Activity 3.5 (Textbook) – Chemistry Form 4 Chapter 3 (The Mole Concept, Chemical Formula and Equation)

Activity 3.5:
Calculating the number of moles and number of particles
[Avogadro constant, NA : 6.02 × 10²³ mol^–1]
1. Calculate the number of atoms found in
(a) 0.1 mol of carbon, C
(b) 3.5 mol of neon gas, Ne

2. Calculate the number of molecules found in
(a) 1.2 mol of hydrogen gas, H₂
(b) 0.8 mol of ammonia, NH₃

3. Calculate the number of formula units found in
(a) 3 mol of sodium chloride, NaCl
(b) 0.25 mol of potassium nitrate, KNO₃


4. Calculate the number of moles of each of the following substances:
(a) 6.02 × 10²⁴ lead atoms, Pb
(c) 9.03 × 10²² bromine molecules, Br₂
(b) 3.02 × 10²³ magnesium oxide units, MgO
(d) 3.612 × 10²⁴ carbon dioxide molecules, CO₂

5. A reagent bottle contains 1.806 × 10²⁵ units of copper(II) oxide, CuO.
(a) How many moles of copper(II) oxide, CuO are found in the bottle?
(b) Calculate the number of ions found in that bottle.

6. A sample contains 0.2 mol of ethene gas, C₂H₄.
(a) How many ethene molecules, C₂H₄ are found in the sample?
(b) How many hydrogen atoms, H are found in the sample?
(c) Calculate the total number of atoms found in the sample.


Answer:
1. (a) 6.02 × 10²² atoms
(b) 2.107 × 10²⁴ atoms

2. (a) 7.224 × 10²³ molecules
(b) 4.816 × 10²³ molecules

3. (a) 1.806 × 10²⁴ formula units
(b) 1.505 × 10²³ formula units


4. (a) 10 mol
(b) 0.5 mol
(c) 0.15 mol
(d) 6 mol

5. (a) 30 mol
(b) 3.612 × 10²⁵ ions

6. (a) 1.204 × 10²³ ethene molecules
(b) 4.816 × 10²³ H atoms
(c) 7.224 × 10²³ atoms