Conservation of Mass

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

  The idea of conservation of mass
• What does the conservation of mass mean 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 if there are two chlorine atoms?

  Two sodium chlorides
• What principle is used every time to balance a chemical equation?

  The principle of conservation of mass
• What happens to the mass when 2.3 grams of sodium reacts with 3.5 grams of chlorine gas?

  The total mass of sodium chloride produced will be 5.8 grams
• What should the mass on the scales show during the entire reaction of sodium and chlorine?

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

  The mass might seem to change when a gas is involved
• What happens when magnesium reacts with oxygen to form magnesium oxide?

  The relative formula mass of magnesium oxide is higher than that of magnesium
• How much magnesium oxide is formed from 1 gram of magnesium?

  About 1.6 grams of magnesium oxide
• Why might it appear that the product weighs more than the reactants in the magnesium and oxygen reaction?

  Because the oxygen comes from the air and is not measured by the scales
• How does conducting the experiment in a sealed container affect the measurement of mass?

  The mass of reactants will balance perfectly with the products
• What happens when calcium carbonate decomposes?

  Carbon dioxide gas may float off into the air
• What is the effect of conducting the calcium carbonate decomposition in a sealed container?

  The mass will stay the same because all gases are trapped
• What are the key points of the conservation of mass principle in chemical reactions?

  • Mass is always conserved in a chemical reaction
  • Mass may appear to change if a gas is involved
  • If mass increases, a gas is likely a reactant
  • If mass decreases, a gas is likely a product
  • Conduct experiments in a sealed container to avoid measurement issues