AP Chemistry Flashcards: Elemental Composition Of Pure Substances

What this deck covers

This deck focuses on Elemental Composition Of Pure Substances, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Identify the primary element in the composition of ammonia (NH₃).

Answer: Nitrogen. Nitrogen has the greatest atomic mass in NH₃ compared to the three hydrogens.

Flashcard 2: Determine the empirical formula of a compound with 79.9% carbon and 20.1% hydrogen.

Answer: CH₃. Converting percentages to moles gives a 1:3 carbon to hydrogen ratio.

Flashcard 3: What is the chemical formula for a compound with 36.8% nitrogen and 63.2% oxygen?

Answer: NO₂. Converting percentages to moles gives a 1:2 nitrogen to oxygen ratio.

Flashcard 4: Find the molar mass of glucose (C₆H₁₂O₆).

Answer: 180.$18 \text{ g/mol}$. Six carbons + twelve hydrogens + six oxygens: 72.06 + 12.12 + 96.00 = 180.18 g/mol.

Flashcard 5: What is the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Answer: CH₂O. Convert percentages to moles, divide by smallest, giving 1:2:1 ratio.

Flashcard 6: Determine the empirical formula of a compound with 79.9% carbon and 20.1% hydrogen.

Answer: CH₃. Converting percentages to moles gives a 1:3 carbon to hydrogen ratio.

Flashcard 7: Find the percent composition of chlorine in NaCl.

Answer: 60.66\text{ %}. Chlorine mass (35.45) divided by NaCl mass (58.44) times 100.

Flashcard 8: Find the molar mass of CO₂.

Answer: 44.$01 \text{ g/mol}$. Carbon (12.01) plus two oxygens (2 × 16.00) equals 44.01 g/mol.

Flashcard 9: What is the percent composition of carbon in $CO_2$?

Answer: $27.29\%$ . Carbon mass (12.01) divided by $CO_2$ mass (44.01) times 100.

Flashcard 10: Find the percent composition of sulfur in Na₂SO₄.

Answer: 22.57\text{ %}. Sulfur mass (32.07) divided by Na₂SO₄ mass (142.05) times 100.

Flashcard 11: Determine the molar mass of ethanol (C₂H₅OH).

Answer: 46.$08 \text{ g/mol}$. Two carbons + six hydrogens + one oxygen: 24.02 + 6.06 + 16.00 = 46.08 g/mol.

Flashcard 12: Find the molar mass of CO₂.

Answer: 44.$01 \text{ g/mol}$. Carbon (12.01) plus two oxygens (2 × 16.00) equals 44.01 g/mol.

Flashcard 13: Determine the percent composition of hydrogen in water (H₂O).

Answer: 11.19\text{ %}. Two hydrogens (2.02 g) divided by water mass (18.02 g) times 100.

Flashcard 14: What is the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Answer: CH₂O. Convert percentages to moles, divide by smallest, giving 1:2:1 ratio.

Flashcard 15: What is the percent composition of hydrogen in H₂SO₄?

Answer: 2.06\text{ %}. Two hydrogens (2.02 g) divided by total H₂SO₄ mass (98.08 g) times 100.

Flashcard 16: Calculate the percent composition of hydrogen in HCl.

Answer: 2.76\text{ %}. One hydrogen (1.01 g) divided by HCl mass (36.46 g) times 100.

Flashcard 17: What is the percent composition of oxygen in ethanol (C₂H₅OH)?

Answer: 34.73\text{ %}. One oxygen (16.00 g) divided by ethanol mass (46.08 g) times 100.

Flashcard 18: Find the molar mass of acetic acid (CH₃COOH).

Answer: 60.$05 \text{ g/mol}$. Two carbons + four hydrogens + two oxygens: 24.02 + 4.04 + 31.99 = 60.05 g/mol.

Flashcard 19: What is the chemical formula for a compound with 36.8% nitrogen and 63.2% oxygen?

Answer: NO₂. Converting percentages to moles gives a 1:2 nitrogen to oxygen ratio.

Flashcard 20: Identify the primary element in the composition of ammonia (NH₃).

Answer: Nitrogen. Nitrogen has the greatest atomic mass in NH₃ compared to the three hydrogens.

Flashcard 21: What is the molecular formula of a compound with an empirical formula of CH₂O and a molar mass of 180 g/mol?

Answer: C₆H₁₂O₆. Molar mass 180 is six times the empirical formula mass of 30, so multiply by 6.

Flashcard 22: Find the molar mass of glucose (C₆H₁₂O₆).

Answer: 180.$18 \text{ g/mol}$. Six carbons + twelve hydrogens + six oxygens: 72.06 + 12.12 + 96.00 = 180.18 g/mol.

Flashcard 23: Determine the percent composition of oxygen in glucose (C₆H₁₂O₆).

Answer: 53.29\text{ %}. Six oxygens (96.00 g) divided by glucose mass (180.16 g) times 100.

Flashcard 24: Calculate the percent composition of oxygen in Na₂CO₃.

Answer: 45.28\text{ %}. Three oxygens (48.00 g) divided by Na₂CO₃ mass (105.99 g) times 100.

Flashcard 25: Find the molar mass of acetic acid (CH₃COOH).

Answer: 60.$05 \text{ g/mol}$. Two carbons + four hydrogens + two oxygens: 24.02 + 4.04 + 31.99 = 60.05 g/mol.

Flashcard 26: What is the empirical formula for a compound with 85.7% carbon and 14.3% hydrogen?

Answer: CH₂. Converting percentages to moles gives a 1:2 carbon to hydrogen ratio.

Flashcard 27: What is the empirical formula for a compound with 85.7% carbon and 14.3% hydrogen?

Answer: CH₂. Converting percentages to moles gives a 1:2 carbon to hydrogen ratio.

Flashcard 28: Calculate the percent composition of hydrogen in HCl.

Answer: 2.76\text{ %}. One hydrogen (1.01 g) divided by HCl mass (36.46 g) times 100.

Flashcard 29: Calculate the percent composition of calcium in CaCl₂.

Answer: 36.11\text{ %}. Calcium mass (40.08) divided by CaCl₂ mass (110.98 g) times 100.

Flashcard 30: Calculate the percent composition of hydrogen in HCl.

Answer: 2.76\text{ %}. One hydrogen (1.01 g) divided by HCl mass (36.46 g) times 100.

Flashcard 31: State the law that governs the fixed proportions by mass in chemical compounds.

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 32: Determine the molar mass of ethanol (C₂H₅OH).

Answer: 46.$08 \text{ g/mol}$. Two carbons + six hydrogens + one oxygen: 24.02 + 6.06 + 16.00 = 46.08 g/mol.

Flashcard 33: State the law that governs the fixed proportions by mass in chemical compounds.

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 34: Determine the percent composition of oxygen in glucose (C₆H₁₂O₆).

Answer: 53.29\text{ %}. Six oxygens (96.00 g) divided by glucose mass (180.16 g) times 100.

Flashcard 35: What is the formula for calculating percent composition by mass?

Answer: $\% \text{ composition} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$. Divides element mass by total compound mass, then multiplies by 100 for percentage.

Flashcard 36: What is the percent composition of hydrogen in acetic acid (C₂H₄O₂)?

Answer: 6.71\text{ %}. Four hydrogens (4.04 g) divided by acetic acid mass (60.05 g) times 100.

Flashcard 37: Which element has the highest percent composition in water (H₂O)?

Answer: Oxygen. Oxygen has atomic mass 16, hydrogen has mass 1, so oxygen dominates in H₂O.

Flashcard 38: Calculate the percent composition of sulfur in H₂SO₄.

Answer: 32.69\text{ %}. Sulfur mass (32.07) divided by H₂SO₄ mass (98.08) times 100.

Flashcard 39: Identify the element with the highest composition in methane (CH₄).

Answer: Carbon. Carbon has atomic mass 12.01, much greater than four hydrogens at 4.04 total.

Flashcard 40: Find the percent composition of chlorine in NaCl.

Answer: 60.66\text{ %}. Chlorine mass (35.45) divided by NaCl mass (58.44) times 100.

Flashcard 41: Calculate the percent composition of sulfur in H₂SO₄.

Answer: 32.69\text{ %}. Sulfur mass (32.07) divided by H₂SO₄ mass (98.08) times 100.

Flashcard 42: What is the molar mass of NaCl?

Answer: 58.$44 \text{ g/mol}$. Sodium (22.99) plus chlorine (35.45) equals 58.44 g/mol.

Flashcard 43: Which element has the highest percent composition in water (H₂O)?

Answer: Oxygen. Oxygen has atomic mass 16, hydrogen has mass 1, so oxygen dominates in H₂O.

Flashcard 44: Determine the percent composition of hydrogen in water (H₂O).

Answer: 11.19\text{ %}. Two hydrogens (2.02 g) divided by water mass (18.02 g) times 100.

Flashcard 45: Calculate the percent composition of carbon in CH₄.

Answer: 74.87\text{ %}. Carbon mass (12.01) divided by methane mass (16.04) times 100.

Flashcard 46: What is the percent composition of oxygen in ethanol (C₂H₅OH)?

Answer: 34.73\text{ %}. One oxygen (16.00 g) divided by ethanol mass (46.08 g) times 100.

Flashcard 47: Find the percent composition of hydrogen in C₆H₁₂O₆.

Answer: 6.71\text{ %}. Twelve hydrogens (12.12 g) divided by glucose mass (180.16 g) times 100.

Flashcard 48: What law states the mass ratio between elements in a compound remains constant?

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 49: What is the formula for calculating percent composition by mass?

Answer: $$. Divides element mass by total compound mass, then multiplies by 100 for percentage.

Flashcard 50: Find the molar mass of acetic acid (CH₃COOH).

Answer: 60.$05 \text{ g/mol}$. Two carbons + four hydrogens + two oxygens: 24.02 + 4.04 + 31.99 = 60.05 g/mol.

Flashcard 51: What is the molar mass of NaCl?

Answer: 58.$44 \text{ g/mol}$. Sodium (22.99) plus chlorine (35.45) equals 58.44 g/mol.

Flashcard 52: Calculate the molar mass of sulfuric acid (H₂SO₄).

Answer: 98.$08 \text{ g/mol}$. Two hydrogens + sulfur + four oxygens: 2.02 + 32.07 + 63.99 = 98.08 g/mol.

Flashcard 53: State the law that governs the fixed proportions by mass in chemical compounds.

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 54: What is the percent composition of oxygen in H₂O₂?

Answer: 94.06\text{ %}. Two oxygens (32.00 g) divided by H₂O₂ mass (34.02 g) times 100.

Flashcard 55: Determine the percent composition of hydrogen in water (H₂O).

Answer: 11.19\text{ %}. Two hydrogens (2.02 g) divided by water mass (18.02 g) times 100.

Flashcard 56: What is the empirical formula of a compound with 92.3% carbon and 7.7% hydrogen?

Answer: CH. Converting percentages to moles gives a 1:1 carbon to hydrogen ratio.

Flashcard 57: What law states the mass ratio between elements in a compound remains constant?

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 58: What is the empirical formula for a compound with 62.1% carbon, 10.4% hydrogen, and 27.5% oxygen?

Answer: C₃H₈O. Converting percentages to moles gives a 3:8:1 carbon to hydrogen to oxygen ratio.

Flashcard 59: Calculate the percent composition of sulfur in H₂SO₄.

Answer: 32.69\text{ %}. Sulfur mass (32.07) divided by H₂SO₄ mass (98.08) times 100.

Flashcard 60: Find the percent composition of sulfur in Na₂SO₄.

Answer: 22.57\text{ %}. Sulfur mass (32.07) divided by Na₂SO₄ mass (142.05) times 100.

Flashcard 61: What is the percent composition of oxygen in H₂O₂?

Answer: 94.06\text{ %}. Two oxygens (32.00 g) divided by H₂O₂ mass (34.02 g) times 100.

Flashcard 62: What is the empirical formula of a compound with 92.3% carbon and 7.7% hydrogen?

Answer: CH. Converting percentages to moles gives a 1:1 carbon to hydrogen ratio.

Flashcard 63: Calculate the percent composition of carbon in CH₄.

Answer: 74.87\text{ %}. Carbon mass (12.01) divided by methane mass (16.04) times 100.

Flashcard 64: What is the molecular formula of a compound with an empirical formula of CH₂O and a molar mass of 180 g/mol?

Answer: C₆H₁₂O₆. Molar mass 180 is six times the empirical formula mass of 30, so multiply by 6.

Flashcard 65: Find the percent composition of hydrogen in C₆H₁₂O₆.

Answer: 6.71\text{ %}. Twelve hydrogens (12.12 g) divided by glucose mass (180.16 g) times 100.

Flashcard 66: Determine the percent composition of oxygen in calcium carbonate (CaCO₃).

Answer: 48.00\text{ %}. Three oxygens (48.00 g) divided by CaCO₃ mass (100.09 g) times 100.

Flashcard 67: What is the percent composition of nitrogen in urea (CH₄N₂O)?

Answer: 46.65\text{ %}. Two nitrogens (28.02 g) divided by urea mass (60.06 g) times 100.

Flashcard 68: What is the percent composition of nitrogen in urea (CH₄N₂O)?

Answer: 46.65\text{ %}. Two nitrogens (28.02 g) divided by urea mass (60.06 g) times 100.

Flashcard 69: What is the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Answer: CH₂O. Convert percentages to moles, divide by smallest, giving 1:2:1 ratio.

Flashcard 70: What is the percent composition of nitrogen in NH₄NO₃?

Answer: 35.00\text{ %}. Two nitrogens (28.02 g) divided by ammonium nitrate mass (80.04 g) times 100.

Flashcard 71: Identify the primary element in the composition of ammonia (NH₃).

Answer: Nitrogen. Nitrogen has the greatest atomic mass in NH₃ compared to the three hydrogens.

Flashcard 72: What is the percent composition of oxygen in ethanol (C₂H₅OH)?

Answer: 34.73\text{ %}. One oxygen (16.00 g) divided by ethanol mass (46.08 g) times 100.

Flashcard 73: What is the percent composition of nitrogen in urea (CH₄N₂O)?

Answer: 46.65\text{ %}. Two nitrogens (28.02 g) divided by urea mass (60.06 g) times 100.

Flashcard 74: What law states the mass ratio between elements in a compound remains constant?

Answer: Law of Definite Proportions. States that compounds always contain the same elements in fixed mass ratios.

Flashcard 75: What is the molecular formula of a compound with an empirical formula of CH₂O and a molar mass of 180 g/mol?

Answer: C₆H₁₂O₆. Molar mass 180 is six times the empirical formula mass of 30, so multiply by 6.

Flashcard 76: Find the percent composition of chlorine in NaCl.

Answer: 60.66\text{ %}. Chlorine mass (35.45) divided by NaCl mass (58.44) times 100.

Flashcard 77: What is the empirical formula for a compound with 85.7% carbon and 14.3% hydrogen?

Answer: CH₂. Converting percentages to moles gives a 1:2 carbon to hydrogen ratio.

Flashcard 78: Determine the percent composition of oxygen in calcium carbonate (CaCO₃).

Answer: 48.00\text{ %}. Three oxygens (48.00 g) divided by CaCO₃ mass (100.09 g) times 100.

Flashcard 79: What is the percent composition of oxygen in H₂O₂?

Answer: 94.06\text{ %}. Two oxygens (32.00 g) divided by H₂O₂ mass (34.02 g) times 100.

Flashcard 80: Find the percent composition of sulfur in Na₂SO₄.

Answer: 22.57\text{ %}. Sulfur mass (32.07) divided by Na₂SO₄ mass (142.05) times 100.

Flashcard 81: What is the empirical formula of a compound with 92.3% carbon and 7.7% hydrogen?

Answer: CH. Converting percentages to moles gives a 1:1 carbon to hydrogen ratio.

Flashcard 82: What is the formula for calculating percent composition by mass?

Answer: $\% \text{ composition} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$. Divides element mass by total compound mass, then multiplies by 100 for percentage.

Flashcard 83: Determine the percent composition of oxygen in calcium carbonate (CaCO₃).

Answer: 48.00\text{ %}. Three oxygens (48.00 g) divided by CaCO₃ mass (100.09 g) times 100.

Flashcard 84: What is the percent composition of hydrogen in H₂SO₄?

Answer: 2.06\text{ %}. Two hydrogens (2.02 g) divided by total H₂SO₄ mass (98.08 g) times 100.

Flashcard 85: What is the percent composition of carbon in benzene (C₆H₆)?

Answer: 92.26\text{ %}. Six carbons (72.06 g) divided by benzene mass (78.12 g) times 100.

Flashcard 86: Which element has the highest percent composition in water (H₂O)?

Answer: Oxygen. Oxygen has atomic mass 16, hydrogen has mass 1, so oxygen dominates in H₂O.

Flashcard 87: Calculate the percent composition of calcium in CaCl₂.

Answer: 36.11\text{ %}. Calcium mass (40.08) divided by CaCl₂ mass (110.98 g) times 100.

Flashcard 88: Calculate the percent composition of carbon in CH₄.

Answer: 74.87\text{ %}. Carbon mass (12.01) divided by methane mass (16.04) times 100.

Flashcard 89: Find the molar mass of CO₂.

Answer: 44.$01 \text{ g/mol}$. Carbon (12.01) plus two oxygens (2 × 16.00) equals 44.01 g/mol.

Flashcard 90: Calculate the percent composition of oxygen in Na₂CO₃.

Answer: 45.28\text{ %}. Three oxygens (48.00 g) divided by Na₂CO₃ mass (105.99 g) times 100.

Flashcard 91: What is the empirical formula for a compound with 62.1% carbon, 10.4% hydrogen, and 27.5% oxygen?

Answer: C₃H₈O. Converting percentages to moles gives a 3:8:1 carbon to hydrogen to oxygen ratio.

Flashcard 92: Calculate the molar mass of sulfuric acid (H₂SO₄).

Answer: 98.$08 \text{ g/mol}$. Two hydrogens + sulfur + four oxygens: 2.02 + 32.07 + 63.99 = 98.08 g/mol.

Flashcard 93: Find the molar mass of glucose (C₆H₁₂O₆).

Answer: 180.$18 \text{ g/mol}$. Six carbons + twelve hydrogens + six oxygens: 72.06 + 12.12 + 96.00 = 180.18 g/mol.

Flashcard 94: Identify the element with the highest composition in methane (CH₄).

Answer: Carbon. Carbon has atomic mass 12.01, much greater than four hydrogens at 4.04 total.

Flashcard 95: What is the percent composition of carbon in benzene (C₆H₆)?

Answer: 92.26\text{ %}. Six carbons (72.06 g) divided by benzene mass (78.12 g) times 100.

Flashcard 96: Determine the empirical formula of a compound with 79.9% carbon and 20.1% hydrogen.

Answer: CH₃. Converting percentages to moles gives a 1:3 carbon to hydrogen ratio.

Flashcard 97: What is the percent composition of carbon in benzene (C₆H₆)?

Answer: 92.26\text{ %}. Six carbons (72.06 g) divided by benzene mass (78.12 g) times 100.

Flashcard 98: What is the percent composition of carbon in CO₂?

Answer: 27.29\text{ %}. Carbon mass (12.01) divided by CO₂ mass (44.01) times 100.

Flashcard 99: What is the percent composition of carbon in CO₂?

Answer: 27.29\text{ %}. Carbon mass (12.01) divided by CO₂ mass (44.01) times 100.