How many moles of hydrogen atoms are present in 135 mg of H_2O?

• A. 0.0150 moles
• B. 0.0150 moles of H_2
• C. 0.0150 moles of H atoms
• D. 0.015 moles

Answer: (C)

Verified step by step guidance

1. Identify the given quantity: 135 mg of H_2O. Convert this mass into grams by dividing by 1000, since 1 g = 1000 mg. So, mass in grams = \( \frac{135}{1000} \) g.
2. Calculate the number of moles of H_2O using its molar mass. The molar mass of H_2O is calculated as: \( 2 \times 1.008 + 16.00 = 18.016 \) g/mol. Use the formula: \( \text{moles of H_2O} = \frac{\text{mass of H_2O in grams}}{\text{molar mass of H_2O}} \).
3. Determine the number of moles of hydrogen atoms in the sample. Each molecule of H_2O contains 2 hydrogen atoms, so multiply the moles of H_2O by 2: \( \text{moles of H atoms} = 2 \times \text{moles of H_2O} \).
4. Interpret the result as the total moles of hydrogen atoms present in the original 135 mg of water.
5. Compare your calculated moles of hydrogen atoms with the given answer choices to confirm the correct answer.