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, meaning no atoms are created or destroyed
• In the reaction of sodium and chlorine to form sodium chloride, how many sodium chlorides are produced if there are two chlorine atoms?

  Two sodium chlorides
• How do you balance a chemical equation based on the conservation of mass?

  You ensure the number of atoms of each element is the same on both sides of the equation
• How do you calculate the total relative formula mass of sodium and chlorine in the reaction?

  By calculating \(2 \times 23\) for sodium plus \(2 \times 35.5\) for chlorine
• What is the total relative formula mass of sodium and chlorine in the reaction?

  117
• 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
• If you measure the mass during a reaction, what should happen to the mass on the scales?

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

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

  The mass of magnesium oxide will be higher than that of magnesium alone
• How much magnesium oxide is formed from 1 gram of magnesium?

  About 1.6 grams of magnesium oxide
• Why might the weight of products seem to decrease when decomposing calcium carbonate?

  Because the gaseous \(CO_2\) can float off into the air
• What happens to the mass if the decomposition of calcium carbonate is done in a sealed container?

  The mass will stay the same because all \(CO_2\) is trapped in the container
• What are the key points to remember about the conservation of mass in chemical reactions?

  • Mass is always conserved in a chemical reaction.
  • If mass seems to increase, a gas is likely a reactant.
  • If mass seems to decrease, a gas is likely a product.
  • Conduct experiments in a sealed container to avoid mass loss.