Question 1

Analysis of a carbohydrate showed that it consisted of 40.0 % C, 6.71 % H, and 53.3 % O by mass. Its molecular mass was found to be between 140 and 160 amu. What is the molecular formula of this compound?

Accepted Answer

The empirical formula based on the given percentages is C₅H₁₀O₅, which matches the molecular mass range of 140-160 amu.

Question 2

Gadolinium oxide, a colorless powder which absorbs carbon dioxide from the air, contains 86.76 mass % Gd. Determine its empirical formula.

Accepted Answer

The empirical formula is determined by the ratio of moles of Gd to O. Given 86.76% Gd, the remaining 13.24% is O. Calculating moles, the ratio is approximately 2:3, corresponding to Gd₂O₃.

Question 3

Household sugar, sucrose, has the molecular formula C₁₂H₂₂O₁₁. What is the percent of carbon in sucrose, by mass?

Accepted Answer

The molar mass of sucrose is 342.3 g/mol. The molar mass of carbon is 12.01 g/mol. There are 12 carbon atoms in a molecule of sucrose. So, the mass of carbon in a molecule of sucrose is 12 * 12.01 = 144.12 g. The percentage of carbon in sucrose, by mass, is (144.12 g / 342.3 g) * 100% = 42.1%.

Question 4

Lead (II) nitrate is a poisonous substance which has been used in the manufacture of special explosives and as a sensitizer in photography. Calculate the mass of lead in 139 g of Pb(NO₃)₂.

Accepted Answer

The molar mass of Pb(NO3)2 is 331.2 g/mol (Pb = 207.2, N = 14.0, O = 16.0). The mass of lead (Pb) in one mole of Pb(NO3)2 is 207.2 g. Therefore, the mass of lead in 139 g of Pb(NO3)2 is (207.2/331.2) * 139 = 87.0 g.

Question 5

Determine the percent composition of potassium dichromate, K₂Cr₂O₇.

Accepted Answer

The formula for potassium dichromate is K2Cr2O7. To find the percent composition, calculate the molar mass of the compound and then find the mass percentage of each element. The molar mass of K2Cr2O7 is approximately 294.185 g/mol (K=39.1*2, Cr=52.0*2, O=16.0*7). The percent composition is calculated as follows: K: (78.2/294.185)*100 ≈ 26.6%, Cr: (104/294.185)*100 ≈ 35.3%, O: (112/294.185)*100 ≈ 38.1%. None of the choices match these calculations.

Question 6

The number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is

Accepted Answer

The number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is 2.4 × 10 ²³ H atoms. This is because there are 8 hydrogen atoms in each molecule of C₃H₈O₃, and 0.050 mol of C₃H₈O₃ contains 0.050 mol × 6.022 × 10 ²³ molecules/mol = 3.011 × 10 ²² molecules. Therefore, the number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is 3.011 × 10 ²² molecules × 8 hydrogen atoms/molecule = 2.4 × 10 ²³ H atoms.

Question 7

Calculate the mass in grams of 8.35 × 10²² molecules of CBr₄.

Accepted Answer

The answer of Calculate the mass in grams of 8.35...

Question 8

A compound containing chromium and silicon contains 73.52 mass percent chromium. Determine its empirical formula.

Accepted Answer

To find the empirical formula, convert the mass percentages to moles. Assume 100 g of the compound: 73.52 g Cr and 26.48 g Si. Moles of Cr = 73.52 g / 51.996 g/mol = 1.414 mol. Moles of Si = 26.48 g / 28.085 g/mol = 0.943 mol. The simplest whole number ratio is Cr:Si = 1.5:1, which is closest to Cr3Si2.

Question 9

A normal breath takes in about 1.0 L of air. Assuming that air has an average molar mass of 28.8 g, and that its density is 0.97 g/L, how many molecules of air do you take in with each breath?

Accepted Answer

The number of moles of air in 1.0 L is:```n = m/M = (0.97 g) / (28.8 g/mol) = 0.0337 mol```The number of molecules of air in 1.0 L is:```N = n * N_A = (0.0337 mol) * (6.022 × 10^23 molecules/mol) = 2.0 × 10^22 molecules```

Question 10

How many atoms are in a drop of mercury that has a diameter of 1.0 mm? (Volume of a sphere is 4πr³/3; density of mercury = 13.6 g/cm³)

Accepted Answer

The volume of the drop is (4/3)π(0.05 cm)3 = 5.24 × 10-3 cm3. The mass of the drop is (5.24 × 10-3 cm3)(13.6 g/cm3) = 0.71 g. The number of atoms in the drop is (0.71 g)(6.02 × 1023 atoms/mol)/(200.59 g/mol) = 2.1 × 1019 atoms.

Question 11

Sulfur trioxide can react with atmospheric water vapor to form sulfuric acid that falls as acid rain. Calculate the mass in grams of 3.65 × 10²⁰ molecules of SO₃.

Accepted Answer

1 mole of SO3 contains 6.022 × 10^23 molecules.

The molar mass of SO3 is 80.06 g/mol.

We can use these values to convert the given number of molecules of SO3 to grams:

3.65 × 10^20 molecules SO3 * 1 mol SO3/6.022 × 10^23 molecules SO3 * 80.06 g/mol SO3 = 4.85 × 10^-12 g SO3

Since one molecule of SO3 produces one molecule of H2SO4, we can say that 3.65 × 10^20 molecules SO3 will produce 3.65 × 10^20 molecules H2SO4.

The molar mass of H2SO4 is 98.07 g/mol.

We can use the number of molecules of H2SO4 to calculate the mass in grams:

3.65 × 10^20 molecules H2SO4 * 1 mol H2SO4/6.022 × 10^23 molecules H2SO4 * 98.07 g/mol H2SO4 = 0.000223 g H2SO4

Therefore, the mass of 3.65 × 10^20 molecules SO3 that react with atmospheric water vapor to form acid rain is 0.000223 g or 4.85 × 10^-12 g SO3.

The closest answer choice is C, 4.85 × 10^-12 g SO3 or 4.85 × 10^-12 g H2SO4.

Question 12

A compound of bromine and fluorine is used to make UF₆, which is an important chemical in processing and reprocessing of nuclear fuel. The compound contains 58.37 mass percent bromine. Determine its empirical formula.

Accepted Answer

The empirical formula is determined by the ratio of moles of each element. Given 58.37% bromine, the remaining 41.63% is fluorine. Using atomic masses (Br = 79.9, F = 19), the mole ratio of Br to F is approximately 1:3, leading to the empirical formula BrF₃.

Question 13

Potassium dichromate, K₂Cr₂O₇, is used in tanning leather, decorating porcelain, and water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of K₂Cr₂O₇.

Accepted Answer

The answer of Potassium dichromate, K₂Cr₂O₇, is used in tanning...

Question 14

How many protons are there in a molecule of adrenaline (C₉H₁₃NO₃), a neurotransmitter and hormone?

Accepted Answer

Adrenaline, with the molecular formula C9H13NO3, consists of 9 carbon (C) atoms, 13 hydrogen (H) atoms, 1 nitrogen (N) atom, and 3 oxygen (O) atoms. The total number of protons is calculated by adding the atomic numbers of these elements: Carbon (6 protons) x 9 = 54, Hydrogen (1 proton) x 13 = 13, Nitrogen (7 protons) x 1 = 7, and Oxygen (8 protons) x 3 = 24. Adding these together gives 54 + 13 + 7 + 24 = 98 protons.

Question 15

Copper(II) sulfate pentahydrate, CuSO₄·5H₂O, is used as a fungicide and algicide. Calculate the mass of oxygen in 1.000 mol of CuSO₄·5H₂O.

Accepted Answer

The formula for copper(II) sulfate pentahydrate is CuSO4·5H2O. This means there are 4 oxygen atoms in the sulfate ion (SO4) and 5 water molecules, each containing 1 oxygen atom, for a total of 9 oxygen atoms per formula unit. The molar mass of oxygen is 16.00 g/mol, so the mass of oxygen in 1 mole of CuSO4·5H2O is 9 mol * 16.00 g/mol = 144.0 g.

Question 16

A single atom of hydrogen has a mass of 1.0 amu, while a mole of hydrogen atoms has a mass of 1.0 g. Select the correct conversion factor between atomic mass units and grams.

Accepted Answer

The conversion factor between atomic mass units (amu) and grams (g) is 1 g = 6.022 x 10^23 amu, which is known as Avogadro's number. Therefore, one mole of hydrogen (which has a mass of 1 g) contains 6.022 x 10^23 hydrogen atoms (each with a mass of 1 amu). So 1 amu is equivalent to 1/6.022 x 10^23 g, or approximately 1.66 x 10^-24 g. Therefore, the correct conversion factor is 1 g = 6.022 x 10^23 amu.

Question 17

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass % O. Determine its empirical formula.

Accepted Answer

The empirical formula is determined by converting the mass percentages to moles and finding the simplest whole number ratio. For hydroxylamine nitrate, the empirical formula is H₂NO₂.

Question 18

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass O. If its molar mass is between 94 and 98 g/mol, what is its molecular formula?

Accepted Answer

The empirical formula based on the given mass percentages is N2H4O4, which matches the molar mass range of 94-98 g/mol.

Question 19

Which of the following samples contains the greatest total number atoms?

Accepted Answer

To determine the total number of atoms in each sample, we need to calculate the number of moles of each compound and then use Avogadro's number to convert to the number of atoms.

A) Li2SO4: 
- Calculate the molar mass: 
- Li: 6.94 g/mol 
- S: 32.07 g/mol 
- O: 15.99 g/mol 
- Total molar mass: 86 g/mol 
- Number of moles in 50.0 g: 0.581 mol 
- Total number of atoms: 3.00 x 10^23 x 0.581 = 1.74 x 10^23 atoms

B) CaO: 
- Calculate the molar mass: 
- Ca: 40.08 g/mol 
- O: 15.99 g/mol 
- Total molar mass: 56.07 g/mol 
- Number of moles in 75.0 g: 1.34 mol 
- Total number of atoms: 7.26 x 10^23 x 1.34 = 9.75 x 10^23 atoms

C) FeSO4: 
- Calculate the molar mass: 
- Fe: 55.85 g/mol 
- S: 32.07 g/mol 
- O: 15.99 g/mol 
- Total molar mass: 151.91 g/mol 
- Number of moles in 200.0 g: 1.32 mol 
- Total number of atoms: 6.02 x 10^23 x 1.32 x 26 = 2.01 x 10^25 atoms (note that there are 26 atoms in each FeSO4 molecule)

D) CO: 
- Calculate the molar mass: 
- C: 12.01 g/mol 
- O: 15.99 g/mol 
- Total molar mass: 28.00 g/mol 
- Number of moles in 50.0 g: 1.79 mol 
- Total number of atoms: 6.02 x 10^23 x 1.79 x 2 = 2.04 x 10^24 atoms (note that there are 2 atoms in each CO molecule)

E) SO3: 
- Calculate the molar mass: 
- S: 32.07 g/mol 
- O: 15.99 g/mol 
- Total molar mass: 80.06 g/mol 
- Number of moles in 100.0 g: 1.25 mol 
- Total number of atoms: 6.02 x 10^23 x 1.25 x 4 = 3.78 x 10^24 atoms (note that there are 3 atoms in each SO3 molecule)

Therefore, the sample with the greatest total number of atoms is C, with a total of 2.01 x 10^25 atoms.

Question 20

Alkanes are compounds of carbon and hydrogen with the general formula C_nH₂n₊₂. An alkane component of gasoline has a molar mass of between 125 and 130 g/mol. What is the value of n for this alkane?

Accepted Answer

The general formula for alkanes is CnH2n+2. To find the value of n for an alkane with a molar mass between 125 and 130 g/mol, we can use the molar masses of carbon (12 g/mol) and hydrogen (1 g/mol) in the formula. For example, if n = 9, the molar mass would be 12n + (2n+2) = 12*9 + (2*9+2) = 108 + 20 = 128 g/mol, which falls within the given range. Other values of n do not meet the criteria when calculated similarly.

Quiz 3: Stoichiometry of Formulas and Equations

Analysis of a carbohydrate showed that it consisted of 40.0 % C, 6.71 % H, and 53.3 % O by mass. Its molecular mass was found to be between 140 and 160 amu. What is the molecular formula of this compound?

Gadolinium oxide, a colorless powder which absorbs carbon dioxide from the air, contains 86.76 mass % Gd. Determine its empirical formula.

Household sugar, sucrose, has the molecular formula C₁₂H₂₂O₁₁. What is the percent of carbon in sucrose, by mass?

Lead (II) nitrate is a poisonous substance which has been used in the manufacture of special explosives and as a sensitizer in photography. Calculate the mass of lead in 139 g of Pb(NO₃) ₂.

Determine the percent composition of potassium dichromate, K₂Cr₂O₇.

The number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is

Calculate the mass in grams of 8.35 × 10²² molecules of CBr₄.

A compound containing chromium and silicon contains 73.52 mass percent chromium. Determine its empirical formula.

A normal breath takes in about 1.0 L of air. Assuming that air has an average molar mass of 28.8 g, and that its density is 0.97 g/L, how many molecules of air do you take in with each breath?

How many atoms are in a drop of mercury that has a diameter of 1.0 mm? (Volume of a sphere is 4πr³/3; density of mercury = 13.6 g/cm³)

Sulfur trioxide can react with atmospheric water vapor to form sulfuric acid that falls as acid rain. Calculate the mass in grams of 3.65 × 10²⁰ molecules of SO₃.

A compound of bromine and fluorine is used to make UF₆, which is an important chemical in processing and reprocessing of nuclear fuel. The compound contains 58.37 mass percent bromine. Determine its empirical formula.

Potassium dichromate, K₂Cr₂O₇, is used in tanning leather, decorating porcelain, and water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of K₂Cr₂O₇.

How many protons are there in a molecule of adrenaline (C₉H₁₃NO₃) , a neurotransmitter and hormone?

Copper(II) sulfate pentahydrate, CuSO₄·5H₂O, is used as a fungicide and algicide. Calculate the mass of oxygen in 1.000 mol of CuSO₄·5H₂O.

A single atom of hydrogen has a mass of 1.0 amu, while a mole of hydrogen atoms has a mass of 1.0 g. Select the correct conversion factor between atomic mass units and grams.

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass % O. Determine its empirical formula.

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass O. If its molar mass is between 94 and 98 g/mol, what is its molecular formula?

Which of the following samples contains the greatest total number atoms?

Alkanes are compounds of carbon and hydrogen with the general formula C_nH₂n₊₂. An alkane component of gasoline has a molar mass of between 125 and 130 g/mol. What is the value of n for this alkane?

Quiz 3: Stoichiometry of Formulas and Equations

Analysis of a carbohydrate showed that it consisted of 40.0 % C, 6.71 % H, and 53.3 % O by mass. Its molecular mass was found to be between 140 and 160 amu. What is the molecular formula of this compound?

Gadolinium oxide, a colorless powder which absorbs carbon dioxide from the air, contains 86.76 mass % Gd. Determine its empirical formula.

Household sugar, sucrose, has the molecular formula C12H22O11. What is the percent of carbon in sucrose, by mass?

Lead (II) nitrate is a poisonous substance which has been used in the manufacture of special explosives and as a sensitizer in photography. Calculate the mass of lead in 139 g of Pb(NO3) 2.

Determine the percent composition of potassium dichromate, K2Cr2O7.

The number of hydrogen atoms in 0.050 mol of C3H8O3 is

Calculate the mass in grams of 8.35 × 1022 molecules of CBr4.

A compound containing chromium and silicon contains 73.52 mass percent chromium. Determine its empirical formula.

A normal breath takes in about 1.0 L of air. Assuming that air has an average molar mass of 28.8 g, and that its density is 0.97 g/L, how many molecules of air do you take in with each breath?

How many atoms are in a drop of mercury that has a diameter of 1.0 mm? (Volume of a sphere is 4πr3/3; density of mercury = 13.6 g/cm3)

Sulfur trioxide can react with atmospheric water vapor to form sulfuric acid that falls as acid rain. Calculate the mass in grams of 3.65 × 1020 molecules of SO3.

A compound of bromine and fluorine is used to make UF6, which is an important chemical in processing and reprocessing of nuclear fuel. The compound contains 58.37 mass percent bromine. Determine its empirical formula.

Potassium dichromate, K2Cr2O7, is used in tanning leather, decorating porcelain, and water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of K2Cr2O7.

How many protons are there in a molecule of adrenaline (C9H13NO3) , a neurotransmitter and hormone?

Copper(II) sulfate pentahydrate, CuSO4·5H2O, is used as a fungicide and algicide. Calculate the mass of oxygen in 1.000 mol of CuSO4·5H2O.

A single atom of hydrogen has a mass of 1.0 amu, while a mole of hydrogen atoms has a mass of 1.0 g. Select the correct conversion factor between atomic mass units and grams.

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass % O. Determine its empirical formula.

Hydroxylamine nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass O. If its molar mass is between 94 and 98 g/mol, what is its molecular formula?

Which of the following samples contains the greatest total number atoms?

Alkanes are compounds of carbon and hydrogen with the general formula CnH2n+2. An alkane component of gasoline has a molar mass of between 125 and 130 g/mol. What is the value of n for this alkane?

Household sugar, sucrose, has the molecular formula C₁₂H₂₂O₁₁. What is the percent of carbon in sucrose, by mass?

Lead (II) nitrate is a poisonous substance which has been used in the manufacture of special explosives and as a sensitizer in photography. Calculate the mass of lead in 139 g of Pb(NO₃) ₂.

Determine the percent composition of potassium dichromate, K₂Cr₂O₇.

The number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is

Calculate the mass in grams of 8.35 × 10²² molecules of CBr₄.

How many atoms are in a drop of mercury that has a diameter of 1.0 mm? (Volume of a sphere is 4πr³/3; density of mercury = 13.6 g/cm³)

Sulfur trioxide can react with atmospheric water vapor to form sulfuric acid that falls as acid rain. Calculate the mass in grams of 3.65 × 10²⁰ molecules of SO₃.

A compound of bromine and fluorine is used to make UF₆, which is an important chemical in processing and reprocessing of nuclear fuel. The compound contains 58.37 mass percent bromine. Determine its empirical formula.

Potassium dichromate, K₂Cr₂O₇, is used in tanning leather, decorating porcelain, and water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of K₂Cr₂O₇.

How many protons are there in a molecule of adrenaline (C₉H₁₃NO₃) , a neurotransmitter and hormone?

Copper(II) sulfate pentahydrate, CuSO₄·5H₂O, is used as a fungicide and algicide. Calculate the mass of oxygen in 1.000 mol of CuSO₄·5H₂O.

Alkanes are compounds of carbon and hydrogen with the general formula C_nH₂n₊₂. An alkane component of gasoline has a molar mass of between 125 and 130 g/mol. What is the value of n for this alkane?