Why KMnO4 is not used as a primary standard? (2024)

FAQs

Why KMnO4 is not used as a primary standard? ›

Hence, is not used as a primary standard, because it is difficult to obtain the pure state of KMnO4 as it is not free from MnO2. Also, the colour is so intense that it acts as its own indicator.

NaOH is not suitable for use as a primary standard because they readily absorb moisture, H2O, from the atmosphere. They readily absorb carbon dioxide from the atmosphere. Why NaOH is not a primary standard.

* Potassium Permanganate can affect you when breathed in. * Contact can severely irritate and burn the skin and eyes with possible eye damage. * Breathing Potassium Permanganate can irritate the nose and throat.

Answer and Explanation:

Potassium Permanganate (KMnO4) is added slowly during redox titration to make sure that the reaction is complete. The reaction is not instantaneous, thus, if the volume added is more than what is necessary, the volume at endpoint will not be accurate. This will cause errors during calculations.

Understanding that potassium permanganate (KMnO₄) solutions are unstable over time because they can decompose and interact with impurities or its container, thus changing their concentration, helps uphold the importance of standardizing a solution before usage.

Sodium hydroxide is deliquescent (absorbs moisture from the atmosphere) solid. It cannot be weighed accurately. Therefore, it is not possible to prepare a standard solution of sodium hydroxide of accurately known concentration by weighing NaOH.

Potassium permanganate is not used as primary standard because is not able to release in MnO2 in the reaction. Potassium permanganate is always in the stable form. The reason KMnO4 is also used as a colour indicator in analysis. According to the above discussion, we conclude KMnO4 is used as the secondary standard.

In summary, the use of potassium permanganate as a titrant has a disadvantage due to its strong oxidizing properties, which can lead to side reactions and potential inaccuracies in titration results.

The Incorrect options are (c) The equivalent weight of KMnO4 in the basic medium is 158. and (d) The number of electrons involved in the oxidation of KMnO4 in an acidic medium is 3. Explanation: Statement (a) HCl cannot be used because some KMnO4 is consumed in the reaction.

KMnO4 acts as on oxidising agent in alkaline medium. When alkaline KMnO4 is treated with KI, iodide ion is oxidised to : I2. IO−

Why is KMnO4 only used in titration? ›

Potassium Permanganate has a unique utility in that it works as a self-indicator. Titration of permanganate must be done in a strong acid solution. When employed in redox titration, it is reduced to a brown-colored ion (in acidic solutions) near the endpoint, and the color transformation may be seen fast.

The end point is indicated by the appearance of permanent light pink colour due to a slight excess of permanganate solution. (v) Repeat the titration till three concordant readings are obtained. Since the solution of KMnO4 is of dark colour, the upper meniscus should be considered for noting the burette readings.

This is because the coloured permanganate ions of alkaline potassium permanganate are consumed to oxidise ethanol solution. When excess of alkaline potassium permanganate is added, the purple colour of alkaline potassium permanganate does not change. This is because there is no more ethanol left for the reaction.

On organic and analytical chemistry, because of its strong color and oxidizing nature, KMnO4 is used in chemistry laboratories as a reagent to calculate the amount of substance that can be oxidized in a sample. In qualitative analysis, this value is referred to as the permanganate value.

A KMnO4 solution can be standarised by titration against As2O3(s). A 0.1156g sample of As2O3 requires 27.06mL of the KMnO4(aq.) for its titration.

Potassium manganate(VII) is not a primary standard. Even the best grade of solid potassium manganate(VII) is contaminated with manganese(IV) oxide. It is therefore not possible to make up solutions of exact concentration directly from the solid reagent. However solutions can be made up and standardised prior to use.

NaOH is one example of a secondary standard. Commercially available NaOH contains impurities of NaCl, Na₂CO₃, and Na₂SO₄, and readily absorbs H₂O from the atmosphere. To determine the concentration of NaOH in a solution, we titrate it against a primary standard weak acid, such as potassium hydrogen phthalate, KHC₈H₄O₄.

Primary standards need to have high purity. KOH absorbs moisture from the air and will not be pure enough. The KOH, NaOH, Ca(OH)2, H2SO4 to name a few, cannot be used as a primary standard because they are hygroscopic.

Answer and Explanation:

NaOH is deliquescent, i.e., it absorbs moisture from the atmosphere resulting in a change in its concentration. Hence NaOH solution can't be used as a primary standard; it needs to be standardized before each titration.

Sodium hydroxide and potassium permanganate are examples of secondary standards. Before starting titrimetric analysis, you should be familiar with some techniques such as, weighing by using chemical balance, preparing standard solution, measuring volume by using burette and pipette.