topic 3 - quantitative chem

• What must not be changed when balancing equations?

  You cannot change the formulae
• What does the law of conservation of mass state?

  No atoms are lost or made during a chemical reaction
• How can chemical reactions be represented?

  By symbol equations that are balanced in terms of the numbers of atoms
• What is the relative formula mass (Mr) of a compound?

  The sum of the relative atomic masses (Ar) of the atoms in the formula
• What does a balanced chemical equation ensure about the relative formula masses?

  The sum of the relative formula masses of the reactants equals that of the products
• What is produced in the thermal decomposition of metal carbonates?

  Carbon dioxide and metal oxide
• Why might some reactions appear to involve a change in mass?

  Because a reactant or product is a gas and its mass has not been accounted for
• What happens when a metal reacts with oxygen?

  The mass of the oxide produced is greater than the mass of the metal
• How do you calculate the number of moles of a substance from its mass?

  Using the equation $moles =$$\frac{mass}{Mr}$
• What is the unit for measuring chemical amounts?

  The mole (mol)
• What does one mole of a substance contain?

  The same number of particles as one mole of any other substance
• What is the value of the Avogadro constant?

  $6.02 \times 10^{23}$ per mole
• How can Avogadro's constant be used?

  To calculate the number of particles in a mole of a substance
• How do you calculate the mass of carbon dioxide produced from heating sodium hydrogencarbonate?

  Using the equation $mass =$$moles \times Mr$
• What is the general method for reacting mass questions?

  Calculate moles, use ratios, and then calculate mass
• What is the first step in the general method for limiting reactant questions?

  Work out the number of moles of each reactant
• What is the limiting reactant?

  The reactant that is completely used up in a reaction
• How do you calculate the mass of magnesium oxide formed from magnesium and oxygen?

  Using the equation $mass =$$moles \times Mr$
• How do you calculate the concentration of a solution?

  Using the formula $concentration =$$\frac{moles}{volume}$
• How do you convert cm3 into dm3?

  By dividing by 1000
• How do you calculate the mass of sodium chloride needed for a solution?

  Using the equation $mass =$$moles \times Mr$
• How do you calculate the concentration of HCl in mol/dm3 from its concentration in g/dm3?

  By dividing the concentration in g/dm3 by the Mr
• What are the steps to balance a chemical equation?

  1. Write the unbalanced equation.
  2. Count the number of atoms of each element on both sides.
  3. Adjust coefficients to balance the atoms.
  4. Ensure the lowest whole number ratios.
• What is the process for calculating the mass of a product from a given mass of a reactant?

  1. Calculate moles of the reactant.
  2. Use the balanced equation to find moles of the product.
  3. Calculate the mass of the product using $mass =$$moles \times Mr$.
• What is the method for determining the limiting reactant in a reaction?

  1. Calculate the number of moles of each reactant.
  2. Use the ratios from the balanced equation to identify the limiting reactant.
  3. Calculate the mass of the product formed from the limiting reactant.
• What are the key concepts in quantitative chemistry?

  • Balancing equations
  • Conservation of mass
  • Relative formula mass
  • Moles and Avogadro's constant
  • Concentration calculations