# Topic 1: Stoichiometric relationships - 1.3 Reacting masses and volumes

Nature of science: Making careful observations and obtaining evidence for scientific theories-Avogadro's initial hypothesis. (1.8)

### Understandings

Reactants can be either limiting or excess.

The experimental yield can be different from the theoretical yield.

Avogadro's law enables the mole ratio of reacting gases to be determined from volumes of the gases.

The molar volume of an ideal gas is a constant at specified temperature and pressure.

The molar concentration of a solution is determined by the amount of solute and the volume of solution.

A standard solution is one of known concentration.

### Applications and skills

Solution of problems relating to reacting quantities, limiting and excess reactants, theoretical, experimental and percentage yields.

Calculation of reacting volumes of gases using Avogadro's law.

Solution of problems and analysis of graphs involving the relationship between temperature, pressure and volume for a fixed mass of an ideal gas.

Solution of problems relating to the ideal gas equation.

Explanation of the deviation of real gases from ideal behaviour at low temperature and high pressure.

Obtaining and using experimental values to calculate the molar mass of a gas from the ideal gas equation.

Solution of problems involving molar concentration, amount of solute and volume of solution.

Use of the experimental method of titration to calculate the concentration of a solution by reference to a standard solution.

### Guidance

The value of the Avogadro's constant (L or NA) is given in the data booklet in section 2 and will be given for paper 1 questions.

The generally used unit of molar mass (g mol-1) is a derived SI unit.