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NEET Chemistry: Estimation of elements Practice Questions

15 free multiple-choice questions on Estimation of elements (Quantitative Analysis) 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.

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  1. Q1. If the relative atomic mass of an element is 32, what does this value primarily represent in the context of elemental estimation?

    • AThe mass of one mole of atoms of the element
    • BThe number of atoms in 32 moles of the element
    • CThe mass of 32 grams of the element
    • DThe number of moles of an atom
    Show answer & explanation

    Correct answer: A — The mass of one mole of atoms of the element

    Relative atomic mass (or atomic mass) indicates the average mass of one mole of atoms of that element, serving as the conversion factor between mass and the number of moles in calculations.

  2. Q2. In a chemical reaction, if reactant A reacts with reactant B in a 1:2 molar ratio, which reactant is the limiting reagent?

    • AReactant A
    • BReactant B
    • CBoth A and B
    • DNeither A nor B
    Show answer & explanation

    Correct answer: A — Reactant A

    The limiting reagent is the reactant that gets completely consumed first. If the ratio requires A to react completely with B (1:2), A is the limiting reagent.

  3. Q3. Which of the following is the most crucial step before estimating the mass of an unknown element in an analytical process?

    • ASeparating the components
    • BDetermining the purity of the sample
    • CCalculating the limiting reactant
    • DDetermining the density of the unknown
    Show answer & explanation

    Correct answer: B — Determining the purity of the sample

    Before any estimation can be accurate, the purity of the sample must be established. Impurities directly affect the final calculated elemental mass.

  4. Q4. In elemental analysis, the stoichiometric ratio derived from the chemical formula is used to determine the relative amounts of elements. This ratio is based on the concept of:

    • AThe Law of Multiple Proportions
    • BConservation of charge
    • CAtomic weights
    • DRadioactivity
    Show answer & explanation

    Correct answer: A — The Law of Multiple Proportions

    The Law of Multiple Proportions states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers. This underpins stoichiometric ratios.

  5. Q5. The mass percentage of an element in a compound is calculated by dividing the mass of the element by the total mass of the compound and multiplying by 100. What is the correct formula?

    • A(Mass of Compound / Mass of Element) * 100
    • BMass of Element / Molar Mass of Compound
    • C(Mass of Element / Mass of Compound) * 100
    • D(Mass of Element * 100) / Mass of Compound
    Show answer & explanation

    Correct answer: C — (Mass of Element / Mass of Compound) * 100

    Mass percentage is defined as (Mass of the specific element / Total mass of the compound) * 100.

  6. Q6. If 1 mole of a gas occupies a volume of 22.4 L at STP, what is the volume occupied by 3 moles of the same gas?

    • A11.2 L
    • B67.2 L
    • C22.4 L
    • D44.8 L
    Show answer & explanation

    Correct answer: D — 44.8 L

    Since the volume is directly proportional to the number of moles (at constant temperature and pressure), 3 moles will occupy 3 times the volume: 3 * 22.4 L = 67.2 L.

  7. Q7. If the density of a metal is 10 g/cm³ and its molar mass is 50 g/mol, what is the mass of 1 mole of this metal?

    • A10 g
    • B50 g
    • C100 g
    • D5 g
    Show answer & explanation

    Correct answer: C — 100 g

    Mass of 1 mole is equal to the molar mass. Given molar mass is 50 g/mol, the mass of 1 mole is 50 g. (Note: Density is extra information not needed for this specific direct calculation).

  8. Q8. If an element has a molar mass of 30 g/mol, what is the mass of 2 moles of this element?

    • A300 g
    • B30 g
    • C15 g
    • D60 g
    Show answer & explanation

    Correct answer: D — 60 g

    Mass = Moles × Molar Mass. Mass = 2 moles × 30 g/mol = 60 g.

  9. Q9. The fundamental principle used in quantitative analysis to determine the amount of an element present in a sample is based on:

    • AMass conservation principle
    • BAufbau principle
    • CLaw of chemical equilibrium
    • DHess's Law
    Show answer & explanation

    Correct answer: A — Mass conservation principle

    Quantitative analysis fundamentally relies on the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction. This principle is essential for calculating elemental composition from measured masses.

  10. Q10. Density is a property used in estimation. If 10 g of a substance occupies a volume of 5 cm³, what is its density?

    • A0.5 g/cm³
    • B15 g/cm³
    • C2 g/cm³
    • D50 g/cm³
    Show answer & explanation

    Correct answer: C — 2 g/cm³

    Density is calculated as Mass / Volume. Density = 10 g / 5 cm³ = 2 g/cm³.

  11. Q11. Which method of analysis relies on the precipitation of a substance formed from the analyte to determine the mass of the element?

    • ACalorimetry
    • BGravimetric Analysis
    • CTitration
    • DVolumetric Analysis
    Show answer & explanation

    Correct answer: B — Gravimetric Analysis

    Gravimetric analysis involves isolating the analyte by converting it into a pure, weighable precipitate, allowing the mass of the precipitate to be used for estimation.

  12. Q12. Which expression relates the volume of a gas to the number of moles at constant temperature and pressure?

    • ABoyle's Law
    • BDalton's Law of Partial Pressures
    • CAvogadro's Law
    • DCharles's Law
    Show answer & explanation

    Correct answer: C — Avogadro's Law

    Avogadro's Law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules (and thus moles).

  13. Q13. Which of the following represents the relationship between mass and the number of moles?

    • AMolar Mass = Mass × Moles
    • BMass = Molar Mass × Moles
    • CMoles = Mass / Molar Mass
    • DMoles = Mass + Molar Mass
    Show answer & explanation

    Correct answer: C — Moles = Mass / Molar Mass

    The fundamental relationship is Moles = Mass / Molar Mass.

  14. Q14. The relationship between the mass of an element and the number of moles is established using:

    • AMolar volume
    • BThe Law of Definite Proportions
    • CThe concept of dimensional analysis
    • DAvogadro's number
    Show answer & explanation

    Correct answer: D — Avogadro's number

    The number of moles is the bridge between the macroscopic mass of a substance and the microscopic quantity (number of particles), linked by Avogadro's number (6.022 × 10²³ mol⁻¹).

  15. Q15. The molar mass of an element is defined as the mass of one mole of that element in grams. Which quantity represents the mass of one mole of carbon atoms?

    • A12 g/mol
    • B120 g
    • C1200 g
    • D12 g
    Show answer & explanation

    Correct answer: D — 12 g

    The molar mass of Carbon (C) is 12 g/mol. Therefore, one mole of carbon atoms has a mass of 12 grams.

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