Foundations of Chemistry & Measurement
Exam With Verified Questions ,Answers And
Rationales
**1. How many significant figures are in 0.004050 L?**
- **Answer:** 4
- **Rationale:** Leading zeros don't count. The digits 4, 0, 5, and 0 are all significant .
**2. Express 0.000407 in scientific notation.**
- **Answer:** 4.07 × 10⁻⁴
- **Rationale:** Move the decimal point 4 places to the right; the number is less than 1, so the
exponent is negative .
**3. A substance has a temperature of 315 K. What is this in °C?**
- **Answer:** 41.85°C
- **Rationale:** °C = K - 273.15 = 315 - 273.15 = 41.85°C .
**4. Convert 55.0 mi/hr to m/s. (1 mi = 1609 m)**
- **Answer:** 24.6 m/s
- **Rationale:** (55.0 mi/hr) × (1609 m/mi) × (1 hr/3600 s) = 24.58 ≈ 24.6 m/s .
**5. A student measures 42.10 g of an empty beaker, then 51.32 g with liquid. Volume is 12.5 mL.
What is density?**
- **Answer:** 0.738 g/mL
- **Rationale:** Mass of liquid = 51.32 - 42.10 = 9.22 g; Density = 9.22 g / 12.5 mL = 0.738 g/mL .
**6. Classify air: pure element, compound, homogeneous mixture, or heterogeneous mixture?**
- **Answer:** Homogeneous mixture
- **Rationale:** Air is a mixture of gases (N₂, O₂, CO₂, etc.) that is uniform throughout .
, ## Atomic Structure & Periodic Properties
**7. Which subatomic particle determines the identity of an element?**
- **Answer:** Proton
- **Rationale:** The atomic number = number of protons. Changing the number of protons changes
the element .
**8. How many protons, neutrons, and electrons are in Cobalt-60 (⁶⁰Co)?**
- **Answer:** 27 protons, 33 neutrons, 27 electrons
- **Rationale:** Atomic number of Co = 27 (protons, electrons in neutral atom). Neutrons = mass
number - protons = 60 - 27 = 33 .
**9. Isotopes of an element have different numbers of:**
- **Answer:** Neutrons
- **Rationale:** Same atomic number (Z), different mass number → different number of neutrons .
**10. Which has the smallest atomic radius: Na, Mg, Al, or Si?**
- **Answer:** Si
- **Rationale:** Atomic radius decreases left to right across a period due to increasing nuclear
charge .
**11. Which has the highest first ionization energy: O, F, N, or Ne?**
- **Answer:** Ne
- **Rationale:** Ionization energy increases up and to the right on the periodic table. Noble gases
have the highest IE in their period .
**12. Most electronegative element: Cl, O, F, or N?**
- **Answer:** F
- **Rationale:** Fluorine is the most electronegative element on the Pauling scale .
**13. Write the complete electron configuration for Sulfur (S).**
Exam With Verified Questions ,Answers And
Rationales
**1. How many significant figures are in 0.004050 L?**
- **Answer:** 4
- **Rationale:** Leading zeros don't count. The digits 4, 0, 5, and 0 are all significant .
**2. Express 0.000407 in scientific notation.**
- **Answer:** 4.07 × 10⁻⁴
- **Rationale:** Move the decimal point 4 places to the right; the number is less than 1, so the
exponent is negative .
**3. A substance has a temperature of 315 K. What is this in °C?**
- **Answer:** 41.85°C
- **Rationale:** °C = K - 273.15 = 315 - 273.15 = 41.85°C .
**4. Convert 55.0 mi/hr to m/s. (1 mi = 1609 m)**
- **Answer:** 24.6 m/s
- **Rationale:** (55.0 mi/hr) × (1609 m/mi) × (1 hr/3600 s) = 24.58 ≈ 24.6 m/s .
**5. A student measures 42.10 g of an empty beaker, then 51.32 g with liquid. Volume is 12.5 mL.
What is density?**
- **Answer:** 0.738 g/mL
- **Rationale:** Mass of liquid = 51.32 - 42.10 = 9.22 g; Density = 9.22 g / 12.5 mL = 0.738 g/mL .
**6. Classify air: pure element, compound, homogeneous mixture, or heterogeneous mixture?**
- **Answer:** Homogeneous mixture
- **Rationale:** Air is a mixture of gases (N₂, O₂, CO₂, etc.) that is uniform throughout .
, ## Atomic Structure & Periodic Properties
**7. Which subatomic particle determines the identity of an element?**
- **Answer:** Proton
- **Rationale:** The atomic number = number of protons. Changing the number of protons changes
the element .
**8. How many protons, neutrons, and electrons are in Cobalt-60 (⁶⁰Co)?**
- **Answer:** 27 protons, 33 neutrons, 27 electrons
- **Rationale:** Atomic number of Co = 27 (protons, electrons in neutral atom). Neutrons = mass
number - protons = 60 - 27 = 33 .
**9. Isotopes of an element have different numbers of:**
- **Answer:** Neutrons
- **Rationale:** Same atomic number (Z), different mass number → different number of neutrons .
**10. Which has the smallest atomic radius: Na, Mg, Al, or Si?**
- **Answer:** Si
- **Rationale:** Atomic radius decreases left to right across a period due to increasing nuclear
charge .
**11. Which has the highest first ionization energy: O, F, N, or Ne?**
- **Answer:** Ne
- **Rationale:** Ionization energy increases up and to the right on the periodic table. Noble gases
have the highest IE in their period .
**12. Most electronegative element: Cl, O, F, or N?**
- **Answer:** F
- **Rationale:** Fluorine is the most electronegative element on the Pauling scale .
**13. Write the complete electron configuration for Sulfur (S).**
