C832 Chemistry with Lab
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Free C832 Chemistry with Lab Questions
1. Balance the equation in acidic solution: __Cr₂O₇²⁻ + __Fe²⁺ → __Cr³⁺ + __Fe³⁺
Coefficient for Fe²⁺ is:
Coefficient for Fe²⁺ is:
- 3
- 6
- 14
- 7
Explanation
Explanation:
In acidic solution, the dichromate ion (Cr₂O₇²⁻) is reduced to Cr³⁺ while Fe²⁺ is oxidized to Fe³⁺. Balancing the half-reactions: Cr₂O₇²⁻ + 14 H⁺ + 6 e⁻ → 2 Cr³⁺ + 7 H₂O and Fe²⁺ → Fe³⁺ + e⁻. To balance the electrons, 6 Fe²⁺ ions are required to provide 6 electrons. Thus, the coefficient for Fe²⁺ in the balanced redox reaction is 6.
Why the other options are incorrect:
3 is half the required electrons; 14 is the coefficient for H⁺ in the reduction half-reaction; 7 is for H₂O in the reduction half-reaction.
Correct Answer: 6
In acidic solution, the dichromate ion (Cr₂O₇²⁻) is reduced to Cr³⁺ while Fe²⁺ is oxidized to Fe³⁺. Balancing the half-reactions: Cr₂O₇²⁻ + 14 H⁺ + 6 e⁻ → 2 Cr³⁺ + 7 H₂O and Fe²⁺ → Fe³⁺ + e⁻. To balance the electrons, 6 Fe²⁺ ions are required to provide 6 electrons. Thus, the coefficient for Fe²⁺ in the balanced redox reaction is 6.
Why the other options are incorrect:
3 is half the required electrons; 14 is the coefficient for H⁺ in the reduction half-reaction; 7 is for H₂O in the reduction half-reaction.
Correct Answer: 6
2. The correct formula for ammonium phosphate is:
- NH₄PO₄
- (NH₄)₃PO₄
- NH₄(PO₄)₃
- (NH₄)₂PO₄
Explanation
Explanation:
The correct formula for ammonium phosphate is (NH₄)₃PO₄. The ammonium ion (NH₄⁺) carries a +1 charge, and the phosphate ion (PO₄³⁻) carries a -3 charge. To balance the charges, three ammonium ions are required for each phosphate ion, resulting in the formula (NH₄)₃PO₄. This compound is commonly used as a fertilizer due to its high nitrogen and phosphorus content.
Correct Answer: (NH₄)₃PO₄
The correct formula for ammonium phosphate is (NH₄)₃PO₄. The ammonium ion (NH₄⁺) carries a +1 charge, and the phosphate ion (PO₄³⁻) carries a -3 charge. To balance the charges, three ammonium ions are required for each phosphate ion, resulting in the formula (NH₄)₃PO₄. This compound is commonly used as a fertilizer due to its high nitrogen and phosphorus content.
Correct Answer: (NH₄)₃PO₄
3. The volume of CO₂ (at STP) produced from the complete combustion of 16 g CH₄ is
- 11.2 L
- 22.4 L
- 44.8 L
- 67.2 L
Explanation
The balanced combustion equation is CH₄ + 2 O₂ → CO₂ + 2 H₂O.
The molar mass of CH₄ is 16 g/mol, so 16 g of CH₄ equals 1 mole.
According to the stoichiometry, 1 mole of CH₄ produces 1 mole of CO₂.
At STP, 1 mole of gas occupies 22.4 L.
Therefore, 16 g of CH₄ produces 22.4 L of CO₂.
Correct Answer: 22.4 L
The molar mass of CH₄ is 16 g/mol, so 16 g of CH₄ equals 1 mole.
According to the stoichiometry, 1 mole of CH₄ produces 1 mole of CO₂.
At STP, 1 mole of gas occupies 22.4 L.
Therefore, 16 g of CH₄ produces 22.4 L of CO₂.
Correct Answer: 22.4 L
4. The formula for aluminum sulfide is:
- AlS
- Al₂S₃
- Al₃S₂
- AlS₃
Explanation
Explanation:
The correct formula for aluminum sulfide is Al₂S₃. Aluminum forms a +3 ion (Al³⁺), while sulfur forms a -2 ion (S²⁻). To balance the charges, two aluminum ions (total +6) combine with three sulfur ions (total -6), forming the neutral compound Al₂S₃. This compound is an ionic solid commonly used in chemical synthesis and materials science.
Correct Answer: Al₂S₃
The correct formula for aluminum sulfide is Al₂S₃. Aluminum forms a +3 ion (Al³⁺), while sulfur forms a -2 ion (S²⁻). To balance the charges, two aluminum ions (total +6) combine with three sulfur ions (total -6), forming the neutral compound Al₂S₃. This compound is an ionic solid commonly used in chemical synthesis and materials science.
Correct Answer: Al₂S₃
5. What is the molecular geometry of a molecule with AX₃E notation?
- Trigonal planar
- Trigonal pyramidal
- T-shaped
- Tetrahedral
Explanation
In VSEPR notation, AX₃E represents a molecule with four electron domains — three bonding pairs and one lone pair on the central atom. The lone pair repels the bonding pairs, slightly compressing the bond angles and resulting in a trigonal pyramidal molecular geometry. This geometry is typical for molecules like ammonia (NH₃), where nitrogen is bonded to three hydrogen atoms and has one lone pair.
Correct Answer: Trigonal pyramidal
Correct Answer: Trigonal pyramidal
6. Which molecule is polar?
- BF₃
- PF₅
- SF₂
- XeF₄
Explanation
Explanation:
SF₂ is a polar molecule because it has a bent molecular geometry due to two lone pairs on the sulfur atom. This geometry creates an uneven distribution of charge, resulting in a dipole moment. In contrast, BF₃ and PF₅ are nonpolar because they are symmetrical, and XeF₄ is also nonpolar due to its square planar geometry, which cancels out dipole moments.
Correct Answer: SF₂
Why the other options are incorrect:
BF₃ trigonal planar symmetry; PF₅ trigonal bipyramidal symmetry; XeF₄ square planar symmetry.
SF₂ is a polar molecule because it has a bent molecular geometry due to two lone pairs on the sulfur atom. This geometry creates an uneven distribution of charge, resulting in a dipole moment. In contrast, BF₃ and PF₅ are nonpolar because they are symmetrical, and XeF₄ is also nonpolar due to its square planar geometry, which cancels out dipole moments.
Correct Answer: SF₂
Why the other options are incorrect:
BF₃ trigonal planar symmetry; PF₅ trigonal bipyramidal symmetry; XeF₄ square planar symmetry.
7. What type of reaction is NaOH + HCl → NaCl + H₂O?
- Decomposition
- Single Replacement
- Double Replacement
- Combustion
Explanation
Explanation:
This reaction is a double replacement reaction because the positive ions (Na⁺ and H⁺) and negative ions (OH⁻ and Cl⁻) exchange places to form two new compounds—sodium chloride (NaCl) and water (H₂O). Such reactions often occur in aqueous solutions and are common in acid-base neutralization, where an acid reacts with a base to produce salt and water.
Correct Answer:
Double Replacement
This reaction is a double replacement reaction because the positive ions (Na⁺ and H⁺) and negative ions (OH⁻ and Cl⁻) exchange places to form two new compounds—sodium chloride (NaCl) and water (H₂O). Such reactions often occur in aqueous solutions and are common in acid-base neutralization, where an acid reacts with a base to produce salt and water.
Correct Answer:
Double Replacement
8. Which molecule exhibits sp² hybridization on the central atom?
- CH₄
- SO₃
- PF₅
- SF₆
Explanation
Explanation:
SO₃ (sulfur trioxide) has a central sulfur atom bonded to three oxygen atoms with no lone pairs. The sulfur atom forms three sigma bonds and uses three hybrid orbitals, which corresponds to sp² hybridization. This allows for a trigonal planar geometry with bond angles of approximately 120°.
Why the other options are incorrect:
In contrast, CH₄ is sp³, PF₅ is sp³d, and SF₆ is sp³d² hybridized.
Correct Answer: SO₃
SO₃ (sulfur trioxide) has a central sulfur atom bonded to three oxygen atoms with no lone pairs. The sulfur atom forms three sigma bonds and uses three hybrid orbitals, which corresponds to sp² hybridization. This allows for a trigonal planar geometry with bond angles of approximately 120°.
Why the other options are incorrect:
In contrast, CH₄ is sp³, PF₅ is sp³d, and SF₆ is sp³d² hybridized.
Correct Answer: SO₃
9. The octet rule is violated in which acceptable Lewis structure?
- BeCl₂
- NH₃
- H₂O
- CH₄
Explanation
Explanation:
The octet rule states that atoms tend to form bonds so that each atom has eight electrons in its valence shell. However, beryllium in BeCl₂ is an exception to this rule. In its Lewis structure, beryllium forms two single bonds with two chlorine atoms, giving it only four electrons in its valence shell. Despite not having a complete octet, BeCl₂ is a stable compound because beryllium can exist comfortably with fewer than eight electrons due to its small size and low electronegativity.
Correct Answer: BeCl₂
Why the other options are incorrect:
NH₃, H₂O, CH₄ all satisfy octet rule for central atoms.
The octet rule states that atoms tend to form bonds so that each atom has eight electrons in its valence shell. However, beryllium in BeCl₂ is an exception to this rule. In its Lewis structure, beryllium forms two single bonds with two chlorine atoms, giving it only four electrons in its valence shell. Despite not having a complete octet, BeCl₂ is a stable compound because beryllium can exist comfortably with fewer than eight electrons due to its small size and low electronegativity.
Correct Answer: BeCl₂
Why the other options are incorrect:
NH₃, H₂O, CH₄ all satisfy octet rule for central atoms.
10. What is the name of H₂SO₄?
- Hydrosulfuric acid
- Sulfuric acid
- Sulfurous acid
- Hydrogen sulfate
Explanation
Explanation:
The correct name for H₂SO₄ is sulfuric acid. This acid is derived from the sulfate ion (SO₄²⁻) and follows the naming convention for oxyacids: when the polyatomic ion ends in “-ate,” the acid name ends in “-ic.” Thus, “sulfate” becomes “sulfuric.” Sulfuric acid is a strong acid widely used in fertilizers, batteries, and industrial chemical processes.
Correct Answer: Sulfuric acid
The correct name for H₂SO₄ is sulfuric acid. This acid is derived from the sulfate ion (SO₄²⁻) and follows the naming convention for oxyacids: when the polyatomic ion ends in “-ate,” the acid name ends in “-ic.” Thus, “sulfate” becomes “sulfuric.” Sulfuric acid is a strong acid widely used in fertilizers, batteries, and industrial chemical processes.
Correct Answer: Sulfuric acid
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