Chapter - Basic Concepts Of Chemistry
*Some useful Facts for In Focus Examinations
• Anything that occupies space and has mass is matter .
• The term precision refers for the closeness of the set of values obtained from identical measurements of a quantity .
• The term accuracy refers to the closeness of a single measurement to its true value .
•All numbers , small or large are expressed as a number between 1.000..........And 9.999 and n is a number divided by 10 , an appropriate number of times . ⇒1426.2 = 1.4262 × 10³
•In scientific notation , a number is generally expressed in the form N x 10 where N is a number ( called digit term ) between 1.000 ......and 9.999 and n is a number called an exponent.
• The significant figures in a number are all the certain digits plus one doubtful digit .
• In addition and subtraction , the final result should be reported to the same number of decimal places as the number with the minimum number of decimal places .
•In multiplication and division , the final result should be reported as having the same number of significant digits as the number with least number of significant digits .
• Law of conservation of mass ( Lavoisier in 1774 ) . During any physical or chemical change , the total mass of the products formed is equal to the total mass of reactants consumed .
• Law of constant composition ( Proust in 1798 ) . A chemical compound always contains same elements combined together in same
• Law of multiple proportions ( John Dalton in 1803 ) . When two elements combine together to form two or more than two compounds then the masses of one of the elements that combine with fixed mass of the other bear a simple whole number ratio to one another .
• Law of reciprocal proportions ( Richter in 1792 ) . When two different elements combine separately with a fixed mass of a third element , then the ratio of their masses in they either the same or some whole number multiple of the ratio in which they combine with each other .
•Gay Lussac's law ( Gay Lussac in 1808 ) . When gases react with each other they do so in volumes which bear a simple whole number ratio to one another and to the volume of the products , if they are also gases , provided all volumes are measured under similar condition of temperature and pressure .
• Avogadro's law . Equal volume of all gases under simulate conditions of temperature and pressure contain equal number of molecules .
•The smallest particle of an element that takes part in chemical reactions is atom .
•The smallest particle of a substance that has independent existence is molecule .
•One twelveth ( 1/12 ) of the mass of an atom of carbon ( C - 12 ) is atomic mass unit . It is equal to 1.66 x 10-2 kg . The average relative mass of an atom of element as compared with mass of a carbon atom ( C - 12 ) taken as 12 a.m.u. is atomic mass .
• The average relative mass of a molecule of the substance as compared with mass of a carbon atom ( C - 12 ) taken as 12 a.m.u. is molecular mass .
•Atomic mass expressed in grams is gram atomic mass and molecular mass expressed in grams is gram molecular mass .
•One mole is 6.022 x 10 to the power 23 specified particles .
• Volume occupied by one mole of a gaseous substance is called gram molecular volume ( G.M.V. ) . Its value is 22.4 L at N.T.P.
•Mass percentage composition of a compound gives the mass of each element expressed as percentage of the total mass .
• The formula which gives the simplest whole number ratio of atoms of different elements present in the molecule of a compound is empirical formula .
•The molecular formula gives the actual number of atoms present in the molecule of the compound . It is whole number multiple of empirical formula .
• Molarity is the number of moles of solute dissolved per litre of solution . It is expressed as mol dm3 or M. Molarity changes with temperature because volume of the solution changes with temperature .
•The reagent that is completely consumed in the reaction is called limiting reagent .
 |
| Class 11 Basics concepts of chemistry |
Comments
Post a Comment
Comment