Convert into molecular equation:

The reaction between potassium dichromate, ferrous sulphate and sulphuric acid:-

Cr2O7^2- + 14H^+ + 6Fe^2+ ---> 6Fe^3+ + 2 Cr^3+ + 7H2O.

I have no idea how to solve this problem, can someone please help. Thanks!

  • 1
    $\begingroup$ What is the issue you are having, where are you stuck? $\endgroup$
    – Tyberius
    Jun 27, 2020 at 20:50
  • 2
    $\begingroup$ You should simply add the spectator ions on the left and on the right hand side, namely the ions $\ce{K^+}$ (and they are 2), and the $\ce{SO_4^{2-}}$ (and they are 6+7 = 13), and make molecules on both sides with them. That's all. $\endgroup$
    – Maurice
    Jun 27, 2020 at 21:00
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    $\begingroup$ The only molecule in here is water. What kind of a teacher asks questions in such sloppy terminology? $\endgroup$
    – Karl
    Jun 27, 2020 at 21:59

1 Answer 1


You showed the correct balanced net-ionic equation:

$$\ce{Cr2O7^2- + 14H+ + 6Fe^2+ -> 6Fe^3+ + 2Cr^3+ + 7H2O}$$

They asked for the molecular equation (I agree the terminology is horrible), which nowadays is taught as putting the ions in their "molecular" form: Potassium Dichromate ($\ce{K2Cr2O7}$), Ferrous Sulphate ($\ce{FeSO4}$), and Sulphuric Acid ($\ce{H2SO4}$)

You need to convert the number of ions that you have into the number of "molecules" (really formula unit of the solid). For example, 14 moles of $\ce{H+}$ turns into 7 moles of $\ce{H2SO4}$ since they told your that your acid is sulphuric acid.

Repeat this on both sides so that you get a formula like so (with no free ions):

$$\ce{K2Cr2O7 + 6FeSO4 + 7H2SO4 -> Cr2(SO4)3 + 3Fe2(SO4)3 + K2SO4 + 7H2O}$$


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