Calculating concentrations

• What is the unit for the amount of substance in chemistry?

  The mole
• How can the number of particles in a substance be found?

  Using the Avogadro constant
• What does the mass of a product in a chemical reaction depend on?

  It depends upon the mass of the limiting reactant
• What is the definition of concentration in a solution?

  • Concentration tells us how much of a substance is dissolved in water.
  • Higher concentration means more particles of the substance are present.
• How can concentration be expressed?

  In g/dm³ or mol/dm³
• Why is it often more useful to know the concentration of a reactant in mol/dm³?

  So that the amount of reactant in a given volume can be calculated
• What is the formula to calculate concentration using moles?

  Concentration in mol/dm³ = \(\frac{\text{amount of solute in mol}}{\text{volume in dm³}}\)
• If 0.5 mol of sodium hydroxide is dissolved in 2 dm³ of water, what is the concentration?

  0.25 mol/dm³
• What must volumes used in concentration calculations be in?

  In dm³, not in cm³
• How do you convert from cm³ to dm³?

  Divide by 1000
• How do you convert from dm³ to cm³?

  Multiply by 1000
• What is 250 cm³ in dm³?

  0.25 dm³
• If 100 cm³ of dilute hydrochloric acid contains 0.02 mol of dissolved hydrogen chloride, what is the concentration in mol/dm³?

  0.2 mol/dm³
• How do you convert between mol/dm³ and g/dm³?

  • To convert from mol/dm³ to g/dm³, multiply by the relative formula mass.
  • To convert from g/dm³ to mol/dm³, divide by the relative formula mass.
• What is the relative formula mass?

  The sum of the relative atomic masses of the atoms in a chemical formula
• If the molar mass of sodium hydroxide (NaOH) is 40, what is the concentration of a 0.1 mol/dm³ solution in g/dm³?

  4 g/dm³
• If the concentration of hydrochloric acid is 7.3 g/dm³ and its molar mass is 36.5, what is the concentration in mol/dm³?

  0.2 mol/dm³
• What is the relationship between the volume of a solution and concentration calculations?

  • Volumes must be in dm³.
  • 1 dm³ = 1000 cm³.