Elemental Composition of Pure Substances - AP Chemistry
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What is the formula for calculating percent composition by mass?
What is the formula for calculating percent composition by mass?
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$% \text{ composition} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$. Divides element mass by total compound mass, then multiplies by 100 for percentage.
$% \text{ composition} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$. Divides element mass by total compound mass, then multiplies by 100 for percentage.
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What is the percent composition of oxygen in H₂O₂?
What is the percent composition of oxygen in H₂O₂?
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94.$06\text{ %}$. Two oxygens (32.00 g) divided by H₂O₂ mass (34.02 g) times 100.
94.$06\text{ %}$. Two oxygens (32.00 g) divided by H₂O₂ mass (34.02 g) times 100.
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State the law that governs the fixed proportions by mass in chemical compounds.
State the law that governs the fixed proportions by mass in chemical compounds.
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Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.
Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.
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Find the molar mass of CO₂.
Find the molar mass of CO₂.
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44.$01 \text{ g/mol}$. Carbon (12.01) plus two oxygens (2 × 16.00) equals 44.01 g/mol.
44.$01 \text{ g/mol}$. Carbon (12.01) plus two oxygens (2 × 16.00) equals 44.01 g/mol.
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What is the empirical formula for a compound with 85.7% carbon and 14.3% hydrogen?
What is the empirical formula for a compound with 85.7% carbon and 14.3% hydrogen?
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CH₂. Converting percentages to moles gives a 1:2 carbon to hydrogen ratio.
CH₂. Converting percentages to moles gives a 1:2 carbon to hydrogen ratio.
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What is the percent composition of nitrogen in urea (CH₄N₂O)?
What is the percent composition of nitrogen in urea (CH₄N₂O)?
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46.$65\text{ %}$. Two nitrogens (28.02 g) divided by urea mass (60.06 g) times 100.
46.$65\text{ %}$. Two nitrogens (28.02 g) divided by urea mass (60.06 g) times 100.
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Calculate the percent composition of carbon in CH₄.
Calculate the percent composition of carbon in CH₄.
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74.$87\text{ %}$. Carbon mass (12.01) divided by methane mass (16.04) times 100.
74.$87\text{ %}$. Carbon mass (12.01) divided by methane mass (16.04) times 100.
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Calculate the percent composition of sulfur in H₂SO₄.
Calculate the percent composition of sulfur in H₂SO₄.
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32.$69\text{ %}$. Sulfur mass (32.07) divided by H₂SO₄ mass (98.08) times 100.
32.$69\text{ %}$. Sulfur mass (32.07) divided by H₂SO₄ mass (98.08) times 100.
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Identify the primary element in the composition of ammonia (NH₃).
Identify the primary element in the composition of ammonia (NH₃).
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Nitrogen. Nitrogen has the greatest atomic mass in NH₃ compared to the three hydrogens.
Nitrogen. Nitrogen has the greatest atomic mass in NH₃ compared to the three hydrogens.
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What is the molecular formula of a compound with an empirical formula of CH₂O and a molar mass of 180 g/mol?
What is the molecular formula of a compound with an empirical formula of CH₂O and a molar mass of 180 g/mol?
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C₆H₁₂O₆. Molar mass 180 is six times the empirical formula mass of 30, so multiply by 6.
C₆H₁₂O₆. Molar mass 180 is six times the empirical formula mass of 30, so multiply by 6.
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Find the percent composition of chlorine in NaCl.
Find the percent composition of chlorine in NaCl.
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60.$66\text{ %}$. Chlorine mass (35.45) divided by NaCl mass (58.44) times 100.
60.$66\text{ %}$. Chlorine mass (35.45) divided by NaCl mass (58.44) times 100.
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Find the molar mass of glucose (C₆H₁₂O₆).
Find the molar mass of glucose (C₆H₁₂O₆).
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180.$18 \text{ g/mol}$. Six carbons + twelve hydrogens + six oxygens: 72.06 + 12.12 + 96.00 = 180.18 g/mol.
180.$18 \text{ g/mol}$. Six carbons + twelve hydrogens + six oxygens: 72.06 + 12.12 + 96.00 = 180.18 g/mol.
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What is the percent composition of carbon in $CO_2$?
What is the percent composition of carbon in $CO_2$?
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$27.29%$ . Carbon mass (12.01) divided by $CO_2$ mass (44.01) times 100.
$27.29%$ . Carbon mass (12.01) divided by $CO_2$ mass (44.01) times 100.
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What is the empirical formula of a compound with 92.3% carbon and 7.7% hydrogen?
What is the empirical formula of a compound with 92.3% carbon and 7.7% hydrogen?
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CH. Converting percentages to moles gives a 1:1 carbon to hydrogen ratio.
CH. Converting percentages to moles gives a 1:1 carbon to hydrogen ratio.
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What is the empirical formula for a compound with 62.1% carbon, 10.4% hydrogen, and 27.5% oxygen?
What is the empirical formula for a compound with 62.1% carbon, 10.4% hydrogen, and 27.5% oxygen?
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C₃H₈O. Converting percentages to moles gives a 3:8:1 carbon to hydrogen to oxygen ratio.
C₃H₈O. Converting percentages to moles gives a 3:8:1 carbon to hydrogen to oxygen ratio.
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What is the molar mass of NaCl?
What is the molar mass of NaCl?
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58.$44 \text{ g/mol}$. Sodium (22.99) plus chlorine (35.45) equals 58.44 g/mol.
58.$44 \text{ g/mol}$. Sodium (22.99) plus chlorine (35.45) equals 58.44 g/mol.
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Find the percent composition of hydrogen in C₆H₁₂O₆.
Find the percent composition of hydrogen in C₆H₁₂O₆.
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6.$71\text{ %}$. Twelve hydrogens (12.12 g) divided by glucose mass (180.16 g) times 100.
6.$71\text{ %}$. Twelve hydrogens (12.12 g) divided by glucose mass (180.16 g) times 100.
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Calculate the molar mass of sulfuric acid (H₂SO₄).
Calculate the molar mass of sulfuric acid (H₂SO₄).
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98.$08 \text{ g/mol}$. Two hydrogens + sulfur + four oxygens: 2.02 + 32.07 + 63.99 = 98.08 g/mol.
98.$08 \text{ g/mol}$. Two hydrogens + sulfur + four oxygens: 2.02 + 32.07 + 63.99 = 98.08 g/mol.
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Identify the element with the highest composition in methane (CH₄).
Identify the element with the highest composition in methane (CH₄).
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Carbon. Carbon has atomic mass 12.01, much greater than four hydrogens at 4.04 total.
Carbon. Carbon has atomic mass 12.01, much greater than four hydrogens at 4.04 total.
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What is the percent composition of hydrogen in H₂SO₄?
What is the percent composition of hydrogen in H₂SO₄?
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2.$06\text{ %}$. Two hydrogens (2.02 g) divided by total H₂SO₄ mass (98.08 g) times 100.
2.$06\text{ %}$. Two hydrogens (2.02 g) divided by total H₂SO₄ mass (98.08 g) times 100.
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What is the chemical formula for a compound with 36.8% nitrogen and 63.2% oxygen?
What is the chemical formula for a compound with 36.8% nitrogen and 63.2% oxygen?
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NO₂. Converting percentages to moles gives a 1:2 nitrogen to oxygen ratio.
NO₂. Converting percentages to moles gives a 1:2 nitrogen to oxygen ratio.
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Determine the molar mass of ethanol (C₂H₅OH).
Determine the molar mass of ethanol (C₂H₅OH).
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46.$08 \text{ g/mol}$. Two carbons + six hydrogens + one oxygen: 24.02 + 6.06 + 16.00 = 46.08 g/mol.
46.$08 \text{ g/mol}$. Two carbons + six hydrogens + one oxygen: 24.02 + 6.06 + 16.00 = 46.08 g/mol.
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Calculate the percent composition of hydrogen in HCl.
Calculate the percent composition of hydrogen in HCl.
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2.$76\text{ %}$. One hydrogen (1.01 g) divided by HCl mass (36.46 g) times 100.
2.$76\text{ %}$. One hydrogen (1.01 g) divided by HCl mass (36.46 g) times 100.
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Find the molar mass of acetic acid (CH₃COOH).
Find the molar mass of acetic acid (CH₃COOH).
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60.$05 \text{ g/mol}$. Two carbons + four hydrogens + two oxygens: 24.02 + 4.04 + 31.99 = 60.05 g/mol.
60.$05 \text{ g/mol}$. Two carbons + four hydrogens + two oxygens: 24.02 + 4.04 + 31.99 = 60.05 g/mol.
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Determine the percent composition of oxygen in calcium carbonate (CaCO₃).
Determine the percent composition of oxygen in calcium carbonate (CaCO₃).
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48.$00\text{ %}$. Three oxygens (48.00 g) divided by CaCO₃ mass (100.09 g) times 100.
48.$00\text{ %}$. Three oxygens (48.00 g) divided by CaCO₃ mass (100.09 g) times 100.
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Determine the empirical formula of a compound with 79.9% carbon and 20.1% hydrogen.
Determine the empirical formula of a compound with 79.9% carbon and 20.1% hydrogen.
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CH₃. Converting percentages to moles gives a 1:3 carbon to hydrogen ratio.
CH₃. Converting percentages to moles gives a 1:3 carbon to hydrogen ratio.
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Find the percent composition of sulfur in Na₂SO₄.
Find the percent composition of sulfur in Na₂SO₄.
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22.$57\text{ %}$. Sulfur mass (32.07) divided by Na₂SO₄ mass (142.05) times 100.
22.$57\text{ %}$. Sulfur mass (32.07) divided by Na₂SO₄ mass (142.05) times 100.
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What law states the mass ratio between elements in a compound remains constant?
What law states the mass ratio between elements in a compound remains constant?
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Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.
Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.
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What is the percent composition of carbon in benzene (C₆H₆)?
What is the percent composition of carbon in benzene (C₆H₆)?
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92.$26\text{ %}$. Six carbons (72.06 g) divided by benzene mass (78.12 g) times 100.
92.$26\text{ %}$. Six carbons (72.06 g) divided by benzene mass (78.12 g) times 100.
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Determine the percent composition of hydrogen in water (H₂O).
Determine the percent composition of hydrogen in water (H₂O).
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11.$19\text{ %}$. Two hydrogens (2.02 g) divided by water mass (18.02 g) times 100.
11.$19\text{ %}$. Two hydrogens (2.02 g) divided by water mass (18.02 g) times 100.
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