CBSE Class 11 Chemistry Notes: Some Basic Concepts of Chemistry (Part - I)
This article provides you the revision notes on Class 11 Chemistry: Chapter- Some Basic Concepts of Chemistry, to give you a quick glance of the chapter. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 11 Chemistry and are sure to help you while preparing for the exams.
This article provides you the revision notes on Class 11 Chemistry: Chapter- Some Basic Concepts of Chemistry, to give you a quick glance of the chapter. In between the various topics included in these chapter notes, you will also find the important questions on relevant topics. These question will help you check your preparedness and clear your doubts. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 11th Chemistry.
Topics covered in this part of chapter notes for ‘Some Basic Concepts of Chemistry’, are:
• Basic physical quantities, their SI units and measurements
• Uncertainties in Measurement
The key notes of the chapter are as follows:
Chemistry is the branch of science that deals with the composition, structure and properties of matter.
- Anything which has mass and occupies space is known as matter.
For example: Air, water, table, pencil, etc.
- Matter can exist in three physical states viz. solid, liquid and gas.
Classification of Matter:
On the basis of chemical composition of various substances matter can be classified as follows:
1. Homogeneous mixture: Uniform composition of constituent particles.
2.Heterogeneous mixture: Nonuniform composition of constituent particles.
- Simplest form of pure substance, which can neither be decomposed into nor built from simpler substances by ordinary physical and chemical methods.
- Contains only one kind of atoms.
- For example: Hydrogen, Oxyen, Nitrogen, etc.
- A form of matter formed by combining two or more elements in a definite ratio by mass.
- Can be decomposed into its constituent elements by suitable chemical methods
- For example: H2O, O2, NO2, etc.
Properties of Matter and Their Measurement
Properties of matter can be classified into two categories:
- Physical properties: These are the properties which can be measured or observed without changing the identity or the composition of the substance. For example: Mass, size, colour, odour, melting point, boiling point, density etc.
- Chemical properties: These are the properties which can be measured by bringing a chemical change in the state or identity of a substance. For example: Acidity, basicity, combustibility etc.
Basic physical quantities and their SI units:
Prefixes used in the SI System:
- It is the amount of matter present in a substance.
- It is a constant quantity.
- Its SI unit is kilogram (Kg).
- It is the force exerted by gravity on an object.
- It varies from one place to another due to change in gravity.
- Its SI unit is Newton.
- It is the volume of space occupied by a substance.
- Its SI unit is cubic metre (m)3.
- Another common unit is litre (L). 1 Cubic Meter = 1000 Liters (1 m3 = 1000L)
- 1 L = 1000 mL, 1000 cm3 = 1 dm3
- It is the amount of mass per unit volume.
- Its SI unit is kilogram per cubic meter (kg/m3)
- Another common unit is gram per cubic meter (g/cm3).
- It is the degree of heat present in a substance.
- Its SI unit is Kelvin (K)
- Another common units are: Degree Celsius (°C) and degree Fahrenheit (°F)
Check your preparedness by solving the following questions:
1. What should be the volume of milk in cubic metre (m3) if it measures 4 L?
(a) 4 × 103 m3 (b) 4 × 106 m3
(c) 4 × 10-3 m3 (d) 4 × 1000 m3
2. Which measurement represents the smallest quantity among the following:
(a) 47.3 mg (b) 4.73 × 10-4 g
(c) 4730 ng (d) 4.73 × 103 kg
3. What is the value of temperature 75o F on the Kelvin scale?
(a) 2015 K (b) 215 K
(c) 297 K (d) 348 K
Uncertainties in Measurement
Numbers are represented in N × 10n form.
N = Digit term
n = exponent having positive or negative value.
12540000 = 1.254 × 107
0.00456 = 4.56 ×10-3
It refers to the closeness of outcomes of different measurements taken for the same quantity
It refers to the agreement of a particular value to the true value of the result.
To express a measurement accurately, it must be represented by the digits that are known with certainty. These are called as Significant figures.
Rules for determining the significant figures:
- All non-zero digits are significant. For example, 3.14 has three significant figures.
- Zeroes preceding the first non-zero digit are not significant. For example, 0.004 has one significant figure.
- Zeroes between two non-zero digits are significant. For example, 6.002 has four significant figures.
- Zeroes at the end of a number are significant when they are on the right side of the decimal point. For example, 14.0 has three significant figures.
- Counting numbers of objects have infinite significant figures.
Calculations Involving Significant Figures
1. Addition & Subtraction
In addition or subtraction, the final result should be reported to the same number of decimal places as that of the term with the least number of decimal places.
2. Multiplication & Division
In multiplication and division, the result should be reported to the same number of significant figures as the term with least number of significant figures.
Rounding Off the Numerical Results
While limiting the result to the required number of significant figures, the number of significant figures is reduced. For this:
- The last digit retained is increased by 1, if the following digit is ≥ 5.
For example: 25.468 can be written as 25.5
And, 489.654 can be written as 489.7
- The last digit retained is written as such, if the following digit is ≤ 4. For example: 12.93 can be written as 12.9
Check your preparedness by solving the following questions:
1. How to write 235.508 in scientific notation?
(a) 23.5508 × 102 (b) 2.35508 × 102
(c) 235.508 × 10 (d) 2355.08 × 100
2. Number of significant figures in 2.005 are:
(a) Three (b) Two
(c) Zero (d) Four
3. What would be the answer in appropriate significant figures to the addition of 3.0223 and 5.041?
(a) 80.633 (b) 8.063
(c) 806.33 (d) 8.0633