Memory Anchor:

• Super Challenge:

  Stretch:

  Challenge:

Key Questions:

1. (Chem only) Suggest why it is not always possible obtain the calculated amount of product from a reaction?
   • You may not always get the maximum yield because the reaction may not go to completion because it is reversible, some of the product may be lost when it is separated from the reaction mixture; or some of the reactants may react in ways different to the expected reaction.
2. (Chem only) What does the term yield refer to?
   • The amount of product obtained
3. (Chem only) What is percentage yield?
   • When the actual yield obtained is compared with the maximum theoretical yield of a reaction is expressed as a percentage, it is called the percentage yield.
4. (Chem only) What is the formula for calculating percentage yield?
   • % Yield = Mass of product actually made / Maximum theoretical mass of product ? 100
5. (Chem only) What mass of carbon dioxide is formed when 12 g of carbon is burned in air?
   • 1.Write out the equation for the reaction. Make sure it is balanced. C O2 -> CO2 (Carbon is the known, carbon dioxide is the unknown) 2.Work out the relative masses of the substances needed in the calculation. Mass of carbon = 12, mass of carbon dioxide = 44 3.Convert the relative masses into the units in the question. Mass of carbon = 12 g, mass of carbon dioxide is 44 g 4.Find the ratio by dividing both numbers by the smallest number. For carbon 12 ? 12 = 1, for carbon dioxide 44 ? 12 = 3.67 5.Find the mass of the unknown by multiplying the mass of the known by the ratio of the unknown. 3.67 ? 12 = 44 g