### Video Transcript

The reaction scheme shows the
addition of two solutions together. What color will the resulting
solution be?

When answering this question, let
us first begin with identifying the solutions. Our reactants are a nitrite salt
solution and an acidified potassium manganate(VII) solution. Let’s remind ourselves of the
difference between the polyatomic nitrate ion and the very similar polyatomic
nitrite ion.

The nitrate ion has the formula
NO3−, while the nitrite ion is NO2−. We only need to consider the
nitrite ion in this problem. So, the anion in solution in a
nitrite salt solution is NO2−. For this problem, we are not given
the counterion, but let’s say the cation is the potassium ion. And so, the solution is potassium
nitrite, KNO2 aqueous. We get this formula by crossing the
charges of one and dropping the plus and minus signs.

Let’s move on to the potassium
manganate(VII) solution. The manganate(VII) ion is also
called the permanganate ion. It gives solutions a purple
color. It is manganese specifically, with
an oxidation number of plus seven, in the permanganate ion, which causes this purple
color. When writing the formula, potassium
has a charge of one plus and permanganate is MnO4−. When we cross the charges and drop
the plus and minus signs, we get the formula KMnO4.

We also need to remember that this
solution is acidified. Let’s assume it is acidified with a
few drops of sulfuric acid. Sulfuric acid is made from hydrogen
one plus ions and sulfate ions which have the formula SO42−. Again, we can cross the charges and
remove the signs. And this gives the formula for
sulfuric acid of H2SO4.

When these two solutions are mixed,
a redox reaction occurs. Potassium nitrate, potassium
sulfate, manganese(II) sulfate, and water are produced. Since it is the manganese in the
permanganate ion, with oxidation number of plus seven, which gives the potassium
permanganate its purple color, we need to determine what has happened to the
oxidation number of manganese to determine what happens to the color of the
solution. So, let’s investigate the charges
and oxidation numbers in the manganese sulfate product.

The sulfate ion has a charge of two
minus and so the manganese ion must have a charge of two plus. We can deduce this since this
compound is electrically neutral overall. The manganese two plus ion is
colorless.

So, what is the color of the
resulting solution when these two solutions are mixed? Since manganese is in the two plus
state after the redox reaction, the answer is colorless.