This is a summary of what Grade 10 IEB students must know; these notes will prove useful for the year and up until Grade 12. It discusses what you need to know regarding percentage purity, molecular formulae, etc
• Stoichiometry is a branch of chemistry that deals with the
quantitative relationships between reactants and products in a
chemical reaction.
• In stoichiometry, we use balanced chemical equations to understand
how reactants are converted into products in terms of the number of
molecules, atoms, or moles.
• The foundation of stoichiometry lies in the Law of Conservation of
Mass, which states that matter cannot be created or destroyed in a
chemical reaction. This law forms the basis for all stoichiometric
calculations.
Mole Concept
• The mole is a fundamental unit in chemistry, representing a specific
number of particles: Avogadro's number, which is approximately
6.022 x 10^23.
• One mole of any substance contains the same number of entities,
whether they are atoms, molecules, or ions.
• The molar mass of an element or compound is the mass of one mole
of that substance, usually expressed in grams per mole (g/mol).
• To calculate the number of moles (n) in a sample, use the formula: n
= mass (g) / molar mass (g/mol).
Stoichiometric Calculations
• Stoichiometry helps us answer questions such as:
• How much of one reactant is needed to react completely with another
reactant?
• How much product can be formed from a given number of reactants?
• Steps for stoichiometric calculations:
• Write a balanced chemical equation to represent the reaction.
• Convert known quantities to moles if they are not already in
moles.
• Use the coefficients in the balanced equation to establish mole-to-
mole ratios between reactants and products.
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, • Calculate the desired quantity (moles or mass) using the mole-to-
mole ratios.
Limiting Reactants and Excess Reactants
• The limiting reactant is the reactant that is completely consumed in
a chemical reaction, determining how much product can be formed.
• The excess reactant is the reactant that is not completely consumed
and is left over when the limiting reactant is used up.
• To determine the limiting reactant, compare the calculated amounts
of product that can be formed from each reactant. The reactant that
produces less product is the limiting reactant.
Stoichiometry in Real Life
• Stoichiometry has numerous real-world applications, including:
• Calculating the number of reactants needed in chemical
manufacturing.
• Determining the amount of fuel required for combustion reactions.
• Analysing chemical reactions in environmental science, such as air
pollution and water treatment.
• It is a fundamental concept used in various industries and scientific
research.
Molecular Formula:
• Definition: The molecular formula of a compound represents the
actual number and type of atoms of each element present in a
molecule of that compound. It provides the specific, exact
composition of the compound.
• Whole Numbers: Molecular formulas give the exact whole-number
ratio of atoms in a molecule. For example, the molecular formula for
glucose is C6H12O6, indicating that one molecule of glucose consists
of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.
• Specific Information: Molecular formulas provide precise details
about the arrangement and quantity of atoms within a molecule,
making them particularly useful for understanding the chemical
structure and behaviour of a compound.
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