Quantitative chemistry

What is relative atomic mass (Ar)?

Relative atomic mass is the weighted average mass of an element’s atoms, considering each isotope's abundance, relative to 1/12th the mass of a carbon-12 atom.

What is a mole in chemistry?

A mole is the amount of a substance containing 6.022 \times 10^{23} particles (Avogadro’s constant), whether atoms, molecules, or ions.

How do you calculate the relative formula mass (Mr) of a compound?

Add the relative atomic masses (Ar) of all atoms in the formula. Example: Mr of CaCO₃ = 40 + 12 + (3 × 16) = 100.

How do you calculate the mass of one mole of a substance?

The mass of one mole equals the Mr of the substance in grams. Example: Mr of CO₂ = 44, so 1 mole of CO₂ = 44 g.

How do you calculate the percentage by mass of an element in a compound?

\text{Percentage by mass} = \left( \frac{\text{Total Ar of element in compound}}{\text{Mr of compound}} \right) \times 100 . Example: % of Na in NaCl = (23 / 58.5) × 100 ≈ 39.3%

What does conservation of mass mean in a chemical reaction?

Conservation of mass means no atoms are created/destroyed, so the total mass of products equals the total mass of reactants.

How do you calculate the mass of a product or reactant from a balanced equation?

1. 1. Find the Mr of substances. 2. Calculate moles of known substance. 3. Use the ratio from balanced equation. 4. Multiply to find unknown mass. Example: 2H2+O2→2H2O2H2+O2→2H2O (4g H₂ → ? g H₂O); Moles of H2H2 = 4/2 = 2 mol; 2 mol H2H2 → 2 mol H2OH2O, 2 mol H2OH2​O = 2 × 18 = 36g

What is yield in chemistry?

Yield is the amount of product actually obtained from a chemical reaction.

What is percentage yield, and how do you calculate it?

\text{Percentage yield} = \left( \frac{\text{Actual yield}}{\text{Theoretical yield}} \right) \times 100

Why is yield usually less than 100%?

Yield is usually < 100% due to incomplete/reversible reactions, product losses, side reactions, or impure reactants.

Why is high percentage yield important for the environment and economy?

High % yield reduces waste, saves raw materials/energy, lowers costs, and promotes sustainability.

What is atom economy

Atom economy is the proportion of total mass of reactants that ends up as the desired product.

How do you calculate percentage atom economy?

\text{Atom economy} = \left( \frac{\text{Mr of desired product}}{\text{Total Mr of all products}} \right) \times 100

Why is high atom economy good for sustainability and cost?

• Resources are used efficiently, reducing waste and the need for additional raw materials.

• Waste is minimized, lowering disposal costs and environmental harm.

• Processes become cheaper due to reduced waste and efficient resource use.