More Balancing of Equations
The following is one of many emails I have recieved basically asking the
same question...
"I am a little confused on why when I
work out the formula for Cr3+ and F- it comes out to CrF3 instead of Cr3F3. In a
sample that is shown, Al3+ and O2- comes out to be Al2O3. We have steps to go through to
get the answer, but I am really confused..." |
The Answer is shown here...
Cr ionises to Cr^{3+} and F ionises to F^{-}
To neutralise the 3 positive charges on the Cr^{3+} will require 3
negative charges. In this case, to obtain 3 negative charges will require 3 ionised
fluorines.
So, 1(Cr^{3+}) reacts with 3(F^{-}). Now, when they react
together, the charges are neutralised, so the ^{3+} on the Cr and
the ^{-} on the F are no longer shown. What you have now is 1Cr3F (written as Cr_{1}F_{3})
BUT the 1 is never written in the molecular formula, so
it becomes CrF_{3} (which is the correct answer).
So, you must balance the positive and negative
charges on the ions to cancel each other out.
In the second equation mentioned, Al ionises to Al^{3+} and O ionises to
O^{2-}. Multiply the number of Al^{3+} by 2 (2Al^{3+}), and we now
have 6+ charges for Al. Multiply the O^{2-} by 3 (3O^{2-}) and we now have
6^{-} charges for O. The 6+ and 6^{-} cancel each other out. So, it took 2 Al^{3+} and 3 O^{2-} this is written as Al_{2}O_{3}. To
balance ionic equations you are cancelling out the positive and negative charges. |