Stoichiometry and Chemical Calculations MCQs 2026
75 questions with detailed answers · 26 from past papers · 8 quiz batches available
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- Q1 easy
One mole of any substance contains ___ particles
💡 Explanation:Avogadro's number, 6.022×10^23, defines the number of particles in one mole.
- Q2 Past Paper · PPSC/FPSC/NTS easy
The molar mass of water (H2O) is
💡 Explanation:Water's molar mass is (2×1) + 16 = 18 g/mol.
- Q3 Past Paper · PPSC/FPSC/NTS easy
The number of moles in 44 g of CO2 (molar mass 44 g/mol) is
💡 Explanation:Moles = mass ÷ molar mass = 44/44 = 1 mole.
- Q4 easy
The mass of 2 moles of NaOH (molar mass 40 g/mol) is
💡 Explanation:Mass = moles × molar mass = 2 × 40 = 80 g.
- Q5 Past Paper · PPSC/FPSC/NTS easy
The number of atoms in 1 mole of helium gas is
💡 Explanation:One mole of any element contains Avogadro's number of atoms, 6.022×10^23.
- Q6 easy
Avogadro's number is approximately
💡 Explanation:Avogadro's number is defined as 6.022×10^23 particles per mole.
- Q7 Past Paper · PPSC/FPSC/NTS easy
The volume occupied by 1 mole of an ideal gas at STP is
💡 Explanation:At standard temperature and pressure, one mole of ideal gas occupies 22.4 liters.
- Q8 easy
The empirical formula represents
💡 Explanation:Empirical formulas give the simplest ratio of elements, not the actual molecular composition.
- Q9 Past Paper · PPSC/FPSC/NTS easy
The molecular formula of a compound is always
💡 Explanation:Molecular formula equals the empirical formula multiplied by a whole number, including 1.
- Q10 easy
If the empirical formula of a compound is CH2O and its molar mass is 180 g/mol, its molecular formula is
💡 Explanation:Empirical formula mass is 30; 180÷30=6, so the molecular formula is (CH2O)×6 = C6H12O6.
- Q11 medium
The percentage composition of an element in a compound is calculated as
💡 Explanation:Percent composition compares the mass contributed by an element to the total molar mass.
- Q12 Past Paper · PPSC/FPSC/NTS medium
The percentage of oxygen by mass in water (H2O, molar mass 18) is approximately
💡 Explanation:Oxygen contributes 16 out of 18 g/mol, giving 16/18 × 100 ≈ 88.9%.
- Q13 medium
The limiting reagent in a reaction is the reactant that
💡 Explanation:The reaction stops producing more product once the limiting reagent is used up.
- Q14 Past Paper · PPSC/FPSC/NTS medium
The reactant that remains after a reaction is complete is called the
💡 Explanation:Any reactant left over after the limiting reagent is consumed is called the excess reagent.
- Q15 medium
Theoretical yield refers to
💡 Explanation:Theoretical yield is the calculated maximum product possible assuming complete reaction.
- Q16 medium
Percentage yield is calculated as
💡 Explanation:Percentage yield compares the actual product obtained to the theoretically possible amount.
- Q17 Past Paper · PPSC/FPSC/NTS medium
A balanced chemical equation obeys the law of
💡 Explanation:Balancing ensures equal numbers of atoms on both sides, honoring conservation of mass.
- Q18 medium
In the reaction N2 + 3H2 → 2NH3, the mole ratio of H2 to NH3 is
💡 Explanation:The balanced equation shows 3 moles of H2 react to form 2 moles of NH3, a 3:2 ratio.
- Q19 Past Paper · PPSC/FPSC/NTS hard
The formula weight of MgO (Mg=24, O=16) is
💡 Explanation:Sum of atomic masses: 24+16 = 40.
- Q20 medium
The number of moles of oxygen atoms in 2 moles of CO2 is
💡 Explanation:Each CO2 molecule has 2 oxygen atoms, so 2 moles of CO2 contain 4 moles of oxygen atoms.
- Q21 Past Paper · PPSC/FPSC/NTS medium
Molarity of a solution is defined as
💡 Explanation:Molarity (M) is defined as moles of solute divided by liters of total solution.
- Q22 medium
The molarity of a solution containing 2 moles of NaCl in 500 mL of solution is
💡 Explanation:Molarity = 2 mol ÷ 0.5 L = 4 M.
- Q23 medium
Molality of a solution is defined as
💡 Explanation:Molality (m) is moles of solute per kilogram of solvent, independent of temperature-based volume changes.
- Q24 Past Paper · PPSC/FPSC/NTS medium
The number of moles of solute in 250 mL of a 2 M solution is
💡 Explanation:Moles = molarity × volume(L) = 2 × 0.25 = 0.5 mol.
- Q25 medium
The mass of 0.25 mol of CaCO3 (molar mass 100 g/mol) is
💡 Explanation:Mass = moles × molar mass = 0.25 × 100 = 25 g.
- Q26 medium
The molar mass of glucose, C6H12O6, is
💡 Explanation:Summing atomic masses: (6×12)+(12×1)+(6×16) = 72+12+96 = 180 g/mol.
- Q27 Past Paper · PPSC/FPSC/NTS medium
The number of moles present in 11.2 L of a gas at STP is
💡 Explanation:Moles = volume ÷ 22.4 L/mol = 11.2/22.4 = 0.5 mol.
- Q28 medium
According to the law of conservation of mass, in a chemical reaction the total mass of reactants
💡 Explanation:Mass is neither created nor destroyed, so total reactant mass equals total product mass.
- Q29 medium
The law of definite proportions states that a chemical compound always contains the same elements
💡 Explanation:A pure compound always has the same elements combined in the same fixed mass ratio.
- Q30 Past Paper · PPSC/FPSC/NTS medium
The law of multiple proportions applies when two elements form
💡 Explanation:When two elements form multiple compounds, the masses of one element combining with a fixed mass of the other form small whole-number ratios.
- Q31 medium
The number of moles of NaOH needed to completely neutralize 1 mole of H2SO4 is
💡 Explanation:H2SO4 is diprotic, requiring 2 moles of NaOH for complete neutralization.
- Q32 medium
In the reaction 2H2 + O2 → 2H2O, the number of moles of water produced from 4 moles of H2 (excess O2) is
💡 Explanation:The 2:2 mole ratio of H2 to H2O means 4 moles of H2 produce 4 moles of water.
- Q33 Past Paper · PPSC/FPSC/NTS medium
A 1 molar solution of a substance contains how many moles of solute per liter
💡 Explanation:By definition, a 1 M solution contains exactly 1 mole of solute per liter of solution.
- Q34 medium
Which quantity remains constant during a chemical reaction, per the law of conservation of mass
💡 Explanation:Total mass of the reacting system stays constant throughout a chemical reaction.
- Q35 medium
The formula mass of Na2CO3 (Na=23, C=12, O=16) is
💡 Explanation:Sum: (2×23)+12+(3×16) = 46+12+48 = 106.
- Q36 Past Paper · PPSC/FPSC/NTS medium
The percentage of carbon by mass in CO2 (molar mass 44) is approximately
💡 Explanation:Carbon contributes 12 out of 44 g/mol, giving 12/44 × 100 ≈ 27.3%.
- Q37 medium
In stoichiometric calculations, mole ratios are obtained directly from the
💡 Explanation:The coefficients in a balanced equation give the exact mole ratio between reactants and products.
- Q38 medium
If 5 moles of a limiting reagent produce 5 moles of product in a 1:1 reaction and only 4 moles of product were actually obtained, the percentage yield is
💡 Explanation:Percentage yield = (4/5) × 100 = 80%.
- Q39 Past Paper · PPSC/FPSC/NTS medium
A solution containing 1 mole of solute dissolved in exactly 1 kg of solvent has a molality of
💡 Explanation:By definition, molality equals moles of solute per kilogram of solvent, giving 1 m here.
- Q40 medium
The relative formula mass of a compound is the sum of the
💡 Explanation:Formula mass is calculated by adding up the atomic masses of every atom shown in the formula.
- Q41 medium
Which of the following best describes an empirical formula determination experiment
💡 Explanation:Empirical formula experiments typically measure the mass of each element present to find their simplest ratio.
- Q42 Past Paper · PPSC/FPSC/NTS hard
The number of moles of ions produced when 1 mole of Na2SO4 fully dissociates in water is
💡 Explanation:Na2SO4 dissociates into 2 Na+ ions and 1 SO4^2- ion, totaling 3 moles of ions.
- Q43 hard
The mass percent of hydrogen in methane, CH4 (molar mass 16 g/mol) is approximately
💡 Explanation:Hydrogen contributes 4 out of 16 g/mol, giving 4/16 × 100 = 25%.
- Q44 hard
1 mole of a diatomic gas at STP occupies a volume of
💡 Explanation:Molar volume at STP is 22.4 L for any ideal gas, regardless of whether it is diatomic.
- Q45 hard
How many moles of oxygen gas (O2) are required to completely combust 1 mole of methane (CH4 + 2O2 → CO2 + 2H2O)
💡 Explanation:The balanced equation shows 2 moles of O2 are needed per mole of methane burned.
- Q46 hard
The number of grams in 0.5 mole of oxygen gas, O2 (molar mass 32 g/mol) is
💡 Explanation:Mass = moles × molar mass = 0.5 × 32 = 16 g.
- Q47 Past Paper · PPSC/FPSC/NTS hard
Gram atomic mass is the mass, in grams, of
💡 Explanation:Gram atomic mass equals the atomic mass expressed in grams for one mole of atoms.
- Q48 hard
The number of moles of electrons required to reduce 1 mole of Al3+ to Al metal is
💡 Explanation:Al3+ requires gaining 3 electrons per ion to become neutral aluminum metal.
- Q49 hard
Stoichiometry is fundamentally based on the relationship between
💡 Explanation:Stoichiometric calculations use the mole ratios from a balanced chemical equation.
- Q50 hard
The number of moles in 9 g of water (molar mass 18 g/mol) is
💡 Explanation:Moles = mass ÷ molar mass = 9/18 = 0.5 mol.
- Q51 medium
The number of moles of oxygen atoms in 2 moles of CO2 is
💡 Explanation:Each CO2 molecule has 2 oxygen atoms, so 2 moles of CO2 contain 4 moles of oxygen atoms.
- Q52 Past Paper · PPSC/FPSC/NTS medium
Molarity of a solution is defined as
💡 Explanation:Molarity (M) is defined as moles of solute divided by liters of total solution.
- Q53 medium
The molarity of a solution containing 2 moles of NaCl in 500 mL of solution is
💡 Explanation:Molarity = 2 mol ÷ 0.5 L = 4 M.
- Q54 medium
Molality of a solution is defined as
💡 Explanation:Molality (m) is moles of solute per kilogram of solvent, independent of temperature-based volume changes.
- Q55 Past Paper · PPSC/FPSC/NTS medium
The number of moles of solute in 250 mL of a 2 M solution is
💡 Explanation:Moles = molarity × volume(L) = 2 × 0.25 = 0.5 mol.
- Q56 medium
The mass of 0.25 mol of CaCO3 (molar mass 100 g/mol) is
💡 Explanation:Mass = moles × molar mass = 0.25 × 100 = 25 g.
- Q57 medium
The molar mass of glucose, C6H12O6, is
💡 Explanation:Summing atomic masses: (6×12)+(12×1)+(6×16) = 72+12+96 = 180 g/mol.
- Q58 Past Paper · PPSC/FPSC/NTS medium
The number of moles present in 11.2 L of a gas at STP is
💡 Explanation:Moles = volume ÷ 22.4 L/mol = 11.2/22.4 = 0.5 mol.
- Q59 medium
According to the law of conservation of mass, in a chemical reaction the total mass of reactants
💡 Explanation:Mass is neither created nor destroyed, so total reactant mass equals total product mass.
- Q60 medium
The law of definite proportions states that a chemical compound always contains the same elements
💡 Explanation:A pure compound always has the same elements combined in the same fixed mass ratio.
- Q61 Past Paper · PPSC/FPSC/NTS medium
The law of multiple proportions applies when two elements form
💡 Explanation:When two elements form multiple compounds, the masses of one element combining with a fixed mass of the other form small whole-number ratios.
- Q62 medium
The number of moles of NaOH needed to completely neutralize 1 mole of H2SO4 is
💡 Explanation:H2SO4 is diprotic, requiring 2 moles of NaOH for complete neutralization.
- Q63 medium
In the reaction 2H2 + O2 → 2H2O, the number of moles of water produced from 4 moles of H2 (excess O2) is
💡 Explanation:The 2:2 mole ratio of H2 to H2O means 4 moles of H2 produce 4 moles of water.
- Q64 Past Paper · PPSC/FPSC/NTS medium
A 1 molar solution of a substance contains how many moles of solute per liter
💡 Explanation:By definition, a 1 M solution contains exactly 1 mole of solute per liter of solution.
- Q65 medium
Which quantity remains constant during a chemical reaction, per the law of conservation of mass
💡 Explanation:Total mass of the reacting system stays constant throughout a chemical reaction.
- Q66 medium
The formula mass of Na2CO3 (Na=23, C=12, O=16) is
💡 Explanation:Sum: (2×23)+12+(3×16) = 46+12+48 = 106.
- Q67 Past Paper · PPSC/FPSC/NTS medium
The percentage of carbon by mass in CO2 (molar mass 44) is approximately
💡 Explanation:Carbon contributes 12 out of 44 g/mol, giving 12/44 × 100 ≈ 27.3%.
- Q68 medium
In stoichiometric calculations, mole ratios are obtained directly from the
💡 Explanation:The coefficients in a balanced equation give the exact mole ratio between reactants and products.
- Q69 medium
If 5 moles of a limiting reagent produce 5 moles of product in a 1:1 reaction and only 4 moles of product were actually obtained, the percentage yield is
💡 Explanation:Percentage yield = (4/5) × 100 = 80%.
- Q70 Past Paper · PPSC/FPSC/NTS medium
A solution containing 1 mole of solute dissolved in exactly 1 kg of solvent has a molality of
💡 Explanation:By definition, molality equals moles of solute per kilogram of solvent, giving 1 m here.
- Q71 medium
The relative formula mass of a compound is the sum of the
💡 Explanation:Formula mass is calculated by adding up the atomic masses of every atom shown in the formula.
- Q72 medium
Which of the following best describes an empirical formula determination experiment
💡 Explanation:Empirical formula experiments typically measure the mass of each element present to find their simplest ratio.
- Q73 Past Paper · PPSC/FPSC/NTS hard
The number of moles of ions produced when 1 mole of Na2SO4 fully dissociates in water is
💡 Explanation:Na2SO4 dissociates into 2 Na+ ions and 1 SO4^2- ion, totaling 3 moles of ions.
- Q74 hard
The mass percent of hydrogen in methane, CH4 (molar mass 16 g/mol) is approximately
💡 Explanation:Hydrogen contributes 4 out of 16 g/mol, giving 4/16 × 100 = 25%.
- Q75 hard
1 mole of a diatomic gas at STP occupies a volume of
💡 Explanation:Molar volume at STP is 22.4 L for any ideal gas, regardless of whether it is diatomic.