Stoichiometry Practice Questions
NECO (Nigeria) · NECO Chemistry · 138 free MCQs with instant results and detailed explanations.
138
Total
37
Easy
76
Medium
25
Hard
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Sample Questions from Stoichiometry
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Q1
Easy
If 2 moles of hydrogen react with 1 mole of oxygen to produce water, how many moles of water are formed?
A.
1 mole
B.
2 moles
C.
3 moles
D.
4 moles
Show Answer & Explanation
Correct Answer: B
According to the balanced chemical equation 2H₂ + O₂ → 2H₂O, 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water. Thus, the correct answer is 2 moles of water.
Q2
Easy
Which of the following statements about stoichiometric coefficients in a balanced equation is true?
A.
They represent the mass of reactants and products.
B.
They indicate the number of moles of substances involved.
C.
They are always whole numbers and fractions.
D.
They are used to balance the total charge in a reaction.
Show Answer & Explanation
Correct Answer: B
Stoichiometric coefficients in a balanced chemical equation specify the relative number of moles of each reactant and product. They are used to determine the proportions in which chemicals react and are produced.
Q3
Easy
Which of the following represents the correct mole ratio of reactants and products in the reaction 4Fe + 3O₂ → 2Fe₂O₃?
A.
4:3:2
B.
2:3:4
C.
3:4:2
D.
2:4:3
Show Answer & Explanation
Correct Answer: A
The balanced chemical equation shows that 4 moles of iron (Fe) react with 3 moles of oxygen (O₂) to produce 2 moles of iron(III) oxide (Fe₂O₃), giving a ratio of 4:3:2.
Q4
Medium
What is the molar mass of calcium carbonate (CaCO3)?
A.
100.09 g/mol
B.
120.09 g/mol
C.
140.09 g/mol
D.
80.09 g/mol
Show Answer & Explanation
Correct Answer: A
The molar mass of calcium carbonate (CaCO3) is calculated by adding the atomic masses of calcium (Ca = 40.08 g/mol), carbon (C = 12.01 g/mol), and three oxygens (O = 16.00 g/mol x 3). Thus, 40.08 + 12.01 + (3 x 16.00) = 100.09 g/mol.
Q5
Medium
If 5 moles of A react with 3 moles of B to produce 4 moles of C, what is the limiting reactant?
A.
A
B.
B
C.
C
D.
Neither
Show Answer & Explanation
Correct Answer: B
In a reaction where 5 moles of A react with 3 moles of B, the stoichiometric ratio dictates the amounts required for complete reaction. If B is consumed at a higher rate than A can supply, B becomes the limiting reactant. Here, 3 moles of B can only react with a maximum of 7.5 moles of A, but only 5 moles are available.
Q6
Medium
How many grams of sodium chloride (NaCl) can be produced from 2 moles of sodium (Na) and excess chlorine gas (Cl2)?
A.
116.88 g
B.
58.44 g
C.
146.88 g
D.
29.22 g
Show Answer & Explanation
Correct Answer: A
The reaction between sodium and chlorine gas to produce sodium chloride is 2Na + Cl2 → 2NaCl. From 2 moles of Na, 2 moles of NaCl are produced. The molar mass of NaCl is 58.44 g/mol, so 2 moles of NaCl yield 2 x 58.44 g = 116.88 g.
Q7
Medium
If 5 grams of sodium chloride (NaCl) are dissolved in water, how many moles of NaCl are present? (Molar mass of NaCl = 58.5 g/mol)
A.
0.085 moles
B.
0.095 moles
C.
0.075 moles
D.
0.065 moles
Show Answer & Explanation
Correct Answer: A
To find moles, use the formula: moles = mass (g) / molar mass (g/mol). Here, 5 g / 58.5 g/mol = 0.085 moles.
Q8
Hard
In a reaction where 4 moles of aluminum react with 3 moles of oxygen to produce aluminum oxide, what is the limiting reactant if only 5 moles of aluminum are available?
A.
Aluminum
B.
Oxygen
C.
Aluminum oxide
D.
None of the above
Show Answer & Explanation
Correct Answer: A
Aluminum is the limiting reactant because it is present in a smaller amount than required by the stoichiometric ratio of the reaction. The reaction requires 4 moles of aluminum for every 3 moles of oxygen, meaning that with only 5 moles of aluminum available, not enough aluminum is present to react completely with the available oxygen.
Q9
Hard
A reaction requires 2 moles of hydrogen gas (H2) and 1 mole of oxygen gas (O2) to produce water (H2O). If 5 moles of hydrogen and 3 moles of oxygen are available, which of the following is the limiting reactant?
A.
Hydrogen (H2)
B.
Oxygen (O2)
C.
Water (H2O)
D.
No limiting reactant
Show Answer & Explanation
Correct Answer: B
Oxygen (O2) is the limiting reactant because producing the maximum amount of water that can be formed is constrained by the quantity of oxygen available, not hydrogen.
Q10
Hard
A chemist reacts 5 moles of hydrogen with 3 moles of oxygen to form water. How many moles of water can be produced, considering the reaction H2 + O2 → H2O?
A.
5 moles
B.
3 moles
C.
6 moles
D.
2.5 moles
Show Answer & Explanation
Correct Answer: C
The reaction ratio shows that 2 moles of H2 react with 1 mole of O2 to produce 2 moles of H2O. Here, 5 moles of H2 would require 2.5 moles of O2. Since we have 3 moles of O2 available, H2 is the limiting reactant, producing 5 moles of H2O.
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Stoichiometry — NECO (Nigeria) NECO Chemistry Practice Questions Online
This page contains 138 practice MCQs for the chapter Stoichiometry in NECO (Nigeria) NECO Chemistry. The questions are organized by difficulty — 37 easy, 76 medium, 25 hard — so you can choose the right level for your preparation.
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