Unit 1 Some Basic Concepts Of Chemistry

VERY SHORT QUESTIONS ANSWER

Q.1.What are the number of significant figures in 0.001620?

Ans. Four.

Q.2.The height of a person is 155.01cm.what is the least count of the scale used?

Ans.01.

Q.3.What is that S.I. unit of energy?

Ans. Joule.

Q.4.Express 5.607892 to four significant figures and write the result in standard form.

Ans.5.608 ×10^6.

Q.5.Express the result of to the appropriate number of significant figures.

Ans.0.561.

Q.6. Is brass a compound or a mixture?

Ans. It is a mixture.

Q.7.What are the number of significant figures in 0.002360?

Ans. Four.

Q.8.How many grams are present in 5.6 liters of CO₂ at N.T.P.?

Ans. 11 grams.

Q.9.The height of a person is 163.07 cm. What is the least count of the scale used?

Ans.0.01 cm.

Q.10. Define the term ’unit of measurement?

Ans. A unit of measurement is a standardized quantity used to quantify and compare different attributes or properties of objects or phenomena.

Q.11.What is the relationship in G.M.W and G.M.V?

Ans. G.M.W. and G.M.V. are usually synonymous terms, both representing the total value of goods or services transacted through a platform or marketplace.

Q.12.What is matter?

Ans. Matter is anything that occupies space and has mass.

Q.13.What are mixtures?

Ans. Mixtures are combinations of two or more substances that are physically intermingled but not chemically bonded.

Q.14.What is homogeneous mixture?

Ans. A homogeneous mixture is a mixture with uniform composition, where the components are evenly distributed and not visibly distinguishable.

Q.15.What is homogenecous mixture?

Ans. Heterogeneous these do not have uniform composition e.g. mixtures.

Q.16.Name physical quantities which are represented by the following units and give their most common names:

(A). kg m²s^-2 (B) kg ms^-2

Ans. (a) Energy, joule (b) Force, Newton.

Q.17. Is low of constant composition true for all types of compounds?

Ans. no, the law of constant composition does not hold true for all types of compounds.

Q.18.Which method will be used for separating a mixture of two components having different adsorbing tendencies on an adsorbate?

Ans. Chromatography.

Q.19. Define area (A)?

Ans. Area (A) =Length x Length =m x m = m²

Q.20.Define unit of work (W)?

Ans. The unit of work (W) is defined as the joule (J).

Q.21. Define Energy?

Ans. Energy is the ability or capacity to do work, it comes in various forms such as kinetic, potential, thermal, chemical, electrical, etc. and is essential for all processes and phenomena in the universe.

Q.22.What is a compound?

Ans. A compound is a substance composed of two or more different elements chemically bonded together.

Q.23.Define Element?

Ans. An element is a pure substance composed of only one type of atom.

Q.24.Define an organic compound Give one example?

Ans. An organic compound is a compound primarily composed of carbon atoms bonded to hydrogen atoms and may also include other elements like oxygen, nitrogen, etc.

Example: Ethanol (C2H5OH)

Q.25.Define an inorganic compound Give one example?

Ans. An inorganic compound is a compound that does not primarily contain carbon-hydrogen (C-H) bonds.

Example: Sodium chloride (NaCl)

Q.26.What does S.T.P. Stand for?

Ans. S.T.P. stands for Standard Temperature and Pressure.

Q.27.Define Avogadro’s Low?

Ans. Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain an equal number of molecules.

Q.28.What is gram atomic mass Give one example?

Ans. Gram atomic mass is the mass of one mole of atoms of an element, expressed in grams.

Example: The gram atomic mass of carbon (C) is approximately 12.01 grams per mole.

Q.29.Define mole in terms of number?

Ans. A mole is a unit of measurement that represents Avogadro's number (approximately 6.022 x 10^23) of particles, such as atoms, molecules, ions, or other entities in a substance.

Q.30. Give important applications of Avogadro’s Law?

1. Ans. Determination of molar volume

2. Gas stoichiometry

3. Ideal Gas Law

4. Determination of molar mass

5. Understanding gas behavior

Q.31. Define a chemical equation?

Ans. A chemical equation is a symbolic representation of a chemical reaction, showing the reactants on the left side and the products on the right side, separated by an arrow.

Q.32.State the law of multiple proportion?

Ans. The law of multiple proportions states that when elements combine to form different compounds, the ratios of the masses of one element that combine with a fixed mass of the other element can be expressed in small whole numbers.

Q.33. How many electrons are present in 16 g of CH₄?

Ans. I molecule of CH₄ = 6 + 4 = 10 electrons.

Q.34.What is the relationship between atomic weight and equivalent weight of an element?

Ans. The relationship between the atomic weight and equivalent weight of an element is that the equivalent weight is equal to the atomic weight divided by the valency (or the number of electrons exchanged in a chemical reaction).

SHORT QUESTIONS ANSWER

Q.1.What is the difference between 4.0 g and 4.00 g?

Ans. The difference between 4.0 g and 4.00 g lies in the level of precision in their measurements.

4.0 g implies that the value has one significant figure, indicating a precision to the tenths place (±0.1 g).

4.00 g, on the other hand, indicates a value with two significant figures, showing precision to the hundredths place (±0.01 g).

In summary, 4.00 g has a higher level of precision compared to 4.0 g.

Q.2.Write main postulates of Dalton‘s Theory?

Ans. Dalton's Atomic Theory, proposed by John Dalton in the early 19th century, consists of the following main postulates:

Elements are composed of indivisible and indestructible particles called atoms.

All atoms of a given element are identical in mass and properties, while atoms of different elements have different masses and properties.

Atoms combine in whole-number ratios to form compounds.

In chemical reactions, atoms are rearranged, but they are neither created nor destroyed.

Atoms of different elements can combine to form compounds in fixed ratios.

These postulates formed the foundation of modern atomic theory and greatly contributed to our understanding of the nature of matter and chemical reactions.

Q.3. Give the points of difference between mixture and compound?

Ans. Points of difference between mixture and compound:

Definition:

Mixture: A mixture is a combination of two or more substances in which each substance retains its individual properties, and they are physically intermingled.

Compound: A compound is a substance composed of two or more different elements chemically bonded together in fixed proportions.

Composition:

Mixture: The composition of a mixture can vary, and the substances involved can be present in any proportion.

Compound: Compounds have a fixed chemical composition, with elements always present in specific and definite ratios.

Separation:

Mixture: Components of a mixture can be separated by physical methods, such as filtration, distillation, or chromatography.

Compound: Compounds can only be separated into their constituent elements through chemical reactions.

Properties:

Mixture: Each component in a mixture retains its individual properties, and the properties of a mixture are a combination of the properties of its constituents.

Compound: Compounds have unique properties different from those of the elements they are composed of.

Formation:

Mixture: Mixtures are formed by physically mixing substances.

Compound: Compounds are formed by chemical bonding between elements.

Examples:

Mixture: Air (a mixture of gases), saltwater (a mixture of salt and water).

Compound: Water (H2O), carbon dioxide (CO2).

In summary, mixtures are physically combined substances with variable composition, while compounds are chemically bonded substances with fixed composition and unique properties.

Q.4.Write some important postulates of Modern Atomic Theory?

Ans. Some important postulates of Modern Atomic Theory include:

Atoms are composed of subatomic particles: Atoms are no longer considered indivisible. They are made up of subatomic particles, namely protons, neutrons, and electrons.

Nucleus and electron cloud model: The atom has a central nucleus containing protons and neutrons, while electrons exist in orbits or energy levels around the nucleus.

Neutral atom and atomic number: In a neutral atom, the number of protons is equal to the number of electrons. The atomic number represents the number of protons in the nucleus of an atom, defining its unique identity.

Isotopes: Atoms of the same element can have different numbers of neutrons, resulting in isotopes with varying atomic masses.

Electron configuration and energy levels: Electrons occupy specific energy levels or shells around the nucleus, and each shell can accommodate a specific number of electrons.

Quantum mechanics: The behavior of subatomic particles is described by quantum mechanics, involving wave-particle duality and quantized energy levels.

Chemical bonding: Atoms can form chemical bonds by sharing, gaining, or losing electrons to achieve a stable electron configuration.

Conservation of mass and energy: The total mass and energy are conserved in chemical reactions. Atoms are rearranged, but no atoms are created or destroyed.

These postulates, based on experimental evidence and quantum theory, form the foundation of our current understanding of atoms and their behavior in chemistry and physics.

Q.5.Write some applications of mole concept?

Ans. The mole concept is a fundamental concept in chemistry that has various applications, including:

Stoichiometry: The mole concept enables stoichiometric calculations, where the quantities of reactants and products in a chemical reaction are determined based on their molar ratios.

Balancing chemical equations: Using the mole concept, chemical equations can be balanced by ensuring that the same number of moles of each element are present on both sides of the equation.

Determining empirical and molecular formulas: The mole concept allows the determination of empirical and molecular formulas based on the molar ratios of elements in a compound.

Concentration calculations: The concept of molarity (moles of solute per liter of solution) is used to express the concentration of a solution in various chemical processes.

Gas laws: The mole concept is essential in the study of gas laws, such as the Ideal Gas Law, which involves the number of moles of gas in a given volume.

Mass-mole conversions: The mole concept facilitates conversions between the mass of a substance and its molar quantity, aiding in various calculations in chemical reactions.

Limiting reactant calculations: The mole concept helps identify the limiting reactant in a chemical reaction, which determines the maximum amount of product that can be formed.

Percent composition: The mole concept allows the determination of the percent composition of elements in a compound based on their molar masses.

Overall, the mole concept is a versatile tool used to understand and solve a wide range of chemical problems and calculations in various fields of chemistry.

Q.6.What do you mean by limiting reagent or limiting reactant?

Ans. The limiting reagent, also known as the limiting reactant, is a key concept in stoichiometry that refers to the reactant that limits the amount of product that can be formed in a chemical reaction. In other words, it is the reactant that is completely consumed or used up during the reaction, determining the maximum amount of product that can be produced.

When two or more reactants are involved in a chemical reaction, they react according to their stoichiometric ratios based on their coefficients in the balanced chemical equation. The reactant that is present in lesser molar quantity compared to the stoichiometric ratio will be the limiting reagent. Once this limiting reagent is consumed, the reaction stops, and any excess of the other reactant(s) remains unreacted.

To find the limiting reagent, one can compare the amounts of each reactant given or available and calculate how much product can be formed from each. The reactant that yields the smallest amount of product is the limiting reagent.

It is essential to identify the limiting reagent accurately in order to calculate the theoretical yield (the maximum amount of product that can be obtained) and to understand the actual yield (the amount of product obtained in a real-world scenario). Stoichiometric calculations are based on the amount of the limiting reagent, as it governs the reaction's outcome.

Q.7.Draw a pictorial presentation for a mole?

Ans. As an AI language model, I don't have the capability to draw images directly. However, I can describe a simple pictorial representation of a mole:

Imagine a group of objects, such as balls or spheres, all of the same size and color. Each ball represents a single particle, like an atom or a molecule. Now, gather a specific number of these balls together to form a group or a pile.

This group of balls represents one mole of particles. The number of balls in this pile corresponds to Avogadro's number, which is approximately 6.022 x 10^23 particles. This large quantity of particles is what a mole represents in chemistry.

Please keep in mind that this is a simplified visual representation to help you grasp the concept of a mole. In reality, individual particles are too tiny to see and count individually, but Avogadro's number represents the incredibly large scale of particles in a mole.

Q.8.What is balancing of chemical equation? On what principle the balancing of a chemical equation is based?

Ans. Balancing a chemical equation is the process of adjusting the coefficients of reactants and products to ensure that the same number of atoms of each element are present on both sides of the equation. It follows the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction.

When balancing a chemical equation, the total number of atoms of each element must be the same on both sides of the equation to maintain the principle of mass conservation. This is because atoms cannot be created or destroyed during a chemical reaction; they can only rearrange to form new compounds.

The steps to balance a chemical equation involve:

Write the unbalanced equation, showing the reactants on the left and the products on the right, separated by an arrow.

Identify the number of atoms of each element present on both sides of the equation.

Start balancing by adjusting the coefficients (whole numbers) in front of the compounds, making sure the number of atoms of each element is the same on both sides.

Continue adjusting coefficients until the equation is balanced, with equal numbers of atoms of each element on both sides.

The balanced equation provides a quantitative representation of the chemical reaction, showing the relative amounts of reactants and products involved, based on the law of conservation of mass. It is a crucial tool for understanding chemical reactions and performing stoichiometric calculations.

Q.9.What are the limitations of a chemical equation how these limitations could be removed?

Ans. The limitations of a chemical equation are as follows:

Lack of Information on Reaction Conditions: Chemical equations do not provide information about reaction conditions such as temperature, pressure, catalysts, or the speed of the reaction.

Incomplete Representation: Chemical equations may not fully capture all the intermediate steps or side reactions that occur during a complex chemical process.

No Information on Mechanism: Chemical equations do not reveal the detailed reaction mechanisms or the path the reaction takes to form products.

Idealized Stoichiometry: Chemical equations assume perfect stoichiometry, but in real-world reactions, actual yields may be different due to limitations like side reactions, impurities, or incomplete conversions.

To remove these limitations, additional information and techniques can be employed:

Reaction Conditions: Provide relevant information about the reaction conditions, such as temperature, pressure, and catalysts, to get a more comprehensive understanding of the reaction.

Mechanism Studies: Experimental techniques, like kinetic studies and spectroscopy, can help reveal the detailed mechanism and intermediate steps of a reaction.

Stoichiometry Adjustments: Use stoichiometry and stoichiometric calculations to account for impurities or to determine the actual yield of a reaction.

Mechanistic Studies: Conducting mechanistic studies using advanced techniques like computational chemistry or NMR spectroscopy can provide insights into reaction pathways and intermediates.

While chemical equations provide a useful framework to represent reactions, these limitations can be addressed through additional experimental data and theoretical studies, allowing for a more accurate and comprehensive understanding of chemical processes.

Q.10. Explain the terms empirical and molecular formulae of a compound how are they related to each other?

Ans. Empirical Formula: The empirical formula of a compound represents the simplest whole-number ratio of atoms of each element present in the compound. It does not provide the actual number of atoms or the arrangement of atoms in the molecule. The empirical formula is derived from the percentage composition or experimental data of a compound.

Molecular Formula: The molecular formula of a compound shows the actual number of atoms of each element present in a single molecule of the compound. It provides the true representation of the composition of the molecule.

Relationship between Empirical and Molecular Formulae: The molecular formula is related to the empirical formula through a simple integer multiple. If the compound's molecular formula is known, the empirical formula can be determined by dividing the subscripts of each element in the molecular formula by their greatest common divisor (GCD).

For example, if the molecular formula of a compound is C6H12O6, the empirical formula can be found by dividing each subscript (6, 12, 6) by their GCD (6), resulting in the empirical formula CH2O.

On the other hand, if only the empirical formula is known, the molecular formula can be obtained by determining the actual molar mass of the compound and comparing it with the empirical formula's molar mass. The molecular formula will be a whole number multiple of the empirical formula to match the actual molar mass.

In summary, the empirical formula gives the simplest ratio of atoms in a compound, while the molecular formula provides the actual number of atoms in a molecule. The two are related by a whole-number multiple, allowing the determination of one from the other given the necessary data.