SOLUTION: Mole concept practice papper - Studypool - Free Printable

Let's solve each question step by step:

---

Question 1: Molecular weight of SO₂ is

- SO₂ consists of one sulfur (S) atom and two oxygen (O) atoms.
- Atomic mass of S = 32 amu
- Atomic mass of O = 16 amu
- Molecular weight of SO₂ = 1 × 32 + 2 × 16 = 32 + 32 = 64 amu

Answer: (2) 64 amu

---

Question 2: Centigrade and Fahrenheit scales are related as:

The relationship between Celsius (C) and Fahrenheit (F) is given by:
\[ F = \frac{9}{5}C + 32 \]
Rearranging for C:
\[ C = \frac{5}{9}(F - 32) \]

Answer: (1) \(\frac{C}{5} = \frac{F - 32}{9}\)

---

Question 3: The modern atomic weight scale is based on:

The modern atomic weight scale is based on the isotope ¹²C, where the atomic mass of ¹²C is defined as exactly 12 amu.

Answer: (1) ¹²C

---

Question 4: 1 amu is equal to:

1 atomic mass unit (amu) is defined as:
\[ 1 \, \text{amu} = \frac{1}{12} \text{ of the mass of one atom of } ^{12}\text{C} \]

Answer: (1) \(\frac{1}{12}\) of C–12

---

Question 5: Avogadro number is:

Avogadro's number (\(N_A\)) is approximately \(6.022 \times 10^{23}\) and represents:
1. The number of atoms in one gram of the element (for monatomic elements).
2. The number of molecules present in one gram molecular mass of a substance.
3. The number of millilitres which one mole of a gaseous substance occupies at NTP (1 atm & 0°C).

All these statements are correct.

Answer: (4) All are correct

---

Question 6: At what temperature, both Celsius and Fahrenheit scale read the same value:

To find the temperature where Celsius (C) and Fahrenheit (F) are equal, set \(C = F\) in the conversion formula:
\[ F = \frac{9}{5}C + 32 \]
\[ C = \frac{9}{5}C + 32 \]
Rearrange:
\[ C - \frac{9}{5}C = 32 \]
\[ \frac{5}{5}C - \frac{9}{5}C = 32 \]
\[ -\frac{4}{5}C = 32 \]
\[ C = 32 \times \left(-\frac{5}{4}\right) \]
\[ C = -40 \]

Thus, at \(-40^\circ\), both scales read the same value.

Answer: (4) –40°

---

Question 7: The weight of one atom of Uranium is 238 amu. Its actual weight is …… g.

The mass of one atom in grams can be calculated using the relationship:
\[ 1 \, \text{amu} = 1.66 \times 10^{-24} \, \text{g} \]
For uranium (238 amu):
\[ \text{Mass of one atom} = 238 \times 1.66 \times 10^{-24} \]
\[ = 3.95 \times 10^{-22} \, \text{g} \]

Answer: (1) \(3.95 \times 10^{-22}\)

---

Question 8: If the atomic mass of Sodium is 23, the number of moles in 46 g of sodium is:

The number of moles (\(n\)) is given by:
\[ n = \frac{\text{mass}}{\text{molar mass}} \]
Here, mass = 46 g and molar mass = 23 g/mol:
\[ n = \frac{46}{23} = 2 \, \text{moles} \]

Answer: (2) 2

---

Question 9: How many atoms are there in 100 amu of He?

The atomic mass of helium (He) is 4 amu. Therefore, 100 amu of He corresponds to:
\[ \text{Number of atoms} = \frac{100 \, \text{amu}}{4 \, \text{amu/atom}} = 25 \, \text{atoms} \]

Answer: (1) 25

---

Final Answers:

1. (2) 64 amu
2. (1) \(\frac{C}{5} = \frac{F - 32}{9}\)
3. (1) ¹²C
4. (1) \(\frac{1}{12}\) of C–12
5. (4) All are correct
6. (4) –40°
7. (1) \(3.95 \times 10^{-22}\)
8. (2) 2
9. (1) 25

Boxed Final Answer:
\[
\boxed{(2), (1), (1), (1), (4), (4), (1), (2), (1)}
\]