CHEM 111 FINAL SNEAD QUESTIONS WITH COMPLETE ANSWERS..
Course
CHEM 111
1. What is the difference between an element, a compound, and a mixture?
Answer:
Element: Pure substance made of one type of atom only (e.g., Fe, O₂).
Compound: Two or more elements chemically bonded in fixed ratios (e.g., H₂O, NaCl).
Mixture: Physical combination of substances not chemically bonded (e.g., air, saltwater).
2. Calculate the number of moles in 18 g of water (H₂O). (H = 1, O = 16)
Answer:
Molar mass of H₂O = 2(1) + 16 = 18 g/mol
Moles = mass ÷ molar mass = 18 ÷ 18 = 1 mole
3. State and explain the law of conservation of mass.
Answer:
Mass is neither created nor destroyed in a chemical reaction; total mass of reactants equals total
mass of products.
4. Balance the equation:
__ Al + __ O₂ → __ Al₂O₃
Answer:
4Al + 3O₂ → 2Al₂O₃
5. Define molarity and give its formula.
Answer:
Molarity is concentration of a solution in moles of solute per liter of solution.
Formula:
M = moles ÷ volume (L)
,6. Calculate the molarity of a solution containing 2 moles of NaCl in 4 liters of solution.
Answer:
M = 2 ÷ 4 = 0.5 M
7. What is an isotope? Give one example.
Answer:
Isotopes are atoms of the same element with the same number of protons but different number of
neutrons.
Example: Carbon-12 and Carbon-14.
8. Determine the empirical formula of a compound containing 40% C, 6.7% H, and 53.3%
O.
Answer:
Assume 100 g:
C = 40 g ÷ 12 = 3.33
H = 6.7 g ÷ 1 = 6.7
O = 53.3 g ÷ 16 = 3.33
Divide by smallest (3.33):
C=1
H=2
O=1
Empirical formula = CH₂O
9. What is the difference between ionic and covalent bonding?
Answer:
Ionic bonding: Transfer of electrons (metal + non-metal), e.g., NaCl.
Covalent bonding: Sharing of electrons (non-metal + non-metal), e.g., H₂O.
, 10. A gas occupies 2.0 L at 1 atm. If pressure increases to 2 atm at constant temperature,
what is the new volume? (Boyle’s Law)
Answer:
P₁V₁ = P₂V₂
1 × 2 = 2 × V₂
V₂ = 1.0 L
11. What is Avogadro’s number and its significance?
Answer:
Avogadro’s number is 6.022 × 10²³ particles per mole.
It represents the number of atoms, molecules, or ions in one mole of a substance.
12. How many atoms are in 2 moles of carbon?
Answer:
Atoms = moles × Avogadro’s number
= 2 × 6.022 × 10²³
= 1.2044 × 10²⁴ atoms
13. Define oxidation and reduction.
Answer:
Oxidation: Loss of electrons
Reduction: Gain of electrons
(Use OIL RIG: Oxidation Is Loss, Reduction Is Gain)
14. Identify the oxidizing and reducing agents in a reaction.
Answer:
Oxidizing agent: Accepts electrons (gets reduced)
Reducing agent: Donates electrons (gets oxidized)
15. What is the pH scale?
Answer:
A scale from 0–14 measuring acidity or alkalinity:
Course
CHEM 111
1. What is the difference between an element, a compound, and a mixture?
Answer:
Element: Pure substance made of one type of atom only (e.g., Fe, O₂).
Compound: Two or more elements chemically bonded in fixed ratios (e.g., H₂O, NaCl).
Mixture: Physical combination of substances not chemically bonded (e.g., air, saltwater).
2. Calculate the number of moles in 18 g of water (H₂O). (H = 1, O = 16)
Answer:
Molar mass of H₂O = 2(1) + 16 = 18 g/mol
Moles = mass ÷ molar mass = 18 ÷ 18 = 1 mole
3. State and explain the law of conservation of mass.
Answer:
Mass is neither created nor destroyed in a chemical reaction; total mass of reactants equals total
mass of products.
4. Balance the equation:
__ Al + __ O₂ → __ Al₂O₃
Answer:
4Al + 3O₂ → 2Al₂O₃
5. Define molarity and give its formula.
Answer:
Molarity is concentration of a solution in moles of solute per liter of solution.
Formula:
M = moles ÷ volume (L)
,6. Calculate the molarity of a solution containing 2 moles of NaCl in 4 liters of solution.
Answer:
M = 2 ÷ 4 = 0.5 M
7. What is an isotope? Give one example.
Answer:
Isotopes are atoms of the same element with the same number of protons but different number of
neutrons.
Example: Carbon-12 and Carbon-14.
8. Determine the empirical formula of a compound containing 40% C, 6.7% H, and 53.3%
O.
Answer:
Assume 100 g:
C = 40 g ÷ 12 = 3.33
H = 6.7 g ÷ 1 = 6.7
O = 53.3 g ÷ 16 = 3.33
Divide by smallest (3.33):
C=1
H=2
O=1
Empirical formula = CH₂O
9. What is the difference between ionic and covalent bonding?
Answer:
Ionic bonding: Transfer of electrons (metal + non-metal), e.g., NaCl.
Covalent bonding: Sharing of electrons (non-metal + non-metal), e.g., H₂O.
, 10. A gas occupies 2.0 L at 1 atm. If pressure increases to 2 atm at constant temperature,
what is the new volume? (Boyle’s Law)
Answer:
P₁V₁ = P₂V₂
1 × 2 = 2 × V₂
V₂ = 1.0 L
11. What is Avogadro’s number and its significance?
Answer:
Avogadro’s number is 6.022 × 10²³ particles per mole.
It represents the number of atoms, molecules, or ions in one mole of a substance.
12. How many atoms are in 2 moles of carbon?
Answer:
Atoms = moles × Avogadro’s number
= 2 × 6.022 × 10²³
= 1.2044 × 10²⁴ atoms
13. Define oxidation and reduction.
Answer:
Oxidation: Loss of electrons
Reduction: Gain of electrons
(Use OIL RIG: Oxidation Is Loss, Reduction Is Gain)
14. Identify the oxidizing and reducing agents in a reaction.
Answer:
Oxidizing agent: Accepts electrons (gets reduced)
Reducing agent: Donates electrons (gets oxidized)
15. What is the pH scale?
Answer:
A scale from 0–14 measuring acidity or alkalinity:
