I/GCSE Chemistry Question Analysis Topic: Chapter 1: Principles of Chemistry - Chemical Formulae (Part 3)
For I/GCSE Chemistry, you should know:
Let's dive into the last part of IGCSE Chemistry's Chapter 1 sub-topic on "Chemical Formulae, Equations, and Calculations." This time, we'll focus on the concepts of empirical and molecular formulae, as well as calculations involving amount of substance, volume, and concentration of solutions, as well as gas volumes and molar volume.
Empirical Formula and Molecular Formula:
The empirical formula of a compound represents the simplest whole number ratio of the atoms of each element present in the compound. For example, the empirical formula of glucose is CH₂O.
The molecular formula, on the other hand, represents the actual number of atoms of each element present in a molecule of the compound. The molecular formula of glucose is C₆H₁₂O₆, which is six times the empirical formula.
To determine the molecular formula from the empirical formula, you need to know the relative molecular mass (Mr) of the compound. The molecular formula can then be calculated as:
Molecular formula = (Relative molecular mass) / (Relative mass of empirical formula)
Calculations Involving Amount of Substance, Volume, and Concentration of Solutions:
When working with solutions, we need to consider the amount of substance, volume, and concentration of the solution. The relationship between these variables is given by the following equation:
n = c × V
Where:
- n is the amount of substance in moles
- c is the concentration of the solution in mol/dm³ (or M)
- V is the volume of the solution in dm³
Using this equation, we can perform various calculations, such as:
- Calculating the amount of substance given the concentration and volume.
- Calculating the concentration given the amount of substance and volume.
- Calculating the volume given the amount of substance and concentration.
Calculations Involving Gas Volumes and Molar Volume:
The molar volume of a gas is the volume occupied by one mole of any gas at room temperature and pressure (RTP). The accepted value for the molar volume of a gas at RTP is 24 dm³ or 24,000 cm³.
Using the molar volume, we can perform calculations involving the volume of gases. For example:
- Calculating the volume of a gas given the amount of substance in moles.
Volume = Amount of substance (n) × Molar volume - Calculating the amount of substance in moles given the volume of a gas.
Amount of substance (n) = Volume / Molar volume
These calculations are particularly useful when working with chemical reactions involving gases, such as the volume of a gas produced or the volume of a gas used in a reaction.
Work hard for your I/GCSE Chemistry examination!
End of analysis. Great!
