The Mole & the Avogrado Constant - Theory Flashcards
Learn the key formulas and ideas behind the mole and the avogrado constant
What is a mole in chemistry?
A mole represents 6.02 × 10²³ particles (atoms, molecules, or ions) of a substance.
How is the mass of one mole of an element calculated?
The mass of 1 mole of an element is equal to its relative atomic mass (Ar) in grams.
What is Avogadro’s constant?
6.02 × 10²³, the number of particles in one mole of a substance.
What is the formula to calculate moles from mass?
Moles = Mass ÷ Mr
What formula links moles, mass, and Mr?
Mass = Moles × Mr
What is water of crystallisation?
Water molecules structurally bound within a salt’s crystal lattice.
How is the formula of a hydrated salt determined?
Measure mass before and after heating, calculate moles of salt & water, and determine their whole-number ratio.
What formula is used to calculate moles in hydrated salts?
Moles = Mass ÷ Mr
How do you calculate the ratio of salt to water?
Divide all mole values by the smallest mole number to get a whole-number ratio.
What does percentage yield measure?
How efficient a reaction is by comparing actual yield to theoretical yield.
What is the formula for percentage yield?
Percentage Yield = (Actual Yield ÷ Theoretical Yield) × 100
Why is 100% yield rarely achieved?
Side reactions, separation losses, reversible reactions, impurities, or incomplete reactions reduce yield.
What does percentage composition tell us?
The proportion of an element’s mass relative to the total compound’s mass.
What is the formula for percentage composition?
Percentage Composition = (Total Mass of the Element ÷ Total Mass of the Compound) × 100
Define percentage purity.
The proportion of pure substance in a sample containing impurities.
What is the formula for percentage purity?
Percentage Purity = (Mass of Pure Substance ÷ Total Mass of Substance) × 100
What is an empirical formula?
The simplest whole-number ratio of atoms in a compound.
What is a molecular formula?
The actual number of atoms in a molecule, which may be a multiple of the empirical formula.
How is empirical formula calculated?
Convert mass into moles, divide by smallest mole number, then adjust ratios to whole numbers.
How is molecular formula calculated?
Molecular Formula = Empirical Formula × (Molecular Mr ÷ Empirical Mr)
What formula is used to calculate moles from mass?
Moles = Mass ÷ M*
Why must molar ratios be considered in reacting mass calculations?
They determine the proportional relationship between reactants and products.
What is a limiting reactant?
The reactant that gets used up first, preventing further product formation.
How do you determine the limiting reactant?
Convert reactant masses to moles, compare with the balanced equation’s molar ratio, and identify the reactant present in the lowest correct proportion.
