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Some basic concepts of chemistry are important chapters in NCERT Class 11 Chemistry. It helps study important topics such as the law of chemical combinations, molarity, normality and the mole concept.
- Some basic concepts of Chemistry include Stochiochemistry, Theory, and Laws.
- Chemistry deals with chemical atoms and molecules along with the different states of matter like solid, liquid and gas.
- It is also known as Central Science.
- Chemistry is interconnected with Geology, Biology, Environmental Science and Physics.
- Ancient Indians had a wide knowledge of the subject before it was introduced.
- Chemical reactions and the formula help find the relationship between two atoms or two molecules.
- It plays an important role in linking physical sciences with applied sciences and life sciences.
- The concept of the subject was used in the fields of engineering, food and drug industry.
- Soap and detergents used in everyday life use the emulsification concept of chemistry.
Key Terms: Some basic concepts of Chemistry, Chemistry, Matter, Solid, Liquid, Gas, Chemical Reactions, Molecules, Atoms, Homogeneous, Heterogeneous, Mixture, Molality, Molarity, Mole, Compounds
Importance of Chemistry
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Chemistry is a vast subject and for understanding its significance we can take help of following points:
- Chemistry plays an important role in understanding various subjects like physics, geology and biology.
- It is a core branch of science that explains us about the various compositional properties and interaction of matter.
- The subject also helps to understand various chemical reactions.
- Chemistry is important to understand the behaviour of fertilizers, alkanes, acid, salts.
- It also helps in dyes, polymers, drugs, soaps and alloys in organic and inorganic chemistry.
- Chemistry plays an important role in various fields like healthcare, industrial, research, food, and farm activities.
Classification of Chemistry
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There are five main branches of chemistry which are as follows:
Physical Chemistry
Physical Chemistry is the branch of chemistry that studies the structure of matter, the state of change of energy, scientific theories and principles at the macroscopic level.
Inorganic Chemistry
Inorganic chemistry is the branch of chemistry that deals with the study of compounds other than carbon and hydrogen.
Organic Chemistry
Organic Chemistry is the branch of chemistry that deals with the study of the properties and compounds of carbon.
Biochemistry
Biochemistry is the branch of chemistry that deals with the study of living organisms. It connects biology and chemistry together.
Analytical Chemistry
Analytical Chemistry is the branch of chemistry that studies the structure, functionalities and properties of substances.
Nature of Matter
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Matter can be defined as anything which has mass and occupies space. It exists in the three types of states namely solid, liquid and gas.
Nature of Matter
Solid State
In solid state, atoms are very closely packed together and there is very little space in between them. It has a definite shape and definite volume.
Liquid State
In liquid state, particles are loosely packed together. In comparison with solid state, particles have more freedom of movement in liquid state. It has a definite volume but do not have a definite shape. They take the shape of the container .
Gaseous State
In gaseous state, particles are very far from each other and can move freely inside the container. They neither have a definite shape nor have a definite volume. It also take the shape of the container in which they are kept.
Example of Nature of MatterExample: Matter can be transformed from one state to another by heating or cooling them. For example, by heating a solid at very high temperatures, it converts into liquid state and if we continue heating, then it converts into gas. |
Nature of Matter
Now, when you are using a huge amount of matter then it will be classified as a mixture and pure substance and both are further classified in the category. Matter can be classified into the following categories:
Mixtures
Mixture is a type of substance that involves addition of two or more substance in any ratio. It is of two types namely Homogeneous and Heterogeneous mixtures.
Homogenous Mixtures
Homogeneous mixture can be defined as a mixture where the composition of the mixture is uniform throughout. It does not have a uniform motion throughout the reaction
Heterogeneous Mixtures
Heterogeneous mixtures are types of mixture where all the elements don't mix up. It has a non uniform motion between the elements.
VS 
Homogeneous and Heterogeneous mixture
Pure Substances
Pure substances are those which have fixed composition. It can be further divided into elements and compounds. An element can be of one type only while the compounds have elements of different types.
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Pure Substances
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Important Topics for JEE MainAs per JEE Main 2024 Session 1, important topics included in the chapter Some Basic Concepts of Chemistry are as follows:
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International System of Units (SI)
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The International System of Units (SI) was first established in eleventh century by General Conference on Weights and Measures. It is divided into seven base units which is summarized in table below which are as follows:
| Name of quantity | Symbol of quantity | Name of SI unit | Symbol of SI unit |
|---|---|---|---|
| Length | l | meter | m |
| Mass | m | kilogram | kg |
| Luminous intensity | Iv | candela | cd |
| Amount of substance | n | mole | mol |
| Temperature | T | kelvin | k |
| Electric current | I | Ampere | A |
| Time | t | second | s |
Important Definitions in Chemistry
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The important definitions used in chemistry are as follows:
Mass and Weight
Mass of any substance is the amount of matter present in that compound while weight is defined as a force extracted by the gravity on the object.
- The mass of any particular subject is a constant entity.
- Weight of any particular object varies from one place to another place.
- The SI unit of mass is kilogram.
Mass and Weight
Volume
Volume is defined as an amount of matter filled in the container. An SI unit of volume is the length cube and the unit of it is a m3. But in chemistry we are using smaller units of volume like cm3 or dm3.
- 1 L = 1000 ml
- 1000 cm3= 1 dm3
Volume
Density
Density of any particular compound is defined as the amount of mass per unit volume of that compound.
- So, Density= SI Unit of mass/Si unit of volume
- kg/m3
Density
Temperature
There are a total of three scales for mapping temperature namely celsius, fahrenheit and kelvin. But we mostly use a kelvin unit for better understanding. K is the SI unit of the temperature.
- The celsius scale is calibrated in between 0 and 100.
- The fahrenheit scale is calibrated in between the 32 to 212 degree celsius.
Degree F = 9/5(degree celsius) + 32
K= degree celsius + 273.15
Temperature
Law of Chemical Combination
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The law of chemical combination are divided into five categories which are as follows:
Law of Conservation of Mass
Law of Conservation of Mass states that the mass of reactants that are consumed is equal to the mass of products formed is same. This means total mass remains conserved.
Law of Multiple Proportions
Law of Multiple Proportions states that when two elements of compounds combine to form one single compound then weight of an element is directly proportionalto the other weight of other element.
Law of Reciprocal Proportions
Law of Reciprocal Proportions states that when two different elements of compounds are combined with mass of the third element then their mass ratio is same. The law was proposed by Richter in 1792.
Gay Lussac’s Law of Gaseous Volumes
Gay Lussac’s Law of Gaseous Volumes states that when gaseous particles react with each other then they so in volumes which is represented by the ratio which is equivalent to whole number.
Avogadro Law
Avogadro Law states that equal volume of gases found at same pressure and temperature is equivalent to number of molecules.
Atomic and Molecular Mass
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Atomic Mass is defined as a mass of the atom. As atoms are extremely small in size, the atomic mass of the atoms is also extremely small. Hydrogen is the lightest atom and the mass of the hydrogen is 1.
- Relative to the mass of hydrogen, other atoms are assigned their mass.
- Earlier, the unit of the atomic mass was amu but later it was replaced by “u”.
- Exact mass of the hydrogen atom = 1.008 amu
Molecular Mass
Molecular Mass is defined as the sum of atomic masses of all the elements that are found in a molecule. It is determined by the multiplying the atomic mass of all the element by the number of its atoms and finally add them together.
Example of Molecular MassExample: Calculate the molecular mass of the glucose. Ans: The chemical formula of glucose is C6H12O6. So, molecular weight = 6(weight of carbon atom)+12(weight of hydrogen atom)+6(weight of oxygen atom) = 6(12.011 u )+12(1.008 u )+6(16.00 u) = 180.162u So, the molecular weight of glucose is 180.162 u . |
Atomic Mass
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Mole Concept and Molar Mass
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Some basic concepts of chemistry includes mole concept and molar mass which are as follows:
Mole Concept
Mole is defined as the amount of a substance that can accomodate as many particles as there are atoms in exactly 12 g (or 0.012 kg) of the 12C isotope. If one mole of carbon is found to be 12 g then number of atoms is equal to 6.0221367 x 1023 atoms/mol.
- The number of atoms obtained is also known as Avogadro constant.
Molar Mass
Molar Mass is defined as the mass of one mole of the required substance in grams.
Stoichiometry
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Stoichiometry is defined as the branch of chemistry that studies about the chemical reactions taking place for a substance. It also takes into account the calculations involved in the reactions.
- The coefficients used to balance the chemical reaction involved is called stiochiometry coefficient.
- It is the ratio of moles of molecules of required atom.
- If less quantity of reagent determines how much product is formed then it is called limiting reagent (LR).
- If more quantity of reagent determines how much product is formed then it is called Excess reagent (ER).
Things to Remember
- Some Basic Concepts of Chemistry deals with atoms and molecules, along with their relation and reactions to other matter in the universe.
- Chemistry is the study of the particles making up the composition of the world.
- It is vital for the cohesive functioning of various industries like healthcare, industrial, research, food, and agricultural activities.
- Matter can be defined as anything which has mass and occupies space.
- Kelvin is the SI unit of the temperature.
- Hydrogen is the lightest atom and the mass of the hydrogen is 1.
- NCERT Solutions For Class 11 Chemistry Chapter 1: Some Basic Concepts of Chemistry and Some Basic Concepts of Chemistry: Important Questions are designed for students preparation.
- For practical purposes students can practice MCQ On Some Basic Concepts of Chemistry: Introduction & Explanation.
Previous Years questions
- Calculate the molar mass of sulfur.
- The equivalent weight of metal carbonate is
- The heat of neutralization is
- 2NHCl solution will have same molar concentration as a
- Mass of sodium nitrate absorbing 1 mole of electron will be
- An unknown element forms an oxide. What will be the equivalent weight of the element if the oxygen content is 20% by weight?
- 1 mole of methyl amine on reaction with nitrous acid gives at NTP
- A metal M (specific heat 0.16) forms a metal chloride with =65% chlorine present in it. The formula of the metal chloride will be
- The weight of oxalic acid that will be required to prepare a 1000mL (N20) solution is
- The fraction of the total pressure exerted by H2 is
- An organic compound made of C,H and N contains 20% nitrogen. Its molecular weight is :
Sample Questions
Ques. Solve the following questions (A) Classify the following into either pure substances or mixtures: Air, Glucose, Gas, Sodium, milk.
(B) What are the systems of measurement? (2 marks)
Ans. (A) Pure substances: Glucose, gold, sodium
- Mixture: Air, Milk
(B) There are two different systems of measurement named the english system and the metric system .
Ques. Show the difference between precision and accuracy? (4 marks)
Ans. The difference between precision and accuracy are as follows:
| Precision | Accuracy |
|---|---|
| Precision is the value that are closest to the value. | Accuracy is defined as the value closest to the true value. |
| It is calculated by using double measurement. | It is calculated by using single measurement. |
| Precision is affected by random error value. | Accuracy is affected by systematic error value. |
| It produce degree of reproductibility. | It produce degree of conformity. |
Ques. Explain the following: (A) State Law of Definite Proportions
(B) Define the value of 1 mole? (2 marks)
Ans. (A) It states that, “A given compound always contains exactly the same proportion of element by weight”.
(B) 1 mole= 6.022 x 1023 atoms/irons/entities.
Ques: What is the element mass number when the atomic number is 20 and the neutron number is 22? (3 marks)
Ans: No. of Neutrons = 22
No. of Protons = 20
Atomic mass number= No. of protons + No. of neutrons
A= 20+22
Mass no. = 42
Ques. Determine the mass of urea (NH2CONH2) which will be needed to make 4.5 kg of 0.45 molal aqueous solution? (3 marks)
Ans. As per the given question,
Moles of urea = 0.45 mole
Mass of solvent (NH2CONH2) = 60 g mol-1
Thus, it can be said that, 0.25 mole of urea = 0.45 x 60 = 27g
Mass of solution = 1000 + 27
= 1027 g
= 1.027 kg
1.027 kg of urea solution is known to have 27g of urea
∴∴ 4.5 kg of solution urea =27/1.027 x 4.5
= 58 g
Ques. 2 ml of water is added to 10g of a powdered drug. The final volume is 3ml. Find the mass-by-volume percentage of the solution? (2 marks)
Ans. Given, Mass of solute = 10 g
- Volume of solution = 2 ml
- Mass by volume percentage
- (Mass of solute) / (volume of solution) × 100 %.
- (10 / 2) × 100 %
- 500%.
- Therefore, the mass by volume percentage is 500%.
Ques. Calculate the moles when Fe = 8.85g? (3 marks)
Ans. 56g Fe has 6.022 × 1023 atoms = 1 mole
56g Fe = 1 mole
So, 8.85g Fe = 1/56 × 8.85
= 0.0201 moles.
Ques. If the initial volume is 3 litres, the initial molarity is 6M and the final volume is 6 litres. Find the Final Molarity. Consider final molarity to be M2? (3 marks)
Ans. The relation between molarity and volume is
M1V1 = M2V2
6M × 3L = M2 × 6L
M2 = 6M × 3L/6L
= 3M
Ques. A gas has a volume of 4.31 l at 0.655 atm pressure. Calculate the volume if the pressure is changed to 2.25 atm? (2 marks)
Ans. From the Boyle’s law,
Initial pressure* initial volume= Final pressure*Final volume,
i.e., P1V1 = P2V2
Let final volume = x
So, 0.655*4.31 = 2.25*x
x = 0.655*4.31/2.25
x = 1.25 liters
Ques. A container holds 600. mL of CO2 at 30.° C and 900 torr. What will be the volume of the CO2 if the pressure is increased to 1200 torr? (2 marks)
Ans. P1= 900 torr
P2 = 1200 torr
V1 = 600. mL
V2 = ?
P1V1 = P2V2
V2 = P1V1/P2
V2= 600 torr x 900. mL/1200 torr
V2= 450 mL CO2
Ques: Water is formed when hydrogen and oxygen mix in a mass ratio of 1:27. How much oxygen gas would it take to totally react with 3 g of hydrogen gas? (2 marks)
Ans: According to the question, 1 gram of Hydrogen reacts with 27 grams of Oxygen
So, 3 grams of Hydrogen will react with 27 x 3 grams = 81 grams
So, 81 grams of oxygen is required to make water.
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