CHEMISTRY
WORKSHEET MOLE CONCEPT AND STOICHIOMETRY
ELEVATE
Formulae:
1. NA = 6.022 × 1023
NA is called Avogadro’s number.
2. 1 mole of a substance = 6.022 × 1023 constituent particles of the substance.
(Constituent particles may be atoms, molecules, ions, or electrons.)
𝒘
3. n =
𝐌
where n = number of moles (mol)
w = mass of the substance (in grams)
M = molar mass of the substance (in g mol-1).
• Molar mass of a substance is numerically equal to the gram atomic mass or gram molecular
mass
of the substance.
4. 1 mole of any gas = 22.4 L at STP
(STP = Standard temperature and pressure = 273 K and 1 atm)
• 1 L = 1000 cm3
5. Mole is also referred to as gram – molecule.
• Gram – molecule = moles of molecules = number of moles of the compound
• Gram – atom = moles of atoms
• Gram – ions = moles of ions
1. Calculate the number of moles of 521.5 mg of potassium chloride.
2. 0.4 mol of a substance weighs 16 g. What is the molar mass of the substance?
3. How many carbon and hydrogen atoms are present in 1 mol of methane gas?
(A) 1 mol C, 1 mol H (B) 2 mol C, 4 mol H
(C) 1 mol C, 4 mol H (D) 4 mol C, 1 mol H
4. Which of the following pairs have the same number of atoms?
(A) 16 g of O2 and 4 g of H2 (B) 16 g of O2 and 28 g of N2
(C) 28 g of N2 and 8 g of He (D) 12 g of C and 32 g of O2
5. The volume occupied by 4 g of sulphur trioxide gas at STP is x × 10–2. The value of x is
6. The mass of one atom of carbon is x × 10–23 grams. Given that, the mass of one mole of carbon
atoms is 12 g, the value of x is ________ (round off to nearest integer).
7. A signature written with carbon pencil weighs 1 mg. If the number of carbon atoms present in
the signature is y × 1018, the value of y will be __________ (round off to the nearest integer).
8. The number of aluminium ions present in 0.051 g of aluminium oxide is 6.022 × 10 y. The value
of y is
9. The number of moles of magnesium phosphate that contains 0.25 mole of oxygen atoms is z ×
10–2. The value of z is ________ (round off to nearest integer.)
10. How many gram – atoms of hydrogen are present in 68 g of hydrogen sulphide?
11. 3.42 g of sucrose (C12H22O11) is dissolved in 36 g of water. What is the total number of oxygen
atoms in the solution?
12. Haemoglobin contains 0.33 % of iron by weight. The molecular weight of haemoglobin is
approximately 67200 u. The number of iron atoms present in one molecule of haemoglobin are
________. (round off to the nearest integer)
[Atomic weight of Fe = 56 u]
13. 24 g of carbon reacts with oxygen to produce 88 g of carbon dioxide. The number of moles of
oxygen used in this reaction is _______.
14. An unknown amount of hexane (C6H14) is burnt to produce 60 mol of gas. The amount of
hexane burnt (in grams) is _______.
15. The mass of sodium nitrate required to produce 128 g of oxygen gas on thermal decomposition
is ________.
16. Quick lime is used to capture carbon dioxide from the atmosphere and form calcium carbonate.
This calcium carbonate is then heated to high temperatures and the CO2 thus released is used in
many industrial applications.
If the lime used in this process can be recycled and reused for up to 5 cycles with 10 % loss of
lime at each cycle, how many grams of carbon dioxide in total can be captured from the
atmosphere at the end of two cycles starting from 1.12 kg of lime?
(A) 1745 (B) 1672 (C) 2102 (D) 1891
17. What mass of 50 % pure calcium carbonate is required to obtain 1.1 g of carbon dioxide on
thermal decomposition?
18. 100 cm3 of a gas A contains y molecules of A. How many molecules of gas B will be present
in 40 cm3 of gas B under the same conditions of temperature and pressure?
19. X is a triatomic gas, while Y is a diatomic gas. 50 litres of Y contains ‘2a’ molecules of Y. At
the same conditions of temperature and pressure, the number of atoms of X in 25 litres of X is
n × a (n is an integer). The value of n is _________.
20. The volume of carbon dioxide formed when 400 mL of acetylene (C2H2) is completely burnt
is _______.
21. 200 cm3 of carbon monoxide is mixed with 200 cm3 of oxygen at room temperature and ignited.
Which is the limiting reagent in this reaction?
22. 56 litres of nitrogen gas is mixed with hydrogen gas and 20 litres of ammonia gas is produced.
The volume of unreacted nitrogen gas is _______ litres.
