Conservation of Mass

• What is one of the most important concepts in chemistry?

  Conservation of mass
• What does the conservation of mass state in a chemical reaction?

  Mass is always conserved; no atoms are created or destroyed
• In the reaction of sodium and chlorine, how many sodium chlorides are formed?

  Two sodium chlorides
• Why do we need two sodiums on the left side of the sodium plus chlorine reaction?

  To balance the two chlorine atoms in the molecule
• How do we verify the conservation of mass in a chemical reaction?

  By comparing total relative formula masses on both sides
• What is the total relative formula mass of sodium and chlorine in the reaction?

  117
• If 2.3 grams of sodium reacts with 3.5 grams of chlorine, what is the mass of sodium chloride produced?

  5.8 grams
• What happens to the mass during a chemical reaction if it involves a gas?

  The mass might seem to change due to gas loss
• Why does magnesium oxide weigh more than magnesium after a reaction?

  Because oxygen from the air is added
• What is the relative formula mass of magnesium oxide compared to magnesium?

  Higher than that of magnesium
• How can we ensure accurate mass measurements in reactions involving gases?

  By conducting experiments in a sealed container
• What happens to the mass when calcium carbonate decomposes?

  It appears to decrease due to gas loss
• What are the key points of the conservation of mass principle?

  • Mass is conserved in chemical reactions
  • Mass may appear to change with gases
  • Increase in mass indicates a gas reactant
  • Decrease in mass indicates a gas product
  • Use sealed containers to avoid measurement issues