Multiple Choice
A 20.0 mL sample of a 15.5% (m/v) KBr solution is taken. What mass of KBr (in grams) is present in this sample?
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3. Chemical Reactions
Mass Percent
Multiple Choice
What is the approximate mass percent of nitrogen and oxygen in nitrogen dioxide (NO_2)?
A
Nitrogen: 50%, Oxygen: 50%
B
Nitrogen: 30%, Oxygen: 70%
C
Nitrogen: 20%, Oxygen: 80%
D
Nitrogen: 44%, Oxygen: 56%
Verified step by step guidance1
Step 1: Write down the molecular formula of nitrogen dioxide, which is \(\mathrm{NO_2}\), indicating 1 nitrogen atom and 2 oxygen atoms per molecule.
Step 2: Find the atomic masses of nitrogen and oxygen from the periodic table. Typically, nitrogen has an atomic mass of approximately 14.0 g/mol, and oxygen has an atomic mass of approximately 16.0 g/mol.
Step 3: Calculate the molar mass of \(\mathrm{NO_2}\) by adding the atomic masses of all atoms in the molecule: \(\mathrm{Molar\ mass} = (1 \times 14.0) + (2 \times 16.0)\) g/mol.
Step 4: Calculate the mass percent of nitrogen using the formula: \(\mathrm{Mass\%\ of\ N} = \left( \frac{\text{mass of N in the formula}}{\text{molar mass of } \mathrm{NO_2}} \right) \times 100\).
Step 5: Calculate the mass percent of oxygen similarly: \(\mathrm{Mass\%\ of\ O} = \left( \frac{\text{mass of O in the formula}}{\text{molar mass of } \mathrm{NO_2}} \right) \times 100\). These percentages should add up to approximately 100%.
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