Question

what mass in kg of K2O contains the same number of moles of K atoms as are present in 1.0 kg of KCl

Answer 1

First step is to calculate how many moles are in 1 kg of KCl.

Formula for calculating moles:

         moles = mass / molar mass

       (mass = 1000g and molar mass = 74.5)

          ∴ moles of 1 kg KCl  =  1000/74.5  = 13.4 moles

Since there is just one mole of K in the KCl compound, that means that the moles of K in this compound is:

                          1 × 13.4 moles = 13.4 moles
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⇒ The next step is to calculate the mass of K₂O that contains 13.4 moles of K

If the moles of the K₂  in the K₂O is 13.4 then the moles of the compound K₂O is:         

                 13.4 moles / 2 = 6.7 moles

Calculate the mass of K₂O that corresponds to 6.7 moles:

mass = moles × molar mass

moles = 6.7

molar mass = 94.2 g/mol

∴ The mass of 6.7 moles of K₂O  =  6.7 mols × 94.2 g/mol = 632.2 g

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Therefore the mass of K₂O that contains the same number of moles of K atoms as are present in 1.0 kg of KCl is 632.2 g