Important Questions for CBSE Class 11 Chemistry Chapter 1 - Some Basic Concepts of Chemistry
CBSE Class 11 Chemistry Chapter-1 Important Questions - Free PDF Download
1 Marks Questions
1.What is chemistry?
Ans: Chemistry is the branch of science that studies the composition, properties and interaction of matter.
2.How has chemistry contributed towards nation’s development?
Ans: chemical principles are important in diverse areas such as weather patterns, functioning of brain, operation of a computer, chemical industries, manufacturing , fertilizers, alkalis, acids, salts, dyes, polymers, drugs, soaps, detergents, metals, alloys, contribute in a big way to national economy.
3.Differentiate solids, liquids & gases in terms of volume & shapes.
Ans:
Property | Solids | Liquids | Gases |
1. Volume | Definite | Definite | Not definite |
2. Shape | Fixed | Not fixed, take the shape of container, | Not fixed, takes the shape of the container |
4.Name the different methods that can be used for separation of components of a mixture. .
Ans:The components of a mixture can be separated by physical methods like handpicking, filtrations, crystallization, distillation etc.
5.Classify following as pure substances and mixtures – Air, glucose, gold, odium and milk.
Ans:
| Pure Substances | Mixtures |
| Glucose | Air |
| Gold | Milk |
| Sodium |
6.What is the difference between molecules and compounds? Give examples of each.
Ans: Molecules consist of different atoms or same atoms. e.g. molecule of hydrogen contains two atoms of hydrogen where as molecule of water contain two atoms of hydrogen and one of oxygen.
Compound is formed when two or more than two different atoms combine in fire propo e.g. water –rtion carbondioxide, sugar etc.
7. How can we separate the components of a compound?
Ans:The constituents of a compound can not be separated by physical methods. They can only be separate by chemical methods.
8.How are physical properties different from chemical properties?
Ans: Physical properties are those properties which can be measured or observed without changing the identity or the composition of the substance whereas the measurement of chemical properties require a chemical change to occur e.g. colour, odour etc are physical properties and combustion, basicity etc are chemical properties.
9.What are the two different system of measurement?
Ans:The different system of measurement are English system and the metric system.
10.What is the SI unit of density?
Ans: The SI Unit of density is Kg m-3 or kg/m3
11.What are the reference points in thermometer with Celsius scale?
Ans:The thermometers with Celsius scale are calibrated form 0o to 100o where there two temperatures are the freezing and boiling of water.
12.What is the SI unit of volume? What is the other common unit which in not
an SI unit of volume.
Ans: The SI unit of volume is m3 whereas litre (L) is the common unit which is not an SI unit.
13.What is the difference between precision and accuracy?
Ans: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.
14.What do you understand by significant figures?
Ans: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.
15.State law of definite proportions.
Ans: Law of definite proportions states that a given compound always contains exactly the same proportion of elements by weight.
16.State Avogadro’s law.
Ans:According to Avogadro’s law, equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
17.Define one atomic mass unit (amu).
Ans: One atomic mass unit (amu) is defined as a mass exactly equal to one – twelfth the mass of one carbon – 12 atom.
18.What is formula mass?
Ans: 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.
19.What is the value of one mole?
Ans:1mole = 
atoms/ ions / entities
20.At NTP, what will be the volume of molecules of H2?
Ans: 22.4 Litres.
21.Calculate the number of molecules present in 0.5 moles of CO2?
Ans: The number of molecules present in 0.5 moles of C02 is 
22. 1L of a gas at STP weighs 1.97g. What is molecular mass?
Ans: 22.4 L of the gas at STP will weigh
i.e. molecular mass = 44.1
23.What is stoichiometry?
Ans: Stoichimetry deals with the calculations of masses of reactants and products involved in a chemical reactions.
24. The substance which gets used up in any reaction is called --------------
Ans: The substance that gets used up in any reaction is called limiting reagent.
25.What is 1molal solution?
Ans: one molal solution is solution in which one mole of solute is present in 1000g of solvent.
2 Marks Questions
1.How can we say that sugar is solid and water is liquid?
Ans: Sugar has close packing of constituent particles, have its own volume and shape therefore, it can be said to be solid whereas in water the constituent particles are not as closely packed as in solid. It has definite volume but not definite shape. Therefore it is a liquid.
2.How is matter classified at macroscopic level?
Ans: Macroscopic classification of matter –
3.Classify following substances as element, compounds and mixtures – water,
tea, silver, steel, carbondioxide and platinum
Ans:
| Compounds | Elements | Mixtures |
| Water | Silver | Tea |
| Carbondioxide | Platinum | Steel |
4.Write seven fundamental quantities & their units.
Ans:
| Physical Quantity | SI unit |
| 1. Length (l) | Metre (m) |
| 2. Mass (m) | Kilogram (kg) |
| 3. Time (t) | Second (s) |
| 4. Electric Current (I) | Ampere (A) |
| 5. Thermodynamic Temperature (T) | Kelvin (K) |
| 6. Amount of substance (n) | Mole (mol) |
| 7. Luminous Intensity (I) | Candela (Cd) |
5.What is the difference between mass & weight? How is mass measured in laboratory?
Ans: Mass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object the mass of a substance is determined with the help of an analytical balance in laboratory.
6.How is volume measured in laboratory? Convent 0.5L into ml and 30cm3 to dm3
Ans: In the laboratory volume of a liquid can be measured by using graduated cylinder, burette, pipette etc.
1L = 1000 ml
1000cm3 = 1dm3
0.5L = 500 ml
30cm3 = 
= 0.03dm3
7.Convert 350C to oF & K.
Ans.oF
K
8.What does the following prefixes stand for –
(a) pico
(b) nano
(c) centi
(d) deci
Ans: Pico = 10-12
nano = 10-9
centi = 10-2
deci = 10-1
9.Explain law of multiple proportions with an example.
Ans: 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.
10.Write Postulates of Dalton’s atomic theory.
Ans. 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
11.Calculate molecular mass of –
C2H6, C12H22O11, H2SO4, H3PO4
Ans: 
12. Give one example each of a molecule in which empirical formula
and molecular formula are (i) same (ii) Different.
Ans:(i) Same molecular formula and empirical formula. Carbon dioxide, both is CO2.
(ii) When molecular formula and empirical formula are different –
Hydrogen peroxide: molecular formula is H2O2 and empirical formula is HO
13.Calculate the number of moles in the following masses –
(i) 7.85g of Fe
(ii) 7.9mg of Ca
Ans. (i) 7.85g of Fe
56g of Fe contains 
atoms = 1mole
56g of Fe = 1mole
7.85g of Fe = 
= 0.14moles
(ii)40g of Ca = 
mg of Ca
40g of Ca = 1mole
Or 
mg of Ca = 1mole
7.9mg of Ca = 
14.How much potassium chlorate should be heated to produce 2.24L of oxygen at NTP?
Ans: 2KClO3 à 2KCl + 3O2
2moles 3moles
2(39 + 35.5 + 3 
16) 22.43L
= 245g = 67.2L
67.2L of oxygen is produced from 245g of KClO3
2.24L of oxygen is produced from = 
= 8.17g of KClO3
15.Write an expression for molarity and molality of a solution.
Ans: 
16.Calculate the weight of lime (CaO) obtained by heating 2000kg of 95% pure lime stone (CaCO3)
Ans:100kg impure sample has pure CaCO3 = 95
= 95kg
200kg impure sample has pure CaCO3 = 
= 190kg
CaCO3 à CaO + CO2
Since 100kg CaCO3 gives CaO = 56kg
190kg CaCO3 will give CaO = 
= 106.4kg
17. 4 litres of water are added to 2L of 6 molar HCl solutions.What is the molarity of resulting solution?
Ans. Initial volume, V1 = 2L
Final volume, V2 = 4L + 2L = 6L
Initial molarity, M1 = 6M
Final molarity = M2
M1V1 = M2V2
Thus the resulting solution is 2M HCl.
18.What volume of 10M HCl and 3M HCl should be mixed to obtain 1L of 6M HCl solution?
Ans: Let the required volume of 10M HCl be V liters.
Then, the required volume of 3M HCl be (1 – V) Liters.
M1V1 + M2V2 = M3V3
Then the volume of 10M HCl required = 428mL
& volume of 3M HCl required = 1000mL – 428mL = 572mL
3 Marks Questions
1.How many significant figures are present in
(a) 4.01 
102
(b) 8.256
(c) 100
Ans:(a) 4.01 102 – Three
(b) 8.256 – Four
(c) 100 – One
2.Vitamin C is essential for the prevention of scurvy. Combustion of 0.2000g of vitamin C gives 0.2998g of CO2 and 0.819g of H2O. What is the empirical formula of vitamin C?
Ans: Percentage of carbon = 
Percentage of Hydrogen 
Percentage of oxygen 
Element | % | Atomic Mass | Relative no. of atoms | Simplest Ratio |
C | 47.69 | 12 |
|
|
H | 4.55 | 1 |
|
|
O | 47.76 | 16 |
|
|
Empirical formula = C1.33 H1.5 O,
= C8H9O6