**NCERT Solutions for Class 11 Chemistry: Chapter 1 (Some Basic Concepts of Chemistry)** are provided on this page for the perusal of Class 11 Chemistry students. These solutions can also be downloaded in a PDF format for free by clicking the download button provided below. The free Class 11 Chemistry NCERT Solutions provided by CoolGyan’S have been prepared by seasoned academics and chemistry experts keeping the needs of Class 11 Chemistry students in mind. The NCERT Solutions provided on this page contain step-by-step explanations in order to help students answer similar questions that might be asked in their examinations.

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## Download NCERT Solutions Class 11 Chemistry Chapter 1 PDF

## NCERT Chemistry – Class 11, Chapter 1: Some Basic Concepts of Chemistry

**“Some Basic Concepts of Chemistry” **is the first chapter in the Class 11 Chemistry syllabus as prescribed by NCERT. The chapter touches upon topics such as the importance of Chemistry, atomic mass, and molecular mass. Some basic laws and theories in Chemistry such as Dalton’s atomic theory, Avogadro law and the law of conservation of mass are also discussed in this chapter.

The types of questions provided in the NCERT Class 11 Chemistry textbook for Chapter 1 include:

- Numerical problems in calculating the molecular weight of compounds.
- Numerical problems in calculating mass percent and concentration.
- Problems on empirical and molecular formulae.
- Problems on molarity and molality.
- Other problems related to the mole concept (such as percentage composition and expressing concentration in parts per million).

The Chemistry NCERT Solutions provided on this page for Class 11 (Chapter 1) provide detailed explanations on the steps to be followed while solving the numerical value questions that are frequently asked in examinations. The subtopics covered under the chapter are listed below.

### NCERT Chemistry Class 11 Chapter 1 Subtopics (“Some Basic Concepts of Chemistry”)

- Importance Of Chemistry
- Nature Of Matter
- Properties Of Matter And Their Measurement
- The International System Of Units (Si)
- Mass And Weight
- Uncertainty in Measurement
- Scientific Notation
- Significant Figures
- Dimensional Analysis
- Laws Of Chemical Combinations
- Law Of Conservation Of Mass
- Law Of Definite Proportions
- Law Of Multiple Proportions
- Gay Lussac’s Law Of Gaseous Volumes
- Avogadro Law
- Dalton’s Atomic Theory
- Atomic And Molecular Masses
- Atomic Mass
- Average Atomic Mass
- Molecular Mass
- Formula Mass
- Mole Concept And Molar Masses
- Percentage Composition
- Empirical Formula For Molecular Formula
- Stoichiometry And Stoichiometric Calculations
- Limiting Reagent
- Reactions In Solutions

### NCERT Solutions for Class 11 Chemistry Chapter 1

**Exercise**

*Q1. Calculate the molar mass of the following:*

*(i) $CH_{4}$ (ii)$H_{2}O$ (iii)$CO_{2}$*

**Ans.**

**(i) **

Molecular weight of methane,

= (1 x Atomic weight of carbon) + (4 x Atomic weight of hydrogen)

= [1(12.011 u) +4 (1.008u)]

= 12.011u + 4.032 u

= 16.043 u

**(ii)**

Molecular weight of water,

= (2 x Atomic weight of hydrogen) + (1 x Atomic weight of oxygen)

= [2(1.0084) + 1(16.00 u)]

= 2.016 u +16.00 u

= 18.016u

So approximately

= 18.02 u

**(iii)**

Molecular weight of carbon dioxide,

= (1 x Atomic weight of carbon) + (2 x Atomic weight of oxygen)

= [1(12.011 u) + 2(16.00 u)]

= 12.011 u +32.00 u

= 44.011 u

So approximately

= 44.01u

* *

*Q2. Calculate the mass per cent of different elements present in sodium sulphate ( $Na_{2}SO_{4}$) .*

**Ans.**

Now for

Molar mass of

= [(2 x 23.0) + (32.066) + 4(16.00)]

=142.066 g

Formula to calculate mass percent of an element =

Therefore, mass percent of the sodium element:

=

= 32.379

= 32.4%

Mass percent of the sulphur element:

=

= 22.57

= 22.6%

Mass percent of the oxygen element:

=

= 45.049

= 45.05%

** **

*Q3. Determine the empirical formula of an oxide of iron, which has 69.9% iron and 30.1% dioxygen by mass.*

**Ans.**

Percent of Fe by mass = 69.9 % [As given above]

Percent of O_{2} by mass = 30.1 % [As given above]

Relative moles of Fe in iron oxide:

=

=

= 1.25

Relative moles of O in iron oxide:

=

=

= 1.88

Simplest molar ratio of Fe to O:

= 1.25: 1.88

= 1: 1.5

Therefore, empirical formula of iron oxide is

* *

*Q4. Calculate the amount of carbon dioxide that could be produced when (i) 1 mole of carbon is burnt in air. (ii) 1 mole of carbon is burnt in 16 g of dioxygen. (iii) 2 moles of carbon are burnt in 16 g of dioxygen.*

**Ans.**

**(i)** 1 mole of carbon is burnt in air.

1 mole of carbon reacts with 1 mole of O_{2} to form one mole of CO_{2}.

Amount of

**(ii)** 1 mole of carbon is burnt in 16 g of O_{2}.

1 mole of carbon burnt in 32 grams of O_{2} it forms 44 grams of

Therefore, 16 grams of O_{2} will form

= 22 grams of

**(iii)** 2 moles of carbon are burnt in 16 g of O_{2}.

Since oxygen is the limiting reactant here, the 16g (0.5 mol) of O_{2} will react with 6g of carbon (0.5 mol) to form 22 g of carbon dioxide. The remaining 18g of carbon (1.5 mol) will not undergo combustion.

*Q5. Calculate the mass of sodium acetate $(CH_{3}COONa)$ required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82.0245 g mol ^{–1}. . *

**Ans.**

0.375 Maqueous solution of

= 1000 mL of solution containing 0.375 moles of

Therefore, no. of moles of

=

= 0.1875 mole

Molar mass of sodium acetate =

Therefore, mass that is required of

=

= 15.38 grams

*Q6. Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%*

**Ans.**

Mass percent of HNO_{3} in sample is 69 %

Thus, 100 g of HNO_{3} contains 69 g of HNO_{3} by mass.

Molar mass of HNO_{3}

= { 1 + 14 + 3(16)}

= 1 + 14 + 48

Now, No. of moles in 69 g of

=

= 1.095 mol

Volume of 100g HNO_{3} solution

=

=

= 70.92mL

=

Concentration of HNO_{3}

=

= 15.44mol/L

Therefore, Concentration of HNO_{3} = 15.44 mol/L

*Q7. How much copper can be obtained from 100 g of copper sulphate (CuSO _{4})? *

**Ans.**

1 mole of

Molar mass of

= (63.5) + (32.00) + 4(16.00)

= 63.5 + 32.00 + 64.00

= 159.5 grams

159.5 grams of

Therefore, 100 grams of

=

=39.81 grams

*Q8. Determine the molecular formula of an oxide of iron, in which the mass percent of iron and oxygen are 69.9 and 30.1, respectively. *

**Ans.**

**Here,**

Mass percent of Fe = 69.9%

Mass percent of O = 30.1%

No. of moles of Fe present in oxide

=

= 1.25

No. of moles of O present in oxide

=

=1.88

Ratio of Fe to O in oxide,

= 1.25: 1.88

=

=

=

Therefore, the empirical formula of oxide is

Empirical formula mass of

= [2(55.85) + 3(16.00)] gr

= 159. 7g

The molar mass of

Therefore n =

= 0.999

= 1(approx)

The molecular formula of a compound can be obtained by multiplying n and the empirical formula.

Thus, the empirical of the given oxide is

** **

**Q9 . Calculate the atomic mass (average) of chlorine using the following data: **

Percentage Natural Abundance | Molar Mass | |

75.77 | 34.9689 | |

24.23 | 36.9659 |

** **

**Ans.**

Average atomic mass of Cl.

= [(Fractional abundance of

= [{(

= 26.4959 + 8.9568

= 35.4527 u

Therefore, the average atomic mass of Cl = 35.4527 u

*Q10. In three moles of ethane (C _{2}H_{6}), calculate the following:*

(i) Number of moles of carbon atoms.

(ii) Number of moles of hydrogen atom

*(iii) Number of molecules of ethane*

**Ans.**

(a) 1 mole

= 2 * 3

= 6

(b) 1 mole

= 3 * 6

= 18

(c) 1 mole

= 3 * 6.023 *

= 18.069 *

*Q11. What is the concentration of sugar (C _{12}H_{22}O_{11}) in mol L^{–1} if its 20 g are dissolved in enough water to make a final volume up to 2L?*

**Ans.**

Molarity (M) is as given by,

=

=

=

=

=

= 0.02925 mol

Therefore, Molar concentration = 0.02925 mol

*Q12. If the density of methanol is 0.793 kg L ^{–1}, what is its volume needed for making 2.5 L of its 0.25 M solution?*

**Ans.)**

Molar mass of

= (1 * 12) + (4 * 1) + (1 * 16)

= 32 g

= 0.032 kg

Molarity of the solution

=

= 24.78 mol

(From the definition of density)

* *

*Q13. Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is as shown below: 1Pa = 1N m ^{–2} If mass of air at sea level is 1034 g cm^{–2}, calculate the pressure in pascal*

**Ans.**

As per definition, pressure is force per unit area of the surface.

P =

=

= 1.01332 ×

Now,

1 N = 1 kg m

Then,

1 Pa = 1

= 1

Pa = 1

*Q14. What is the SI unit of mass? How is it defined?*

**Ans.**

The SI Unit of mass: Kilogram (kg)

Mass:

“The mass equal to the mass of the international prototype of kilogram is known as mass.”

*Q15. Match the following prefixes with their multiples:*

* *

| Prefixes | Multiples |

(a) | femto | 10 |

(b) | giga | |

(c) | mega | |

(d) | deca | |

(e) | micro |

**Ans.**

Prefixes | Multiples | |

(a) | femto | |

(b) | giga | |

(c) | mega | |

(d) | deca | 10 |

(e) | micro |

*Q16. What do you mean by significant figures?*

**Ans.**

Significant figures are the meaningful digits which are known with certainty. Significant figures indicate uncertainty in experimented value.

e.g.: The result of the experiment is 15.6 mL in that case 15 is certain and 6 is uncertain. The total significant figures are 3.

Therefore, “the total number of digits in a number with the Last digit that shows the uncertainty of the result is known as significant figures.”

*Q17. A sample of drinking water was found to be severely contaminated with chloroform, CHCl _{3}, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass). (i) Express this in per cent by mass. (ii) Determine the molality of chloroform in the water sample. *

**Ans.**

(a) 1 ppm = 1 part out of 1 million parts.

Mass percent of 15 ppm chloroform in H_{2}O

=

=

(b) 100 grams of the sample is having 1.5 ×

1000 grams of the sample is having 1.5 ×

=

Molar mass (

= 12 + 1 + 3 (35.5)

= 119.5 grams

Therefore, molality of

= 1.25 ×

*Q18. Express the following in the scientific notation: (i) 0.0048 (ii) 234,000 (iii) 8008 (iv) 500.0 (v) 6.0012*

** **

**Ans.**

(a) 0.0048= 4.8 ×

(b) 234,000 = 2.34 ×

(c) 8008= 8.008 ×

(d) 500.0 = 5.000 ×

(e) 6.0012 = 6.0012 ×

*Q19. How many significant figures are present in the following? *

*(a) 0.0027*

*(b) 209*

*(c) 6005*

*(d) 136,000*

*(e) 900.0 *

*(f) 2.0035*

**Ans.**

(i) 0.0027: 2 significant numbers.

(ii) 209: 3 significant numbers.

(iii) 6005: 4 significant numbers.

(iv) 136,000:3 significant numbers.

(v) 900.0: 4 significant numbers.

(vi) 2.0035: 5 significant numbers.

* *

*Q20. Round up the following upto three significant figures:*

*(a) 34.216*

*(b) 10.4107*

*(c)0.04597 *

*(d)2808*

**Ans.**

(a) The number after round up is: 34.2

(b) The number after round up is: 10.4

(c)The number after round up is: 0.0460

(d)The number after round up is: 2808

* *

*Q21. The following data are obtained when dinitrogen and dioxygen react together to form different compounds:*

| Mass of dioxygen | Mass of dinitrogen |

(i) | 16 g | 14 g |

(ii) | 32 g | 14 g |

(iii) | 32 g | 28 g |

(iv) | 80 g | 28 g |

* *

**(a) Which law of chemical combination is obeyed by the above experimental data?****Give its statement.****(b) Fill in the blanks in the following conversions:****(i) 1 km = …………………. mm = …………………. pm****(ii) 1 mg = …………………. kg = …………………. ng****(iii) 1 mL = …………………. L = …………………. dm ^{3}**

**Ans.**

**(a)** If we fix the mass of N_{2} at 28 g, the masses of O_{2} that will combine with the fixed mass of N_{2} are 32 grams, 64 grams, 32 grams and 80 grams.

The mass of O_{2} bear whole no. ratio of 1: 2: 1: 5. Therefore, the given information obeys the law of multiple proportions.

The law of multiple proportions states, “If 2 elements combine to form more than 1 compound, then the masses of one element that combines with the fixed mass of another element are in the ratio of small whole numbers.”

**(b)** Convert:

(a) 1 km = ____ mm = ____ pm

- 1 km = 1 km *
$frac{ 1000 ; m }{ 1 ; km }$ ×$frac{ 100 ; cm }{ 1 ; m }$ *$frac{ 10 ; mm }{ 1 ; cm }$

- 1 km = 1 km *
$frac{ 1000 ; m }{ 1 ; km }$ *$frac{1 ; pm}{10^{ -12 } ; m}$

Therefore, 1 km =

(b) 1 mg = ____ kg = ____ ng

- 1 mg = 1 mg *
$frac{ 1 ; g }{ 1000 ; mg }$ *$frac{ 1 ; kg }{ 1000 ; g }$

1 mg =

- 1 mg = 1 mg *
$frac{ 1 ; g }{ 1000 ; mg }$ *$frac{ 1 ; ng }{ 10^{ -9 } ; g }$

1 mg =

Therefore, 1 mg =

(c) 1 mL = ____ L = ____

- 1 mL = 1 mL *
$frac{1 ; L}{1000 ; mL}$

1 mL =

- 1 mL = 1
$cm^{ 3 }$ = 1 *$frac{1 ; dm ; imes ; 1 ; dm ; imes ;1 ; dm }{10 ; cm ; imes ; 10 ; cm ; imes ; 10 ; cm } cm^{ 3 }$

1 mL =

Therefore, 1 mL =

*Q22. If the speed of light is 3.0 × 10 ^{8} m s^{–1}, calculate the distance covered by light in 2.00 ns*

**Ans.**

Time taken = 2 ns

= 2 ×

Now,

Speed of light = 3 ×

So,

Distance travelled in 2 ns = speed of light * time taken

= (3 ×

= 6 ×

= 0.6 m

*Q23. In a reaction A + B _{2} → AB_{2} Identify the limiting reagent, if any, in the following reaction mixtures. *

*(i) 300 atoms of A + 200 molecules of B*

*(ii) 2 mol A + 3 mol B*

*(iii) 100 atoms of A + 100 molecules of B*

*(iv) 5 mol A + 2.5 mol B*

*(v) 2.5 mol A + 5 mol B*

**Ans.**

Limiting reagent:

It determines the extent of a reaction. It is the first to get consumed during a reaction, thus causes the reaction to stop and limiting the amt. of products formed.

**(i)** 300 atoms of A + 200 molecules of B

1 atom of A reacts with 1 molecule of B. Similarly, 200 atoms of A reacts with 200 molecules of B, so 100 atoms of A are unused. Hence, B is the limiting agent.

**(ii)** 2 mol A + 3 mol B

1 mole of A reacts with 1 mole of B. Similarly, 2 moles of A reacts with 2 moles of B, so 1 mole of B is unused. Hence, A is the limiting agent.

**(iii)** 100 atoms of A + 100 molecules of Y

1 atom of A reacts with 1 molecule of Y. Similarly, 100 atoms of A reacts with 100 molecules of Y. Hence, it is a stoichiometric mixture where there is no limiting agent.

**(iv)** 5 mol A + 2.5 mol B

1 mole of A reacts with 1 mole of B. Similarly 2.5 moles of A reacts with 2 moles of B, so 2.5 moles of A is unused. Hence, B is the limiting agent.

**(v)** 2.5 mol A + 5 mol B

1 mole of A reacts with 1 mole of B. Similarly, 2.5 moles of A reacts with 2.5 moles of B, so 2.5 moles of B is unused. Hence, A is the limiting agent.

* *

*Q24. Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation: N _{2} (g) + H_{2}(g)→ 2NH_{3} (g) *

*(i) Calculate the mass of $NH_{ 3 }$ produced if $2 ; imes ;10^{ 3 }$ g N*

_{2}reacts with $1 ; imes ;10^{ 3 }$ g of H

_{2}?

* (ii) Will any of the two reactants remain unreacted? *

*(iii) If yes, which one and what would be its mass.*

**Ans.**

**(i)** Balance the given equation:

Thus, 1 mole (28 g) of N_{2} reacts with 3 mole (6 g) of H_{2} to give 2 mole (34 g) of

_{2}will react with

_{3}

_{2}will react with 428.6 g of H

_{2}.

Given:

Amt of H_{2} =

28 g of

Therefore, mass of

=

**= **2430 g of

**(ii)**

**(iii)** Mass of H_{2} unreacted

=

= 571.4 g

* *

*Q25. How are 0.50 mol Na _{2}CO_{3} and 0.50 M Na_{2}CO_{3} different?*

**Ans.**

Molar mass of

= (2 × 23) + 12 + (3 × 16)

= 106 g

1 mole of

Therefore, 0.5 mol of

=

= 53 g of

0.5 M of

Hence, 0.5 mol of

* *

*Q26. If 10 volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?*

**Ans.**

Reaction:

2 volumes of dihydrogen react with 1 volume of dioxygen to produce two volumes of vapour.

Hence, 10 volumes of dihydrogen will react with five volumes of dioxygen to produce 10 volumes of vapour.

*Q27. Convert the following into basic units:*

*(i) 28.7 pm *

*(ii) 15.15 pm *

*(iii) 25365 mg*

**Ans.**

**(i)** 28.7 pm

1 pm =

28.7 pm = 28.7 ×

= 2.87 ×

**(ii)** 15.15 pm

1 pm =

15.15 pm = 15.15 ×

= 1.515 ×

**(iii)** 25365 mg

1 mg =

25365 mg = 2.5365 ×

25365 mg = 2.5365 ×