g/mol corresponds to an alkane with 9 carbon atoms. This can be determined by calculating the molar mass of C9H20, the alkane with the closest molar mass range to 125-130 g/mol. C9H20 has a molar mass of approximately 128 g/mol, so n in the general chemical formula C_nH₂_n₊₂ must be equal to 9. Therefore, the answer is B.

Question 7

When are an empirical formula and a molecular formula the same?

Accepted Answer

The molecular formula is a multiple of the empirical formula, so if the mass of the empirical formula unit is equal to the molecular mass, then the empirical formula and molecular formula must be the same. This situation occurs when the empirical formula represents the actual composition of the compound and there are no subscripts that can be reduced further.

Question 8

A hydrocarbon is found to be 85.63% C by mass.What is its empirical formula?

Accepted Answer

The answer of A hydrocarbon is found to be 85.63%...

Question 9

Metallic copper can be obtained from the mineral chalcocite (Cu₂S).What is the mass percent of copper in chalcocite?

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The answer of Metallic copper can be obtained from the...

Question 10

Paris green is a highly toxic emerald green compound with the formula Cu(C₂H₃O₂)₂.3Cu(AsO₂)₂.What is its percent by mass arsenic?

Accepted Answer

The answer of Paris green is a highly toxic emerald...

Question 11

Hydroxylamine contains 42.41% N and 9.15% H by mass,with the remainder being oxygen.Determine its empirical formula.

Accepted Answer

To find the empirical formula, we calculate the moles of each element based on their given mass percentages and atomic masses. For nitrogen (N) with an atomic mass of approximately 14 g/mol, 42.41% by mass corresponds to 42.41/14 = 3.03 moles. For hydrogen (H) with an atomic mass of approximately 1 g/mol, 9.15% by mass corresponds to 9.15/1 = 9.15 moles. The remainder is oxygen (O), which makes up 100 - 42.41 - 9.15 = 48.44% by mass. With an atomic mass of approximately 16 g/mol, this corresponds to 48.44/16 = 3.03 moles. The ratio of N:H:O is thus approximately 1:3:1, leading to the empirical formula NH3O.

Question 12

The empirical formula for buckminsterfullerene is C₁,and its molar mass is 720.6 g/mol.What is its molecular formula?

Accepted Answer

The answer of The empirical formula for buckminsterfullerene is C₁,and...

Question 13

Putrescine,a foul-smelling compound produced by decaying tissue,has the empirical formula C₂H₆N,and its molecular mass is found to be between 87 and 90 amu.How many empirical units are in the actual molecular formula?

Accepted Answer

The empirical formula mass of C2H6N is 58 amu (2*12 for C + 6*1 for H + 14 for N). The molecular mass is between 87 and 90 amu, which is approximately 2 times the empirical formula mass (58*2 = 116, which is close to the given range). Therefore, there are 2 empirical units in the molecular formula.

Question 14

An iron ore,magnetite,contains only iron and oxygen.In refining 100.0 g of the ore,72.35 g of iron are obtained.What is the empirical formula of the ore?

Accepted Answer

The answer of An iron ore,magnetite,contains only iron and oxygen.In...

Question 15

A uranium oxide compound is found to be 88.15% U by mass.What is the empirical formula for the compound?

Accepted Answer

To find the empirical formula, calculate the moles of uranium and oxygen in 100g of the compound. Uranium's atomic mass is approximately 238 g/mol, and oxygen's is 16 g/mol. For 88.15g of U, moles = 88.15/238. For 11.85g of O, moles = 11.85/16. The mole ratio of U to O is approximately 1:2, giving the empirical formula UO₂.

Question 16

Analysis of two uranium fluoride compounds yields the following data: Compound I is 75.80% U by mass; compound II has an F-to-U mass ratio that is 1.5 times that of compound I.What is the empirical formula for compound II?

Accepted Answer

The answer of Analysis of two uranium fluoride compounds yields...

Question 17

A gas that is produced when fruit ripens contains 85.62% C and 14.38% H by mass.The molecular mass was found to be twice the empirical formula unit molecular mass.What is the molecular formula of this gas?

Accepted Answer

The answer of A gas that is produced when fruit...

Question 18

Han purple,a synthetic inorganic pigment developed in China in ancient times,has the chemical formula BaCuSi₂O₆.What is its percent by mass silicon?

Accepted Answer

To calculate the percent by mass of silicon, we need to find the molar mass of silicon in the compound and divide it by the molar mass of the entire compound, then multiply by 100. The molar mass of silicon is 28.0855 g/mol (from the periodic table), and the molar mass of the entire compound is 1131.1 g/mol. Therefore, the percent by mass of silicon is (28.0855/1131.1) x 100 = 2.48%. However, the question asks for the percent by mass of SiS, which has a molar mass of 96.198 g/mol. In the compound formula, there are two SiS units, so the total mass of SiS is 96.198 x 2 = 192.396 g/mol. Therefore, the percent by mass of SiS is (192.396/1131.1) x 100 = 15.9%, which is closest to choice B.

Question 19

Caffeine has an elemental analysis of 49.48% C,5.190% H,16.47% O,and 28.85% N.It has a molar mass of 194.19 g/mol.What is the molecular formula of caffeine?

Accepted Answer

First, calculate the empirical formula:
- Divide the percent composition of each element by its atomic weight to get the ratio of each atom: C: 49.48/12.01 = 4.119, H: 5.190/1.008 = 5.157, O: 16.47/16.00 = 1.029, N: 28.85/14.01 = 2.063
- Divide each ratio by the smallest ratio to get whole number subscripts: C4.119H5.157O1.029N2.063 (rounded to the nearest whole number)
- The empirical formula is C4H5O1N2
Next, calculate the molecular formula:
- Divide the molar mass of caffeine by the molar mass of the empirical formula: 194.19/194.19 = 1
- The molecular formula is the same as the empirical formula: C4H5O1N2
- Multiply the subscripts by the integer obtained above: C4x1H5x1O1x1N2x1 = C4H5O1N2
- The molecular formula is B, which matches the calculated empirical formula.

Question 20

Phthalocyanine is a large molecule used in printing inks and dyes.Elemental analysis showed that it consists of 74.69% C,3.525% H,and 21.77 % N,and has a molar mass of 514.54 g/mol.What is its molecular formula?

Accepted Answer

The empirical formula is determined by converting the percentages to moles and finding the simplest ratio. The empirical formula mass is then compared to the molar mass to find the molecular formula. C₃₂H₁₈N₈ matches the given molar mass of 514.54 g/mol.

Quiz 7: Stoichiometry-Mass Relationships and Chemical Reactions

A compound containing bromine and fluorine used in the production of UF₆ is 58.37% Br by mass.What is the empirical formula for the compound?

Ibuprofen is 75.69% C,8.80% H,and 15.51% O by mass.What is its empirical formula?

A compound known to contain platinum,nitrogen,and hydrogen was analyzed and found to contain 74.1% Pt and 21.3% N; the remainder was hydrogen.What is the empirical formula for the compound?

Which of the following does NOT share the same empirical formula as the others?

A 2.00 g sample of methamphetamine was found to contain 1.61 g C,0.203 g H,and 0.188 g N.What is its empirical formula?

Alkanes share a general chemical formula of C_nH₂_n₊₂.What is n of an alkane with a molar mass in the range of 125-130 g/mol?

When are an empirical formula and a molecular formula the same?

A hydrocarbon is found to be 85.63% C by mass.What is its empirical formula?

Metallic copper can be obtained from the mineral chalcocite (Cu₂S) .What is the mass percent of copper in chalcocite?

Paris green is a highly toxic emerald green compound with the formula Cu(C₂H₃O₂) ₂.3Cu(AsO₂) ₂.What is its percent by mass arsenic?

Hydroxylamine contains 42.41% N and 9.15% H by mass,with the remainder being oxygen.Determine its empirical formula.

The empirical formula for buckminsterfullerene is C₁,and its molar mass is 720.6 g/mol.What is its molecular formula?

Putrescine,a foul-smelling compound produced by decaying tissue,has the empirical formula C₂H₆N,and its molecular mass is found to be between 87 and 90 amu.How many empirical units are in the actual molecular formula?

An iron ore,magnetite,contains only iron and oxygen.In refining 100.0 g of the ore,72.35 g of iron are obtained.What is the empirical formula of the ore?

A uranium oxide compound is found to be 88.15% U by mass.What is the empirical formula for the compound?

Analysis of two uranium fluoride compounds yields the following data: Compound I is 75.80% U by mass; compound II has an F-to-U mass ratio that is 1.5 times that of compound I.What is the empirical formula for compound II?

A gas that is produced when fruit ripens contains 85.62% C and 14.38% H by mass.The molecular mass was found to be twice the empirical formula unit molecular mass.What is the molecular formula of this gas?

Han purple,a synthetic inorganic pigment developed in China in ancient times,has the chemical formula BaCuSi₂O₆.What is its percent by mass silicon?

Caffeine has an elemental analysis of 49.48% C,5.190% H,16.47% O,and 28.85% N.It has a molar mass of 194.19 g/mol.What is the molecular formula of caffeine?

Phthalocyanine is a large molecule used in printing inks and dyes.Elemental analysis showed that it consists of 74.69% C,3.525% H,and 21.77 % N,and has a molar mass of 514.54 g/mol.What is its molecular formula?

Quiz 7: Stoichiometry-Mass Relationships and Chemical Reactions

A compound containing bromine and fluorine used in the production of UF6 is 58.37% Br by mass.What is the empirical formula for the compound?

Ibuprofen is 75.69% C,8.80% H,and 15.51% O by mass.What is its empirical formula?

A compound known to contain platinum,nitrogen,and hydrogen was analyzed and found to contain 74.1% Pt and 21.3% N; the remainder was hydrogen.What is the empirical formula for the compound?

Which of the following does NOT share the same empirical formula as the others?

A 2.00 g sample of methamphetamine was found to contain 1.61 g C,0.203 g H,and 0.188 g N.What is its empirical formula?

Alkanes share a general chemical formula of CnH2n+2.What is n of an alkane with a molar mass in the range of 125-130 g/mol?

When are an empirical formula and a molecular formula the same?

A hydrocarbon is found to be 85.63% C by mass.What is its empirical formula?

Metallic copper can be obtained from the mineral chalcocite (Cu2S) .What is the mass percent of copper in chalcocite?

Paris green is a highly toxic emerald green compound with the formula Cu(C2H3O2) 2 . 3Cu(AsO2) 2.What is its percent by mass arsenic?

Hydroxylamine contains 42.41% N and 9.15% H by mass,with the remainder being oxygen.Determine its empirical formula.

The empirical formula for buckminsterfullerene is C1,and its molar mass is 720.6 g/mol.What is its molecular formula?

Putrescine,a foul-smelling compound produced by decaying tissue,has the empirical formula C2H6N,and its molecular mass is found to be between 87 and 90 amu.How many empirical units are in the actual molecular formula?

An iron ore,magnetite,contains only iron and oxygen.In refining 100.0 g of the ore,72.35 g of iron are obtained.What is the empirical formula of the ore?

A uranium oxide compound is found to be 88.15% U by mass.What is the empirical formula for the compound?

Analysis of two uranium fluoride compounds yields the following data: Compound I is 75.80% U by mass; compound II has an F-to-U mass ratio that is 1.5 times that of compound I.What is the empirical formula for compound II?

A gas that is produced when fruit ripens contains 85.62% C and 14.38% H by mass.The molecular mass was found to be twice the empirical formula unit molecular mass.What is the molecular formula of this gas?

Han purple,a synthetic inorganic pigment developed in China in ancient times,has the chemical formula BaCuSi2O6.What is its percent by mass silicon?

Caffeine has an elemental analysis of 49.48% C,5.190% H,16.47% O,and 28.85% N.It has a molar mass of 194.19 g/mol.What is the molecular formula of caffeine?

Phthalocyanine is a large molecule used in printing inks and dyes.Elemental analysis showed that it consists of 74.69% C,3.525% H,and 21.77 % N,and has a molar mass of 514.54 g/mol.What is its molecular formula?

A compound containing bromine and fluorine used in the production of UF₆ is 58.37% Br by mass.What is the empirical formula for the compound?

Alkanes share a general chemical formula of C_nH₂_n₊₂.What is n of an alkane with a molar mass in the range of 125-130 g/mol?

Metallic copper can be obtained from the mineral chalcocite (Cu₂S) .What is the mass percent of copper in chalcocite?

Paris green is a highly toxic emerald green compound with the formula Cu(C₂H₃O₂) ₂.3Cu(AsO₂) ₂.What is its percent by mass arsenic?

The empirical formula for buckminsterfullerene is C₁,and its molar mass is 720.6 g/mol.What is its molecular formula?

Putrescine,a foul-smelling compound produced by decaying tissue,has the empirical formula C₂H₆N,and its molecular mass is found to be between 87 and 90 amu.How many empirical units are in the actual molecular formula?

Han purple,a synthetic inorganic pigment developed in China in ancient times,has the chemical formula BaCuSi₂O₆.What is its percent by mass silicon?