Higher Secondary Plus One Chemistry Notes for Kerala Board Syllabus. It’s a fascinating subject that helps us understand the world around us at a molecular level. Hsslive.net provided Plus One Chemistry notes for students. Topics- “Some Basic Concepts of Chemistry” that are usually covered in the first year of chemistry at the higher secondary level. valuable for both Kerala Syllabus and CBSE students with knowledge cultivated over two decades of teaching experience.
Some Basic Concepts of Chemistry
Chemistry is the study of matter and the changes it can undergo. Matter is anything that has mass and occupies space. Matter can be classified into different types based on its physical state (solid, liquid, or gas), composition (element, compound, or mixture), and properties (physical or chemical).
Some basic concepts of chemistry that we will learn in this chapter are:
- The International System of Units (SI) and the rules for using them.
- The concepts of atomic mass, molecular mass, formula mass, and molar mass.
- The laws of chemical combination and their applications.
- The mole concept and its relation to mass, volume, and number of particles.
- The methods of expressing concentration of solutions.
- The calculations involving stoichiometry and limiting reagents.
The International System of Units (SI)
The International System of Units (SI) is a standard system of measurement that is widely used in science and engineering. It consists of seven base units and several derived units. The base units are:
- Metre (m) for length
- Kilogram (kg) for mass
- Second (s) for time
- Ampere (A) for electric current
- Kelvin (K) for temperature
- Mole (mol) for amount of substance
- Candela (cd) for luminous intensity
The derived units are obtained by combining the base units with appropriate prefixes and exponents. For example, the unit of force is newton (N), which is defined as kg m s-2.
Some rules for using the SI units are:
- Use a decimal point as the separator for fractional parts of a number.
- Use a space to separate the digits into groups of three, starting from the decimal point.
- Do not use commas or spaces within a number.
- Use a space to separate the number and the unit symbol.
- Do not use a period after the unit symbol unless it ends a sentence.
- Use capital letters for unit symbols derived from proper names, such as N for newton or K for kelvin.
- Use lowercase letters for unit symbols derived from common names, such as m for metre or s for second.
- Do not use plural forms or hyphens for unit symbols, such as ms for milliseconds or kg-m for kilogram-metre.
Atomic Mass, Molecular Mass, Formula Mass, and Molar Mass
The atomic mass of an any element is the average mass of its atoms relative to one-twelfth of the mass of a carbon-12 atom. It is called in atomic mass units (u), where 1 u = 1.66 x 10-27 kg. The atomic masses of different elements can be found in the periodic table.
The molecular mass of a any compound is the sum of the atomic masses of all the atoms in one molecule of the compound. It is also called in atomic mass units (u). For example, the molecular mass of water (H2O) is 2 x 1.008 u + 16.00 u = 18.016 u.
The formula mass of an ionic compounds is the sum of the atomic masses of all the ions present in one formula unit of the compound. It is also expressed in atomic mass units (u). For example, the formula mass of sodium chloride (NaCl) is 22.99 u + 35.45 u = 58.44 u.
The molar mass of a any substance is the mass of one mole of that substance. It is expressed in grams per mole (g mol-1). One mole of a substance contains 6.022 x 1023 particles (atoms, molecules, or ions) of that substance. This number is called Avogadro’s constant (NA). The molar mass of a substance is equal to its atomic mass, molecular mass, or formula mass in grams. For example, the molar mass of water is 18.016 g mol-1 and the molar mass of sodium chloride is 58.44 g mol-1.
Laws of Chemical Combination
There are four laws that govern the combination of different elements to form compounds. They are:
- Law of Conservation Of Mass: This law states that matter can neither be created nor destroyed in a chemical reactionyouca, n also say that total mass of the reactants is equal to the total mass of the final products in a chemical reaction.
- Law of Definite Proportions: This law states that a given compound always contains the same elements in the same fixed ratio by mass, regardless of its source or method of preparation. For example, water always contains hydrogen and oxygen in the ratio 1:8 by mass.
- Law of Multiple Proportions: This law states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a simple ratio of whole numbers. For example, carbon and oxygen can combine to form two compounds: carbon monoxide (CO) and carbon dioxide (CO2). In these compounds, 12 g of carbon combine with 16 g and 32 g of oxygen, respectively. The ratio of the masses of oxygen that combine with a fixed mass of carbon is 16:32 or 1:2.
- Law of Reciprocal Proportions: This law states that when two elements combine separately with a third element, the ratio of the masses in which they do so is either the same or a simple multiple of the ratio in which they combine with each other. For example, hydrogen and oxygen can combine separately with nitrogen to form ammonia (NH3) and nitric oxide (NO), respectively. In these compounds, 14 g of nitrogen combine with 3 g and 8 g of hydrogen and oxygen, respectively. The ratio of the masses of hydrogen and oxygen that combined with a fixed mass of nitrogen is 3:8. This is the same as the ratio in which hydrogen and oxygen combine with each other to form water.
The Mole Concept
The mole concept is a convenient way of expressing the amount of a substance in terms of its particles. One mole of a substance is defined as the amount that contains as many particles as there are atoms in 12 g of carbon-12. This number is equal to Avogadro’s constant (NA), which is 6.022 x 1023. The mole concept can be used to relate the mass, volume, and number of particles of a substance.
- Mass-Mole Relationship: The mass-mole relationship is based on the molar mass of a any substance, which is the mass of one mole of that substance. The molar mass can be calculated by multiplying the atomic mass, molecular mass, or formula mass by NA. The mass-mole relationship can be expressed as:
- Mass (g) = Number of moles (mol) x Molar mass (g mol-1)
- For example, to calculate the mass of 2 moles of water, we use the formula:
- Mass (g) = 2 mol x 18.016 g mol-1 = 36.032 g
- Volume-Mole Relationship: The volume-mole relationship is based on the molar volume of a gas, which is the volume occupied by one mole of any gas at standard temperature and pressure (STP). STP is defined as 0°C (273 K) and 1 atm (101.3 kPa). The molar volume of any gas at STP is 22.4 L mol-1. The volume-mole relationship can be expressed as:
- Volume (L) = Number of moles (mol) x Molar volume (L mol-1)
- For example, to calculate the volume occupied by 0.5 moles of oxygen gas at STP, we use the formula:
- Volume (L) = 0.5 mol x 22.4 L mol-1 = 11.2 L
- Particle-Mole Relationship: The particle-mole relationship is based on Avogadro’s constant (NA), which is the number of particles in one mole of a substance. The particles can be atoms, molecules, or ions, depending on the nature of the substance. The particle-mole relationship can be expressed as:
- Number of particles = Number of moles (mol) x Avogadro’s constant (NA)
- For example, to calculate the number of molecules in 3 moles of carbon dioxide, we use the formula:
- Number of molecules = 3 mol x 6.022 x 1023 = 1.807 x 1024
Concentration of Solutions
A solution is a homogeneous mixture of two or more substances. The substance that dissolves in another substance is called the solute, and the substance that does the dissolved is called the solvent. The concentration of a solution is a measure of how much solute is present in a given amount of solvent or solution. There are different ways of expressing concentration, such as:
- Mass Percent: Mass % is defined as the mass of solute per 100 g of solution. It can be calculated by this formula:
- Mass percent (%) = Mass of solute (g) / Mass of solution (g) x 100
- For example, to calculate the mass percent of sodium chloride in a solution containing 5 g