There can be no progress in science without chemistry. Chemical research is changing in a big way. Chemistry is no longer making a few compounds and studying their properties. We now design new materials with the properties that are desired by us. Some of the important problems faced by humanity can eventually be solved by the use of chemistry.
Chemistry is the study of substances, their makeup and applications. Organic Chemistry, Inorganic Chemistry, Analytical chemistry and Biochemistry are the main branches of chemistry.
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Water occurs in the form of snow, as water in rivers, lakes, sea, etc. and as vapour in the atmosphere. Water is a covalent compound made up of two hydrogen atoms linked with one oxygen atom through covalent bonds.
Alkenes undergo electrophilic addition reactions with hydrogen halides, to form alkyl halides. When halogen acids (HX) are added to alkenes, hydrogen adds to one carbon atom whereas halogen atom adds to the second carbon atom of the double bond.
If a haloalkane is heated with concentrated alcoholic potassium hydroxide, the major product formed is an alkene due to the elimination of hydrogen halide. This is called β-elimination or dehydrohalogenation.
Alcohols can be dehydrated to alkenes. Alkenes are prepared from alcohols by dehydration in the presence of a suitable dehydrating agent such as
An alkene can be synthesized by the process of dehydrogenation (removal of hydrogen atoms), by heating an alkane up to about 700-750°C.
Steroisomerism is exhibited by the compounds which have similar attachment of atoms but differ in their arrangement in space. There are two types of stereoisomerism:
The chemical reactions in which a hydrogen atom of an alkane is replaced by a halogen atom are known as halogenation.
Alkanes undergo oxidation or combustion in excess of oxygen and produce carbon dioxide and water. This reaction is highly exothermic in nature.
Electrons are found in regions around the nucleus in an atom. and those regions are called orbitals. The orbitals can be defined and differentiated by size, shape, and orientation. Valence electrons are electrons that are found in the outermost shell. The carbon atom has four valence electrons. These valence electrons are involved in chemical reactions and bonding.
Elements can be broadly divided into two categories: metals and non-metals. They differ both in physical and chemical properties.
Carbon is an important non-metallic element. It is the sixth most abundant element in the universe. It can exist in the free state or in the form of its compounds. It is the major chemical constituent of most organic matter. Carbon is the second most common element in the human body after oxygen. Carbon is present in coal, oil and natural gas.
Dissolve a pinch of organic compound in water or alcohol. A few drops of this solution are mixed with neutral ferric chloride solution. If a red, blue or violet colouration appears, then the presence of phenolic group is confirmed.
In an organic compound, unsaturation is due to the presence of double (>C=C<) or triple (–C≡C–) bonds in the molecule. The presence of unsaturation is tested by the following two methods:
Ketones do not give Fehling's and Tollen's tests. Ketones give the following two tests which are not given by aldehydes.
The organic compound is treated with Fehling's solution and warmed over a water bath. Appearance of a red or orange precipitate confirms the presence of aldehyde group.
Both aldehydes and ketones contain the carbonyl group (>C=O). The carbonyl group can be confirmed by:
The carboxylic group can be tested by:
Litmus Test
Put a drop of an aqueous solution of the compound on blue litmus paper. If the blue litmus turns red, acidic nature is indicated.
Titration of Ferrous Ammonium Sulphate solution against Potassium Permanganate solution
Potassium permanganate is an oxidising agent, both in alkaline and acidic medium. Oxidation is always accompanied by reduction. In this titration, the ferrous ion is oxidised to ferric ion by permanganate ion, [Mn (VII)] and at the same time permanganate ion is reduced to manganese (II) [Mn (II)].
Titration of oxalic acid solution against sodium hydroxide
In this acid-base titration, oxalic acid is completely neutralized by the base (NaOH) according to the following reaction:
Suppose you are asked to prepare 100 mL 1.0M solution of oxalic acid. As a first step you have to calculate the mass of oxalic acid required for preparing 100 mL of solution.
Volumetric analysis is quantitative analysis in which the results are expressed in a certain definite volume. It involves the use of at least one solution of known strength. It may be prepared by dissolving a definite amount of a solute in a solvent to get a known volume of solution. The volume of this solution which reacts with a volume of the solution of unknown strength of another substance is determined. The process is known as titration.
Proteins are complex nitrogenous organic compounds of high molecular mass. These help in the growth and maintenance of living body and in transmission of genetic information. Proteins are made up of α-amino acids as the basic building blocks. In all, there are 20 different amino acids required by the body. Some of these are called essential amino acids as they cannot be synthesized by the organisms. These must form a part of our food.
Fats are triesters of long chain fatty acids and glycerol. One of the function of fats in the body is to provide energy. Fats provide twice as much energy as that provided by the same amount of carbohydrates.
Carbohydrates are polyhydroxy aldehydes or ketones and the substances which yield these on hydrolysis. Carbohydrates are classified as:
For detecting the presence of elements in a compound, these have to be converted into ionic forms. This is done by fusing the compound with sodium metal. The elements present in the compound are converted into soluble sodium salts.
For detecting the presence of elements in a compound, these have to be converted into ionic forms. This is done by fusing the compound with sodium metal. The elements present in the compound are converted into soluble sodium salts.
For detecting the presence of elements in a compound, these have to be converted into ionic forms. This is done by fusing the compound with sodium metal. The elements present in the compound are converted into soluble sodium salts.
For detecting the presence of elements in a compound, these have to be converted into ionic forms. This is done by fusing the compound with sodium metal. The elements present in the compound are converted into soluble sodium salts.
Chromatography is a technique by which a mixture of various substances can be separated, purified and identified. The term chromatography is applied to separation processes based on the principle of distribution of a sample between two phases:
Acetanilide is the acetyl derivative of aniline. It is widely used in industry for the preparation of a number of important organic compounds. It is usually prepared by acetylation of aniline with acetic anhydride and glacial acetic acid.
Iodoform (CHI3) is the iodine analogue of chloroform. It is a pale yellow crystalline solid (m.p. 119°C), having a characteristic odour. It is used as a mild antiseptic and disinfectant. It is also used in the preparation of many medicinal ointments used as pain-relievers.
Potassium ferric oxalate is an inorganic complex which dissociates in a suitable solvent to give simple potassium (K+) and the complex ferric oxalate, [Fe(C2O4)3]3– ions. In the complex ferricoxalate ion, ferric (Fe3+) ion is linked to three oxalate groups (C2O4)2– through six covalent bonds.
Potash alum is a double salt of potassium sulphate and aluminium sulphate. Hence, it is prepared by taking the amount of K2SO4 and Al2(SO4)3.18H2O in the ratio of their molecular masses, preparing their concentrated solutions separately followed by mixing the concentrated solutions and heating the resulting solution to the crystallization point when white crystals of potash alum (octahedral in shape) are obtained.
Mohr salt is a double salt containing ferrous sulphate and ammonium sulphate in equimolar amounts. Hence, when these two salts are mixed in the ratio of their molecular masses and then a hot saturated solution prepared, filtered and the hot filtrate cooled, light blue or green crystals of Mohr salt (octahedral in shape) are obtained.
The rate of reaction depends upon the temperature. Arrhenius equation gives the relationship between the two:
k = A.e–Ea/RT
where k is the rate constant of the reaction at temperature T.
Effect of concentration on rate of a reaction is given by its rate law. For a general reaction
aA + bB → Products
A reversible reaction never reaches the completion stage but results in an equilibrium state in which concentrations of all the reactants and products become constant. This equilibrium is dynamic in nature and it is the result of two opposite reactions occurring simultaneously and at the same rate. However, no net change occurs in the system.
Heat is evolved during neutralization of an acid with an alkali. Known quantities of the standard solutions of an acid and alkali are mixed and the change in temperature is noted and from this, the enthalpy of neutralization is calculated.
The EMF of a cell varies with the concentration of the two electrolyte solutions according to the following Nernst equation:
Weak acids and bases do not dissociate completely. An equilibrium exists between the dissociated and un-dissociated molecules.
Solutions of weak acids and bases in water have hydronium ions [H3O+] and hydroxyl ions [OH–] in different concentrations.
The most commonly used acids in laboratories are hydrochloric, sulphuric and nitric acids. The concentration of these commercially available acids are 12M, 18M and 16M respectively. But except a few cases, you need these acids in lower concentrations. The acids in their lower concentrations can be obtained by dilution of concentrated acids.
The melting point of a solid is that constant temperature at which the solid and liquid phases of the substance are in equilibrium with each other.
The method of preparation of the colloidal sol of AI(OH)3 is exactly similar to that of Fe(OH)3 sol except that instead of FeCl3, 2% AlCl3 solution is used.
Ferric hydroxide forms a hydrophobic sol. Hence it is prepared indirectly by the hydrolysis of ferric chloride with boiling water.
Like gum and egg albumin, starch forms a stable hydrophilic sol. However, the preparation is carried out with boiling water for better and quicker dispersion of starch into water.
Take 5 ml original solution in a test tube. Add aqueous NH3. Now add 1 mL solution of NaH2PO4 and scratch the walls of test tube with the glass rod.
A pinch of NH4Cl is added to original solution. On adding excess of NH4OH to make the solution alkaline then add freshly prepared (NH4)2CO3 solution, a white precipitate is obtained.
A pinch of NH4Cl is added to original solution. On adding excess of NH4OH to make the solution alkaline then add freshly prepared (NH4)2CO3 solution, a white precipitate is obtained.