Chemistry in Every day life: Perfumes

Perfumes

Perfumes are the materials which give fragrance. A good perfume should have three essential ingredients. They are
1. Vehicle or Solvent
2. Fixative
3. Odorous substance

1. Vehicle or Solvent

The vehicle or Solvent is used to keep the odour producing substances in solution. Ethanol and water mixture is most commonly used in perfumery.

2. Fixative

Fixative regulate the evaporation of various odoriferous components of perfumes. Sandal wood oil, Benzoin, glyceryl diacetate and esters of cinnamyl alcohols are used as fixative.

3. Odorous Substance

The function of odorous substance is to provide pleasant fragrance to perfume. Odorous substances may be natural or synthetic. Terpenoids like linalool is a natural odoriferous substance. Anisaldehyde (p-methoxy benzaldehyde) is an example for synthetic odoriferous substance.


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Chemicals in Food

Preparation of Potassium permanganate (KMnO4)

Pottassium Permanganate (KMnO₄) is prepared from Pyrolusite ore (MnO₂). The finely powdered Pyrolusite ore (MnO₂) is fused with an alkali metal hydroxide like KOH in the presence of air or an oxidizing agent like KNO₃ to give the dark green potassium Manganate (K₂MnO₄). Potassium manganate disproportionate in a neutral or acidic solution to give potassium permanganate.

2 MnO₂ + 4 KOH + O₂ ----------> 2K₂MnO₄ + 2H₂O


3 MnO₄^2- + 4H⁺ ------------> 2MnO₄^- + MnO₂ + 2H₂O

Commercially potassium permanganate is prepared by the alkaline oxidative fusion of Pyrolusite ore (MnO₂) followed by the electrolytic oxidation of manganate (4) ion.

2 MnO₂ + 4KOH + O₂ -----------> 2K₂MnO₄ + 2H₂O


MnO₄^2- ------(electrolytic oxidation)----> MnO₄^- + e^-

Properties

Potassium permanganate forms dark purple (almost black) crystals, which are iso structural with those of KCLO₄. It has weak temperature dependent paramagnetism. the manganate and permanganate ions are tetrahedral. The green manganate is paramagnetic with one unpaired electron but the permanganate is diamagnetic. The pie-bonding takes place by overlaping of P orbitals of oxygen with d orbitals of manganese.

Preparation and properties of Potassium dichromate (K2Cr2O7)

Preparation of Potassium dichromate (K₂Cr₂O₇)

Potassium dichromate (K₂Cr₂O₇) is prepared from chromite ore FeCr₂O₄. The chromite ore is fused with sodium or potassium carbonate in free access of air.

4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ -------> 8Na₂CrO₄ + 2FeO₃ + 8CO₂

The yellow solution of sodium chromate is filtered and acidified with sulfuric acid to give a solution from which orange sodium dichromate , Na2Cr2O7 2H2O can be crystallized.

2Na₂CrO₄ + 2H⁺ ---------> Na₂Cr₂O₇ + 2Na⁺ + H₂O

Sodium dichromate is more soluble than potassium dichromate. Hence sodium dichromate when fused with KCl forms orange crystals of potassium dichromate.

Na₂Cr₂O₇ + 2KCl --------> K₂Cr₂O₇ + 2NaCl

The chromates and dichromates can be inter convertible.

2CrO₄ ^2- + 2H²⁺ ---------> Cr₂O₇ ^2- + H₂O

Cr₂O₇ ^2- + 2OH- ---------> 2CrO₄ ^2- + H₂O

The dichromate ion and chromate ion exist in equilibrium with each other at a pH of 4. Yellow chromate changes into orange dichromate in acid medium and dichromate changes into chromate in basic medium.


2CrO₄ ^2- + 2H⁺ <-_-_^Acid_Alkali-_-_> 2HCrO₄^- (Hydrogen chromate)


2HCrO4^-<-_-_^Acid_Alkali-_-_> Cr₂O₇ ^2- + H₂O Dichromate (orange)

The chromate ion is tetrahedral and the dichromate ion consists of two tetrahedral sharing at one corner, with Cr-O-Cr bond angle 126 degree.

Properties Potassium dichromate (K₂Cr₂O₇)

Action of heat

Potassium dichromate decomposes on heating to from potassium chromate, chromic oxide and oxygen.

4K₂Cr₂O₇ ------> 4K₂CrO₄ + 2CrO₃ + 3O₂

Oxidizing properties

Potassium dichromate is a powerful oxidizing-agent in acidic medium.

Cr₂O₇ ^2- + 14H⁺ + 6 electron -------> 2Cr³⁺ + 7H₂O

A few examples for this oxidizing character in acidic medium are

1. It oxidize iodides to iodine.

Cr₂O7 ^2- + 14H⁺ + 6I- ------> 2Cr ³⁺ + 7H₂O + 3I₂

2. It oxidizes ferrous salts to ferric salts.

Cr₂O₇ ^2- + 14H⁺ + 6 Fe2+ -------> 2Cr ³⁺+ 7H₂O + 6Fe³⁺

3. It oxidizes stannous salts to stannic salts.

Cr₂O₇ ^2- + 14H⁺ + 3Sn ²⁺ --------> 2Cr ³⁺ + 7H₂O + 3Sn ⁴⁺

4. It oxidizes H2S to sulphur

Cr₂O₇ ^2- + 8H⁺ + 3H₂S -------> 2Cr ³⁺ + 7H₂O + 3S

Uses of potassium dichromate

(K₂Cr₂O₇)

Sodium and potassium dichromate are strong oxidizing agents. Potassium dichromate is used as a primary standard in volumetric analysis. It is also used in chrome plating.


Related articles Copper sulphate penta hydrate

For articles about Extraction of metals visit Extraction

Forth flotation process: ore dressing

Concentration Beneficiation by Forth flotation



This method is used for the concentration of sulphide ores which are lighter than the impurities. The powdered ore is added to water containing pine oil (frothing agent) and sodium ethyl xanthate (collecting agent). The mixture is strongly agitated by passing compressed air. The sulphide particles stick to the oil droplets forming a forth which rises to the surface. The heavier gangue particles settle to the bottom of the vessel. The forth is skimmed off and heated to separate the oil and the sulphide.


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