Amount of substance exam tips

Exam tips

• Show all steps in calculations

  When solving problems using the ideal gas equation, clearly show the rearrangement of the equation, substitution of values, and unit conversions.

  This helps to avoid mistakes and allows partial credit for correct methodology even if the final answer is incorrect.

• Check units and significant figures

  Write down the units of every quantity, convert to consistent units, and round the final answer to the correct number of significant figures.

  The ideal gas equation is sensitive to unit consistency; incorrect units lead to wrong answers. Significant figures reflect the precision of the given data.

• Show All Steps in Calculations

  Always show the governing relationship, substitution, units, and significant figures in your calculations.

  This helps to ensure clarity in your working and can earn partial credit even if the final answer is incorrect.

• Check units before calculation

  Always convert all variables to the same unit system (SI) before plugging them into PV = nRT.

  This prevents errors and ensures the calculated pressure or amount of substance is correct.

• Show Your Work

  Always show your calculations step-by-step when determining empirical and molecular formulas.

  This helps to ensure you receive partial credit for your reasoning, even if the final answer is incorrect.

• Show all working in calculations

  Always show your calculations step-by-step, including units.

  This helps to avoid mistakes and allows partial credit for correct methods even if the final answer is incorrect.

• Check the integer ratio first

  Before assigning a molecular formula, calculate the ratio of the relative molecular mass to the empirical formula mass and confirm it is an integer.

  This prevents mis‑assignment of the molecular formula and ensures consistency with the law of conservation of mass.

• Show all workings in calculations

  Always write down the steps taken to arrive at your answer, including units.

  This helps in gaining partial credit even if the final answer is incorrect.

• Show your working in calculations

  Always show each step in your calculations, including how you derived the empirical formula from the given percentages.

  This helps to gain partial credit even if the final answer is incorrect and demonstrates your understanding of the process.

• Double-check your balancing

  After writing a balanced equation, count the atoms of each element on both sides to ensure they match.

  This helps prevent simple mistakes that can lead to incorrect answers in stoichiometric calculations.