Quantitative Chemistry

• What is the equation for relative atomic mass (Ar)?

  (A1 * M1)+(A2*M2)/100
• How do you find relative formula mass (Mr)?

  Work out the sum of the relative atomic masses of all component atoms
• What is the equation for percentage by mass?

  $\frac{Ar\times number\ of\ atoms}{Mr}\times100$
• What is the value of Avogadro's constant?

  6.022 x 10$^{23}$ mol$^{-1}$
• What is the equation for number of moles?

  n=$\frac{m}{Mr}$
• What is a limiting reactant?

  The reactant that is completely consumed in a chemical reaction and limits the amount of product that can be formed.
• How do you work out the limiting reactant?

  1. work out the moles of both reactants
  2. compare their ratios
  3. then compare their ratio to the ratio in the chemical equation
• The ratio of Mg to HCl is 1:2, the actual ratio is 1:1. Which is the limiting reactant?

  HCl is the limiting reactant, Mg is in excess
• What is the equation for percentage yield?

  actual yield / theoretical yield $\times$ 100
• What is atom economy?

  Atom economy is a measure of waste
• What is the equation for percentage atom economy?

  Mr of desired product / total Mr of reactants $\times$ 100
• What is the equation for volume of a gas?

  number of moles $\times$ 24dm$^3$
• What is the volume of 1 mole of gas at room temperature pressure?

  24dm$^3$ or 24,000cm$^3$
• How do you convert g/dm$^3$ to mol/dm$^3$?


  divide by the Mr
• What must results be to be used in titration calculations?

  Concordant. At GCSE this means that results must be within 0.1 of each other
• What colour is phenolphthalein in acid? And alkali?

  Acid - colourless

  Alkali - pink
• What colour is methyl orange in acid? And alkali?

  Acid - red

  Alkali - yellow
• What is the equation for concentration?

  concentration (mol/dm$^3$) = mass (mol)/volume (dm$^3$)

  OR

  concentration (g/dm$^3$) = mass (g)/volume (dm$^3$)