Stoichiometry Test 2025
Chapter: Fundamentals of Chemistry | Subject: Chemistry
1. According to the S.I. system, ___ is used to measure the amount of substance.Easy
Answer: A — The mole is the base unit in the International System of Units (SI) for the amount of substance. Mass is measured in kilograms (kg), and weight is a force measured in Newtons (N).
2. The number of particles or substances present in moles is known by:Easy
Answer: B — Avogadro's number (approximately 6.022 × 1023) is the constant that represents the number of constituent particles (usually atoms or molecules) per mole of a substance.
3. Azhar has 1 mole of N2, which contains X number of particles, and Aamir has 1 mole of NH3 (Note: NH3 has twice the number of atoms than N2). What is the number of particles in NH3?Medium
Answer: C — One mole of any molecular substance contains exactly the same number of molecules (Avogadro's number), regardless of the number of atoms within those molecules. Since both Azhar and Aamir have 1 mole, both samples contain X molecules (particles).
4. What will be the estimated theoretical yield of CO2 obtained from 3 moles of carbon and 5 moles of oxygen gas?Medium
Answer: A — The chemical equation for the combustion of carbon is C + O2 → CO2. According to stoichiometry, 1 mole of C reacts with 1 mole of O2 to produce 1 mole of CO2. Since we have 3 moles of C and 5 moles of O2, Carbon is the limiting reactant. Therefore, a maximum of 3 moles of CO2 can be produced. Mass = moles × molar mass = 3 × 44 g/mol = 132 g.
5. Two molecules of same molar mass having the same given mass must have:
I. Same number of atoms
II. Same number of particles
III. Same number of molesMedium
I. Same number of atoms
II. Same number of particles
III. Same number of molesMedium
Answer: B — Since Moles = Mass / Molar Mass, having the same mass and same molar mass results in the same number of moles (III). Number of particles = Moles × Avogadro's number, so the number of particles is also the same (II). However, different molecules can have the same molar mass but different numbers of atoms (e.g., CO2 and C3H8 both have a molar mass of ~44 g/mol but different atom counts), so I is not necessarily true.
6. Find the incorrect statement about stoichiometry:Easy
Answer: C — Stoichiometry is the quantitative study of reactants and products in a chemical reaction. It focuses on numerical relationships (mass-mass, mole-mole, etc.) rather than just qualitative descriptions.
7. Ali loves ionic compounds, so he took 58.45 g of NaCl. Choose the best option:Medium
Answer: D — The molar mass of NaCl is 58.44 g/mol, so 58.45 g is approximately 1 mole. 1 mole of NaCl contains 1 mole of sodium ions (Na+) and 1 mole of chloride ions (Cl-). Option A is wrong (it's 1 mole). Option B is technically incorrect because NaCl consists of ions, not 'atoms'. Option C is wrong (that would be 2 moles). Thus, 'None of these' is the most accurate selection given the technical terminology.
8. 12.06 × 1023 atoms of oxygen contain:Medium
Answer: C — First, calculate the moles of oxygen atoms: (12.06 × 1023) / (6.03 × 1023) = 2 moles of O atoms. Since oxygen gas is diatomic (O2), 1 mole of O2 contains 2 moles of O atoms. Therefore, 2 moles of O atoms correspond to 1 mole of oxygen gas.
9. If 1 mole of alkyne combusts and produces 4 moles of CO2, what is the hydrocarbon and how many moles of H2O are produced?Hard
Answer: D — The general formula for an alkyne is CnH(2n-2). During complete combustion, 1 mole of alkyne produces 'n' moles of CO2 and (n-1) moles of H2O. If 4 moles of CO2 are produced, then n = 4. The alkyne with 4 carbons is Butyne (C4H6). The number of water moles produced is n − 1 = 4 − 1 = 3.
10. What is the number of particles in 10 moles of hydrochloric acid?Medium
Answer: A — One mole of any substance contains 6.022 × 1023 particles. Therefore, 10 moles contain 10 × 6.022 × 1023 = 6.022 × 1024 particles. 602.2 × 1022 is mathematically equivalent to 6.022 × 1024.
11. During an experiment, 12.04 × 1023 particles of CaCO3 produced 40 g of CaO. What will be the percentage yield?Medium
Answer: B — First, find the moles of CaCO3: 12.04 × 1023 / 6.02 × 1023 = 2 moles. According to the balanced equation CaCO3 → CaO + CO2, 1 mole of CaCO3 produces 1 mole of CaO. Thus, 2 moles of CaCO3 should produce 2 moles of CaO. The molar mass of CaO is 56 g/mol, so the theoretical yield is 2 × 56 = 112 g. The actual yield is 40 g. Percentage yield = (Actual Yield / Theoretical Yield) × 100 = (40 / 112) × 100 = 35.71%.
12. In a vessel, 20 g He, 20 g F2, and 20 g Cl2 are present. Which one will have the least number of atoms?Medium
Answer: C — To find the number of atoms, calculate moles of each: Moles of He = 20/4 = 5 mol (5 NA atoms). Moles of F2 = 20/38 = 0.526 mol (1.052 NA atoms). Moles of Cl2 = 20/71 = 0.282 mol (0.564 NA atoms). Chlorine (Cl2) has the highest molar mass, resulting in the smallest number of moles and consequently the least number of atoms for the given mass.
13. Consider the reaction: 2Na(s) + 2H2O(l) → 2NaOH + H2. When 69 g of Na reacts with water, the volume of H2 gas obtained at room temperature is:Medium
Answer: B — Moles of Na = 69 / 23 = 3 moles. According to the balanced equation, 2 moles of Na produce 1 mole of H2 gas. Therefore, 3 moles of Na produce 1.5 moles of H2. At room temperature (RTP), the molar volume of a gas is approximately 24 L/mol. Volume = 1.5 moles × 24 L/mol = 36 L.
14. The volume occupied by 1.6 g of O2 at STP is:Easy
Answer: C — Molar mass of O2 is 32 g/mol. Moles of O2 = 1.6 g / 32 g/mol = 0.05 moles. At STP, 1 mole of any ideal gas occupies 22.4 dm3. Volume = 0.05 mol × 22.4 dm3/mol = 1.12 dm3.
15. The total number of covalent bonds in 18 g of water (NA is Avogadro's number) is:Easy
Answer: C — 18 g of water is equal to 1 mole (18 g / 18 g/mol). Each water molecule (H2O) contains two O-H covalent bonds. Therefore, 1 mole of water molecules contains 2 moles of covalent bonds, which is equal to 2 NA.
16. For the reaction 2A + B → C, the amount of C formed by starting the reaction with 5 moles of B and 8 moles of A is:Medium
Answer: D — First, identify the limiting reactant. According to the stoichiometry, 1 mole of B reacts with 2 moles of A. So, 5 moles of B would require 10 moles of A. Since only 8 moles of A are available, A is the limiting reactant. Using stoichiometry for A: 2 moles of A produce 1 mole of C. Thus, 8 moles of A will produce 4 moles of C.
17. 1 dm3 of water contains how many moles?Easy
Answer: D — 1 dm3 of water is equal to 1000 cm3. Given that the density of water is approximately 1 g/cm3, the mass of 1 dm3 of water is 1000 g. The molar mass of water is 18 g/mol. Moles = Mass / Molar Mass = 1000 g / 18 g/mol = 55.5 moles.
18. Which one of the following compounds contains the highest percentage by mass of nitrogen?Medium
Answer: C — Percentage by mass is calculated as (Mass of N / Molar mass of compound) × 100. For NH3: 14/17 = 82.3%. For NH4OH: 14/35 = 40%. For N2H4: 28/32 = 87.5%. For NO: 14/30 = 46.7%. Hydrazine (N2H4) has the highest percentage.
19. Number of moles of CO2 that contain 16 g of oxygen is:Easy
Answer: C — One molecule of CO2 contains two atoms of oxygen. Therefore, 1 mole of CO2 contains 2 moles of oxygen atoms. The mass of 2 moles of oxygen atoms is 32 g. Since 1 mole of CO2 contains 32 g of oxygen, 16 g of oxygen will be present in 0.5 moles of CO2.
20. Number of hydrogen atoms in 6.0 g of acetic acid is:Medium
Answer: D — The molar mass of acetic acid (CH3COOH) is 60 g/mol. Moles of acetic acid = 6.0 g / 60 g/mol = 0.1 moles. Each molecule of acetic acid contains 4 hydrogen atoms. Therefore, 0.1 moles of acetic acid contains 0.1 × 4 = 0.4 moles of hydrogen atoms, which equals 0.4 NA atoms.
21. In a particular reaction, one of the reactants limits the number of products formed. This is called the:Easy
Answer: A — A limiting reagent is the reactant that is entirely consumed first in a chemical reaction, thereby determining the maximum amount of product that can be formed. Once this reactant is exhausted, the reaction stops, regardless of the amount of other reactants remaining.
22. Which of the following is not true regarding balanced chemical equations?Medium
Answer: C — In a balanced chemical equation, the number of atoms for each element and the total charge must be equal on both the reactant and product sides, satisfying the law of conservation of mass. However, the total number of molecules or moles does not need to be the same on both sides (e.g., N2 + 3H2 → 2NH3 has 4 molecules on the left and 2 on the right).
23. Which of the given reactions are counted as balanced reactions?Easy
Answer: B — A balanced chemical equation must have the same number of atoms of each element on both sides. In option B, there are 4 Aluminum atoms and 6 Oxygen atoms on both the reactant and product sides. The other options have discrepancies in the atom counts for hydrogen, magnesium, or nitrogen.
24. What is the amount of water produced when 8 g of hydrogen reacts with 32 g of oxygen?Medium
Answer: A — The reaction is 2H2 + O2 → 2H2O. 32 g of O2 corresponds to 1 mole, and 8 g of H2 corresponds to 4 moles. Stoichiometrically, 1 mole of O2 requires 2 moles of H2 to produce 2 moles of water. Since we have 4 moles of H2, O2 is the limiting reagent, and it will produce exactly 2 moles of water.
25. Calculate the mass percent (expressed as a decimal) of magnesium in the formation of magnesium oxide (MgO).Medium
Answer: D — The molar mass of MgO is approximately 40.3 g/mol (Mg = 24.3, O = 16). The mass percent of magnesium is calculated as (Atomic mass of Mg / Molar mass of MgO) × 100 = (24.3/40.3) × 100 = 60%. In decimal form, this is 0.6.
26. In a container, there are 4 moles of nitrogen, 3 moles of oxygen, and 7 moles of hydrogen. Find the mole fraction of oxygen.Medium
Answer: B — The mole fraction of a component is the number of moles of that component divided by the total number of moles in the system. Total moles = 4 + 3 + 7 = 14. Mole fraction of oxygen = 3 / 14 = 0.214285. Based on the options provided, 0.2142 is the matching choice.
27. Find the amount of carbon dioxide produced (in grams) by the complete combustion of 20 g of methane (CH4).Medium
Answer: C — The combustion of methane is represented by CH4 + 2O2 → CO2 + 2H2O. One mole of methane (16 g) produces one mole of carbon dioxide (44 g). To find the mass produced by 20 g of methane, we use the ratio: (44 g CO2 / 16 g CH4) × 20 g CH4 = 55 g of CO2.
28. What is the balanced equation for the synthesis of glucose: CO2 + H2O → C6H12O6 + O2?Easy
Answer: B — In the photosynthesis reaction, 6 molecules of carbon dioxide (6CO2) provide the 6 carbon atoms, and 6 molecules of water (6H2O) provide the 12 hydrogen atoms needed for one molecule of glucose (C6H12O6). The total 18 oxygen atoms on the reactant side are balanced by 6 oxygens in the glucose molecule and 12 oxygens in 6 molecules of O2.
29. How many moles of CH4 are required to produce 10 moles of H2O in a combustion reaction (considering O2 in excess)?Easy
Answer: C — The balanced equation for the combustion of methane is CH4 + 2O2 → CO2 + 2H2O. The molar ratio of methane (CH4) to water (H2O) is 1:2. Therefore, to produce 10 moles of water, exactly half the amount of methane is required, which is 5 moles.
30. Using the equation CH4 + 2O2 → CO2 + 2H2O, calculate the theoretical yield of CO2 in grams when 24 grams of CH4 reacts with excess oxygen.Medium
Answer: A — First, find the moles of methane: 24 g / 16 g/mol = 1.5 moles. According to the stoichiometry (a 1:1 ratio between CH4 and CO2), 1.5 moles of CH4 will produce 1.5 moles of CO2. The mass of CO2 produced is 1.5 moles × 44 g/mol = 66 g.
31. Calculate the volume of CO2 at STP that can be obtained by complete burning of 100 dm3 of butane:
2C4H10 + 13O2 → 8CO2 + 10H2OMedium
2C4H10 + 13O2 → 8CO2 + 10H2OMedium
Answer: C — According to the balanced chemical equation, 2 volumes of butane (C4H10) produce 8 volumes of carbon dioxide (CO2). This gives a stoichiometric ratio of 2:8, which simplifies to 1:4. Therefore, burning 100 dm3 of butane will yield 400 dm3 of CO2 (100 dm3 × 4).
32. The number of moles in 6.4 g of SO2 is:Easy
Answer: D — Moles are calculated using the formula: Moles = Mass / Molar mass. The molar mass of sulfur dioxide (SO2) is approximately 32 (S) + 2 × 16 (O) = 64 g/mol. Thus, 6.4 g / 64 g/mol = 0.1 mol.
33. Maximum number of molecules is present in:Medium
Answer: A — The number of molecules is directly proportional to the number of moles (n = mass / molar mass). Since the mass is constant (100 g) for all options, the substance with the smallest molar mass will have the highest number of moles and molecules. Molar masses: H2 = 2 g/mol, N2 = 28 g/mol, CO2 = 44 g/mol, and SO2 = 64 g/mol. H2 has the smallest molar mass, so it contains the most molecules.
34. Generally, actual yield is:Easy
Answer: B — In practical chemical reactions, the actual yield is almost always less than the theoretical yield. This occurs due to various factors including incomplete reactions, side reactions producing unwanted products, mechanical loss during filtration or transfer, and the reversible nature of many reactions.
35. The volume of N2 gas occupied by 1.5 moles at STP is:Easy
Answer: D — At Standard Temperature and Pressure (STP), 1 mole of any ideal gas occupies a volume of 22.4 dm3. For 1.5 moles of nitrogen gas (N2), the volume is 1.5 × 22.4 dm3 = 33.6 dm3.
36. Molar mass of FeCl3 is:Easy
Answer: B — The molar mass of FeCl3 is calculated by summing the atomic masses of iron and chlorine. Atomic mass of Fe = 55.85 g/mol and Cl = 35.5 g/mol. Calculation: 55.85 + (3 × 35.5) = 162.35 g/mol.
37. Mass-volume relationship is based on:Medium
Answer: C — The mass-volume relationship in stoichiometry uses the molar volume of gases. Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain equal numbers of moles. At STP, this allows us to use the molar volume (22.4 dm3/mol) to convert between the mass (moles) of a substance and its gas volume.
38. Which is the excess reactant in the reaction: C5H12 + 8O2 → 5CO2 + 6H2O, if the initial moles of C5H12 and O2 are 2 and 8, respectively?Medium
Answer: A — According to the balanced equation, 1 mole of C5H12 reacts with 8 moles of O2. If 2 moles of C5H12 are provided, they would require 16 moles of O2 (2 × 8) to react completely. Since only 8 moles of O2 are available, O2 is the limiting reactant and C5H12 is the excess reactant.
39. Which is the limiting reactant in the reaction: C5H12 + 8O2 → 5CO2 + 6H2O, if the initial moles of C5H12 and O2 are 2 and 8, respectively?Medium
Answer: B — The stoichiometric ratio of C5H12 to O2 is 1:8. With 2 moles of C5H12 and 8 moles of O2, we check the requirements: 2 moles of C5H12 need 16 moles of O2. Since we only have 8 moles of O2, it will be consumed entirely before the C5H12 is exhausted, making O2 the limiting reactant.
40. How many moles of C5H12 remain unreacted after completion: C5H12 + 8O2 → 5CO2 + 6H2O, if the initial moles of C5H12 and O2 are 2 and 8, respectively?Medium
Answer: B — O2 is the limiting reactant with 8 moles. According to the 1:8 ratio in the balanced equation, 8 moles of O2 will react with exactly 1 mole of C5H12. Since the initial amount of C5H12 was 2 moles, the amount remaining is 2 moles − 1 mole = 1 mole.
41. One mole of any substance contains:Easy
Answer: C — By definition, one mole of any substance contains Avogadro's number of particles, which is approximately 6.022 × 1023. These particles can be atoms, molecules, or ions depending on the nature of the substance.
42. One mole of sucrose contains how many grams?Easy
Answer: A — The molar mass of sucrose (C12H22O11) is calculated by adding the atomic masses of its components: (12 × 12) + (22 × 1) + (11 × 16) = 144 + 22 + 176 = 342 g/mol. Thus, one mole of sucrose has a mass of 342 g.
43. If 1 mole of ammonia is 17 g, then the mass of 0.3 moles is:Easy
Answer: B — The mass of a substance is equal to the number of moles multiplied by its molar mass. Mass = 0.3 moles × 17 g/mol = 5.1 g.
44. One mole of ethanol and one mole of ethane have an equal:Medium
Answer: D — According to Avogadro's law, one mole of any molecular substance contains exactly the same number of molecules (6.022 × 1023). Their molar masses, atomic counts per molecule, and total electron counts are different.
45. Methane reacts with steam to form H2 and CO: CH4 + H2O → CO + 3H2. What volume of H2 can be obtained from 100 cm3 of methane at STP?Medium
Answer: A — From the balanced equation, 1 mole of CH4 reacts to produce 3 moles of H2. According to Avogadro's law, gas volumes at the same temperature and pressure are proportional to their moles. Therefore, 1 volume of CH4 produces 3 volumes of H2. Thus, 100 cm3 of CH4 will yield 100 × 3 = 300 cm3 of H2.
46. A flask contains 500 cm3 of SO2 at STP. The flask contains:Medium
Answer: D — At STP, 1 mole of a gas occupies 22400 cm3. The number of moles in 500 cm3 of SO2 is 500 / 22400 = 0.02232 moles. The molar mass of SO2 is 32 + (16 × 2) = 64 g/mol. The mass of SO2 is 0.02232 moles × 64 g/mol = 1.428 g, which matches option D.
47. What is the mass of aluminium in 204 g of aluminium oxide (Al2O3)?Medium
Answer: D — The molar mass of Al2O3 is (2 × 27) + (3 × 16) = 54 + 48 = 102 g/mol. The mass of Al in 102 g of Al2O3 is 54 g. For 204 g of Al2O3, the mass of Al is (54/102) × 204 = 108 g.
48. The Avogadro's constant is the number of:Easy
Answer: B — Avogadro's constant (approximately 6.022 × 1023) represents the number of fundamental entities (like molecules) found in one mole of a substance. While it is defined by the number of atoms in 12g of C-12, it is most frequently used to quantify molecules in a molar sample.
49. If four moles of SO2 are oxidized to SO3, how many moles of O2 are required?
2SO2 + O2 → 2SO3Easy
2SO2 + O2 → 2SO3Easy
Answer: D — According to the balanced equation 2SO2 + O2 → 2SO3, 2 moles of SO2 require 1 mole of O2. Therefore, 4 moles of SO2 will require (1/2) × 4 = 2 moles of O2.
50. A ring was found to have 24 g of diamond. What is the number of atoms in it?Easy
Answer: B — Diamond is an allotrope of carbon (atomic mass = 12 g/mol). The number of moles of carbon in 24 g of diamond is 24 / 12 = 2 moles. Since 1 mole contains NA atoms, 2 moles contain 2 NA atoms.
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