P l e a s e h e l p

Question

Question: A 5.207-g sample of calcium is burned in air to produce a mixture of two ionic compounds, calcium oxide and calcium nitride. Water is added to this mixture. It reacts with calcium oxide to form 4.726 g of calcium hydroxide. How many grams of calcium oxide are formed? How many grams of calcium nitride?

Answer 1

So Emily S.,

You work this problem backwards. Write the reaction for the hydration of the CaO to Ca(OH)₂ . Use molar masses to convert the end product given to moles, then backwards to moles of CaO. This represented the oxidation of the same number of moles of Ca : 2Ca + O₂ = 2CaO

Next, convert the initial Ca to moles (via atomic weight). Subtract the Ca that formed an oxide. The rest of it must have formed the nitride. Write the Balanced reaction for Ca + N₂ --> Ca nitride (figure out the formula!).

Take the "rest of it" through the reaction, stoichiometrically!, to obtain moles Ca nitride. Convert to mass using the molar mass of it.

Take-aways: usually you are given mass, and mass is the desired output answer. But all reactions are done via the moles of reactants and products, so you must be agile in converting back and forth.

-- Cheers, --Mr. d.