Mass calculations

Steps: 1. Find the mass of each element. 2. Divide by the relative atomic mass (Ar). 3. Divide all results by the smallest number. 4. Write the ratio as the empirical formula.

Relative Formula Mass (Mr): Sum of the relative atomic masses of all atoms in a compound. Example: MrofH2O=(2×1)+16=18

Empirical Formula: Simplest whole-number ratio of atoms in a compound. Molecular Formula: Actual number of atoms in one molecule of a compound. Example: CH2O O (Empirical) vs C6H12O6 (Molecular)

Example: Molecular Formula C4H10 → Empirical Formula = C2H5 (Divide by 2).

Definition: Mass is conserved in a reaction; mass of reactants = mass of products.

Steps: 1. Find the Mr of the empirical formula. 2. Divide the relative molecular mass by the empirical formula mass. 3. Multiply the subscripts in the empirical formula by this number.

Method: 1. Heat a metal (e.g., magnesium) in excess oxygen. 2. Measure the mass before and after. 3. Use mass data to calculate the empirical formula (mass of metal and oxygen).

Non-Enclosed System: Mass may appear to change due to gas release or absorption (e.g., burning wood, CO₂ released).

Numberofparticles=Moles×6.02×10^23

Formula; Moles = Mass(g) —————– Relative Formula Mass(Mr)

Steps: 1. Write the balanced equation. 2. Find the moles of reactant. 3. Use mole ratio to find moles of product. 4. Convert moles of product to mass.

Definition: A mole is: 6.02×10^23 particles of a substance (Avogadro’s number). Molar Mass: Mass of one mole of a substance in grams = Mr (e.g., 1 mole of H₂O = 18g).

Steps: 1. Write the balanced equation. 2. Find the moles of product. 3. Use mole ratio to find moles of reactant. 4. Convert moles of reactant to mass.

Formula: Concentration(g/dm^3)= mass of solute(g) ————————– Volume of solution(dm^3)

Mass(g)=Moles×Mr

6.02 x 10^23

Limiting Reactant: The reactant that is used up first, controlling the amount of product. Mass of Product: Depends on the amount of limiting reactant.

Steps: Find the moles of each substance. Simplify the mole ratio. Write the balanced equation based on this ratio.