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: 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 3: 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 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 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 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: 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 8: 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 9: 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 10: 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 11: 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 12: 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 13: 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 14: 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 15: 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 16: 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 17: 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 18: 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 19: 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 20: 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 21: 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 22: 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 23: 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 24: 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 25: 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 26: 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 27: 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 28: 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 29: 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 30: 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 31: 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 32: 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 33: 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 34: 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 35: 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 36: 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 37: 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 38: 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 39: 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 40: 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 41: 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 42: 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 43: 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 44: 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 45: 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 46: 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 47: 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 48: 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 49: 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 50: 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 51: 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 52: 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 53: 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 54: 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 55: 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 56: 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 57: 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 58: 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 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: 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 61: 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 62: 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 63: 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 64: 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 65: 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 66: 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 67: 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 68: 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 69: 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 70: 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 71: 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 72: 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 73: 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 74: 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 75: 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 76: 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 77: 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 78: 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 79: 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 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 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 82: 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 83: 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 84: 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 85: 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 86: 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 87: 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 88: 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 89: 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 90: 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 91: 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 92: 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 93: 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 94: 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 95: 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 96: 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 97: 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 98: 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 99: 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 100: 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.