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JEE Chapter - Some Basic Concepts of Chemistry

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Introduction to Some Basic Concepts of Chemistry

Introduction to Some Basic Concepts of Chemistry

Science can be defined as a continuous human attempt to organise knowledge for the purpose of describing and comprehending nature. The production of curd from milk, as well as the production of sugarcane juice vinegar after a lengthy period of time and the rusting of iron, are two instances of changes that occur. We come across this a lot. For the purpose of simplicity. Science is organised into several disciplines: chemistry, biology, geology, and other sciences. The field of research in which investigates the composition, characteristics, structure, and reactions of a substance. Chemistry is the study of material substances.


Important Topics of Some Basic Concepts of Chemistry

  • Properties of Matter and their Measurements

  • Uncertainty of Measurement 

  • Percentage composition

  • Importance of chemistry 

  • Dalton's Atomic Theory

  • Stoichiometry and Stoichiometric calculations

  • Nature of Matter 

  • Atomic and molecular masses

  • Mole concept and molar masses


1. Importance of Chemistry

Chemistry is an important part of science that is frequently interwoven with other disciplines. Weather patterns, brain function, computer operation, chemical industry production, making fertilisers, alkalis, acids, salts, dyes, polymers, medicines, soaps, detergents, metals, alloys, and new materials are all examples of where chemistry principles can be applied.


2. Nature of Matter

Matter is defined as everything that has mass and takes up space. Everything around us is made up of matter, including books, pens, pencils, water, air, and all living things.


(a) States of Matter

  • Anything that occupies space, has mass, and whose presence can be felt by any one or more of our five senses is classified as matter.

  • Solid, liquid, and gas are the three physical states in which matter can exist.

  • Solid - a substance is said to be solid if it has a fixed volume and shape, such as sugar, iron, gold, or wood.

  • Liquid- If a substance has a specific volume but no distinct shape, it is said to be liquid. Water, milk, oil, mercury, alcohol, and other liquids take on the shape of the vessel in which they are placed.

  • Gaseous- If a substance has neither a specific volume nor a definite shape, it is said to be gaseous. This is due to the fact that they are completely full.

Gaseous- If a substance has neither a specific volume nor a definite shape, it is said to be gaseous.

(b) Classification of Matter

A mixture contains two or more substances (in any ratio) that are referred to as their constituents.

  • Mixtures: A mixture contains two or more substances (in any ratio) that are referred to as their constituents.

  • A mixture might be homogeneous or heterogeneous.

  • Homogeneous mixture- a homogeneous mixture is one in which all of the components are the same, components are entirely mixed together, and The composition is consistent throughout, i.e. it is made up of only one type of material.  As a result, sugar solution and air are two examples of homogenous mixes a type of mixture in which all of the ingredients are the same.

  • Heterogeneous mixtures- A heterogeneous mixture is one in which the constituents are heterogeneous. The composition is not consistent throughout. There are several phases that can be seen. Grains, for example,  Pulses, as well as some soil (typically stone) fragments, are used.

  • Pure substances:- A material containing only one substance is called a pure substance.

  • A pure substance containing only one type of particle is defined as an element. The elements are further classified based on their physical and chemical properties. Metals are separated into three categories: (1) Metals, (2) Non-Metals, and (3) Metalloids.

  • A compound is a pure material that contains other pure substances, two or more parts combined in a fixed configuration.


3. Properties of Matter and their Measurements

  • Physical attributes are those that may be measured or observed without affecting the substance's identity or composition. Colour, odour, melting point, boiling temperature, density, and other physical qualities are examples.

  • Chemical properties are those in which the substance  must undergo a chemical change. Chemical characteristics include acidity or basicity, combustibility, and other characteristic responses of different compounds.

  • Physical quantities refer to all of the quantities we encounter during our scientific investigations. Any physical quantity is evidently measured in two parts: (1) the number, and (2) the unit.

  • A unit is a unit of measurement that is used to measure any physical amount.

  • The 11th General Conference on Weights and Measures developed the International System of Units (in French, Le Systeme International d'Unités - shortened as SI) (CGPM from Conference Generale des Poids at Measures).

  • The CGPM is an intergovernmental treaty body established by the Metre Convention, a diplomatic convention signed in Paris in 1875.


(a) Mass and Weight

  • The mass of a material is the amount of matter it contains, whereas the weight of a thing is the force exerted by gravity.

  • A substance's mass is constant, but its weight can fluctuate from one location to another due to changes in gravity.

  • The kilogram is the SI unit of mass (kg). The newton is the SI derived unit (a unit derived from SI base units) for weight.


(b) Volume

  • Volume is the amount of three-dimensional space enclosed by a closed boundary, such as the space occupied or contained by a substance (solid, liquid, gas, or plasma). The SI derived unit, the cubic metre, is frequently used to quantify volume numerically.


(c) Density 

  • A material's mass density, sometimes known as density, is defined as its mass per unit volume. The most common symbol for density is (the lowercase Greek letter rho). 

kg m–3 is the SI unit for density.


(d) Temperature

  • The term "temperature" refers to a physical attribute of matter that quantifies the concepts of hot and cold. Temperature is measured using three different scales: °C (degrees Celsius), °F (degrees Fahrenheit), and K (degrees Kelvin).

°F = 9/5 (°C) + 32  

K = °C + 273.15 


4. Uncertainty in Measurement

  • Significant figures are a combination of significant digits that are known with certainty and one that is estimated or questionable. By printing the certain numerals and the last doubtful digit, the uncertainty is communicated. Thus, if a result is written as 11.2 mL, we can state that the 11 is certain and the 2 is unknown, with the uncertainty being +1 in the last digit. An uncertainty of +1 in the last digit is always assumed unless otherwise stated.

  • The number of significant figures is determined according to a set of rules. These are as follows:

(1) All digits that are not zero are significant. For example, there are three significant figures in 285 cm and two significant figures in 0.25 mL.

(2) The zeros before the first non-zero digit are unimportant. The position of the decimal point is indicated by a zero. As a result, 0.03 has one significant figure, while 0.0052 has two.

(3) There are significant zeros between two non-zero digits. As a result, 2.005 is a four-digit number.

(4) If the zeros at the end or right of a number are on the right side of the decimal point, they are significant.

  • Precision refers to how near different measurements for the same quantity are to each other. 

  • Accuracy, on the other hand, is the agreement of a given value with the true value of the result.

  • When working with numbers, it's common to need to convert units from one system to another. Factor label method, unit factor method, or dimensional analysis are the methods used to do this.


5. Laws of Chemical Combinations

(a) Law of Conservation of Mass

"Mass is conserved in a chemical reaction because the mass of reactants used and the mass of products generated are the same." This is a direct result of the atomic conservation rule. In 1789, Antoine Lavoisier proposed this law.


(b) Law of Constant / Definite Proportions

The proportions in which two or more elements combine to form a compound stay constant and are unaffected by the compound's source. Joseph Proust, a French chemist, gave this law.


(c) Law of Multiple Proportions

The ratio of masses of one element that combines with a fixed mass of the other element in the two compounds is a simple whole-number ratio when two elements mix to generate two or more compounds. Dalton proposed this legislation in 1803.


(d) Law of Reciprocal Proportions

When three elements combine in a combination of two to make three compounds, the ratio of the masses of the two elements combined with the fixed mass of the third and the ratio in which they combine are both simple whole-number ratios. Richter enacted this law in 1792.


(e) Gay Lussac’s Law of Gaseous Volumes

Gay Lussac gave this law in 1808. When gases join or are generated in a chemical process, he discovered that they do so in a simple volume ratio if all gases are at the same temperature and pressure.


(f) Avogadro Law

Avogadro hypothesised in 1811 that equal quantities of gases at the same temperature and pressure contain the same number of molecules.


6. Dalton's Atomic Theory

Dalton wrote 'A New System of Chemical Philosophy' in 1808, in which he proposed:

1. The matter is made up of indestructible atoms.

2. The properties of all atoms of a given element are the same, including their mass. The mass of atoms in different elements varies.

3. When atoms of different elements mix in a specific ratio, compounds are produced.

4. Chemical processes entail atom reconfiguration. In a chemical reaction, they are neither generated nor destroyed.


7. Atomic and Molecular Masses

  • The mass of one carbon atom is 12 to one-twelfth of the mass of one carbon atom - 12 atoms. Moreover, 1 amu = 1.6605610–24 g.

  • ‘Amu’ has been replaced by ‘u’, which is known as a unified mass.

  • The total of the atomic masses of the atoms in a molecule is called molecular mass. It's calculated by multiplying each element's atomic mass by the number of atoms in its nucleus and adding the results.


8. Mole concept and Molar Masses

  • The mole (sign mol) is the SI unit of material quantity. There are exactly 

  • 6.02214076 x1023 elementary entities in one mole.

  • This is the Avogadro number, which is the fixed numerical value of the Avogadro constant, NA, as represented in the unit mol–1. A system's amount of substance, denoted by the symbol n, is a count of the number of defined elementary things.

  • The molar mass of a substance is the mass of one mole in grammes. The atomic/molecular/formula mass in u is mathematically equal to the molar mass in grams.


9. Percentage Composition

The percentage composition of both these elements can be calculated as follows: 

Mass % of an element 

= mass of that element in the compound/ molar mass of the compound ×100

The molecular formula displays the exact number of distinct types of atoms present in a molecule of a compound, whereas the empirical formula shows the simplest whole-number ratio of various atoms present in a compound.


10. Stoichiometry and Stoichiometric Calculations

  • Stoichiometry is the study of chemical processes and the calculations that go along with them. Stoichiometric coefficients are the coefficients that are utilised to balance the reaction.

  • If the reactants are not mixed in stoichiometric proportions, the reactant that is present in less than the needed amount affects how much product is created and is known as the Limiting Reagent, while the reactant that is present in excess is known as the Excess Reagent.

  • Mole fraction “X “ is defined as the moles of a component / Total moles of solution.

  • Mass% is defined as the Mass of solute (in g) present in 100g of solution.

  • Molarity (M) is defined as moles of solute/volume of solution (L).

  • Molality (m)  is defined as moles of solute /mass of solvent (kg).


Solved Examples from Chapter

Example 1: Is the constant composition law applicable to all sorts of compounds? 

Sol. No, the law of constant composition does not apply to all compounds. This is only true for compounds made from a single isotope. Carbon, for example, has two common isotopes: 12C and 14C.


Key point to remember: Need to remember the Law of Constant Proportions.

 

Example 2: Why should the Law of Conservation of Mass be renamed the Law of Conservation of Mass and Energy?

Sol. The mass of the products in nuclear reactions is found to be less than the mass of the reactants. According to Einstein's equation, E = ∆mc2, the mass discrepancy, also known as the mass defect, is turned into energy. As a result, we should refer to it as a law of mass and energy conservation.


Key point to remember: According to the law of conservation of mass, the mass of products is equal to the mass of reactants.


Solved Examples from Previous Year’s Questions

Question 1:Select dimensionless quantity(ies):

(a) vapour density 

(b) molality

(c) specific gravity

(d) mass fraction

Solution: The dimensionless quantities are

Vapour density

Specific gravity

Mass fraction

Therefore, options (a,c,d) are the answer.

Trick: Physical quantities are of two types dimensional and dimensionless.

 

Question2: 2.76 g of silver carbonate on being strongly heated yields a residue weighing

(a) 2.16 g

(b) 2.48 g

(c) 2.32 g

(d) 2.64 g

Solution: 2Ag2CO3(s) →4Ag(s) + 2CO2(g) + O2(g)

So, strongly heating silver carbonate will produce silver.

No of moles of silver carbonate = 2.76 g/ 275.7g = 0.0100

275.7 g of Ag2CO3 produces 108 x 2 g of Ag.

2.76 g will produce = 108 x 2 x 2.76 / 275.7 = 2.16 g of silver.

Therefore,  option (a) is the answer.

Trick:  Need to remember the Law of conservation of mass as the mass of products is equal to the mass of products.


Question 3: 11.2 L of a gas at STP weighs 14 g. The gas could be :

(a) N2

(b) CO

(c) NO

(d) N2O

Solution: 11.2L of an ideal gas at STP =0.5 moles.

0.5moles = 14g

​1mole = 28g

​It could be any gas that has a molar mass equal to or closer to 28g/mole. (Nitrogen, molar mass=28 g/mol)

⟹ The gas could be N2.

​Therefore,  option (a) is the answer

Trick: Need to remember the mole concept.


Practice Questions

1. If we consider that 1/6, in place of 1/12, the mass of a carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will 

(a) be a function of the molecular mass of the substance

(b) remain unchanged

(c) increase two-fold 

(d) decrease twice

Answer: (d) decrease twice


Question 2: The ratio of masses of oxygen and nitrogen in a particular gaseous mixture is 1 : 4. The ratio of number of their molecule is : 

(a) 7 : 32 

(b) 1 : 8

(c) 3 : 16 

(d) 1 : 4

Answer: (a) 7 : 32


Conclusion

Chemistry is an important subject to study because its domain spans all aspects of life. Chemists investigate the qualities and structure of substances, as well as the changes that they undergo. Matter is found in all substances and can exist in three states: solid, liquid, or gas. In these states of matter, the component particles are retained in various ways and exhibit their unique features. Elements, compounds, and mixes are all types of matter. An element is made up of only one type of particle, such as atoms or molecules. Compounds are created when atoms from two or more elements mix in a specific ratio. Mixtures are common, and many of the compounds in our environment are mixtures.

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FAQs on JEE Chapter - Some Basic Concepts of Chemistry

FAQ

1. Is it necessary to understand some basic chemistry concepts?

Many industrially generated fertilisers, alkalis, acids, salts, dyes, polymers, medicines, soaps, detergents, metal alloys, and other inorganic and organic chemicals, as well as novel materials, owe their existence to chemistry.

2. What are the many types of chemistry?

Chemistry is traditionally divided into five subdisciplines: organic, analytical, physical, inorganic, and biochemistry.

3. Which of the two major branches of chemistry that we are familiar with?

Chemistry is separated into branches based on the substances investigated or the types of research performed. The first category is divided into two parts: inorganic chemistry and organic chemistry. Physical chemistry and analytical chemistry are two divisions of the second category.