Chemistry in Every day life: 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 MnO42- + 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

MnO42- ------(electrolytic oxidation)----> MnO4- + e-


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 (

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+ <-_-_AcidAlkali-_-_> 2HCrO4- (Hydrogen chromate)

2HCrO4-<-_-_AcidAlkali-_-_> 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

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.

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For articles about Extraction of metals visit Extraction

Forth flotation process: ore dressing

Concentration Beneficiation by Forth flotation

Forth flotation process

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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