Page 26 - Focus SPM KSSM F4 2020 - Chemistry

Chemistry Form 4 Chapter 3 The Mole Concept, Chemical Formula and Equation
Observations:
Section Observations Inferences
A • Copper(II) carbonate changes colour • Copper(II) carbonate decomposes into copper(II)
from green to black. oxide that is black in colour.
• Limewater turns cloudy. • Carbon dioxide is released.

B • Thick white fumes are produced at the • Ammonium chloride powder is produced.
mouths of the test tubes.
C • Yellow precipitate is produced. • Lead(II) iodide precipitate is produced.
Discussion:
1. When copper(II) carbonate is heated, it decomposes into copper(II) oxide and carbon dioxide. The
presence of carbon dioxide is confirmed by the cloudiness of limewater.
Chemical equation:
CuCO (s) CuO(s) + CO (g)
2
3
Copper(II) carbonate Copper(II) oxide Carbon dioxide
2. Concentrated hydrochloric acid and concentrated ammonia solution are left aside for a minute to
Chapter
3 produce hydrogen chloride gas and ammonia gas respectively.
3. The hydrogen chloride gas combines with the ammonia gas to form fine white solid of ammonium
chloride which are seen as thick white fumes.
Chemical equation:
HCl(g) + NH (g) NH Cl(s)
4
3
Hydrogen chloride gas Ammonia gas Ammonium chloride
4. When the colourless solution of potassium iodide is added to the lead(II) nitrate solution which
is also colourless, a yellow precipitate of lead(II) iodide is produced. At the same time, potassium
nitrate solution which is colourless is formed.
Chemical equation:
2KI(aq) + Pb(NO ) (aq) PbI (s) + 2KNO (aq)
2
3 2
3
Potassium iodide Lead(II) nitrate Lead(II) iodide Potassium nitrate
Qualitative and quantitative aspects of chemical equations
1. Qualitative information from chemical equations:
• Reactants and products
• Physical state of each reactant and product
2. Quantitatively, the coefficients in a balanced equation show the ratio of amounts of reactants and
products. See Figure 3.21.
Qualitative information: The reactants are The product is
potassium solid potassium bromide
and bromine gas solid
Equation: 2K (s) + Br (g) → 2KBr (s)
2
Quantitative information: 2 mol 1 mol 2 mol
or 2 atoms 1 molecule 2 formula units
Figure 3.21 Qualitative and quantitative aspects of a chemical equation
3. From the equation in Figure 3.21, we know that 2 moles of potassium will react with 1 mole of bromine
gas to produce 2 moles of potassium bromide.
4. At the microscopic level, we know that every 2 K atoms will react with 1 Br molecule to produce 2
2
units of KBr.

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