Memory Anchor:

• Super Challenge:

  Stretch:

  Challenge:

Key Questions:

1. When a gas is produced in a chemical reaction, why would the mass of the products appear to be less than that of the reactants?
   • The mass of the products will be reduced because the gas escapes into the surroundings. The total number of atoms will not have changed.
2. Explain why in the reaction below the mass of the products would be greater than that of the reactants 2Mg (s) O2 (g) -> 2MgO (s)
   • Because oxygen gas would not be accounted for when the mass of the reactants are recorded, yet form part of the solid MgO produced. Therefore giving an increase in mass, but no new atoms were created or destroyed within the reaction.
3. What does the term uncertainty mean?
   • Whenever a measurement is made there is always some uncertainty about the result obtained.
4. How would you represent the distrubtion of results to make estimations of uncertainty?
   • To represent the distrubution of results and make estimations of uncertainty you should use error bars on a graph.
5. A pippette has an uncertainty of /-0.01mL. It is used three times in a practical. What is the mean measure of uncertainty?
   • The uncertainty of a pippette that is used three times is = 3 x 0.01 = /- 0.03mL