Problem Type 3 : Given is in grams, unknown in moles

• Sample Problem 1: How many moles of aluminum will be produced from 30.0 kg Al₂O₃ in the following reaction?

  2Al₂O₃ → 4Al + 3O2

• What do we have?

  • 30.0 kg Al₂O₃

  • Mole Ration: 2Al₂O₃ : 4 Al​

• Steps to solve

  • Change kg to grams​

  • Change Grams to moles

• What do we need?

  • ​Molar mass of Al₂O₃

Problem Type 3 : Given is in grams, unknown in moles

• Sample Problem 1: How many moles of aluminum will be produced from 30.0 kg Al₂O₃ in the following reaction?

  2Al₂O₃ → 4Al + 3O2

• What do we have?

  • 30.0 kg Al₂O₃

  • Mole Ratio: 2Al₂O₃ : 4 Al​

  • Molar Mass of Al₂O₃: 101.96 g/mol

• Steps to solve

  • kg to grams​, grams to moles

Problem Type 4 : Given is in grams, unknown in grams

​Methane burns in air by the following reaction:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

What mass of water is produced by burning 500. g of methane?

• ​Start with identifying what you have

  • 5 grams CH₄

• Identify a process

  • grams methane -> moles Methane ->moles water -> grams water

• Step one find needed mola​r masses for Methane and water

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Problem Type 4 : Given is in grams, unknown in grams