There are certain rules for determining the number of significant figures-
All non-zero digits are significant. For example in 285 cm, there are three significant figures and in 0.25 mL, there are two significant figures.
Zeros preceding to first non-zero digit are not significant. Such zero indicates the position of decimal point. Thus, 0.03 has one significant figure and 0.0052 has two significant figures.
Zeros between two non-zero digits are significant. Thus, 2.005 have four significant figures.
Zeros at the end or right of a number are significant provided they are on the right side of the decimal point. For example, 0.200 g has three significant figures.
Exact numbers have infinite zeros at the end or right of a number is significant provided they are on the right side of the number of significant figures.
Often while calculating, there is a need to convert units from one system to other. The method used to accomplish this is called factor label method or unit factor method or dimensional analysis.
Law of Conservation of Mass-It states that matter can neither be created nor destroyed. This law was put forth by Antoine Lavoisierin 1789.
Law of Definite Proportions-This law was given by, a French chemist, Joseph Proust. He stated that a given compound always contains exactly the same proportion of elements by weight.
Law of Multiple Proportions-This law was proposed by Dalton in 1803.According to this law, if two elements can combine to form more than one compound, themasses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.
Gay Lussac's Law of Gaseous Volumes-This law was given by GayLussac in 1808. He observed 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 same temperature and pressure.
Avogadro Law-In 1811, Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
Dalton's Atomic Theory-Matter consists of indivisible atoms. All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass. Compounds are formed when atoms of different elements combine in a fixed ratio. Chemical reactions involve reorganization of atoms. These are neither created nor destroyed in a chemical reaction. Dalton's theory could explain the laws of chemical combination.
One atomic mass unit (amu) is defined as a mass exactly equal to onetwelfth the mass of one carbon-12 atom.
And 1 amu = 1.66056×10-24 g.
Molecular mass is the sum of atomic masses of the elements present in a molecule. It is obtained by multiplying the atomic mass ofeach element by the number of its atoms andadding them together.
One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012kg) of the 12C isotope.
The mass of one mole of a substance in grams is called its molar mass. The molar mass in grams is numerically equal to atomic/molecular/formula mass in u.
An empirical formula represents the simplest whole number ratio of various atoms present in a compound whereas the molecular formula shows the exact number of different types of atoms present in a molecule of a compound.
Stoichiometry is the study of the relationships or ratios between two or more substances undergoing a physical or chemical change
According to the law of conservation of mass, a balanced chemical equation has the same number of atoms of each element on both sides of the equation.
Thereactant which gets consumed, limits the amount of product formed is called the limiting reagent.
Mole fraction-It is the ratio of number of moles of a particular component to the total number of moles of the solution. If a substance 'A' dissolves in substance 'B' and their number of moles arena and nb respectively; then the mole fractions of A and B are given as.
Molarity=No of moles/Volume of Solution.
Molality-It is defined as the number of moles of solute present in 1 kg of solvent. It is denoted by m.