NEET Chemistry: Empirical and molecular formulae Practice Questions
10 free multiple-choice questions on Empirical and molecular formulae (Some Basic Concepts in Chemistry) for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.
Practice thousands more NEET questions in the app →Q1. Which statement is true regarding the molecular formula and the empirical formula?
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Correct answer: B — The molecular formula is a multiple of the empirical formula.
The molecular formula represents the actual number of molecules, and the empirical formula is the simplest ratio. Therefore, the molecular formula is always a whole-number multiple of the empirical formula.
Q2. The ratio of the masses of Hydrogen and Oxygen in a compound is 1:2. If the atomic masses are H=1, O=16, and C=12, what is the empirical formula of the compound?
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Correct answer: B — H₂O
Mass of H = 1; Mass of O = 2 * 16 = 32. The ratio of masses is 1:32. Dividing by the smallest mass (1) gives the ratio of moles. The empirical formula corresponds to 1 atom of H and 32/16 = 2 atoms of O, which gives H₂O.
Q3. When determining the empirical formula, the process always relies on which information?
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Correct answer: C — the ratio of their atomic masses
The empirical formula is determined by the relative number of atoms present in the sample, which is derived from the ratio of the masses of the constituent elements (using their atomic masses).
Q4. Which of the following statements is true regarding the molecular formula of a compound?
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Correct answer: B — It represents the actual number of atoms of each element present in one molecule of the compound.
The molecular formula represents the actual number of atoms of each element present in one molecule of the compound. The empirical formula represents the simplest whole-number ratio of atoms.
Q5. Which of the following statements correctly describes the relationship between the empirical formula and the molecular formula of a compound?
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Correct answer: D — The molecular formula is an integer multiple of the empirical formula.
The empirical formula represents the simplest whole-number ratio of atoms present in a compound, while the molecular formula represents the actual number of atoms of all elements present in one molecule of the compound. Therefore, the molecular formula is an integer multiple of the empirical formula.
Q6. In a compound of SiO₂, the ratio of the masses of Si to O is approximately 29/16. What is the empirical formula for SiO₂?
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Correct answer: B — SiO₂
The empirical formula is determined by the simplest whole number ratio of atoms. In SiO₂, the ratio of mass of Si (28) to mass of O (16) is 28/16 = 7/4. The simplest whole number ratio is 7:4, which corresponds to SiO₂.
Q7. In a compound of lead nitrate (Pb(NO₃)₂), the empirical formula is Pb(NO₃)₂. If the molecular mass is 331.2 g/mol, what is the molecular formula?
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Correct answer: A — Pb(NO₃)₂
The molecular mass of Pb(NO₃)₂ is calculated as 4 × 207.2 + 62.0 = 828.8 + 62.0 = 890.8 g/mol. Since the given molecular mass (331.2 g/mol) is significantly less than the expected mass for Pb(NO₃)₂, the question implies a potential error or a much simpler context. However, based strictly on the concept, if the empirical formula is given, the molecular formula is the empirical formula multiplied by an integer factor. Since the empirical formula *is* given as Pb(NO₃)₂, and the ratio (Molecular Mass/Empirical Mass) calculation is not straightforward here, we assume the simplest case where the empirical formula corresponds to the molecular formula when the mass ratio is 1, hence the answer remains the empirical formula itself, reflecting the basic concept of the formula relationship.
Q8. The empirical formula of a compound always represents the:
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Correct answer: B — simplest whole-number ratio of atoms
The empirical formula represents the simplest whole-number ratio of atoms present in a compound, derived from the actual composition.
Q9. The empirical formula of a compound is obtained by dividing the relative masses of all constituent elements by their smallest common multiple. Which of the following is NOT a requirement for determining the empirical formula?
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Correct answer: A — The molecular mass of the compound
Determining the empirical formula relies on the relative masses of the elements present in the compound, not the overall molecular mass itself.
Q10. If an element 'X' and 'Y' form a compound, and the empirical formula is XY, this implies that the ratio of the atoms of X to Y in the compound is:
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Correct answer: A — 1:1
The empirical formula XY directly indicates the simplest whole-number ratio of X to Y atoms in the molecule.
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