Chm 104 practice set

Multiple choice

  1. B. ductility — ability to be drawn into thin wires.

  2. D. Metalloids/Semimetals — elements with properties of both metals and nonmetals.

  3. B. metal — description matches a metal.

  4. B. element — cannot be broken down by ordinary chemical means.

  5. D. theory — general statement explaining many observations.

Short answer

7. Exact or measured
a. 2 dozen roses — exact (defined count: 24)
b. Distance New York → Chicago — measured (depends on route/method)
c. Number of centimeters in a meter — exact (100 cm = 1 m exactly)
d. Mass of a car — measured
e. Amount of water in a glass — measured

8. Chemical or physical property
a. temperature — physical
b. mass — physical
c. density — physical
d. combustibility — chemical
e. reactivity — chemical

9. Physical or chemical change
a. leaves changing color in autumn — chemical (pigment/biochemical changes)
b. yeast rolls rising — chemical (CO₂ produced by fermentation)
c. dissolving Kool-Aid in water — physical (physical mixing; typically no new substance)
d. a nail rusting — chemical (oxidation)
e. melting a popsicle — physical

10. Element / compound / mixture
a. calcium — element
b. sodium hydroxide — compound (NaOH)
c. sweet tea — mixture (solution; tea + sugar + water)
d. soil — mixture
e. carbon — element

Problems — sig figs & calculations

11. Number of significant figures
a. 4,200 m — 2 significant figures (ambiguous unless decimal shown; assume 2)
b. 0.00533 cm — 3 sig figs
c. 3.0593 ft — 5 sig figs
d. 106.00 mi — 5 sig figs
e. 100 mL — 1 significant figure (ambiguous without decimal)

12. Calculations (correct sig-fig rules applied)
a. 10.536 cm + 9.34 cm = 19.876 → round to 2 decimal places (least decimal places = 2) → 19.88 cm
b. 13.425 cm × 4.63 cm = 62.15775 → least sig figs = 3 → 62.2 cm²
c. 25 g + 10.5 g = 35.5 → least decimal places = 0 (25 has 0 decimal places) → round to 0 dp → 36 g
d. 40.52 mL × 2.7 g/mL = 109.404 → least sig figs = 2 → 1.10×10^2 g or 110 g (2 sig figs)

13. Dimensional analysis conversions (I used common US metric factors)

a. 95.4 lb → kg
1 lb = 0.45359237 kg → 95.4 × 0.45359237 = 43.2727... → 3 sig figs (95.4 has 3) → 43.3 kg

b. 36.9 qt → gal
1 gal = 4 qt → 36.9 ÷ 4 = 9.225 → 3 sig figs → 9.23 gal

c. 7.368 ft → mm
1 ft = 304.8 mm → 7.368 × 304.8 = 2245.7664 mm → 4 sig figs (7.368 has 4) → 2246 mm (or 2.246×10^3 mm)

d. 26.38 g → lb
1 lb = 453.59237 g → 26.38 ÷ 453.59237 = 0.0581579... → 4 sig figs (26.38 has 4) → 0.05816 lb

e. 68.36 L → gal
1 gal = 3.785411784 L → 68.36 ÷ 3.785411784 = 18.0588... → 4 sig figs → 18.06 gal

14. Volume of a cube (edge = 4.70 cm)
V = a³ = 4.70³ = 103.823 cm³ → 3 significant figures (4.70 has 3) → 1.04×10^2 cm³ or 104 cm³

15. Mass of ethyl alcohol filling 200.0 mL
density = 0.789 g/mL. m = 200.0 mL × 0.789 g/mL = 157.8 g → least sig figs = 3 (0.789 has 3) → 158 g

16. Density of sulfuric acid
ρ = mass / volume = 65.14 g / 35.4 mL = 1.84011... g/mL → least sig figs = 3 (35.4 has 3) → 1.84 g/mL

17. Density of lead block
Volume = 4.50 cm × 5.20 cm × 6.00 cm = 140.4 cm³ (product of three values with 3 sig figs → report density to 3 sig figs).
Density = mass / volume = 1587 g / 140.4 cm³ = 11.303... g/cm³ → 11.3 g/cm³
(If you want the volume reported to 3 sig figs: 1.40×10^2 cm³.)

18. Mass of 250.0 mL benzene (ρ = 0.8765 g/mL)
m = 250.0 × 0.8765 = 219.125 g → 4 sig figs (both inputs have 4) → 219.1 g

19. Volume of silver with mass 2500.0 g (ρ = 10.5 g/cm³)
V = m / ρ = 2500.0 / 10.5 = 238.095... cm³ → least sig figs = 3 (10.5 has 3) → 238 cm³

Multiple Choice — answers

  1. A. Electron

  2. A. number of protons in the atom

  3. B. 237.94

  4. B. isotopes

  5. D. Atoms of the same element are not the same always.

  6. D. atomic mass

Short Answer

7. Subatomic particles, charges, and locations

  • Proton — charge: +1 (positive). Location: nucleus. Mass ≈ 1 amu.

  • Neutron — charge: 0 (neutral). Location: nucleus. Mass ≈ 1 amu.

  • Electron — charge: −1 (negative). Location: electron cloud / orbitals around nucleus. Mass ≈ 1/1836 amu.

8. Nuclear symbols (mass number and atomic number)
(written as atomicNumber^massElement )
a. strontium-88: 38^88Sr
b. bromine-82: 35^82Br
c. boron-10: 5^10B
d. neon-20: _10^20Ne

9. Number of protons, neutrons, electrons (for neutral atoms)
a. Strontium-88 (Sr): protons = 38, neutrons = 88 − 38 = 50, electrons = 38.
b. Bromine-82 (Br): protons = 35, neutrons = 82 − 35 = 47, electrons = 35.
c. Boron-10 (B): protons = 5, neutrons = 10 − 5 = 5, electrons = 5.
d. Neon-20 (Ne): protons = 10, neutrons = 20 − 10 = 10, electrons = 10.

10. Classify as metal / nonmetal / metalloid
a. Sodium — metal (alkali metal)
b. Chlorine — nonmetal (halogen)
c. Oxygen — nonmetal (chalcogen)
d. Copper — metal (transition metal)
e. Silicon — metalloid
f. Potassium — metal (alkali metal)
g. Selenium — nonmetal (often grouped with the chalcogens; sometimes described as metalloid-like)

11. Identify the element from each description
a. Period 5 transition metal with 2 valence electrons → Yttrium (Y).
b. A metalloid in period 3 → Silicon (Si).
c. A noble gas in period 6 → Radon (Rn).
d. A nonmetal with 5 valence electrons in period 2 → Nitrogen (N).
e. An element in period 4 and group 17 → Bromine (Br).
f. An element in group 15 and period 4 → Arsenic (As).

12. Family names
a. Helium — Noble gas (inert gases / group 18)
b. Sulfur — Chalcogens (group 16)
c. Sodium — Alkali metals (group 1)
d. Magnesium — Alkaline earth metals (group 2)
e. Iron — Transition metals
f. Bromine — Halogens (group 17)
g. Phosphorus — Pnictogens (nitrogen group, group 15)