Chemistry Notes 24X7

A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by (CH2). Meaning of Homologous Series A homologous series refers to a series of carbon compounds which have a different number of carbon atoms. However, they contain the same functional group. In this series, a group of compounds share similar basic chemical makeup. Also, in such a series, the compounds show a difference in the number of iterations of a certain aspect of their structure. Properties of Homologous Series  Repeating unit is the most important characteristic of a homologous series. An example can be the alkaline group which consists of the CH2 repeating unit. What this means is that the compounds are identical with the notable exception of the number of CH2 units existing in the compound. Organic compounds certainly have functional groups. Moreover, these groups define the fundamental and basic properties of the compound. M

example of rancidity Some examples of rancidity are - Food when exposed to atmospheric air for a long duration becomes rancid. Butter changes its taste and smell when kept in an open atmosphere for a longer duration. Some precaution to prevent rancidity : Food should be kept in sealed containers. Food that needs to be refrigerated. Foods containing fat and oil can be packaged in nitrogen gas to prevent rancidity. To avoid rancidity, food should be stored away from light. Antioxidants can be added to food.

The oxidation of oils or fats in food resulting in a bad taste and smell is called rancidity.  OR It is a condition in which aerial oxidation of unsaturated fat present in food gives it an unpleasant flavour and odour. Rancidity makes food undesirable for consumption. This process is also called rancidification.

Answer :  Baking soda (NaHCO 3 ) liberates carbon dioxide gas on heating, confirmed by passing it in lime water. Whereas on heating washing soda Na 2 CO 3 .10H 2 O water of crystallisation is given out, the salt becomes anhydrous. Reaction: 2NaHCO 3  → Na 2 CO 3  + H 2 O + CO 2 Na 2 CO 3 .10H 2 O → Na 2 CO 3  + 10 H 2 O

Answer :  Eggshells contain calcium carbonate. Calcium carbonate reacts with nitric acid to form calcium nitrate and carbon dioxide gas. CaCO 3  (s) + HNO 3  (aq) → CaNO 3  (aq) + CO 2  (g) + H 2 O (l)

Law of Chemical Combination Given by Lavoisier and Joseph L. Proust as follows: 1. Law of conservation of mass Mass can neither be created nor destroyed in a chemical reaction. e.g. A + B → C + D  Reactants → Products, Mass of reactants = Mass of products 2. Law of constant proportion In a chemical substance the elements are always present in definite proportions by mass. e.g.,  in water, the ratio of the mass of hydrogen to the mass of oxygen is always 1 : 8 respectively. These laws lacked explanation. Hence, John Dalton gave his theory about the matter. He said that the smallest particle of matter is called ‘atom’. Dalton’s Atomic Theory ·        Every matter is made up of very small or tiny particles called atoms. ·        Atoms are not divisible and cannot be created or destroyed in a chemical reaction. ·        All atoms of a given element are same in size, mass and chemical properties. ·        Atoms of different elements are different in size, mass and