UNIT 1 SOME BASIC CONCEPTS OF CHEMISTRY
NATURE OF MATTER
Matter exists in three physical states i.e. solid, liquid and gas.
CLASSIFICTAION OF MATTER
Matter can be classified into mixtures and pure substances.
PROPERTIES OF MATTER
Properties of matter can be classified into:
MASS: Mass of a substance is the amount of matter present in it.
WEIGHT: Weight of a substance is the force exerted by gravity on an object.
VOLUME: Volume is the amount of space that a substance occupies.
TEMPERATURE: Temperature is the measure of the degree of hotness or coldness of the substance.
PRECISION AND ACCURACY
Precision refers to the closeness of various measurements for the same quantity.
Accuracy is the agreement of a particular value to the true value of the result.
Significant figures are meaningful digits which are known with certainty. The rules to determine the number of significant figures are:
ROUNDING OFF NUMBERS
The rules for rounding off numbers are:
LAWS OF CHEMICAL COMBINATIONS
Law of conservation of mass: It states that matter can neither be created nor destroyed.
Law of definite proportions: It states that a given compound always contains exactly the same proportion of elements by weight. It is also known as Law of definite composition.
Law of multiple proportions: It states that if two elements combine to form more than one compound, the masses of one element that combines with a fixed mass of the other element, are in the ratio of small whole numbers.
Law of gaseous volume: This law was given by Gay Lussac. It states that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at the same temperature and pressure.
Avogadro’s Law: It states that equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
Dalton’s Atomic Theory: This theory proposed the following:
The atomic mass of an element is expressed relative to carbon-12 isotope of carbon which has an exact value of 12.
In a balanced chemical reaction, the coefficients indicate the molar ratios and the respective number of particles taking part in a particular reaction. The quantitative study of the reactants required or the products forms is called stoichiometry.
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