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 on the right
• How do we verify the conservation of mass using relative formula masses?

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

  117
• What is the total relative formula mass on the right side of the sodium and chlorine 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 when measured on scales?

  The mass should remain the same
• What is an important exception to the conservation of mass rule?

  Gas reactions may seem to change mass
• Why might the mass appear to increase when magnesium reacts with oxygen?

  Oxygen from the air is not measured
• How much magnesium oxide is formed from one gram of magnesium?

  About 1.6 grams
• What happens to the mass if the reaction is done in a sealed container?

  The mass will balance perfectly
• What happens when calcium carbonate decomposes?

  Carbon dioxide gas may escape
• How can we ensure mass conservation in experiments involving gases?

  Conduct experiments in a sealed container
• What is the principle of conservation of mass?

  • Mass is conserved in chemical reactions
  • No atoms are created or destroyed
  • Only bonds between atoms change
• What should you remember about mass changes in reactions involving gases?

  • Mass may appear to change
  • Increase likely due to gas reactants
  • Decrease likely due to gas products
• How can we summarize the key points about conservation of mass?

  • Mass is always conserved
  • Use sealed containers to measure accurately
  • Gaseous reactants/products can affect measurements