What Is The Molecular Mass Of Br2 ? A) 79.90 Amu B) 79.90 G C) 159.8 Amu D) 159.8 G E) 2.65 X 10-22 Amu 2. What Is The Mass Of 4.50 X 1022 Cu Atoms? A) 7.47 X 10-2g B) 7.47 X 10-2 Amu C) 4.75 G D) 63.55 Amu E) 63.55 G 3.Determine The Number Of Moles Of Aluminum In 96.7 G Of Al. A) 0.279 Mol B) 3.58 Mol C) 7.43 Mol D) 4.21 Mol E) 6.02 X 1023 Mol 4.How Many
The Correct Answer and Explanation is:
Here are the correct answers and detailed explanations for each of the chemistry questions you’ve asked:
1. What is the molecular mass of Br₂?
Correct Answer: C) 159.8 amu
Explanation:
The molecular mass (also called molecular weight) is the sum of the atomic masses of all atoms in a molecule.
- Bromine (Br) has an atomic mass of approximately 79.90 atomic mass units (amu).
- Br₂ is a diatomic molecule, meaning it consists of two bromine atoms bonded together.
So, the molecular mass of Br₂ is:
$$
79.90 \, \text{amu} \times 2 = 159.8 \, \text{amu}
$$
Let’s analyze the other options:
- A) 79.90 amu is the atomic mass of one Br atom, not Br₂.
- B) 79.90 g and D) 159.8 g are values that might represent molar masses (mass per mole), not molecular masses.
- E) 2.65 x 10⁻²² amu is nonsensical in this context — that’s far too small.
The key idea is that molecular mass is always expressed in amu, not grams. Grams relate to the mass of moles, not individual molecules.
2. What is the mass of 4.50 × 10²² Cu atoms?
Correct Answer: A) 7.47 × 10⁻² g
Explanation:
To find the mass of a number of atoms, use this formula:
$$
\text{Mass} = \left( \frac{\text{Number of atoms}}{\text{Avogadro’s number}} \right) \times \text{Molar mass}
$$
Where:
- Number of atoms = $4.50 \times 10^{22}$
- Avogadro’s number = $6.022 \times 10^{23} \, \text{atoms/mol}$
- Molar mass of Cu = 63.55 g/mol
$$
\text{Mass} = \left( \frac{4.50 \times 10^{22}}{6.022 \times 10^{23}} \right) \times 63.55
\approx 0.0747 \, \text{g} = 7.47 \times 10^{-2} \, \text{g}
$$
This confirms option A is correct.
3. Determine the number of moles of aluminum in 96.7 g of Al.
Correct Answer: B) 3.58 mol
Explanation:
To find the number of moles:
$$
\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar mass (g/mol)}}
$$
- Mass = 96.7 g
- Molar mass of aluminum (Al) ≈ 26.98 g/mol
$$
\text{Moles} = \frac{96.7}{26.98} \approx 3.58 \, \text{mol}
$$
Thus, 3.58 mol is correct (Option B).
