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Not Everything That Stops Working Has Lost Its Value Feeling broken by life's setbacks? Discover why your value never decreases because of failure, pain, or difficult seasons. Learn the powerful lesson behind the broken machine and why your worth remains unchanged. The Broken Machine That Changed Everything Imagine walking into a workshop and finding an old industrial machine covered in dust and rust. It has not worked for years. Most people pass it without a second thought. "It is finished." "It is useless." "It belongs in the scrapyard." Those are the words many would use. Then an experienced engineer enters. Instead of seeing a useless machine, he sees possibility. He opens the casing, examines the internal parts, replaces a few worn components, reconnects the wiring, and powers it on. Within moments, the machine is running again. What changed? Not its value. Only its condition. That simple scene teaches one of the most important lessons about human...
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Calculations in chemistry

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JAMB Chemistry Practice Questions

JAMB Chemistry Practice Questions and Answers

1. Calculate the number of moles in 36 grams of water (H₂O).

Molar mass of H₂O = (2 × 1) + 16 = 18 g/mol.
Number of moles = mass / molar mass = 36 g / 18 g/mol = 2 moles.

2. What is the empirical formula of a compound that contains 4 g of nitrogen and 12 g of oxygen?

Moles of nitrogen = 4 g / 14 g/mol = 0.286 mol.
Moles of oxygen = 12 g / 16 g/mol = 0.75 mol.
Divide both by the smallest value (0.286):
Nitrogen: 0.286 / 0.286 = 1
Oxygen: 0.75 / 0.286 = 2.6 ≈ 3
The empirical formula is NO₃.

3. What is the molecular formula of a compound if its empirical formula is CH₂ and its molar mass is 56 g/mol?

Molar mass of CH₂ = 12 + (2 × 1) = 14 g/mol.
Ratio of molecular mass to empirical formula mass = 56 / 14 = 4.
The molecular formula is C₄H₈.

4. How many molecules are there in 2 moles of methane (CH₄)?

1 mole = 6.022 × 10²³ molecules.
Number of molecules in 2 moles = 2 × 6.022 × 10²³ = 1.2044 × 10²⁴ molecules.

5. Calculate the mass of 0.5 moles of sodium chloride (NaCl).

Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol.
Mass = moles × molar mass = 0.5 × 58.5 = 29.25 grams.

6. Calculate the number of moles in 45 grams of carbon dioxide (CO₂).

Molar mass of CO₂ = 12 + (2 × 16) = 44 g/mol.
Number of moles = 45 g / 44 g/mol = 1.02 moles.

7. What is the empirical formula of a compound that contains 12 g of carbon and 32 g of oxygen?

Moles of carbon = 12 g / 12 g/mol = 1 mol.
Moles of oxygen = 32 g / 16 g/mol = 2 mol.
Divide both by the smallest value (1):
Carbon: 1 / 1 = 1
Oxygen: 2 / 1 = 2
The empirical formula is CO₂.

8. The molecular weight of a compound is 88 g/mol, and its empirical formula is CH₄. What is the molecular formula?

Molar mass of CH₄ = 12 + (4 × 1) = 16 g/mol.
Ratio of molecular mass to empirical formula mass = 88 / 16 = 5.
The molecular formula is C₅H₁₀.

9. Calculate the number of moles in 100 g of sodium (Na).

Molar mass of Na = 23 g/mol.
Number of moles = 100 g / 23 g/mol = 4.35 moles.

10. What is the mass of 0.5 moles of a substance that weighs 18 g per mole?

Mass = moles × molar mass = 0.5 × 18 = 9 grams.

11. What is the valency of oxygen in H₂O?

In H₂O, hydrogen has a valency of 1. Oxygen must balance this by having a valency of 2 to make the compound neutral.

12. How many molecules are in 10 grams of oxygen gas (O₂)?

Molar mass of O₂ = 32 g/mol.
Number of moles = 10 g / 32 g/mol = 0.3125 moles.
Number of molecules = 0.3125 × 6.022 × 10²³ = 1.88 × 10²³ molecules.

13. What is the empirical formula of a compound that contains 2.8 g of nitrogen and 8.0 g of hydrogen?

Moles of nitrogen = 2.8 g / 14 g/mol = 0.2 mol.
Moles of hydrogen = 8.0 g / 1 g/mol = 8 mol.
Divide both by the smallest value (0.2):
Nitrogen: 0.2 / 0.2 = 1
Hydrogen: 8 / 0.2 = 40
The empirical formula is NH₄.

14. What is the molecular formula of a compound with an empirical formula of CH₂ and a molar mass of 28 g/mol?

Molar mass of CH₂ = 12 + (2 × 1) = 14 g/mol.
Ratio of molecular mass to empirical formula mass = 28 / 14 = 2.
The molecular formula is C₂H₄.

15. How many grams are in 0.25 moles of potassium chloride (KCl)?

Molar mass of KCl = 39 + 35.5 = 74.5 g/mol.
Mass = 0.25 × 74.5 = 18.625 grams.

16. Calculate the number of moles in 3.2 × 10²⁴ molecules of methane (CH₄).

Number of moles = 3.2 × 10²⁴ / 6.022 × 10²³ = 5.3 moles.
Molar mass of CH₄ = 12 + (4 × 1) = 16 g/mol.
Mass = 5.3 × 16 = 84.8 grams.

17. Find the number of atoms in 4 moles of aluminum (Al).

1 mole = 6.022 × 10²³ atoms.
Number of atoms in 4 moles = 4 × 6.022 × 10²³ = 2.4088 × 10²⁴ atoms.

18. What is the empirical formula of a compound containing 2.4 g of nitrogen and 7.2 g of oxygen?

Moles of nitrogen = 2.4 g / 14 g/mol = 0.171 mol.
Moles of oxygen = 7.2 g / 16 g/mol = 0.45 mol.
Divide both by the smallest value (0.171):
Nitrogen: 0.171 / 0.171 = 1
Oxygen: 0.45 / 0.171 = 2.63 ≈ 3
The empirical formula is NO₃.

19. Calculate the number of moles in 72 grams of carbon (C).

Molar mass of C = 12 g/mol.
Number of moles = 72 g / 12 g/mol = 6 moles.

20. If 1 mole of a substance weighs 58.5 grams, how many grams will 0.2 moles weigh?

Mass = moles × molar mass = 0.2 × 58.5 = 11.7 grams.

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