Chemical Calculations — A/L Chemistry

What must I remember about Chemical Calculations?

• The mole connects microscopic particles to macroscopic mass: n = m / M, where 1 mole contains 6.022 × 10²³ entities (Avogadro constant L).
• Empirical formula is the simplest integer atom ratio; molecular formula is a whole-number multiple of the empirical formula (Molar mass = n × empirical formula mass).
• Solution concentration expressions: molarity (mol dm⁻³), mass concentration (g dm⁻³), and parts per million (ppm = mg dm⁻³ or mg kg⁻¹).
• Stoichiometry and limiting reactants: the limiting reagent is completely consumed first and determines the theoretical yield of products.
• Volumetric analysis: applying stoichiometric mole ratios to calculate unknown concentrations in acid-base and redox titrations.

Test yourself (1 minute)

1. Ideal gas equation

   PV = nRT with consistent SI units (P in Pa, V in m³, T in K, R = 8.314 J K⁻¹ mol⁻¹).

2. Standard conditions

   STP is 0 °C (273.15 K) and 100 kPa; molar volume of an ideal gas at STP = 22.7 dm³ mol⁻¹ (or 22.4 dm³ mol⁻¹ at 1 atm).

3. How is percentage purity calculated?

   Percentage purity = (mass of pure substance / total mass of impure sample) × 100%.

Practise Chemical Calculations questions today

Source: NIE G.C.E. (A/L) Chemistry Syllabus (Unit 3)

What should I study first?

Next in the syllabus

Where does Chemical Calculations fit in the syllabus?

Grade 12 · Term 1