Question 1

Which of the following statements regarding mass spectrometry is NOT true?

Accepted Answer

The signal detected at the highest mass-to-charge ratio is typically representative of the molecular ion or parent ion, not the smallest fragment. This molecular ion peak indicates the molecule's total mass, providing crucial information about the molecular weight. Smaller fragments, resulting from the molecule breaking apart, appear at lower mass-to-charge ratios.

Question 2

A uranium oxide compound is found to be 84.80% U by mass.What is the empirical formula for the compound?

Accepted Answer

To find the empirical formula, calculate the moles of U and O. Assume 100g of the compound: 84.80g U and 15.20g O. Moles of U = 84.80g / 238.03g/mol = 0.356 moles. Moles of O = 15.20g / 16.00g/mol = 0.950 moles. The mole ratio of U:O is approximately 3:8, giving the empirical formula U₃O₈.

Question 3

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

Compound I has a formula of UF4 (since 75.80% U by mass corresponds to this formula). The F-to-U mass ratio for UF4 is 4:1. Compound II has an F-to-U mass ratio 1.5 times that of compound I, which means it has a ratio of 6:1, corresponding to UF6.

Question 4

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 percentage composition to moles and finding the simplest ratio. The empirical formula mass is then compared to the molar mass to find the molecular formula. The calculations show that the molecular formula is C₃₂H₁₈N₈.

Question 5

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...

Question 6

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 empirical formula is CH2, with a molecular mass of 14. The molecular mass is twice the empirical formula mass, so the molecular formula is C2H4.

Question 7

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

To find the empirical formula, calculate the moles of Br and F in 100 g of the compound. With 58.37 g of Br (molar mass = 79.9 g/mol) and 41.63 g of F (molar mass = 19 g/mol), the mole ratio is approximately 1:3, leading to the empirical formula BrF₃.

Question 8

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

Accepted Answer

Butyric acid has an empirical formula of C4H8O2, which is different from the others that have the empirical formula CH2O.

Question 9

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,...

Question 10

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 11

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 12

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

Accepted Answer

The empirical formula represents the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule. They are the same when the mass of the empirical formula unit equals the molecular mass, meaning the empirical formula directly reflects the actual molecular composition without needing to be multiplied by any factor to get the molecular formula.

Question 13

Licopene, a red pigment found in tomatoes, has the empirical formula C₅H₇, and its molecular mass is found to be approximately 537 amu.How many empirical units are in the actual molecular formula?

Accepted Answer

The empirical formula mass of C5H7 is 67 amu (5*12 + 7*1). The molecular mass of lycopene is 537 amu. Dividing the molecular mass by the empirical formula mass gives 537/67 = 8, indicating there are 8 empirical units in the molecular formula.

Question 14

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 15

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 empirical formula is the simplest whole number ratio of the elements in a compound. To find the empirical formula, we need to convert the mass of each element to moles.Mass of C = 1.61 gMoles of C = 1.61 g / 12.01 g/mol = 0.134 molMass of H = 0.203 gMoles of H = 0.203 g / 1.01 g/mol = 0.201 molMass of N = 0.188 gMoles of N = 0.188 g / 14.01 g/mol = 0.0134 molThe mole ratio of C:H:N is 0.134:0.201:0.0134. Dividing each mole ratio by the smallest mole ratio (0.0134) gives the empirical formula:C10H15N

Question 16

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 17

Alkanes share a general chemical formula of C_n H₂_n+2 .What is n of an alkane with a molar mass in the range of 140-145 g/mol?

Accepted Answer

The general formula for alkanes is CnH2n+2. Given the molar mass range of 140-145 g/mol, we can calculate the number of carbon atoms (n) by considering the molar mass of carbon (12 g/mol) and hydrogen (1 g/mol). For an alkane, the molar mass can be approximated as 12n + (2n+2) = 14n + 2. Setting this equal to the average value in the given range (142.5 g/mol) and solving for n gives a value close to 10, making option A correct.

Question 18

A hydrocarbon molecule contains twice as many hydrogen atoms as carbon atoms.Its molar mass is 84.15 g/mol.What is the molecular formula for the hydrocarbon?

Accepted Answer

The answer of A hydrocarbon molecule contains twice as many...

Question 19

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...

Question 20

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

The empirical formula mass of C₄H₅N₂O is approximately 97.1 g/mol. The molar mass of caffeine is 194.19 g/mol, which is about twice the empirical formula mass, indicating the molecular formula is C₈H₁₀N₄O₂.

Quiz 7: Stoichiometry Mass Relationships and Chemical Reactions

Which of the following statements regarding mass spectrometry is NOT true?

A uranium oxide compound is found to be 84.80% 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?

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?

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

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?

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?

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

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

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

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

Licopene, a red pigment found in tomatoes, has the empirical formula C₅H₇, and its molecular mass is found to be approximately 537 amu.How many empirical units are in the actual molecular formula?

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?

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?

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

Alkanes share a general chemical formula of C_n H₂_n+2 .What is n of an alkane with a molar mass in the range of 140-145 g/mol?

A hydrocarbon molecule contains twice as many hydrogen atoms as carbon atoms.Its molar mass is 84.15 g/mol.What is the molecular formula for the hydrocarbon?

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?

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?

Quiz 7: Stoichiometry Mass Relationships and Chemical Reactions

Which of the following statements regarding mass spectrometry is NOT true?

A uranium oxide compound is found to be 84.80% 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?

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?

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

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?

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?

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

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

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

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

Licopene, a red pigment found in tomatoes, has the empirical formula C5H7, and its molecular mass is found to be approximately 537 amu.How many empirical units are in the actual molecular formula?

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?

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?

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

Alkanes share a general chemical formula of Cn H2n+2 .What is n of an alkane with a molar mass in the range of 140-145 g/mol?

A hydrocarbon molecule contains twice as many hydrogen atoms as carbon atoms.Its molar mass is 84.15 g/mol.What is the molecular formula for the hydrocarbon?

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?

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?

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?

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

Licopene, a red pigment found in tomatoes, has the empirical formula C₅H₇, and its molecular mass is found to be approximately 537 amu.How many empirical units are in the actual molecular formula?

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?

Alkanes share a general chemical formula of C_n H₂_n+2 .What is n of an alkane with a molar mass in the range of 140-145 g/mol?