Question Video: Identifying the Color of the Product Solution When a Nitrite Solution and a Potassium Permanganate Solution Are Mixed | Nagwa Question Video: Identifying the Color of the Product Solution When a Nitrite Solution and a Potassium Permanganate Solution Are Mixed | Nagwa

Question Video: Identifying the Color of the Product Solution When a Nitrite Solution and a Potassium Permanganate Solution Are Mixed Chemistry • Second Year of Secondary School

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

03:45

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.

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