(3) 20 questions

• State the law of conservation of mass.

  total mass of reactants is equal to the total mass of products
• Calculate the relative formula mass of calcium carbonate (CaCO3).

  40+12+(16x3)=100
• Why must a symbol equation balance?

  because no atoms are made or lost, the amount of atoms in the reaction need to be equal to the amount of atoms in the products
• When a metal forms a metal oxide, why does the mass increase?

  because oxygen has been chemically bonded to the metal atoms
• Calculate the relative formula mass of water.

  (2x1)+16=18
• What does the state symbol (aq) stand for?

  aq = aqueous (dissolved in water)
• What is avogadro’s number (number of atoms/molecules in a mole)?

  6.02 x 10^23
• What is the equation that links moles, mass and Mr?

  Mass = Mr x moles
• 69g of sodium reacts with chlorine to produce sodium chloride:​

  2Na  +  Cl2  →  2NaCl​

  Calculate the number of moles of sodium present.

  69g / 23 = 3 moles of Na
• calculate the number of moles of Chlorine (Cl2) that would be required to react exactly with the sodium.

  2Na  +  Cl2  →  2NaCl


  ratio is Na : Cl - 2 : 1, but we have 3 moles of Na, so 3 : 1.5, so 1.5 moles of Cl is needed
• What is the equation we use to calculate the concentration of a liquid?

  concentration = mass or moles/volume (in dm3)
• What are the units of concentration?

   g/dm3  or  moles/dm3
• 1.50 moles of solute is dissolved in 1.00dm3 of solvent. What is the concentration of the solution formed?

  1.5/1 = 1.5 mol/dm3
•  2.00g of solute is dissolved in 2.00dm3 of solvent. What is the concentration of the solution formed?

  2/2 = 1g/dm3
• 0.20moles of solute is dissolved in 500cm3 of solvent. What is the concentration of the solution formed?

  0.2/0.5 = 0.4mol/dm3
• Why might the actual yield of a reaction be less than the theoretical yield of the reaction?

  some product might be lost when it is separated from the reaction mixture

  if the reaction is reversible, the reaction might not have been done to completion

  some reactants react in different ways to the expected reaction and by-products are formed
• A reaction has a theoretical yield of 13g but an actual yield of 8.5g. What is the percentage yield of this reaction?

  (8.5/13) x 100 = 65.4 %
• Why are reactions that have a high atom economy good for the environment?

  because the produce less waste material which could damage the environment
• The equation for the formation of ammonia, NH3, is:  N2 + 3H2 → 2NH3​

  What is the percentage atom economy of this reaction?

  100% - there is only one product
• What is a limiting reactant?

  a reaction finishes when one of the reactants are all used up. the other reactant has nothing left to react with, so there might be some left over. the reactant that is all used up is known as the limiting reactant