NEET

  Class Aves   Class Aves.               (i) General Characters             (1) Feather-clad, air-breathing, warm-blooded, oviparous, bipedal flying vertebrates. (2) Limbs are two pairs. Forelimbs are modified as wings for flying. Hind limbs or legs are large, and variously adapted for walking, running scratching, perching, food capturing, swimming more...

  Class 4 Mammalia    Class 4 Mammalia.             (i) General characters             (1) Hair-clad, mostly terrestrial, air-breathing, warm blooded, viviparous, tetrapod vertebrates.             (2) Limbs 2 pairs, pentadactyle, each with 5 or fewer digits. Hind limbs absent in cetaceans and sirenians. more...

Significant Figures             In the measured value of a physical quantity, the digits about the correctness of which we are surplus the last digit which is doubtful, are called the significant figures. Number of significant figures in a physical quantity depends upon the least count of the instrument used for its measurement. (1) Common rules for counting significant figures : Following are some of the common rules for counting significant figures in a given expression: Rule 1. All non zero digits are significant. Example : \[x=1234\] has four significant figures. Again \[x=189\] has only three significant figures. Rule 2. All zeros occurring between two non zero digits are significant. Example : \[x=1007\] has four significant figures. Again \[x=1.0809\] has five significant figures. Rule 3. In a number less than one, all zeros to the right of decimal point and more...

  Laws of Chemical Combination   Various chemical reactions take place according to the certain laws, known as the Laws of chemical combination. These are as follows, (1) Law of conservation of mass : It was proposed by Lavoisier and verified by Landolt. According to this law, Matter is neither created nor destroyed in the course of chemical reaction though it may change from one form to other.  The total mass of materials after a chemical reaction is same as the total mass before reaction.             Example :  A reaction between \[AgN{{O}_{3}}\] solution and \[KI\] solution.                \[AgN{{O}_{3}}_{(aq)}\,\,+\,\,K{{I}_{(aq)}}\,\,\xrightarrow{{}}\,\,AgI+\,NaN{{O}_{3}}_{(aq)}\] (yellow ppt.)                         Mass of \[AgN{{O}_{3}}_{(aq)}\,\,+\,\,\text{Mass of }K{{I}_{(aq)}}\,\,\,=\,\,\,\text{Mass of the ppt}\text{. of }AgI\,\,+\,\,\text{Mass of }NaN{{O}_{3}}_{(aq)}\]           According to the modified statement of the law, The total sum of mass and energy of the system remains constant.   (2) Law of constant more...

 Atomic, Molecular and Equivalent Masses             (1) Atomic Mass : It is the average relative mass of atom of element  as compared with an atom of carbon –12 isotope taken as 12. \[\text{Atomic mass }=\frac{\text{Average mass of an atom}}{\text{1/12}\times \text{ss of an atom of }{{C}^{12}}\,}\]             Average atomic mass : If an elements exists in two isotopes having atomic masses ‘a’ and ‘b’ in the ratio   m : n, then average atomic mass =\[\frac{(m\times a)+(n\times b)}{m+n}.\] Since the atomic mass is a ratio, it has no units and is expressed in amu, 1 amu = \[1.66\times {{10}^{-24}}g\]. One atomic mass unit (amu) is equal to \[\frac{1}{12}th\] of the mass of an atom of carbon-12 isotope.             Gram atomic mass (GAM) : Atomic mass of an element expressed in grams is called Gram atomic mass or gram atom more...

  The Mole Concept   The mole (abbreviated as mol) is the SI base unit for a amount of a chemical species. It is always associated with a chemical formula and refers to Avogadro’s number (\[6.022\times {{10}^{23}}\]) of particles represented by the formula. It is designated as \[{{N}_{0}}\]. Thus, 12 molecules of \[HCl\] is a dozen, 144 molecules of \[HCl\] is a gross and \[6.022\times {{10}^{23}}\] molecules of \[HCl\] is a mole.                      1 mole of a substance = \[6.022\times {{10}^{23}}\] species             The molar mass of a substance is the mass in grams of 1 mole of that substance. \[\text{Mole of a substance }=\frac{\text{mass in grams}}{\text{molar mass}}\]             Under STP conditions when temperature is 273K and pressure is 1 atm, volume of one mole of more...

  Percentage Composition and Molecular Formula   (1) Percentage composition of a compound : Percentage composition of the compound is the relative mass of each of the constituent element in 100 parts of it. If the molecular mass of a compound is M and B is the mass of an element in the molecule, then                         \[\text{Percentage of element }=\frac{\text{Mass of element }}{\text{Molecular mass}}\times 100=\frac{X}{M}\times 100\]              (2) Empirical formula : The chemical formula that gives the simplest whole number ratio between the atoms of various elements present in one molecule of the compound is known as empirical formula (simplest formula).             For example, the empirical formula of glucose is \[C{{H}_{2\,}}O\]which shows that C, H and O are present in the ratio 1 : 2 : 1 in a molecule of glucose.             Empirical formula mass of a compound is equal to the sum of atomic more...

  Chemical Stoichiometry             Calculation based on chemical equations is known as chemical stoichiometry. Stoichiometry can be broadly classified into two groups: (1) Gravimetric analysis (Stoichiometry-I), (2) Volumetric analysis (Stoichiometry-II)             (1) Gravimetric analysis (Stoichiometry-I) : With the help of chemical equation, we can calculate the weights of various substances reacting and weight of substances formed. For example,                                                             \[MgC{{O}_{3}}\xrightarrow{{}}MgO+C{{O}_{2}}\uparrow \]             This equation implies :             (i) 1 mol of \[MgC{{O}_{3}}\] gives 1 mol of \[MgO\] and 1 mol of \[C{{O}_{2}}\].             (ii) 84 g of \[MgC{{O}_{3}}\] (Mol. wt. of \[MgC{{O}_{3}}\]) gives 40 g of \[MgO\] and 44 g of \[C{{O}_{2}}\].             Hence, chemical equation provide us information regarding :             (i) Molar ratio of reactants and products.             (ii) Mass ratio between reactants and products.             (iii) Volume ratio between gaseous reactant and products.             more...

Critical Thinking               In many situations, an excess of one or more substance is available for chemical reaction. Some of these excess substances will therefore be left over when the reaction is complete; the reaction stops immediately as soon as one of the reactant is totally consumed.             The substance that is totally consumed in a reaction is called limiting reagent because it determines or limits the amount of product. The other reactant present in excess are called as excess reagents.             Let us consider a chemical reaction which is initiated by passing a spark through a reaction vessel containing 10 mole of H2 and 7 mole of O2.                                                             \[2\underset{{}}{\mathop{\,{{H}_{2}}\,}}\,(g)\,\,+\,\,\underset{{}}{\mathop{{{O}_{2}}\,}}\,(g)\,\xrightarrow{{}}\,\,2\,\,\underset{{}}{\mathop{{{H}_{2}}O}}\,\,(v)\]             Moles before reaction            10             7         0             Moles after reaction               0               2                 10 more...

Arthritis and Cancer   (1) Arthritis             (a) Arthritis is any inflammatory condition of the joints characterised by pain and swelling.             (b) Two kinds of arthritis are : rheumatoid arthritis and osteoarthritis.             (c) There is no cure for arthritis; drugs are available which relieve pain.             (d) Rheumatoid arthritis is characterised by inflammation of the synovial membrane.             (e) A kind of rheumatoid arthritis that occurs in younger people is Still?s disease. (f) Osteoarthritis is a disease common among the elderly persons resulting from erosion of articular cartilage.             (g) Paraplegia refer to weakness or paralysis of both legs, often accompanied by loss of sensation. (h) Paraplegia is usually caused by a motor vehicle accident, sports accident, fall or gunshot wounds.   more...