Chapter 3 - "Stoichiometry" - MCQ's

 "Stoichiometry" - MCQ's

Stoichiometry & Chemical Formulae – MCQs

1. What does stoichiometry mainly deal with?

A. Colour changes in reactions

B. Energy changes in reactions

C. Quantitative relationships between reactants and products

D. Speed of reactions

Answer: C

2. Which law explains why chemical equations must be balanced?

A. Law of definite proportions

B. Law of conservation of mass

C. Law of multiple proportions

D. Avogadro’s law

Answer: B

3. Which element exists naturally as a diatomic molecule?

A. Neon

B. Magnesium

C. Chlorine

D. Iron

Answer: C

4. What is the correct formula for hydrogen gas?

A. H

B. H₂

C. H₃

D. H₂O

Answer: B

5. Which of the following exists as single atoms?

A. Oxygen

B. Nitrogen

C. Argon

D. Chlorine

Answer: C

6. Which chemical symbol is written incorrectly?

A. Na

B. Mg

C. FE

D. Cu

Answer: C

7. Which formula represents a compound?

A. O₂

B. N₂

C. H₂O

D. He

Answer: C

8. What does the formula CO₂ show?

A. Two carbon atoms and one oxygen atom

B. One carbon atom and two oxygen atoms

C. Two carbon atoms and two oxygen atoms

D. One carbon atom only

Answer: B

9. Which compound has the formula CH₄?

A. Carbon dioxide

B. Methane

C. Ammonia

D. Carbon monoxide

Answer: B

10. Which ionic compound has a 1:2 ratio of ions?

A. NaCl

B. MgO

C. CaCl₂

D. Al₂O₃

Answer: C

11. What does the formula Al₂O₃ represent?

A. Two aluminium atoms and three oxygen atoms

B. Two aluminium ions and three oxide ions

C. Three aluminium ions and two oxide ions

D. Aluminium and oxygen molecules

Answer: B

12. Why do ionic compounds have no overall charge?

A. They contain molecules

B. Charges cancel each other

C. They contain only metals

D. They dissolve in water

Answer: B

13. What is the molecular formula of ammonia?

A. NH₂

B. NH₃

C. N₂H₃

D. NH₄

Answer: B

14. How many hydrogen atoms are in one molecule of methane?

A. 1

B. 2

C. 3

D. 4

Answer: D

15. Which formula is written incorrectly?

A. H₂SO₄

B. CaCl₂

C. Mg₂O

D. CO

Answer: C

16. What does a subscript in a chemical formula show?

A. The charge on an ion

B. The number of molecules

C. The number of atoms of an element

D. The mass of atoms

Answer: C

17. What is the simplest ratio of atoms in H₄O₂?

A. H₄O₂

B. H₂O

C. HO

D. H₂O₂

Answer: B

18. Which formula represents carbon monoxide?

A. CO₂

B. CO

C. C₂O

D. O₂C

Answer: B

19. What type of bonding is present in water?

A. Ionic

B. Metallic

C. Covalent

D. Hydrogen

Answer: C

20. Which substance is a covalent compound?

A. Sodium chloride

B. Magnesium oxide

C. Water

D. Calcium chloride

Answer: C

21. What is shown by a molecular formula?

A. Shape of molecule

B. Bond angles

C. Exact number of atoms in one molecule

D. Simplest ratio of atoms

Answer: C

22. Which molecular formula could represent more than one compound?

A. H₂O

B. CO₂

C. C₂H₆O

D. NH₃

Answer: C

23. What is the empirical formula of glucose, C₆H₁₂O₆?

A. C₆H₁₂O₆

B. C₃H₆O₃

C. CH₂O

D. C₂H₄O₂

Answer: C

24. Which reaction shows a metal reacting with oxygen?

A. Acid + base → salt + water

B. Metal + oxygen → metal oxide

C. Acid + metal → salt + water

D. Base + metal → hydrogen

Answer: B

25. What is the balanced equation for magnesium reacting with oxygen?

A. Mg + O → MgO

B. Mg + O₂ → MgO

C. 2Mg + O₂ → 2MgO

D. Mg₂ + O₂ → 2MgO

Answer: C

26. What do coefficients in equations represent?

A. Masses of substances

B. Number of atoms

C. Number of molecules or moles

D. Charges on ions

Answer: C

27. Which equation is correctly balanced?

A. H₂ + O₂ → H₂O

B. 2H₂ + O₂ → 2H₂O

C. H₂ + O → H₂O

D. H₂ + O₂ → 2H₂O₂

Answer: B

28. Which state symbol represents an aqueous solution?

A. (s)

B. (l)

C. (g)

D. (aq)

Answer: D

29. Which substance is a gas at room temperature?

A. Mg(s)

B. NaCl(s)

C. H₂(g)

D. H₂O(l)

Answer: C

30. Which equation includes correct state symbols?

A. Mg + 2HCl → MgCl₂ + H₂

B. Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

C. Mg(l) + HCl(g) → MgCl₂(s)

D. Mg(aq) + HCl(s) → H₂(aq)

Answer: B

31. What is produced when zinc reacts with hydrochloric acid?

A. Zinc oxide and hydrogen

B. Zinc chloride and hydrogen

C. Zinc hydroxide and water

D. Zinc sulfate and oxygen

Answer: B

32. Which word equation is correct?

A. Acid + metal → salt + water

B. Acid + base → salt + hydrogen

C. Metal + acid → salt + hydrogen

D. Base + metal → salt + water

Answer: C

33. What type of reaction is CaCO₃ → CaO + CO₂?

A. Neutralisation

B. Combustion

C. Decomposition

D. Displacement

Answer: C

34. What state symbol is used for carbon dioxide in decomposition?

A. (s)

B. (l)

C. (aq)

D. (g)

Answer: D

35. Which ion is a spectator ion in AgNO₃ + NaCl?

A. Ag⁺

B. Cl⁻

C. Na⁺

D. AgCl

Answer: C

36. Which ionic equation is correct?

A. Na⁺ + Cl⁻ → NaCl

B. Ag⁺ + Cl⁻ → AgCl

C. Na⁺ + NO₃⁻ → NaNO₃

D. H⁺ + OH⁻ → H₂

Answer: B

37. What does (s) mean in an equation?

A. Soluble

B. Solid

C. Solution

D. Stable

Answer: B

38. Which substance forms a precipitate?

A. NaCl(aq)

B. AgCl(s)

C. HCl(aq)

D. NaNO₃(aq)

Answer: B

39. Which formula shows fixed composition?

A. H₂O

B. Air

C. Alloy

D. Solution

Answer: A

40. Which compound always has a 2:1 ratio of hydrogen to oxygen?

A. Hydrogen peroxide

B. Water

C. Oxygen

D. Hydroxide

Answer: B

41. Why must subscripts never be changed when balancing equations?

A. It changes the number of molecules

B. It changes the identity of the substance

C. It breaks the law of conservation of energy

D. It affects state symbols

Answer: B

42. What is shown in a word equation?

A. Atom numbers

B. Masses

C. Names of substances

D. Charges

Answer: C

43. Which formula represents an ionic compound?

A. H₂O

B. CO₂

C. NaCl

D. CH₄

Answer: C

44. What is the formula for calcium oxide?

A. CaO

B. Ca₂O

C. CaO₂

D. Ca₂O₂

Answer: A

45. Which diagram would represent NH₃?

A. One N with two H

B. One N with three H

C. Two N with three H

D. Three N with one H

Answer: B

46. What ratio is shown by MgCl₂?

A. 1 Mg : 1 Cl

B. 2 Mg : 1 Cl

C. 1 Mg : 2 Cl

D. 2 Mg : 2 Cl

Answer: C

47. Which compound contains only covalent bonds?

A. NaCl

B. MgO

C. NH₃

D. CaCl₂

Answer: C

48. Why are chemical formulae considered a universal language?

A. They are written in English

B. They use symbols understood worldwide

C. They describe colour

D. They show physical states

Answer: B

49. Which formula shows the simplest ratio of ions?

A. Molecular formula

B. Structural formula

C. Empirical formula

D. Displayed formula

Answer: C

50. Why is stoichiometry important in chemistry?

A. It explains colours of compounds

B. It predicts reaction speed

C. It allows accurate calculations of amounts

D. It explains atomic structure

Answer: C

Empirical Formula

51. What is an empirical formula?

A. The exact number of atoms in a molecule

B. The simplest whole-number ratio of atoms or ions in a compound

C. The arrangement of atoms in a compound

D. The total number of electrons in a compound

Answer: B

52. The molecular formula C₂H₆ has what empirical formula?

A. CH₃

B. C₂H₆

C. CH₂

D. C₃H

Answer: A

53. The molecular formula C₆H₁₂O₆ has what empirical formula?

A. C₃H₆O₃

B. CH₂O

C. C₆H₁₂O₆

D. C₂H₄O₂

Answer: B

54. Which compound has the same empirical and molecular formula?

A. H₂O

B. C₂H₄

C. C₆H₁₂O₆

D. C₄H₈

Answer: A

55. If a compound has atoms in the ratio 4:6, what is the simplest ratio?

A. 2:3

B. 4:6

C. 1:2

D. 3:2

Answer: A

56. A ratio of 1.5 : 1 must be converted to whole numbers. What is the simplest whole-number ratio?

A. 1:1

B. 2:1

C. 3:2

D. 3:1

Answer: C

57. Why are empirical formula ratios always whole numbers?

A. Atoms are continuous

B. Atoms and ions are discrete particles

C. Molecules always have even numbers of atoms

D. Charges must always be +1 and −1

Answer: B

58. Which statement about empirical formulae is correct?

A. They always show the size of the molecule

B. They always show the structure of the molecule

C. They show the simplest ratio of atoms or ions

D. They are only used for covalent compounds

Answer: C

59. Which pair of compounds share the same empirical formula CH₂?

A. CO and CO₂

B. C₂H₄ and C₃H₆

C. H₂O and H₂O₂

D. NaCl and MgCl₂

Answer: B

60. Which is an example where empirical and molecular formula are different?

A. H₂O

B. CO₂

C. CH₄

D. C₂H₄

Answer: D

Formulae of Ionic Compounds

61. The formula of an ionic compound represents:

A. A single molecule

B. The simplest whole-number ratio of ions

C. The number of ions in one crystal

D. The arrangement of ions in space

Answer: B

62. Why do ionic compounds not have molecular formulae?

A. They are liquids

B. They do not form lattices

C. They do not exist as discrete molecules

D. They contain no atoms

Answer: C

63. What is the correct formula for magnesium chloride?

A. MgCl

B. MgCl₂

C. Mg₂Cl

D. Mg₂Cl₂

Answer: B

64. Ca²⁺ and O²⁻ combine to form:

A. CaO

B. Ca₂O

C. CaO₂

D. Ca₂O₂

Answer: A

65. Which formula is correct for aluminium oxide?

A. AlO

B. Al₂O

C. Al₂O₃

D. Al₃O₂

Answer: C

66. Which ions form Na₂O?

A. Na⁺ and O⁻

B. Na²⁺ and O²⁻

C. Na⁺ and O²⁻

D. Na⁻ and O²⁺

Answer: C

67. Which combination gives the formula MgO?

A. Mg⁺ and O⁻

B. Mg²⁺ and O²⁻

C. Mg²⁻ and O²⁺

D. Mg⁺ and O²⁻

Answer: B

68. Aluminium ions are Al³⁺ and chloride ions are Cl⁻. What is the formula?

A. AlCl

B. AlCl₂

C. AlCl₃

D. Al₂Cl₃

Answer: C

69. Calcium ions are Ca²⁺ and nitrate ions are NO₃⁻. What is the formula?

A. CaNO₃

B. Ca(NO₃)₂

C. Ca₂NO₃

D. Ca₂(NO₃)₂

Answer: B

70. Why are brackets used in (NH₄)₂SO₄?

A. To show it is a solid

B. To show two sulfate ions

C. To show the polyatomic ion repeats

D. To show a double bond

Answer: C

Symbol Equations, State Symbols, Ionic Equations

71. What must be true for any balanced symbol equation?

A. Same number of molecules on both sides

B. Same number of atoms of each element on both sides

C. Same total charge on both sides only

D. Same number of products and reactants

Answer: B

72. In balancing equations, which is allowed?

A. Changing subscripts

B. Changing chemical formulae

C. Adding coefficients

D. Removing atoms

Answer: C

73. What does (aq) mean?

A. A pure liquid

B. A gas dissolved in water

C. Dissolved in water

D. A solid mixed with water

Answer: C

74. Which state symbol shows a gas?

A. (s)

B. (l)

C. (g)

D. (aq)

Answer: C

75. Which equation is correctly balanced?

A. Mg + O₂ → MgO₂

B. 2Mg + O₂ → 2MgO

C. Mg + O → MgO

D. Mg₂ + O₂ → MgO

Answer: B

76. Which equation correctly shows zinc reacting with hydrochloric acid?

A. Zn + HCl → ZnCl + H₂

B. Zn + 2HCl → ZnCl₂ + H₂

C. Zn + HCl₂ → ZnCl₂ + H₂

D. Zn₂ + HCl → ZnCl₂ + H₂

Answer: B

77. Which reaction pattern is correct?

A. Metal + acid → salt + water

B. Metal + acid → salt + hydrogen

C. Acid + alkali → salt + hydrogen

D. Metal + oxygen → salt + water

Answer: B

78. What is the correct equation for neutralisation of HCl with NaOH?

A. HCl + NaOH → NaCl + H₂O

B. HCl + NaOH → NaOHCl

C. HCl + NaOH → Na + H₂O + Cl

D. H₂ + O₂ → H₂O

Answer: A

79. Which equation represents thermal decomposition of calcium carbonate?

A. CaCO₃(aq) → Ca(aq) + CO₃(aq)

B. CaCO₃(s) → CaO(s) + CO₂(g)

C. CaCO₃(g) → CaO(g) + CO₂(g)

D. CaCO₃(s) → Ca(s) + CO₃(s)

Answer: B

80. In the reaction AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq), what is the precipitate?

A. AgNO₃

B. NaCl

C. AgCl

D. NaNO₃

Answer: C

81. What is a spectator ion?

A. An ion that forms a precipitate

B. An ion that changes charge

C. An ion unchanged during the reaction

D. An ion that becomes a gas

Answer: C

82. Which is the ionic equation for forming silver chloride?

A. Ag(s) + Cl₂(g) → AgCl(s)

B. Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

C. Na⁺(aq) + NO₃⁻(aq) → NaNO₃(aq)

D. AgNO₃(aq) + NaCl(aq) → AgCl(aq)

Answer: B

83. Which is the ionic equation for neutralisation?

A. H⁺(aq) + OH⁻(aq) → H₂O(l)

B. Na⁺(aq) + Cl⁻(aq) → NaCl(aq)

C. H₂(g) + O₂(g) → H₂O(l)

D. H⁺(aq) + Cl⁻(aq) → HCl(aq)

Answer: A

84. Which state symbols are correct for magnesium reacting with hydrochloric acid?

A. Mg(aq) + HCl(g) → MgCl₂(s) + H₂(aq)

B. Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

C. Mg(g) + HCl(l) → MgCl₂(aq) + H₂(s)

D. Mg(l) + HCl(aq) → MgCl₂(g) + H₂(g)

Answer: B

85. Why are aqueous compounds split into ions when writing ionic equations?

A. To show molecules clearly

B. Because they exist as ions in solution

C. Because solids are always ionic

D. Because gases dissolve completely

Answer: B

Relative Atomic Mass (Ar)

86. What is relative atomic mass (Ar)?

A. Mass of one atom in grams

B. Atomic number of an element

C. Average mass of isotopes compared to 1/12 of carbon-12

D. Number of neutrons in an atom

Answer: C

87. Why is carbon-12 used as the reference standard?

A. It is radioactive

B. It is very rare

C. It is stable and assigned mass 12 exactly

D. It has the highest atomic number

Answer: C

88. What does “relative” mean in Ar?

A. It changes daily

B. It compares atomic mass to a standard

C. It measures volume

D. It is always a whole number

Answer: B

89. Why is Ar often not a whole number?

A. Atoms have fractional protons

B. Atoms have no neutrons

C. It is an average of isotopes with different abundances

D. Elements contain mixtures of compounds

Answer: C

90. Chlorine has Ar ≈ 35.5 because it:

A. Is made of two different elements

B. Has isotopes with different masses and abundances

C. Contains 35.5 protons

D. Has 35.5 neutrons

Answer: B

91. What is an isotope?

A. Atoms with different numbers of protons

B. Atoms with same protons but different neutrons

C. Atoms with same neutrons but different electrons

D. Atoms with different atomic numbers and same mass number

Answer: B

92. Which statement is correct?

A. Ar equals the mass number of the most common isotope always

B. Ar is the same as atomic number

C. Ar is a weighted average based on isotopic abundance

D. Ar is measured using a balance in grams

Answer: C

93. Where are Ar values commonly found?

A. In the catalyst list

B. On the Periodic Table

C. In the solubility chart only

D. In the reactivity series only

Answer: B

94. Which instrument is used to measure isotopic masses and abundances?

A. Bunsen burner

B. Mass spectrometer

C. Thermometer

D. Titration burette

Answer: B

95. What is one atomic mass unit (1 u) defined as?

A. Mass of 1 hydrogen atom exactly

B. 1/6 of carbon-12

C. 1/12 of the mass of a carbon-12 atom

D. 12 grams of carbon

Answer: C

96. An element has Ar = 24. What does this mean?

A. It has 24 protons

B. It has 24 isotopes

C. Its atoms are 24 times heavier than 1/12 of carbon-12

D. It has mass of 24 g per atom

Answer: C

97. Which value is most likely to be an Ar value?

A. 11

B. 12

C. 16.0

D. 6

Answer: C

98. What is a common misconception about Ar?

A. It is relative

B. It is based on carbon-12

C. It is the mass of a single atom in grams

D. It is an average value

Answer: C

99. Which statement correctly compares atomic number and Ar?

A. Both represent proton number

B. Atomic number is protons; Ar is average isotopic mass

C. Ar is protons; atomic number is average mass

D. Both are always whole numbers

Answer: B

100. Why is Ar important in stoichiometry?

A. It shows state symbols

B. It helps calculate formulae and reacting masses

C. It shows the shape of molecules

D. It explains reaction colours

Answer: B

101. Why does Mr have no units?

A. It is measured in cm³

B. It is measured in grams

C. It is a ratio (relative value)

D. It is always a whole number

Answer: C

102. Which type of substance uses relative molecular mass?

A. Ionic lattices

B. Covalent molecules

C. Metals only

D. All solids

Answer: B

103. Which type of substance uses relative formula mass?

A. Simple molecules

B. Covalent gases only

C. Ionic compounds

D. Noble gases

Answer: C

104. What is the Mr of H₂O? (H = 1, O = 16)

A. 16

B. 17

C. 18

D. 20

Answer: C

105. What is the Mr of CO₂? (C = 12, O = 16)

A. 28

B. 32

C. 44

D. 48

Answer: C

106. What is the Mr of NH₃? (N = 14, H = 1)

A. 14

B. 15

C. 17

D. 18

Answer: C

107. What is the Mr of CH₄? (C = 12, H = 1)

A. 12

B. 14

C. 16

D. 18

Answer: C

108. What is the Mr of C₂H₆? (C = 12, H = 1)

A. 24

B. 26

C. 30

D. 32

Answer: C

109. What is the relative formula mass of NaCl? (Na = 23, Cl = 35.5)

A. 45.5

B. 58.5

C. 60.5

D. 68.5

Answer: B

110. What is the relative formula mass of MgO? (Mg = 24, O = 16)

A. 28

B. 32

C. 40

D. 48

Answer: C

111. What is the relative formula mass of Al₂O₃? (Al = 27, O = 16)

A. 86

B. 96

C. 102

D. 108

Answer: C

112. Which value best represents Mr of a compound?

A. Always a whole number

B. Always less than Ar of its elements

C. Sum of Ar values in the formula

D. Number of protons in the compound

Answer: C

113. Why is “molecular mass” not used for ionic compounds?

A. Ionic compounds are liquids

B. Ionic compounds have no atoms

C. Ionic compounds do not exist as discrete molecules

D. Ionic compounds do not contain ions

Answer: C

Reacting Masses in Simple Proportions

114. What must you write first before any reacting mass calculation?

A. Ionic equation

B. Unbalanced equation

C. Balanced symbol equation

D. Word equation only

Answer: C

115. In 2Mg + O₂ → 2MgO, what does the “2” in front of Mg represent?

A. 2 grams of magnesium

B. 2 magnesium atoms/moles in the ratio

C. 2 oxygen atoms

D. 2 magnesium ions

Answer: B

116. In 2Mg + O₂ → 2MgO, what mass of Mg reacts? (Mg = 24)

A. 24

B. 32

C. 48

D. 56

Answer: C

117. In 2Mg + O₂ → 2MgO, what mass of O₂ reacts? (O = 16)

A. 16

B. 32

C. 48

D. 64

Answer: B

118. The reacting mass ratio Mg : O₂ in 2Mg + O₂ → 2MgO is:

A. 24:16

B. 48:32

C. 32:48

D. 16:24

Answer: B

119. Simplify the ratio 48:32.

A. 3:2

B. 2:3

C. 1:2

D. 4:3

Answer: A

120. If 3 g of Mg reacts with 2 g of O (ratio 3:2), how much O reacts with 12 g of Mg?

A. 6 g

B. 8 g

C. 10 g

D. 12 g

Answer: B

121. In 2H₂ + O₂ → 2H₂O, what is the mass ratio H₂ : O₂? (H = 1, O = 16)

A. 2:16

B. 4:32

C. 1:4

D. 8:1

Answer: B

122. Simplify the ratio 4:32 in the water equation.

A. 1:2

B. 1:4

C. 1:8

D. 2:1

Answer: C

123. In C + O₂ → CO₂, what mass of O₂ reacts with 12 g of carbon?

A. 12 g

B. 16 g

C. 24 g

D. 32 g

Answer: D

124. In C + O₂ → CO₂, if 6 g of carbon reacts, how much O₂ is needed?

A. 8 g

B. 16 g

C. 24 g

D. 32 g

Answer: B

125. In Zn + 2HCl → ZnCl₂ + H₂, what is the Mr of HCl? (H = 1, Cl = 35.5)

A. 34.5

B. 35.5

C. 36.5

D. 37.5

Answer: C

126. In Zn + 2HCl → ZnCl₂ + H₂, what mass of 2HCl reacts?

A. 36.5

B. 65

C. 73

D. 101.5

Answer: C

127. In Zn + 2HCl → ZnCl₂ + H₂, if 13 g of Zn reacts, how much HCl is needed? (Zn = 65; 2HCl = 73)

A. 7.3 g

B. 14.6 g

C. 26.0 g

D. 73.0 g

Answer: B

128. In CaCO₃ → CaO + CO₂, what is Mr of CaCO₃? (Ca = 40, C = 12, O = 16)

A. 56

B. 84

C. 100

D. 112

Answer: C

129. In CaCO₃ → CaO + CO₂, what mass of CO₂ forms from 100 g CaCO₃?

A. 28 g

B. 44 g

C. 56 g

D. 100 g

Answer: B

130. In CaCO₃ → CaO + CO₂, what mass of CaO forms from 100 g CaCO₃?

A. 44 g

B. 50 g

C. 56 g

D. 60 g

Answer: C

Concentration of Solutions

131. What is concentration?

A. Mass of solvent only

B. Amount of solute in a fixed volume of solution

C. Volume of solute in a fixed mass of solution

D. Temperature of a solution

Answer: B

132. A concentrated solution contains:

A. Little solute in much solvent

B. Much solute in a given volume

C. No solute

D. Only solvent

Answer: B

133. Which unit is commonly used for concentration at IGCSE?

A. g / cm³ only

B. g / dm³ and mol / dm³

C. kg / m³ only

D. mol / cm³ only

Answer: B

134. 1 dm³ is equal to:

A. 10 cm³

B. 100 cm³

C. 1000 cm³

D. 10 000 cm³

Answer: C

135. What is 1 dm³ equal to in litres?

A. 0.1 L

B. 1 L

C. 10 L

D. 100 L

Answer: B

136. What does g / dm³ measure?

A. Moles per litre

B. Mass of solute per dm³ of solution

C. Volume of solute per dm³

D. Temperature per dm³

Answer: B

137. 25 g of solute in 2 dm³ of solution has concentration:

A. 50 g/dm³

B. 12.5 g/dm³

C. 10 g/dm³

D. 5 g/dm³

Answer: B

138. Which solution is more concentrated?

A. 5 g/dm³

B. 10 g/dm³

C. 15 g/dm³

D. 2 g/dm³

Answer: C

139. What does mol / dm³ measure?

A. Mass of solute per dm³

B. Amount (moles) of solute per dm³

C. Volume of solute per dm³

D. Mass of solvent per dm³

Answer: B

140. A 2 mol/dm³ solution has:

A. Half as many particles as 1 mol/dm³

B. Twice as many particles per dm³ as 1 mol/dm³

C. The same particles as 1 mol/dm³

D. No particles

Answer: B

141. Why is mol / dm³ often preferred for reaction calculations?

A. Reactions depend on colour

B. Reactions depend on number of particles

C. Reactions depend on density only

D. Reactions depend on melting point

Answer: B

142. A solution is diluted by adding water. What happens?

A. Concentration increases

B. Volume decreases

C. Concentration decreases

D. Solute mass increases

Answer: C

The Mole and the Avogadro Constant

143. What is the mole used for in chemistry?

A. Measuring temperature

B. Counting particles indirectly

C. Measuring volume only

D. Measuring density

Answer: B

144. What is the value of the Avogadro constant?

A. 6.02 × 10²²

B. 6.02 × 10²³

C. 6.02 × 10²⁴

D. 6.02 × 10²¹

Answer: B

145. One mole of any substance contains:

A. 12 particles

B. 1000 particles

C. 6.02 × 10²³ particles

D. 1 particle

Answer: C

146. Which can be counted using moles?

A. Atoms only

B. Molecules only

C. Ions, atoms, molecules, and formula units

D. Solvents only

Answer: C

147. Which statement is correct?

A. 1 g of hydrogen has the same number of particles as 1 g of oxygen

B. Equal masses always have equal particles

C. The mole allows comparison using equal numbers of particles

D. The mole measures volume

Answer: C

148. What is meant by “amount of substance” in chemistry?

A. Mass in grams

B. Volume in cm³

C. Number of particles present

D. Temperature of sample

Answer: C

149. What does the equation 2H₂ + O₂ → 2H₂O mean in moles?

A. 2 g H₂ reacts with 1 g O₂

B. 2 moles H₂ react with 1 mole O₂ to form 2 moles H₂O

C. 2 molecules H₂ react with 1 molecule O₂ to form 1 molecule H₂O

D. 2 moles H₂ react with 2 moles O₂ to form 1 mole H₂O

Answer: B

150. What is relative molecular mass (Mr)?

A. Mass of one molecule in grams

B. Sum of the Ar values of atoms in one molecule

C. Number of atoms in a molecule

D. Mass compared to 1 g of hydrogen

Answer: B

Using moles, mass, and molar mass

151. What is the correct formula linking mass, moles, and molar mass?

A. mass = moles ÷ molar mass

B. moles = mass × molar mass

C. moles = mass ÷ molar mass

D. molar mass = moles ÷ mass

Answer: C

152. What is the molar mass of magnesium?

A. 12 g/mol

B. 16 g/mol

C. 24 g/mol

D. 40 g/mol

Answer: C

153. How many moles are present in 12 g of magnesium?

A. 0.25 mol

B. 0.5 mol

C. 1.0 mol

D. 2.0 mol

Answer: B

154. What mass of sodium chloride is present in 2 mol of NaCl? (Mr = 58.5)

A. 29.25 g

B. 58.5 g

C. 117 g

D. 234 g

Answer: C

155. A substance has a mass of 10 g and an amount of 0.25 mol. What is its molar mass?

A. 20 g/mol

B. 25 g/mol

C. 40 g/mol

D. 50 g/mol

Answer: C

156. Which unit is used for molar mass?

A. g

B. g/mol

C. mol

D. dm³

Answer: B

Moles and particles

157. How many particles are in 1 mol of any substance?

A. 6.02 × 10²²

B. 6.02 × 10²³

C. 1.00 × 10²³

D. 12.0

Answer: B

158. How many molecules are present in 0.5 mol of CO₂?

A. 3.01 × 10²²

B. 6.02 × 10²³

C. 3.01 × 10²³

D. 1.20 × 10²⁴

Answer: C

159. Which quantity links mass to number of particles?

A. Density

B. Molar mass

C. Atomic number

D. Volume

Answer: B

Gas volume at r.t.p.

160. What volume does 1 mol of any gas occupy at r.t.p.?

A. 22 dm³

B. 23 dm³

C. 24 dm³

D. 25 dm³

Answer: C

161. What volume will 2 mol of oxygen occupy at r.t.p.?

A. 12 dm³

B. 24 dm³

C. 36 dm³

D. 48 dm³

Answer: D

162. A gas occupies 12 dm³ at r.t.p. How many moles of gas are present?

A. 0.25 mol

B. 0.5 mol

C. 1.0 mol

D. 2.0 mol

Answer: B

163. Which relationship is correct for gases at r.t.p.?

A. volume = mass × 24

B. volume = moles ÷ 24

C. volume = moles × 24

D. volume = molar mass × 24

Answer: C

164. How many cm³ are equal to 24 dm³?

A. 2400 cm³

B. 12 000 cm³

C. 24 000 cm³

D. 240 000 cm³

Answer: C

Stoichiometry and reacting masses

165. Why must a chemical equation be balanced before calculations?

A. To show states of matter

B. To show reaction speed

C. To show correct mole ratios

D. To show energy change

Answer: C

166. In 2Mg + O₂ → 2MgO, what mass of magnesium reacts with oxygen?

A. 24 g

B. 32 g

C. 48 g

D. 56 g

Answer: C

167. In the same reaction, what mass of oxygen reacts?

A. 16 g

B. 24 g

C. 32 g

D. 48 g

Answer: C

168. What is the simplified mass ratio Mg : O in MgO?

A. 1 : 1

B. 2 : 1

C. 3 : 2

D. 4 : 3

Answer: C

169. If 6 g of magnesium reacts, how much oxygen is needed?

A. 2 g

B. 3 g

C. 4 g

D. 6 g

Answer: C

Limiting reactants

170. What is the limiting reactant?

A. The reactant in excess

B. The catalyst

C. The reactant that is used up first

D. The product formed

Answer: C

171. Which reactant limits the amount of product formed?

A. The one with greater mass

B. The one with smaller Mr

C. The one that runs out first

D. The one in solution

Answer: C

172. In Zn + 2HCl → ZnCl₂ + H₂, what is the mole ratio Zn : HCl?

A. 1 : 1

B. 1 : 2

C. 2 : 1

D. 2 : 2

Answer: B

173. If less hydrochloric acid than required is present, which is limiting?

A. Zinc

B. Zinc chloride

C. Hydrogen

D. Hydrochloric acid

Answer: D

Concentration of solutions

174. What does concentration measure?

A. Volume of solvent

B. Amount of solute per unit volume

C. Mass of solvent only

D. Temperature of solution

Answer: B

175. What is the unit g/dm³ used for?

A. Amount of substance

B. Volume of solution

C. Mass of solute per dm³

D. Number of particles

Answer: C

176. What is the concentration when 10 g of solute is dissolved in 0.5 dm³?

A. 5 g/dm³

B. 10 g/dm³

C. 20 g/dm³

D. 50 g/dm³

Answer: C

177. Which unit measures amount of substance per volume?

A. g/dm³

B. mol/dm³

C. cm³

D. g/mol

Answer: B

178. A 1.0 mol/dm³ solution contains:

A. 1 g of solute per dm³

B. 1 mol of solute per dm³

C. 24 dm³ of solute

D. 6.02 × 10²³ dm³

Answer: B

179. What happens to concentration when water is added?

A. It increases

B. It decreases

C. It stays the same

D. It becomes zero

Answer: B

Titration calculations

180. What is the main purpose of a titration?

A. To purify substances

B. To measure temperature

C. To find concentration

D. To separate mixtures

Answer: C

181. Which piece of apparatus delivers accurate variable volumes?

A. Pipette

B. Measuring cylinder

C. Burette

D. Beaker

Answer: C

182. What must always be used in titration calculations?

A. Empirical formula

B. Balanced equation

C. Gas volume

D. Percentage yield

Answer: B

183. In HCl + NaOH → NaCl + H₂O, what is the mole ratio?

A. 1 : 2

B. 2 : 1

C. 1 : 1

D. 2 : 2

Answer: C

184. Which indicator is commonly used in acid–alkali titrations?

A. Bromine water

B. Phenolphthalein

C. Potassium manganate

D. Limewater

Answer: B

Empirical and molecular formulae

185. What does an empirical formula show?

A. Exact number of atoms

B. Simplest whole-number ratio of atoms

C. Structure of molecule

D. Shape of molecule

Answer: B

186. A compound contains 12 g C and 2 g H. What is its empirical formula?

A. CH

B. CH₂

C. C₂H

D. C₂H₄

Answer: B

187. Why are masses converted to moles when finding empirical formulae?

A. To balance equations

B. To compare particle numbers

C. To find volume

D. To calculate yield

Answer: B

188. An empirical formula has mass 14 and Mr = 42. What is the molecular formula?

A. CH₂

B. C₂H₄

C. C₃H₆

D. C₄H₈

Answer: C

Percentage yield

189. What is percentage yield?

A. Actual mass ÷ theoretical mass × 100

B. Theoretical mass ÷ actual mass × 100

C. Mass of reactants × 100

D. Mass of products only

Answer: A

190. If theoretical yield is 10 g and actual yield is 8 g, what is the percentage yield?

A. 20%

B. 80%

C. 125%

D. 18%

Answer: B

191. Why is percentage yield often less than 100%?

A. Reactants are heavier

B. Products are lost or side reactions occur

C. Equations are wrong

D. Atoms are destroyed

Answer: B

Percentage composition

192. Percentage composition by mass shows:

A. Volume of elements

B. Mass of each element as a percentage

C. Number of atoms

D. Number of molecules

Answer: B

193. What is the formula for percentage composition?

A. (total mass ÷ mass of element) × 100

B. (mass of element ÷ total mass) × 100

C. mass × 100

D. moles ÷ mass

Answer: B

194. Which element contributes most to the mass of water?

A. Hydrogen

B. Oxygen

C. Both equal

D. Neither

Answer: B

Percentage purity

195. Percentage purity measures:

A. Reaction speed

B. Efficiency of reaction

C. Proportion of pure substance in a sample

D. Amount of solvent

Answer: C

196. What is the formula for percentage purity?

A. pure mass ÷ impure mass × 100

B. impure mass ÷ pure mass × 100

C. pure mass ÷ total mass × 100

D. total mass ÷ pure mass × 100

Answer: C

197. A 10 g sample contains 8 g of pure substance. What is its percentage purity?

A. 20%

B. 80%

C. 125%

D. 8%

Answer: B

198. Why does impurity affect reacting mass calculations?

A. It increases temperature

B. Only pure substance reacts

C. It changes the equation

D. It increases yield

Answer: B

Mixed stoichiometry concepts

199. Which quantity is always conserved in chemical reactions?

A. Mass

B. Volume

C. Concentration

D. Temperature

Answer: A

200. Why are moles preferred over grams in reactions?

A. Grams are inaccurate

B. Reactions depend on particle ratios

C. Grams are too large

D. Moles measure volume

Answer: B

201. Equal volumes of different gases at r.t.p. contain:

A. Equal masses

B. Equal numbers of particles

C. Different numbers of particles

D. No particles

Answer: B

202. Which calculation links titration data to stoichiometry?

A. Mass ÷ volume

B. Concentration × volume

C. Volume ÷ Mr

D. Percentage yield

Answer: B

203. What must be converted to dm³ before mole calculations?

A. Mass

B. Concentration

C. Volume in cm³

D. Temperature

Answer: C

204. Which concept connects experimental data to formulae?

A. Limiting reactant

B. Empirical formula

C. Percentage purity

D. Titration

Answer: B

205. Which value is needed to convert mass to moles?

A. Density

B. Concentration

C. Molar mass

D. Gas volume

Answer: C

206. Why is Mr important in percentage composition?

A. It gives volume

B. It gives total relative mass

C. It gives concentration

D. It gives number of particles

Answer: B

207. In multi-step stoichiometry problems, what should be done first?

A. Calculate gas volume

B. Identify limiting reactant

C. Write balanced equation

D. Convert to cm³

Answer: C

208. Which calculation uses both purity and yield?

A. Empirical formula

B. Simple reacting masses

C. Real industrial yield problems

D. Gas volume only

Answer: C

209. What does a low percentage purity indicate?

A. Efficient reaction

B. High concentration

C. Many impurities present

D. High yield

Answer: C

210. Why are these calculations essential for IGCSE Chemistry?

A. They test memory only

B. They link theory with experimental data

C. They avoid equations

D. They replace practical work

Answer: B

Thank You!

Sana Shariq

For revision visit

https://youtu.be/F5tHn4W1XSk