Some Basic Concepts of Chemistry Class 11

 Some Basic Concepts of Chemistry Class 11

Chapter : Some Basic Concepts of Chemistry 

What is the difference between precision and accuracy?
Precision means the closeness of various measurements for the same quantity. Accuracy is the agreement of a particular value to the true value of the result.


What do you understand by significant figures?
Significant figures are meaningful digits which are known with certainty. The uncertainty in experimental or the calculated value is indicated by mentioning the number of significant figures.


State law of definite proportions.
Law of definite proportions states that a given compound always contains exactly the same proportion of elements by weight


. Explain law of multiple proportions with an example.
The law of multiple proportions rays that if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of other element are in a ratio of small whole numbers. e.g. hydrogen and oxygen can combine to form water as well as hydrogen peroxide. Here, the masses of oxygen (16g & 32g) which combine with a fixed mass of hydrogen (2g) bear a simple ratio i.e., 16:32 = 1:2.


State Avogadro’s law.
According to Avogadro’s law, equal volumes of gases at the same temperature and pressure should contain equal number of molecules.


Write Postulates of Dalton’s atomic theory.
Postulates of Dalton’s atomic theory –
1. Matter consists of indivisible atoms.
2. All the atoms of a given element have identical properties including atomic mass. Atoms of different element differ in mass.
 3. Compounds are formed when atoms of different elements combine in a fixed ratio.
 4. Chemical reaction involves reorganization of atoms. These are neither created nor destroyed



. Define one atomic mass unit (amu).
One atomic mass unit (amu) is defined as a mass exactly equal to one – twelfth the mass of one carbon – 12 atom.


. What is formula mass?
When a substance does not contain discrete molecules as their constituent units and have a three dimensional structure, formula mass is used to calculate molecular mass which is sum of all the atomic masses of atom present in the formula.


What is stoichiometry?
Stoichimetry deals with the calculations of masses of reactants and products involved in a chemical reactions.


The substance which gets used up in any reaction is called -------------- limiting reagent.